SIMBIOS Project Annual Report

NASA/TM--1999-208645

SIMBIOS Project 1998 Annual Report

Charles R. McClain, Goddard Space Flight Center, Greenbelt, Maryland

Giulietta S. Fargion, SAIC General Sciences Corporation, Beltsville, Maryland
SIMBIOS Project Annual Report

PREFACE

The purpose of this series of technical reports is to provide current documentation of the SIMBIOS Project activities,

NASA Research Announcement (NRA) research status, satellite data processing, data product validation and field 

calibration. This documentation is necessary to ensure that critical information is related to the scientific community and

NASA management. This critical information includes the technical difficulties and challenges of combining 

ocean color data from an array of independent satellite systems to form consistent and accurate global bio-optical 

time series products. This technical report is not meant to substitute for scientific literature. Instead, it will provide a

ready and responsive vehicle for the multitude of technical reports issued by an operational project.
SIMBIOS Project Annual Report

Table of Contents

1. SIMBIOS BACKGROUND................................................................................................................................................. 1

2. SIMBIOS PROGRAM AND PROJECT GOALS................................................................................................................ 4

3. SIMBIOS: NRA CONTRACTS............................................................................................................................................ 7

4. SIMBIOS PROJECT ACTIVITIES (1997-1998) .............................................................................................................. 11

5. VALIDATION OF SURFACE BIO-OPTICAL PROPERTIES IN THE GULF OF MAINE AS A MEANS

FOR IMPROVING SATELLITE PRIMARY PRODUCTION ESTIMATES ................................................................... 32

6. OCTS AND SEAWIFS BIO-OPTICAL ALGORITHM AND PRODUCT VALIDATION AND

INTERCOMPARISON IN U.S. COASTAL WATERS ..................................................................................................... 35

7. VALIDATION OF OCEAN COLOR SATELLITE DATA PRODUCTS IN UNDER-SAMPLED MARINE AREAS .. 39

8. STRAY LIGHT AND ATMOSPHERIC ADJACENCY EFFECTS FOR LARGE-FOV, OCEAN VIEWING

 SPACE SENSORS............................................................................................................................................................. 42

9. BIO-OPTICAL MEASUREMENTS AT OCEAN BOUNDARIES IN SUPPORT OF SIMBIOS. ................................... 44

10. REMOTE SENSING OF OCEAN COLOR IN THE ARCTIC: ALGORITHM DEVELOPMENT AND

 COMPARATIVE VALIDATION. ..................................................................................................................................... 47

11. HIGH FREQUENCY, LONG TIME SERIES MEASUREMENTS FROM THE BERMUDA TESTBED

MOORING IN SUPPORT OF SIMBIOS. .......................................................................................................................... 50

12. HIGH-LATITUDE INTERCOMPARISON AND VALIDATION EXPERIMENT (HIVE)............................................. 52

13. SATELLITE OCEAN COLOR VALIDATION USING MERCHANT SHIPS................................................................. 55

14. HIGH ATTITUDE MEASUREMENTS OF RADIANCE AT HIGH SPECTRAL AND SPATIAL

RESOLUTION FOR SIMBIOS SENSOR CALIBRATION,VALIDATION, AND INTERCOMPARISONS................ 58

15. MERGING OCEAN COLOR DATA FROM MULTIPLE MISSIONS............................................................................. 61

16. VALIDATION OF BIO-OPTICAL PROPERTIES IN COASTAL WATERS: A JOINT NASA NAVY PROJECT....... 63

17. BIO-OPTICAL MEASUREMENT AND MODELING OF THE CALIFORNIA CURRENT AND

POLAR OCEANS........................................................................................................................66

18. SIMBIOS NORMALIZED WATER LEAVING RADIANCE CALIBRATION AND VALIDATION:

SENSOR RESPONSE, ATMOSPHERIC CORRECTIONS, STRAY LIGHT AND SUN GLINT................................... 69
SIMBIOS Project Annual Report

Table of Contents (cont.)

19. VALIDATION OF CARBON FLUX AND RELATED PRODUCTS FOR SIMBIOS AT THE CARIACO

CONTINENTAL MARGIN TIME SERIES....................................................................................................................... 71

20. THE BERMUDA BIO-OPTICS PROGRAM (BBOP)....................................................................................................... 74

21. SIMBIOS DATA PRODUCT AND ALGORITHM VALIDATION WITH EMPHASIS ON THE

BIOGEOCHEMICAL AND INHERENT OPTICAL PROPERTIES. ............................................................................... 77

22. VALIDATION OF THE SEAWIFS ATMOSPHERIC CORRECTION SCHEME USING MEASUREMENTS

OF AEROSOL OPTICAL PROPERTIES. ......................................................................................................................... 80

23. MEASUREMENTS OF AEROSOL, OCEAN AND SKY PROPERTIES AT THE HOTS SITE IN THE

CENTRAL PACIFIC. ......................................................................................................................................................... 83

24. ASSESSMENT OF THE CONTRIBUTION OF THE ATMOSPHERE TO UNCERTAINTIES IN NORMALIZED

WATER-LEAVING RADIANCE: A COMBINED MODELING AND DATA ANALYSIS APPROACH..................... 86

25. VALIDATION OF THE WATER-LEAVING RADIANCE DATA PRODUCT. ............................................................. 88

26. OCI DATA VALIDATION IN THE WATER ADJACENT TO TAIWAN. ..................................................................... 96

GLOSSARY................................................................................................................................................................................. 97

REFERENCES............................................................................................................................................................................. 99
SIMBIOS Project Annual Report
SIMBIOS Project Annual Report

1

Chapter 1

SIMBIOS Background

Charles R. McClain

NASA Goddard Space Flight Center

Greenbelt, Maryland

The Sensor Intercomparison and Merger for

Biological and Interdisciplinary Ocean Studies

(SIMBIOS) program was conceived in 1994 as a

result of a National Aeronautics and Space

Administration (NASA) management review of the

agency's strategy for monitoring the bio-optical

properties of the global ocean through ocean color

remote sensing from space. At that time, the NASA

ocean color flight manifest included two data buy

missions, the Sea-viewing Wide Field-of-view Sensor

(SeaWiFS) and Earth Observing System (EOS) Color,

and two sensors, Moderate Resolution Imaging

Spectroradiometer (MODIS) and Multi-angle Imaging

Spectro-Radiometer (MISR), scheduled for flight on

the EOS-AM (1998) and -PM (2001) satellites.

Considerable effort was spent by Dr. McClain

(Project Scientist) and Dr. Kirk (Study Manager) on

examining mission scenarios for EOS Color because

of the slips being encountered with SeaWiFS.

However, with the delay of SeaWiFS and an uncertain

launch schedule, it was not clear that EOS Color was

needed to fill a potential gap between SeaWiFS and

MODIS, especially when five additional ocean color

systems with similar global capabilities [Ocean Color

and Temperature Sensor (OCTS), Japan; Global

Imager (GLI), Japan; Polarization Detecting

Environmental Radiometer-1 (POLDER-1) and -2,

France; and Medium Resolution Imaging

Spectrometer (MERIS), European Space Agency] and

several other non-global missions by Argentina,

Germany, Taiwan, India, Korea, the U.S. Navy, and

the People’s Republic of China, were planned for

launch during the late 1990s.

The review led to a decision that the international

assemblage of ocean color satellite systems provided

ample redundancy to assure continuous global

coverage, with no need for the EOS Color mission. At

the same time, it was noted that non-trivial technical

difficulties attended the challenge (and opportunity) of

combining ocean color data from this array of

independent satellite systems to form consistent and

accurate global bio-optical time series products

(Figure 1). Thus, it was announced at the October,

1994 EOS Interdisciplinary Working Group meeting

that some of the resources budgeted for EOS Color

should be redirected into an intercalibration and

validation program. NASA Goddard Space Flight

Center (GSFC) was directed to develop a plan for

submission to NASA Headquarters (HQ) by May

1995. As a result of the directive from NASA/HQ, the

ocean color group lead by Dr. McClain at

NASA/GSFC organized an international

organizational meeting in February 1995 at the

University of Miami Rosenstiel School for Marine and

Atmospheric Sciences. The objective was develop a

conceptual plan for a comparison program. The plan

(Ocean Color Multisensor Data Evaluation and

Utilization Plan, under SIMBIOS Documents,

http://simbios.gsfc.nasa.gov/) which outlined NASA’s

contribution to the international effort was completed,

submitted, externally reviewed, and revised in 1995.

Based on the final approved plan, a NASA

Research Announcement (NRA) was released in July

1996, and the SIMBIOS Project Office was

established at the NASA (GSFC) in January 1997 (colocated with the SeaWiFS Project). The initial

SIMBIOS Program was scoped for five years (1997-

2001) and included separate support for a science

team (NRA selections) and the Project Office.

Dr. Mueller (San Diego State University) acted

as an interim project manager at NASA/GSFC under a

one-year assignment to assist in getting the project

office organized and the science team contracts

executed. His assistance in this capacity was essential

as the SIMBIOS Project was beginning just as the

SeaWiFS Project was preparing for launch.

 In parallel with the NASA SIMBIOS Program

planning, the international effort was being organized.

The initial meeting was held in Vittoria, British

Columbia during September, 1995. As a result of the

recommendations from that meeting, the International

Ocean Colour-Coordinating Group (IOCCG) was

formed (http://www.ioccg.org/). The IOCCG

presently operates under the auspices of the Scientific

Committee on Oceanic Research (SCOR) and

chairmanship of Dr. Platt (Bedford Institute of

Oceanography). The IOCCG meets one or two times

per year and is generating a series of special reports on

topics essential to the coordination of the international

ocean color community (e.g., IOCCG, 1998).

During calendar year 1997, Dr. Mueller’s tenure

as SIMBIOS Project Manager, the primary

accomplishments included the following:
SIMBIOS Project Annual Report

2

The science team contracts or interagency

agreements were negotiated (3-year contracts)

and first year funds were distributed. Several

additional investigations, primarily for

atmospheric correction studies, were solicited and

funded.

The initial Project Office staffing actions were

completed.

The SIMBIOS processing systems were

purchased and installed.

An instrument pool was established. Submersible

instruments for field studies were purchased

through some of the science team contracts. The

Project also purchased 12 MicroTops hand-held

sun photometers, 2 PREDE (Japanese built) sun

photometers, and a micro-pulse lidar as part of the

instrument pool. Twelve CIMEL (French built)

sun photometers were also purchased to augment

the Aerosol Robotic Network (AERONET) for

deployment at coastal sites.

A satellite overflight prediction service was

established to assist in coordinating field studies

in synchronizing data collection with satellite

passes (http://simbios.gsfc.nasa.gov/, and http: //

simbios.gsfc.nasa.gov/~schedule/Predictions/

Current_Cruises.html).

The first SIMBIOS science team meeting was

held in August at Solomons Island, Maryland.

During the second year of the SIMBIOS Project,

Dr. McClain assumed project management of both the

SeaWiFS and SIMBIOS as both Dr. Cleave and Dr.

Mueller stepped down in their roles as project

managers of these two projects, respectively. In the

second year, many of the original objectives of

SIMBIOS began to come to fruition, some of which

are discussed in more detail in subsequent chapters.

Project accomplishments included:

The first SIMBIOS intercalibration round-robin

experiment (Riley and Bailey, 1998) was

completed.

The CIMEL sun photometers were re-engineered

by Meridian Engineering of Hanover, Maryland

to improve their survivability in the field.

Confirmed (delivered or negotiated) CIMEL sites

include Lanai (Hawaii) with a backup in

Honolulu, Ascension Island, Bahraine, Turkey

(Black Sea), Tahiti, Wallops Island (Virginia),

and South Korea. Additional sites being

considered are Perth, Australia and Iceland.

Delivery of equipment for calibrating polarized

bands was received from the University of Lille

as part of the collaboration with the AERONET

group at NASA/GSFC [Brent Holben, principal

investigator (P.I.)]. An automated procedure for

extracting data from the AERONET archive for

satellite match-up comparisons was completed.

The micropulse lidar environmental container was

re-engineered by Meridian Engineering to

improve temperature stability.

A second copy of the SeaWiFS Transfer

Radiometer (SRX), the SXR-2, was built by

Reyer Corporation of New Market, Maryland for

use in the calibration round-robin.

A Marine Optical Spectroradiometer (MOS)

ground station subsystem was purchased from

Antrix Corporation Limited (Bangalore, India) for

installation at Wallops Flight Facility.

Data processing (Level-0 to Level-3) software for

OCTS and MOS were completed. This activity

included evaluations of the navigation, band

coregistration, calibration, destripping,

atmospheric correction, and bio-optical

algorithms. Match-up comparisons with field data

and OCTS were also completed using match-up

subscenes provided by National Space

Development Agency of Japan (NASDA) Earth

Observation Research Center (EORC).

SeaWiFS Bio-Optical Archive and Storage

System (SeaBASS) holdings were greatly

expanded as the science team field activities got

underway.

The SIMBIOS website was substantially

enhanced including monthly reports posted by the

science team investigators.

Science team contract performance was reviewed

and the contracts were revised as necessary and

renewed.

The second science team meeting was held at

Scripps Institution of Oceanography (SIO) in

September 1998.

In 1999, the SIMBIOS Project will finalize the

processing of it holdings of OCTS data, i.e., all the

OCTS data collected at Wallops Flight Facility (east

coast of North America, Gulf of Mexico, and the

Caribbean Sea), which should be completed by early

spring. The OCTS processing software will be

incorporated into SeaWiFS Data Analysis System

(SeaDAS) Version 3.3. The next ocean color

instrument data set to be evaluated will be ADEOS1/POLDER in cooperation with Centre National

d’Edudes Spatialle (CNES) and the POLDER science

team. The SIMBIOS Project and science team will

assist the ROCSAT Ocean Color Imager (OCI)

(launched in January) and MODIS (launch scheduled

for July) instrument teams in their evaluations,

primarily by providing match-up data for calibration

and validation analyses. The SIMBIOS Project will

also assist NASA/HQ in drafting the second

SIMBIOS NRA which is scheduled for release

sometime this summer. Finally, the third science team

meeting will be held in September in the Washington,

D.C. area.
Instrument (Mission: Country) 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 

78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 

Proof-of-Concept

CZCS (Nimbus-7: U.S.)

Global

OCTS (ADEOS-I: Japan)

POLDER (ADEOS-I/II: France & Japan)

SeaWiFS (OrbView-2: U.S.)

MODIS (EOS-AM: U.S.)

MISR (EOS-AM: U.S.)

MERIS (ENVISAT: ESA)

GLI (ADEOS-II: Japan)

MODIS (EOS-PM: U.S.)

Limited Coverage

MOS (Priroda: Germany & Russia)

MOS (IRS: Germany & India)

OCI (ROCSAT: Taiwan)

OSMI (KOMPSAT: South Korea)
SIMBIOS Project Annual Report

4

Chapter 2

SIMBIOS Program and Project Goals

Giulietta S. Fargion

SAIC General Sciences Corporation

Beltsville, Maryland

2.1 PROGRAM GOALS

The purpose of the SIMBIOS project is to

develop a methodology and operational capability to

combine data products from various ocean color

missions in a manner that ensures the best possible

global coverage and best exploits the complementary

missions of the sensors. NRA 96-MTPE-04

specifically defines the scientific goals in support of

this undertaking. “Specifically, the objectives are (1)

to quantify the relative accuracies of the products from

international ocean color missions, (2) to improve the

level of confidence and compatibility among the

products, and (3) to generate merged, improved level3 products” (NASA, 1996). A major goal of the

Program is to foster collaborations with the various

space agencies and science working groups to assist

each other in achieving these objectives. Presently,

SIMBIOS is collaborating with Japan on OCTS and

GLI, with India and Germany on MOS and just 

started a relationship with France on POLDER.

2.2 PROJECT OBJECTIVES

The SIMBIOS Program consists of the SIMBIOS

Science Team and the SIMBIOS Project. The

SIMBIOS Science Team, as initially defined by the

NRA selections, was expanded to include additional

investigations for atmospheric correction algorithm

validation. The SIMBIOS Project has been established

to provide support and coordination for the SIMBIOS

Program such as administration, project

documentation, complete data processing of

complementary ocean color missions, support for each

of the individual elements, and oversight of data

processing systems supported by the Project.

“Specifically, the SIMBIOS Project is responsible for

the following:

Assistance in the collection, processing, archiving

and documentation of the calibration (including

instrument round-robins, pre- and post-launch

sensor calibration) and bio-optical data sets;

Maintenance of a data archive and storage system

for tracking instrument calibrations and validating

bio-optical algorithms or merger methodologies

with in situ data;

Planning and execution of instrument and

analysis round-robins which will include

coincident intercomparisons of hardware and

software performance;

Oversight of the regular revision of the ocean

optics protocols which will establish the

methodologies and standards for calibrating

instruments, collecting data, and producing final

results from approved analysis procedures.

Assistance in data acquisition during field studies;

Management of a centralized facility for

providing portable field sources which will be

used for tracking the calibration of instruments

while they are used in the field;

Assistance in product validation and quality

control assessment;

Technical monitoring of the prototyping,

deployment, or production of new technology

developments;

Assistance in the development, evaluation, and

implementation of product merger schemes and

algorithms; and

Administer and oversee the regular meeting of

working subgroups concerned with specific issues

important to the success of the SIMBIOS Project”

(NASA, 1996).

The SIMBIOS Program is augmented by the

participation of the NASA-supported MODIS Oceans

Team and SeaWiFS Calibration and Validation

Program. SIMBIOS calibration activities are

accomplished using the calibration activities of the

various independent participating missions,

coordinating activities of the SIMBIOS Project, and

complementary activities of individual investigators

selected by the NRAs. The SIMBIOS Project goal is

to help science users with a long time series of

calibrated radiances extending across the boundaries

of individual missions. Close cooperation with the

SeaWiFS Project is essential to the success of the

SIMBIOS Project. The SIMBIOS Project is co-located

with the SeaWiFS Project at GSFC, and many of

SIMBIOS staff are shared with SeaWiFS to guarantee

a close cooperation to quantify the relative accuracy of

the data products from different ocean color sensors

and the improve level of confidence and compatibility

among the products.
SIMBIOS Project Annual Report

5

Table 1. SIMBIOS Project

SIMBIOS Project Address

NASA/Goddard Space Flight Center

SIMBIOS Project

Code 970.2, Building 28

Greenbelt, MD 20771

Telephone: (301) 286-9676

FAX: (301) 286-0268

E-mail: project@simbios.gsfc.nasa.gov

 Personnel of SIMBIOS Project

Sean Bailey

Robert Barnes *

Patty Clow *

Giulietta Fargion

Gene Feldman *

Ian Durham *

Bryan Franz *

Lynne Hoppel *

Alice Isaacman

Charles McClain *

Fred Patt *

Christophe Pietras

Tom Riley

India Robinson *

Kellie Ruebens *

Brian Schieber *

Linwood Smith *

Paul Smith *

Sung Lee *

Tamara Tucker *

Grey Valenti *

Menghua Wang

Bill Woodford *

FutureTech Corporation

SAIC General Sciences Corporation

NASA

SAIC General Sciences Corporation

NASA

SAIC General Sciences Corporation

SAIC General Sciences Corporation

NASA

SAIC General Sciences Corporation

NASA

SAIC General Sciences Corporation

SAIC General Sciences Corporation

NASA

NASA

SAIC General Sciences Corporation

SAIC General Sciences Corporation

FutureTech Corporation

SAIC General Sciences Corporation

SAIC General Sciences Corporation

SAIC General Sciences Corporation

SAIC General Sciences Corporation

Univ. of Maryland Baltimore

FutureTech Corporation

Note: total civil servant staff ~ 2.5 man year

*shared with SeaWiFS Project

2.3 PROJECT ORGANIZATION

The SIMBIOS Project organization structure is

scoped to support the primary activities: 1) sensor

engineering and calibration, 2) satellite data

processing; 3) data product validation, 4) SIMBIOS

Science Team, and 5) SIMBIOS Project Office. The

SIMBIOS Project organization chart is shown in

Figure 1 and illustrates the individual subtasks under

each primary activity with staff associations. The

SIMBIOS Project key personnel and their areas of

responsibility at GSFC are also given in Table 1. The

satellite data processing elements requires close

coordination between the data product validation and

the sensor engineering and calibration. A complete

overview of the primary activities 1 to 4 will be

described in the following chapter. The Project Office

administrative structure is as follows: system support,

administrative support, technical support, science

team support, procurement support, and resources

support. At the present time, only SeaWiFS and

SIMBIOS participants and collaborators associated

with other relevant programs, and science teams who

actively contribute data or algorithms, are given

access to SIMBIOS Project resources, such as the

SeaWiFS Bio-optical Archive and Storage System

(SeaBASS) and Field Instrument Pool. This limitation

is to protect the interests of the researchers currently

submitting to the SeaBASS archive.

The SIMBIOS Project policy is to have all

documents easily available to the SIMBIOS PIs and to

the larger ocean color scientific community. Access to

the information is gained through the SIMBIOS

website. The SIMBIOS website was organized to

serve as the main information resource to access the

Project activities, Project Office and Science Team.

The website is organized under five main topics:

News and Information, Support Services and

Schedule, Project Status, Instrument Pool and

Contacts. Briefly, under Project Status are found

monthly progress updates from the Project and the

Science Team. The Project update covers processing

and calibration accomplishments for the various

missions, the instrument pool and real-time cruise

support, and other key events or Project issues. The

Science Team oversight is divided into two categories:

funded PIs and international collaboration. Under

Status of Contracted PIs, the abstracts of the funded

research, monthly progress reports, documents in

process, and other key events can be found.

Under News and Information, is an archive of

most of the produced SIMBIOS documentation and

calendar of events. In this section, a user can easily

find out which conferences or symposia the Project

staff is attending, documents on SIMBIOS workshops

and team meetings, and special activities, such as the

SIMBIOS participation in Indian Ocean Experiment

(INDOEX). An online bibliography includes

SIMBIOS technical memoranda or papers presented

and published, with online abstracts. SeaWiFS

scheduling and the SeaBASS database are accessible

online. For further information see http://simbios.gsfc.

nasa.gov. All sections are updated as needed.

In addition, the SIMBIOS Project has an internal

web interface to closely follow the contractual status

of the funded PIs. Contractual issues such as data

delivery, contract evaluation performance, contract

modifications, requested extensions, procurement

support performance, and other items are tracked here.

In addition, the SIMBIOS Project holds bimonthly

staff meetings, weekly review on technical papers or

project issues (such as calibration, in situ matchups,

etc.), and key staff attends the SeaWiFS meetings.

Monthly SIMBIOS Project progress reports are

generated and posted to the SIMBIOS website. The

Project also gives a formal oral presentation to the

Earth Science Directorate (Code 900) management.
* The SIMBIOS Project is co-located with the SeaWiFS Project and many of the SIMBIOS Staff are shared.

G. Fargion

Assistant Project Manager

F. Patt*

Contract Staff Supervisor

M. He

O. Kopelevich

G. Korotaev

H. Li

S. Saitoh 

F. Chavez

B. Chen

G. Cota

T. Dickey

P. Flateau

R. Frouin

R. Green

W. Gregg

M. Miller

R. Miller

US SIMBIOS PI's

A. Subramaniam

K. Stamnes

R. Zaneveld

International SIMBIOS PIs

W. Balch

J. Brock

C. Brown

D. Capone

K. Carder

G. Mitchell

J. Mueller

F. Muller-Karger

J. Porter

D. Siegel

SIMBIOS Science Team NRA-96

G. Feldman

Satellite Data Processing

Satellite Data Processing

Satellite Data Analysis

Data Set Management

B. Franz*

J. Gales

Processing System Support

S. Lee *

P. Smith *

B. Woodford *

C. McClain*

Data Product Valid

Merged Data Set Asse

Algorithm Developm

Algorithm Validation

A. Isaacman

M. Wang

SeaBASS Interface

J. Werdell*

Cruise Schedule

Satellite Overflight Su

S. Bailey *

Match-up Data Analy

S. Bailey *

J. Werdell 

G. Fargion

Sensor Engineering 

& Calibration 

SIRREX Program

AERONET Interface

C. Pietras

G. Meister

Satellite Sensor 

Characterization and

Data Calibration

R. Barnes*

Field Instrument Pool

S. Bailey*

rement Support

w *

ppel*

er*

ical Support

onenko*

m Support

nistration Support

rces Support

inson *

bblefield*

ker*

IOS Science

Support

gion

OS Project Office

C. McClain*

Project Scientist & Manager

..

SIMBIOS Project Organization Chart
SIMBIOS Project Annual Report

7

Chapter 3

SIMBIOS: NRA Contracts

Giulietta S. Fargion

SAIC General Sciences Corporation

Beltsville, Maryland

3.1 PROJECT RESPONSIBILITY

Contract administration involves ensuring

compliance with contract terms and conditions during

the performance of the contract. The performance of

SIMBIOS Project contracts are monitored in several

ways by several individuals in the Project office.

These individuals include a Contracting Officer

specialist, a Resource/Finance person, the Assistant

Project Manager with technical background and

experience with projects and their costs, and the

Program Manager. The SIMBIOS Project contract

personnel and their areas of responsibility at GSFC are

given in Table 1. The most important step of contract

administration is to review the requirements and

specific obligations set forth in the contract. This role

is performed primarily by the Assistant Project

Manager. In matters related to contract laws and

interpretation, assistance is given by the Contracting

Officer. In matters related to the status of payments or

provisions relating to payments, assistance is given by

the Resource/Finance person. While SIMBIOS

contractors have historically addressed questions

about contract administration to the Assistant Project

Manager, they are entirely free to address questions

directly to the appropriate personnel.

A wide selection of contract types is available for

use between the Project office and contractors. This

selection provides a wide selection of services and a

large degree of flexibility of contract conditions (FAR,

1998). GSFC Procurement Office selected a Research

and Development Service, firm-fixed price (FFP)

contract-type for the NASA Research Announcement

(NRA) selections. The FFP contract provides for a

price that is not subject to any adjustment by reason of

the cost experience of the contractor in the

performance of the contract. Use of the FFP contract

imposes a minimum administrative burden on the

contracting parties. Contracts are very different from

the usual scientific research grants in three main

aspects: 1) a work statement concerning the end

objectives of the research (i.e., the proposal), 2) the

technical data to be delivered under the contract with

time delivery specifications, and 3) scientific and

technical reports, consistent with the objectives of the

effort involved, as a permanent record of the work

accomplished under the contract.

3.2 CONTRACTS OVERVIEW

The initial SIMBIOS program was scoped for five

years (1997-2001) and includes support for the NRA

selections (i.e., science team) and the SIMBIOS

Project. The Interim SIMBIOS Office (ISPO)

successfully negotiated specific work statements for

the 21 NRA selections and issued contracts starting

from late summer 1997. SIMBIOS funded contracts,

PI names and delivery requirements are summarized

in Table 2.

NASA Procurement requires formal evaluations

for all contracts at the end of each contract year. These

evaluations are to go into a database and will be

shared with the PIs’ institutions. The performance

evaluation has four categories: quality, time, other and

price (price is not relevant here because contracts are

fixed cost). SIMBIOS Project Office procedure is to

coordinate an inside panel to perform an across-theboard evaluation of all funded contracts. Under quality

will be considered 1) data quality and completeness,

2) ancillary information provided on the data

(metadata), 3) the data's usefulness in relation to

SIMBIOS goals, i.e., calibration, validation, and

algorithm development, and 4) quality of technical

reports. Time is a mixed bag, but will be viewed in

respect to data and documentation (monthly, year-end

reports, and special topic publications) and delivery

times. Under “other” will be considered 1) scientific

publications and scientific achievements, 2) science

team collaboration and involvement, and 3) other

significant events occurring during the contract period

evaluate.

Table 1. Contract key personnel

SIMBIOS NRA Organization

Contracting Officer: Lynne Hoppel

Resource/Financial Officer: Patty Clow

Assistant Project Manager: Giulietta Fargion

Program Manager: Charles McClain
SIMBIOS Project Annual Report

8

3.3 SCIENCE TEAM

NASA SIMBIOS Science Team Principal

Investigators are composed of those selected under the

NRAs, some members of the MODIS Ocean Teams,

and certain members the SeaWiFS Project. The

Science Team can be grouped under three working

areas: 1) Ocean Bio-optical and Sensor

Characterization Studies, 2) Data Merger Studies, and

3) Atmospheric Correction Studies. There are many

more U.S. and international co-investigators and

collaborators actively participating in the NASA

component of the international SIMBIOS program.

 The funded Principal Investigators and

collaborators are shown in Table 3. SIMBIOS Science

Team meeting is held each year, information and

documentation’s produced in the two previous

meetings (1997 and 1998) are posted on the SIMBIOS

website.

Figure 1 shows the global distribution of the

NRA-selected SIMBIOS field studies, and following

chapters from 5 to 27 describe the funded research

topics, field studies and the first year research results.

Table 2. SIMBIOS contracts and government interagency agreements *.

Principal Investigator

Contract

Number

Begin Date

Monthly Report

End-year TM

Cruise Report

Metadata

Special Topic TM

Field Data Within

3 or 6 Months

Algorithm

Development

Science Team

Meeting

William Balch 97268 9/23/97 ÷ ÷ ÷ ÷ ÷

J. Brock / C. Brown * 7/21/97 ÷ ÷ ÷ ÷ ÷

D. Capone / E. Carpenter 97131 9/11/97 ÷ ÷ ÷ ÷ ÷

Ken Carder 97137 9/23/97 ÷ ÷ ÷ ÷ ÷

Francisco Chavez 97134 9/26/97 ÷ ÷ ÷ ÷ ÷

Glenn Cota 97132 9/26/97 ÷ ÷ ÷ ÷ ÷

Tom Dickey 97127 7/15/97 ÷ ÷ ÷ ÷ ÷

Dave Eslinger 97133 9/17/97 ÷ ÷ ÷ ÷ ÷

Robert Frouin 97135 9/22/97 ÷ ÷ ÷ ÷ ÷

Robert Green * 8/6/97 ÷ ÷ ÷ ÷ ÷

Watson Gregg * 2/5/97 ÷ ÷ ÷ ÷ ÷

Rick Miller * 12/16/97 ÷ ÷ ÷ ÷ ÷

Greg Mitchell 97130 8/18/97 ÷ ÷ ÷ ÷ ÷ ÷

Jim Mueller 97126 8/18/97 ÷ ÷ ÷ ÷ ÷

Frank Müller-Karger 97128 8/18/97 ÷ ÷ ÷ ÷ ÷

Dave Siegel 97125 7/11/97 ÷ ÷ ÷ ÷ ÷ ÷

Ron Zaneveld 97129 8/18/97 ÷ ÷ ÷ ÷ ÷ ÷

Piotr Flatau 97139 9/22/97 ÷ ÷ ÷ ÷ ÷ ÷

Mark Miller * 9/23/97 ÷ ÷ ÷ ÷ ÷ ÷

John Porter 97136 9/29/97 ÷ ÷ ÷ ÷ ÷

Knut Stamnes 97138 9/15/97 ÷ ÷ ÷ ÷ ÷ ÷ ÷

 * Interagency agreement
SIMBIOS Project Annual Report

9

Table 3. Funded Principal Investigators (PI) and collaborators *. Collaborators are funded via EOS

(MODIS Ocean Team) and/or SeaWiFS Project.

I. Ocean Bio-optical and Sensor Characterization Studies

 K. Arrigo * (NASA)

W. Balch (Bigelow Lab.)

J. Brock (NOAA)

C. Brown (NOAA)

D. Capone (U. of Maryland)

E. Carpenter (State U. of New York)

K. Carder (U. South Florida)

F. Chavez (Monterey Bay Aquarium Res. Inst.)

D. Clark * (NOAA)

G. Cota (Old Dominion U.)

T. Dickey (U. of California/Santa Barbara)

M. He (Peoples Republic of China, Ocean U. of Qingdao)

W. Esaias * (NASA)

D. Eslinger (U. of Alaska)

R. Evans *(U. of Miami)

R. Frouin (Scripps Inst. Oceanography)

R. Green (Jet Propulsion Lab.)

F. Hoge *(NASA)

S. Hooker *(NASA)

O. Kopelevich (Soviet Union, P.P. Shirshov Inst. of Oceanology)

G. Korotaev (Ukraine, Marine Hydrophysical Inst.)

H. Li (Taiwan, Nat. Taiwan Ocean U.)

R. Miller (NASA)

G. Mitchell (Scripps Inst. of Oceanography)

J. Mueller (San Diego State U.)

H. Li (Taiwan, Nat. Taiwan Ocean U.)

R. Miller (NASA)

G. Mitchell (Scripps Inst. of Oceanography)

J. Mueller (San Diego State U.)

 F. Müller-Karger (U. South Florida)

 S. Saitoh (Japan, Hokkaido U.)

 D. Siegel (U. of California/Santa Barbara)

 R. Zaneveld (Oregon State U.)

II. Data Merger Studies

W. Gregg (NASA)

 D. Siegel (U. of California/Santa Barbara)

III Atmospheric Correction Studies

P. Flateau (Scripps Inst. of Oceanography)

H. Gordon * (U. of Miami)

M. Wang (UMD/Baltimore)

M. Miller (Brookhaven National Lab.)

J. Porter (U. of Hawaii)

K. Stamnes (U. of Alaska)
SIMBIOS Project Annual Report

10

1. Global distribution of the NRA-selected SIMBIOS field studies. United States: (1) Balch; (2) Brown/Brock

Carder; (5) Chavez; (6) Cota; (7) Dickey; (8) Eslinger; (9) Frouin; (4/14) Green;

Hoge; (11) Miller; (12) Mitchell; (13) Müller-Karger; (14) Porter; (15) Siegel; (16) Zaneveld/Mueller;

Kopelevich; (19) Korotaev; (20) Li; and (21) Satoh
SIMBIOS Project Annual Report

11

Chapter 4

SIMBIOS Project Activities (1997-1998)

Menghua Wang

University of Maryland Baltimore County

at Goddard Space Flight Center, Greenbelt, Maryland

Brian Franz, Alice Isaacman, Christopher Pietras, Brian Schieber and Paul Smith

SAIC General Sciences Corporation

Beltsville, Maryland

Tom Riley and Gene Feldman

NASA Goddard Space Flight Center

Greenbelt, Maryland

Sean Bailey

FutureTech Corporation

Greenbelt, Maryland

The project accomplishments during this first

period (1997-1998) under (a) satellite data processing,

(b) data product validation, and (c) sensor engineering

and calibration activities are described below.

4.1 SATELLITE DATA

PROCESSING

One of the primary goals of the SIMBIOS project

is to develop methods for meaningful comparison and

possible merging of data products from multiple ocean

color missions. Direct comparison of such products is

complicated by differences in sensor characteristics

and processing algorithms, as well as spatial and

temporal coverage.

4.1.1 MOS

The German Modular Optoelectronic Scanner

(MOS) (Zimmermann and Neumann, 1997) is an

imaging pushbroom Charge-Coupled Device (CCD)

spectrometer that was launched in a sun-synchronous

polar orbit in the spring of 1996 on the Indian Remote

Sensing (IRS-P3) satellite.

MOS is a technology demonstrator instrument

with limited geographic coverage capabilities. With

the successful launch of NASA’s SeaWiFS on August

1 of 1997, there are now two ocean color missions in

concurrent operation. Table 1 provides characteristics

of MOS compared with SeaWiFS. Therefore, we have

an unprecedented opportunity to compare ocean color

data from two sensors in simultaneous operation on

two different satellite platforms. We have extensively

studied the ocean color measurements compared

between MOS and SeaWiFS and developed a

vicarious calibration approach in which the MOS

spectral bands can be recalibrated from the SeaWiFS

measurements, which are considered as “truth,”

thereby allowing remotely retrieved ocean color

results from the two sensors to be meaningfully

compared (Wang and Franz, 1998 and 1999). The

vicarious calibration method has also been

successfully applied to Japan’s OCTS data, and will

also be tested with the French POLDER data. In here,

we give some summaries about these studies.

The MOS calibrated and geo-located data (L1B

data) are provided by the MOS project at Institute of

Space Sensor Technology, Deutshe Forshungsanstalt

Luft-und Raumfarhrt (DLR), Berlin, Germany. The

MOS L1B data file is prepared as size of 384 x 384.

In the following sub-sections, we give brief discuss of

our efforts in comparing the MOS results with

SeaWiFS.

Atmospheric Correction and Destriping

It is well known that the atmospheric correction,

which removes more than 90% of sensor-measured

signals contributed from atmosphere in the visible, is

the key procedure in ocean color imagery data

processing. We have implemented the SeaWiFS

atmospheric correction algorithm (Gordon and Wang,

1994b) into the MOS imagery data processing using
SIMBIOS Project Annual Report

12

the method outlined by Wang (1999). Therefore, a

consistent atmospheric correction method can be

applied to both SeaWiFS and MOS.

The MOS radiance image has along-track stripes

due to variations in the relative response of the individual detectors on the MOS CCD array (total of

384 CCD detectors). Therefore, we have developed a

simple destriping algorithm and applied it to the MOS

radiance imageries. The MOS destriping procedure

can be briefly outlined as follows. First, for each scan

(along the detector array) and a given spectral band, fit

the radiance to a least-square cubic polynomial along

the scan and compute relative gain at each detector.

Next, for each detector select the median gain over all

scans in the scene to derive the nominal gain factor for

that detector. Finally, the MOS radiance image can be

recomputed with the destriping correction using the

median gain factor.

A complicated stray light and striping correction

algorithm is now available from the MOS project.

Some study and tests are needed to see the efficacy of

this algorithm. We applied the atmospheric correction

to both MOS and SeaWiFS for co-located images and

compared the retrieved ocean and atmospheric optical

properties. Two MOS-SeaWiFS co-located images

acquired on January 29, 1998 in the Atlantic ocean

(latitude 27° and longitude -32°) and February 28,

1998 in the Mediterranean Sea (latitude 38° and

longitude 3°) were first tested. These two scenes,

acquired one month apart, differ significantly in their

ocean and atmospheric optical properties. In comparing the MOS retrieved ocean and atmospheric optical

results with that of SeaWiFS, however, we found that:

the MOS retrieved aerosol optical thickness at the

NIR band was usually a factor of 2-3 times higher

than that of SeaWiFS;

the MOS retrieved (7,8) which characterizes the

spectral variation of aerosol optical properties is

unreasonably low; and

the MOS retrieved normalized water-leaving

reflectances [ rw

(l)]N in the visible are

significantly different from those of SeaWiFS.

Since we are applying an identical atmospheric

correction process to the two sets of measurements,

the large discrepancy in the retrieved results between

the two sensors can probably be interpreted as a

difference in sensor calibrations. It is therefore

necessary to recalibrate one sensor to the other, to

allow for meaningful comparisons of the retrieved

ocean optical properties.

A Vicarious Intercalibration for MOS

The vicarious intercalibration procedure between

MOS and SeaWiFS can be described as follows. We

assume that the gain of the MOS 868 nm band is

unchanged because of differences in the orbits of

MOS and SeaWiFS, thereby using the aerosol

concentration from the MOS measurements, and only

accept that the aerosol model determined by SeaWiFS

is still valid. Next, by using the SeaWiFS retrieved

aerosol models we can theoretically predict the

atmospheric effects in the MOS imagery. The

whitecap radiance contribution can be estimated in the

same way as SeaWiFS (Gordon and Wang, 1994a).

Finally, using the SeaWiFS retrieved normalize waterleaving reflectance, [ rw

(l)]N

, the water-leaving and

total radiance at the TOA in the MOS imagery can be

computed, and the gain coefficients for the MOS

bands can be derived. To reduce the variation of the

derived gain coefficients with various scans, multiple

scans within the MOS scene can be used to obtain

coefficient data and derive a best fit for the MOS 384

detectors. Table 2 provides the derived MOS recalibration gain coefficients fitted with the leastsquare cubic polynomial. These coefficients were

derived from two MOS data set acquired on January

29 and February 28, 1998. We found that the derived

gain coefficients for the MOS bands 1-6 have very

similar values in the two different cases, indicating

that they are nearly independent of temporal and

spatial variations. The derived gain coefficients for

band 7, however, are different in the two cases. It

appears that the MOS 750 nm band performance is

related to the atmospheric optical conditions and its

gain adjustment is in opposite to other bands (gain

coefficient > 1).

Since the derived MOS 750 nm band recalibration gain coefficients depend on the

atmospheric optical properties, we have modified the

atmospheric correction algorithm such that the

correction can also be operated using the MOS 685

and 868 nm bands. Therefore, a consistent recalibration gain coefficients for the MOS bands 1-6

and band 8 can be applied.

Results and Discussions

We applied the derived MOS gain coefficients as

in Table 2 to the MOS measured-radiance at the TOA,

and retrieved ocean and atmospheric optical properties

for comparison with results from the SeaWiFS

measurements. Figure 1(a) and 1(b) provide examples

of the histogram (%) for the retrieved normalize

water-leaving reflectances (%) for bands 2 from MOS

in comparison with SeaWiFS for the case of January

29 and February 28, 1998. There are four cases in

each figure: (i) results from the SeaWiFS

measurements with the bands 7 and 8 used in the

atmospheric corrections, (ii) results from the MOS recalibrated radiances with the bands 7 and 8 used in the

corrections, (iii) same as in (ii) except that the MOS

bands 6 and 8 were used in the corrections, and (iv)

results from the MOS original radiance data with the
SIMBIOS Project Annual Report

13

bands 7 and 8 used in the corrections. Note that for

cases in which the MOS bands 7 and 8 were used for

the atmospheric corrections, two different calibration

gain coefficients were applied for the MOS 750 nm

band for cases of January 29 and February 28, 1998.

However, when the MOS bands 6 and 8 were used in

the corrections, the MOS band 7 reflectance data were

simply not used, thereby allowing a consistent set of

recalibration gain coefficients for the MOS bands 1-6

and 8 to be applied for both cases. Figures 1(a) and

1(b) show that the vicarious calibration improves the

agreement significantly.

To further test the efficacy of the vicarious recalibration approach, we have applied the MOS recalibration gain coefficients, which were derived from

January 29 and February 28, 1998 data, to a MOS

image acquired on September 24, 1997 (4-5 months

before) at a location of about latitude 45° and

longitude 13° in the Adriatic Sea, and compared the

results to those obtained from a co-located SeaWiFS

image. Again, MOS results were improved

significantly with vicarious re-calibration (Wang and

Franz, 1999).

We conclude from these studies that, with the

vicarious calibration approach, the retrieved results

from different sensors can be meaningfully compared

and possibly merged. More importantly, with the

same procedure, one can re-calibrate satellite sensors

using in situ ocean and atmospheric optical property

measurements.

Table 1. Characteristics of MOS with SeaWiFS.

Instrument MOS SeaWiFS

Platform I RS-P3 OrbView-2

Launch date March 21, 96 August 1, 97

Altitude (km) 817 705

Equatorial crossing time 10:30 AM 12:00 Noon

Resolution at nadir (km) 0.5 1.1

Scan swath (km) 200 2800

Time for one orbit (minutes) 101 99

Spectral range (nm) 408-1010 412-865

Instrument calibration Lamp Solar & Lunar

Table 2. The derived MOS gain coefficients as G(l, i) = c

n

n= 0

3

(l )i

n

, for i = 1-384

MOS

 (nm)

c0( ) c1( ) c2( ) c3( )

408 0.9029 3.5 10-4 -9.0 10-7 1.4 10-9

443 0.8453 3.8 10-4 -7.0 10-7 6.5 10-10

485 0.8097 3.8 10-4 -5.3 10-7 2.1 10-10

520 0.8693 1.7 10-4 -4.9 10-8 2.8 10-10

570 0.8701 1.8 10-4 2.2 10-7 -4.6 10-10

685 0.9287 7.6 10-4 -2.6 10-6 3.5 10-9

 750† 1.3208 -3.5 10-4 -2.9 10-6 7.4 10-9

 750‡ 1.2287 5.1 10--4 -5.3 10-6 -3.2 10-10

868 1.0000 0.0 0.0 0.0

 † From case of Jan. 29, 1998 ‡ From case of Feb. 28, 1998
SIMBIOS Project Annual Report

14

Figure 1. The histogram (%) of the MOS retrieved normalized water-leaving reflectances (%) with and

without recalibrations in comparison with the SeaWiFS measurements for 443 nm band for case of (a) January

29, 1998 (Atlantic Ocean) and (b) February 28, 1998 in the Mediterranean Sea.

0

5

10

15

20

0 1 2 3 4 5 6

MOS and SeaWiFS (Band 2)

 SeaWiFS

 MOS (bands 7 & 8)

 MOS (bands 6 & 8)

 MOS (original)

% of Pixels

[ 

w

(2) ]

 N

 (%)

(a) Atlantic Ocean (Jan. 29, 1998)

0

5

10

15

0 1 2 3 4 5

MOS and SeaWiFS (Band 2)

 SeaWiFS

 MOS (bands 7 & 8)

 MOS (bands 6 & 8)

 MOS (original)

% of Pixels

[ 

w

(2) ] N (%)

(b) Mediterranean Sea (Feb. 28, 1998)
SIMBIOS Project Annual Report

15

4.1.2 OCTS

The OCTS is an optical radiometer which flew on

the Japanese Advanced Earth Observing Satellite

(ADEOS) from August 1996 to June 1997, collecting

10-months of global ocean color data (Kawamura,

1998). During the ADEOS mission lifetime,

approximately 450 GB of real-time, 700m-resolution

OCTS data was collected by the SeaWiFS project

through NOAA ground stations at Wallops, Virginia

and Fairbanks, Alaska. The archive consists of 337

scenes of the U. S. East Coast and 1311 scenes over

Alaska.

Since no standard software was publicly

available, the coastal U.S. data set was originally

processed and distributed in near-real time using

NASA software developed under rapid prototyping

conditions. Over the past year, the SIMBIOS project

has been engaged in a comprehensive program to

enhance the algorithms and software used to process

the OCTS data, with specific attention given to

improving the geolocation and image registration,

atmospheric correction algorithms, and vicarious

calibration. In addition, through its close working

relationship with the OCTS team at the Japanese

Space Agency (NASDA) Earth Observation Research

Center (EORC), the project has collected an archive of

OCTS Level-1B and Level-2 NASDA products

corresponding to times and locations where in situ

data is available. This match-up data set has been

used to validate the Level-2, Version-3 products from

NASDA (Shimada, 1998b), as well as the Level-2

products generated using SIMBIOS project software

and algorithms.

Processing to Level-0

The U.S. Coastal data set must first be converted

from a raw 10-bit format to a 16-bit Level-0 format.

The original processing made use of a NASA-defined

Level-0 format, which was inconsistent with the

NASDA Level-0 format (NASDA, 1994). To

eliminate this inconsistency, the SIMBIOS software

was enhanced to generate NASDA format, including

headers containing the definitive spacecraft

ephemeredes and spacecraft clock timing data. The

entire raw-data archive was then reprocessed to

NASDA Level-0 format, and the data set was again

made available to the public. It can be accessed via the

"File Request and Staging" function of the SeaWiFS

data processing system at http://falefa.gsfc.nasa.gov

/~seawifsd/sdpsdoc/html/main.html.

Processing to Level-1B

In general, the processing of Level-0 data to

Level-1B includes conversion of raw sensor counts to

physical units and the assignment of geolocation

information to each observation (pixel, detector, and

band). Several factors in the design of the OCTS

instrument complicate this process. Each OCTS band

is divided into 10 individual detectors, where each

detector is associated with a separate scan line. Each

detector has a slightly different and apparently nonlinear responsively, which gives rise to horizontal

striping in the OCTS imagery. The basis for the

SIMBIOS calibration is the NASDA Version 3

preflight calibration and relative detector calibration

(Shimada, 1998a). The relative detector calibration

substantially reduces the striping effects, but low-level

artifacts are still visible and they can become

significant following removal of the large,

comparatively smooth atmospheric signal.

The design of the OCTS scan mirror and focal

plane results in severe misalignment of the line-of-site

for different spectral bands viewing at essentially the

same time. To perform atmospheric correction or

derive chlorophyll concentration at a given location

requires that the bands be co-registered to that

location.

The SIMBIOS project developed a registration

technique in which an idealized focal-plane geometry

is defined, and all bands are re-sampled using a

nearest neighbor approach to match the idealized

ground track. This method is similar in concept to the

NASDA approach (NASDA, 1994), but it will result

in slightly different re-sampling. Furthermore, while

the registration process can correct for differences in

geolocation between bands, the re-sampled

observations come from different lines-of-sight with

unique sensor-to-ground and sun-to-ground

geometries.

To ensure accurate atmospheric correction, the

true solar and sensor view angles per band are saved

in the Level-1B file for use in Level-2 processing.

Before the registration process can begin, however,

the observations from each band must be accurately

navigated. The geolocation algorithm used for

SIMBIOS OCTS processing is a modified version of

the method used for SeaWiFS navigation (Patt and

Gregg, 1994). This technique has the potential to yield

an exact solution to the geolocation of each scan line,

when the spacecraft position and sensor geometry are

accurately known.

Some sources of error include: inexact knowledge

of the instrument design and installed, post-launch

sensor and mirror alignments (NASDA, 1994),

uncertainties in orbit location or spacecraft attitude,

and variations in the scan-rate or sensor tilt.

To improve geolocation accuracy, the SIMBIOS

project derived time-dependent attitude and tilt

adjustments using an automated navigation

assessment technique based on island targets (Patt et

al., 1997). The final navigation is still being assessed,

but preliminary indications show that it is accurate to

approximately one kilometer.
SIMBIOS Project Annual Report

16

Processing to Level-2

Within the SIMBIOS project, Level-1B to Level2 processing includes application of the vicarious

calibration, removal of the atmospheric signal to

retrieve the water-leaving radiances, and generation of

derived products such as chlorophyll concentration. It

is most appropriate to apply the vicarious calibration

at this stage, as it must account for deficiencies in the

atmospheric correction algorithm, as well as for

changes in the preflight calibration. Since this same

approach was used by NASDA, the Level-1B products

from the Japanese Space Agency and the SIMBIOS

project are calibration equivalent, though the

atmospheric correction algorithms and file formats

differ.

The SIMBIOS OCTS atmospheric correction

algorithm is based on the SeaWiFS algorithm of

Gordon and Wang (1994a). The SIMBIOS approach

has been to identify those few parts of the algorithm

which are sensor or band-pass specific, and develop a

software package which can process data from

multiple ocean color remote sensors. The sensitivity of

the algorithm to differences in spectral bands was

carefully assessed by Wang (Wang, 1999), wherein he

showed by simulation that these differences can be

accurately accounted for through exact calculation of

the Rayleigh reflectances and minor modifications to

the diffuse transmittance calculation. The multi-sensor

Level-1B to Level-2 code (MSl12) has been used

successfully to process and intercalibrate MOS and

SeaWiFS data (Wang and Franz, 1999), and it is now

being employed to process the entire SIMBIOS OCTS

archive.

When processing OCTS data, the MSl12 software

is able to make use of the band-dependent solar and

view angles. If these angles are provided in the Level1B input file, they will be used in the atmospheric

correction process when computing the Rayleigh

radiances, the air-mass calculations that affect

estimates of white-cap radiance and diffuse

transmittance, and the normalization of the waterleaving radiances.

The atmospheric correction process includes

masking for land, clouds, and saturation and masking

for stray-light in the vicinity of those bright sources.

To mitigate the effects of residual striping or other

forms of systematic or random noise, the MSl12 code

includes options for various types of statistical, spatial

filtering. For OCTS processing, a 5x5-pixel median

filter is applied to the Rayleigh-subtracted radiances in

the near-IR bands, based on the assumption that the

spatial scale of aerosol variability is expected to be

greater than a few kilometers. This smoothing

effectively reduces the tendency for the atmospheric

correction algorithm to select different aerosol types

from pixel-to-pixel. Additional smoothing with a 3x3-

pixel median on the Rayleigh-subtracted radiances is

applied to the visible bands, reducing the effect of

residual striping at the cost of degraded resolution of

the in-water spatial structure.

For purposes of vicarious calibration, the

SIMBIOS project is fortunate to have time and spacecoincident in situ water-leaving radiance spectra from

the Marine Optical Buoy (MOBY) buoy (Clark et al.,

1997) to match a series of OCTS over-flights. This

same buoy is the basis for the SeaWiFS calibration,

providing a convenient bridge to connect the two

mission life-spans. Unfortunately, there were some

problems with the early deployment of MOBY,

limiting the number of usable calibration samples to

seven measurements spanning the period November

1996 to February 1997. In addition, MOBY

measurements are not sufficient to calibrate the nearIR bands at 765 nm and 865 nm, where water-leaving

radiances are very close to zero. It was therefore

assumed that the 865 nm vicarious calibration was

equal to the value suggested in the NASDA Version-4

calibration (Fukushima, pers. comm.), and the 765 nm

band was adjusted to force the atmospheric correction

algorithm to select, on average, a maritime aerosol

type over the MOBY site. This assumption is

consistent with the typical aerosol-type retrievals

derived from SeaWiFS data in the vicinity of MOBY.

The entire vicarious calibration process can be

performed in a single processing step in which the

OCTS match-up data set is corrected to retrieve the

normalized water-leaving radiances, the retrieved

normalized water-leaving radiances are replaced with

the in situ values, and the atmospheric correction

algorithm is reversed to derive the theoretical top-ofatmosphere radiances. These theoretical radiances are

divided by the observed radiances to derive correction

factors for each in situ match-up point, and those

ratios are averaged within each band to derive the

vicarious calibration coefficients.

The final calibration coefficients are listed in the

Table 3, with the equivalent NASDA Version-4

calibration shown for comparison. Considering that

the two projects use different atmospheric correction

algorithms ( Fukushima et al., 1998) and different in

situ measurements for calibration, the results are in

good agreement.

Table 3.

Band NASDA SIMBIOS

1 1.14 1.13

2 1.03 1.01

3 0.9394 0.94

4 1.00 1.00

5 1.04 1.03

6 1.00 0.99

7 1.02 0.91

8 0.89 0.89
SIMBIOS Project Annual Report

17

The largest difference is in the 765 nm band,

which NASDA does not use for atmospheric

correction (Shimada, 1998). Since SIMBIOS does

make use of the 765 nm band for aerosol model

selection, a correction for oxygen absorption was

necessarily performed, which accounts for the

discrepancy.

Validation Analyses

An extensive set of in situ data taken during the

time of the OCTS mission was made available to the

SIMBIOS project for match-up analysis from the

SeaBASS database. Over 600 data points taken on

134 separate days exist in this set.

OCTS Satellite data used in the match-up analysis

was obtained from two different sources and two

different processing methods were used. Files in the

U.S. Coastal archive which matched in situ data points

were processed from Level 0 to Level 2 using the

SIMBIOS algorithms and calibration described above.

Level 1B data files supplied to the SIMBIOS Project

by NASDA/EORC were processed to Level 2 using

the SIMBIOS atmospheric correction algorithms and

vicarious calibration. Level 2 data supplied by

NASDA/EORC were also matched to in situ data, but

these data were processed using Version 3 of the

NASDA calibration and so results obtained are of

historic interest only.

Normalized water-leaving radiance (nLw) values

were extracted from the Level 2 records and

acceptable pixels within a 1.05-km radius were

weighted by the inverse of their distance to the matchup site and then averaged to derive nLw values for

comparison to in situ data. This technique usually

resulted in obtaining data from 9 pixels in a square

centered about the in situ data point, although the

actual number can vary due to the complex scan

geometry of the OCTS instrument. Match-up values

were also calculated for an area within a 2-km radius

if there were not enough acceptable pixels within the

1.05-km limit.

The in situ water-leaving radiances were

normalized using theoretical estimates of surface

irradiance (Es). The Es values were calculated from

the Solar radiance model of Neckel and Labs (Neckel

and Labs, 1984), weighted by the OCTS band passes,

and transmitted to the surface using measurements of

the local ozone concentration, knowledge of the

Rayleigh optical thickness, and estimates of the

aerosol transmittance. The resulting nLw values were

then compared to the weighted average nLw values

from OCTS.

Where possible, the match-ups of satellite to in

situ data were judged acceptable by the same criteria

used to judge SeaWiFS match-ups to in situ data.

Specifically, match-ups were rejected if:

The time difference between satellite and in situ

measurements was more than 4 hours (6 hours for

chlorophyll).

Difference in solar zenith angle was more than

15o

In situ data were from a duplicate cast and had a

lower K490 value than other casts.

Wavelengths of in situ data differed from OCTS

wavelengths by more than 5 nm.

Satellite data coefficient of determination (the

ratio of standard deviation to average) was greater

than 0.5

The usable number of satellite pixels was less

than 5, after tests for clouds and sunglint.

For the data processed from NASDA Level 1B to

Level 2 using SIMBIOS methods, 13 match-up points

were deemed acceptable. An additional 10 match-up

points were obtained from the Wallops Level 0

dataset. Data collected over the MOBY site were

excluded from this analysis, since they were used to

derive the vicarious calibration.

Table 4.

Band

Number of

Match-ups

nLw ratio

OCTS retrieval / in situ

1 18 1.20

2 18 1.06

3 19 1.01

4 13 0.998

5 9 1.04

The Table 4 summarizes the match-up results

between in situ water-leaving radiance data (excluding

MOBY) and OCTS retrievals processed using the

SIMBIOS atmospheric correction algorithms.

Sargasso Sea Validation Study

Due to the small number of usable match-up in

situ data in existence for the OCTS mission, additional

validation of the SIMBIOS OCTS calibration was

sought. A time series of averaged normalized waterleaving radiances derived from 27 scenes centered in

the Sargasso Sea was generated and compared to

nominal water-leaving radiances derived from MOBY

in situ data and to a time series from one year later in

the Sargasso Sea area created from SeaWiFS data.

The Sargasso Sea area was chosen for the OCTS

data because it yielded the largest number of clearwater scenes within the OCTS data set acquired by

the Wallops receiving station. In addition, six clearwater scenes centered over Bermuda were generated

from the same archive and compared to in situ data

from that area.

The SeaWiFS Sargasso time-series data was

taken from the standard 8-day time-binned dataset, for

a 3° square box centered at Latitude 25.5° and
SIMBIOS Project Annual Report

18

Longitude -71.5° from 57 8-day periods between

November 1997 and December 1998. The SeaWiFS

time binning procedure averages all acceptable values

over each time period on a pixel-by-pixel basis. The

nominal clear-water radiances used for comparison

were derived from MOBY in situ data tuned to the

OCTS and SeaWiFS wavelengths respectively. In situ

chlorophyll and water leaving radiances for the

Bermuda site were taken from the Bermuda Atlantic

Time Series (BATS) conducted by the Center for

Remote Sensing and Environmental Optics at the

University of California, Santa Barbara (Garver and

Siegel, 1997). For each scene in the Sargasso Sea and

Bermuda area, normalized water-leaving radiances

were averaged, excluding values where chlorophyll

was not within acceptable limits, i.e. data not between

.0005 g/L and .30 g/L, as well as data of

unacceptable quality, e.g., clouds, etc. The averaged

Sargasso Sea nLw values were compared to nominal

MOBY-derived OCTS nLw values and to SeaWiFS

values from 1997-1998 while the Bermuda area nLw

values were compared to nominal MOBY-derived

nLw values and to contemporary in situ data from the

BATS experiment. For both Sargasso Sea and

Bermuda area data, chlorophyll values were computed

from the average nLw using both the OC2 algorithm

of O'Reilly et al. (1998) adjusted to the OCTS spectral

bands and the standard NASDA OCTS-C algorithm

(Kishino et al., 1998). In addition, pigment

concentrations were computed using the Normalized

Difference Pigment Index (Frouin, personal comm.).

The agreement in the general behavior of the

OCTS data with the SeaWiFS data from one year later

suggests that the variability seen in the Sargasso Sea

nLw values is due to seasonal variation rather than

instrument instability. The mean nLw values from

OCTS agree reasonably well with MOBY-derived

nominal nLw values, suggesting that the SIMBIOS

calibration is working well. The three chlorophyll

algorithms used on OCTS data agree in the average

but the distribution of the chlorophyll derived by the

OC2 algorithm is somewhat broader than that

obtained using the NASDA chlorophyll or NDPI

pigment algorithm. The results of this study were

presented at the Alps ’99 Conference in Meribel,

France in January, 1999

4.2 PRODUCT VALIDATION

The Project is comparing and validating

SeaWiFS satellite measurements with in situ

atmospheric and bio-optical measurements.

4.2.2 SeaWiFS AOT Comparisons

The theoretical basis of the SeaWiFS aerosol

retrieval algorithm are described in both Gordon and

Wang, (1994b) and Wang et al., (1999). In this

section, we briefly outline our efforts in comparing

and validating the SeaWiFS aerosol optical products

with the in situ measurements mainly from the data of

the Aerosol Robotic Network (AERONET) (Holben et

al., 1998). The majority of the instruments within the

AERONET network are in continental locations. The

SIMBIOS Project augumented this network with

coastal and island stations. Some other in situ

measurements from calibration and validation

campaigns within the SIMBIOS project are also

analyzed. The primary objectives for these

comparisons are to:

validate the SeaWiFS aerosol optical thickness

(AOT) products, and

determine the validity of the suite of aerosol

models currently used by SeaWiFS for

atmospheric correction.

In Situ Data Acquisition

The ground-based measurements utilized for the

aerosol optical thickness matchup analyses come from

two primary sources: automated CIMEL sun/sky

scanning radiometer managed as part of the

AERONET network, and hand-held MicroTops II

sunphotometers. A select group of the ground stations

from the AERONET was chosen. These instruments

were located at either coastal or island stations and

were operational for a reasonable length of time after

SeaWiFS went into operation. Table 1 provides the

AERONET station name, location (latitude and

longitude), and corresponding responsible AERONET

principle investigator (PI). The hand-held MicroTops

II sunphotometer data, on the other hand, were

collected by various investigators in field campaigns

associated with the SIMBIOS Project. Data from the

MicroTops instruments are reprocessed from raw

voltages using code adapted from the AERONET

standard CIMEL processing code. This ensures that

the ta

 data derived from the MicroTops

measurements will be comparable to the data provided

by the AERONET.

SeaWiFS Data Acquisition

The SeaWiFS aerosol optical thickness data were

obtained by spatially co-locating a 5x5 pixel grid box

around the pixel containing the ground-base

measurement station, thereby providing a maximum

25 SeaWiFS retrievals in each matchup. The

SeaWiFS operational code has been modified to
SIMBIOS Project Annual Report

19

output, at a pixel by pixel level, the aerosol optical

thickness at wavelength 865 nm, values of retrieved

two aerosol models, as well as the model partition

ratio ra

 value. Therefore, aerosol optical thicknesses

at all the SeaWiFS wavelengths can be calculated

(Wang et al., 1999).

Data Analyses

SeaWiFS data were obtained by averaging over a

5x5 pixel grid box spatially, whereas the ta data from

the CIMEL measurements were derived by a timeweighted averaging during the SeaWiFS overpass (± 1

hour). Usually, the CIMEL instruments routinely take

one measurement every 15 minutes. Therefore, for a

given SeaWiFS file there may be as many as eight

AERONET measurements that qualify as a match for

the 2-hour time window. The number of hand-held

MicroTops II measurements that match a given

SeaWiFS file, however, varies greatly since the

measurement protocol for these instruments is not yet

well-defined. In general, there should be a minimum

of three MicroTops measurements per matched

SeaWiFS file. The ground-based measurements are

averaged after weighting by the time difference

between the in situ measurement and the SeaWiFS

overpass. Once averaged, the ground based

measurements are compared with the SeaWiFS

derived values on a band by band basis for each

ground station. Due to a limited number of

MicroTops data, these data are grouped together as

one “station.”

Preliminary Results

We compared the SeaWiFS derived aerosol

optical thicknesses with those from the ground in situ

measurements. Figure 2 provides an overall

comparison results of ta (l) between SeaWiFS and

CIMEL measurements at wavelength 865 nm (870 nm

for CIMEL). The CIMEL measurements were from

the AERONET stations listed in Table 5. The dotted

lines in Figure 2 is the 1:1 line. Though the

comparison results varying both in time and location,

it appears that SeaWiFS has tendency of

overestimating ta

(l) with respect to the in situ

measurements. Note that, however, since the

SeaWiFS band 8 has not been absolutely calibrated on

orbit, any error in calibration may contribute to the

error in the ta (865) evaluations. On the other hand,

some in situ data are suspected to be erroneous due to

instrument calibration. Obviously, more studies are

needed to understand all of these. We want to

emphasize that all results are preliminary.

Similarly, the in situ MicroTops II data, which

were from the various SIMBIOS calibration and

validation campaigns, have been compared with the

SeaWiFS measurements. Although this work is still

in the initial phase, some results are promising. Table

6 shows three sample comparison results from three

field experiments. In these three examples, the

SeaWiFS results were almost all underestimated as

compared with the MicroTops II measurements (Ratio

< 1), though the three results usually agreed

reasonable well.

Figure 2. The retrival SeaWiFS aerosol optical thickness ta

(l) compared with the ground in situ

measurements from AERONET at 865 nm (870 nm for CIMEL Data).

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5

 Cimel 

a (87

0)

 SeaWiFS 

a

 (865)

SeaWiFS (5x5)
SIMBIOS Project Annual Report

20

Table 5. AERONET sites utilized for the aerosol matchup analyses.

AERONET Station Latitude Longitude AERONET PI

Bahrain 26.32 50.50 Charles McClain*

Bermuda 32.37 -64.70 Brent Holben

Dry Tortugas 24.60 -82.80 Ken Voss/Howard Gordon

Kaashidhoo 4.97 73.47 Brent Holben

Lanai 20.83 -156.99 Charles McClain*

San Nicolas Island 33.26 -119.49 Robert Frouin

*SIMBIOS Project Office

Table 6. Three samples of MicroTops II data compared with SeaWiFS

 Aerosol Optical Thickness t a(l)

Jason Project

G. Feldman

GOCAL97-98

J. Mueller

JULNAN98

B. Schieber and

A. Subramaniam

 (nm)

SeaWiFS Ratio SeaWiFS Ratio SeaWiFS Ratio

440

500

670

865

0.0555 0.7603

0.0509 0.9204

0.0395 0.8857

0.0304 0.9102

0.1635 0.8678

0.1469 0.9767

0.1076 1.1811

0.0774 0.8113

0.1775 0.9168

0.1538 0.9031

0.1013 0.9217

0.0641 0.8456

4.2.3 SeaBASS INTERFACE

The SeaWiFS Bio-optical Archive and Storage

System (SeaBASS) was created by the SeaWiFS

Project to provide a data archive for in situ products

used in scientific analysis. This system has been

expanded to additionally contain data sets of interest

to the SIMBIOS Project.

The in situ data in SeaBASS include

measurements of water-leaving radiance and other

related optical and pigment measurements, from ships,

moorings and drifters. Various methods are deployed

in the collection of SeaBASS data, including the use

of standard profiles, floating radiometers and abovewater measurement devices. In addition to the optical

and pigment products listed, measurements of total

suspended matter (TSM), chromophoric dissolved

organic matter (CDOM), and other typically nonplankton derived optical components are recorded in

SeaBASS.

The products are used by the SIMBIOS Project in

validation of SeaWiFS and other (OCTS, POLDER,

etc.) postlaunch imagery and development of new

operational chlorophyll algorithms. Additional uses

under SIMBIOS will likely include field data

calibration comparisons, algorithm workshops, and

time series studies. A detailed description of the

original SeaBASS design and scope is provided in the

SeaWiFS Technical Report Series, specifically

volume 20. A current description of the SeaBASS

system is available via the World Wide Web at

http://seabass.gsfc.nasa.gov.

Data Design

The SeaBASS system contains data from well

over 150 separate experiments with thousands of files

requiring over 22 megabytes of storage space. In

addition, the historical optics database holds over

300,000 records related to phytoplankton pigments

and is expected to grow as new pigment data is

collected. Since the SeaBASS system is continuously

growing with new data, a method for efficiently

ingesting and storing field data was needed. It was

deemed important that the data ingest be as

straightforward and effortless as possible on the part

of the contributing investigators, while still offering a

useful and correct data archive for analysis efforts.

The following aspects were considered to be the most

important in the design of the system:

Simple data format

Global portability
SIMBIOS Project Annual Report

21

Data update simplicity

Web accessible data holdings

Support for existing Web standards

To accomplish the above goals, the SeaBASS

system was designed to support standard ASCII files

which can be managed from any computer platform.

The files use a simple descriptive header format which

contains descriptor=value pairs to explain the specifics

(“metadata”) of a data file. For example:

/begin_header

/affiliations = University_of_Maryland

/investigators = John_Creamer

/contact=johnc@umd.edu

/parameters=Ed,Lu,Kd,CHL

/north_latitude=59.10[DEG]

/south_latitude=58.65[DEG]

/east_longitude=-13.11[DEG]

/west_longitude=-13.50[DEG]

! Comments: data file to be updated

...

/end_header@

The header or metadata section is intended to

fully describe the data in a file. Each header contains

information on time and location of the in situ

measurements, the investigators involved, values

measured, comments, and other related descriptive

information. Frequently, SeaBASS files will contain

references to other files with additional descriptive

details (e.g., README files).

Following the header information, the actual

measured optics or pigment data is listed in columnar

format. Typical data files include optical profiles,

summary pigment files, or along track measurements.

Specific information and examples of the formats can

be referenced at the SeaBASS web site.

Following an series of redesign modifications in

the first year of the SIMBIOS effort, the SeaBASS file

formats have not changed significantly. However,

additional changes may need to be made in the near

future as new instrumentation and collection methods

continue to populate the archive, some of which may

warrant variations in the current data archive approach

(i.e., hyper-spectral data).

Format Checking

Early in the development of the SeaBASS web

site it was realized that each data provider can have

very different views on data format or presentation. In

order to establish a standard format for SeaBASS

incoming data files which met the dual goals of

simplicity and portability, feedback software was

developed.

The primary component of this software is the

FCHECK script. FCHECK is written in the PERL

scripting language with connections to look-up tables

and UNIX mail handling utilities. Data providers

from any platform can test their data for compatibility

with the SeaBASS format by simply e-mailing their

file to fcheck@seabass.gsfc.nasa.gov. The FCHECK

program will receive the incoming mail file from the

system mail handler, parse the data, and thoroughly

compare it to the established SeaBASS format.

FCHECK will then report back to the data provider on

the file’s compliance. This file testing function

happens automatically with no intervention required,

but the SeaBASS administrator is sent a copy of all

incoming data files, for review. The FCHECK

program has been used by many SeaBASS data

providers as a quick format checker and has saved

many hours of processing time for both the SeaBASS

administrator and contributing investigators.

Once the data provider is sure that their files will

work with the SeaBASS archive, they can send the

data, and related documents, to the SeaBASS archive

via the file transfer protocol (FTP). From there, the

SeaBASS administrator will move the files into their

appropriate position in the archive and will initiate a

database update to register the new data to the

SeaBASS online system.

Data Security Issues

A concern of some contributors to SeaBASS

involves outside user accessibility. Some investigators

have been concerned that when data is quickly

submitted to the archive, others may use the data

without proper notification or acknowledgement. To

address these concerns, and to afford continued rapid

submission of data sets, the SeaBASS web server has

been configured as a password protected system.

Typically, only SeaWiFS or SIMBIOS authorized

investigators who also submit data to the archive are

allowed access. Others may be allowed access on a

case-by-case basis. Additionally, the web server and

SeaBASS software log all user activity. This

information is available to contributing investigators.

It is expected that all users who use data from the

SeaBASS archive will offer collaboration or

authorship to the data provider.

Specific Matchup Format

To expedite comparisons between in situ data and

SeaWiFS (or other satellite) products, a specific file

format has been developed. This file format, known as

the “matchup” format, follows a similar logic to that

of the other SeaBASS in situ files, that being a

simple, easy to implement format in standard ASCII.

However, unlike the general format for SeaBASS

data, the matchup format expects a strict adherence in

the positions and units of data fields. This requirement

is to allow for automated comparisons between in situ
SIMBIOS Project Annual Report

22

and satellite data. The format is also used in

interactions with the SeaWiFS/SIMBIOS satellite data

archive. The matchup format is structured in standard

ASCII columnar format with the following fields in

each data record:

Year, Month, Day, Hour, Minute, Second, Latitude,

Longitude, Lw412, Lw 443, Lw 490, Lw 510, Lw 555,

Lw 670, Es412, Es 443, Es 490, Es 510, Es 555, Es 670,

Kd490, Chl a

Where the time and location values identify when

and where the measurement was taken. Water-leaving

radiance (Lw) and downwelling irradiance (Es) values

may be extrapolated from below the surface or

measured above the surface, depending upon the

instrumentation used. The vertical attenuation of

irradiance at 490 nm (Kd 490) as well as in situ

measured values of chlorophyll a (Chl a) are also

recorded if available. Missing data values are

represented by a placeholder. As in the case of other

SeaBASS submitted data, the matchup file also

contains a metadata section to describe the enclosed in

situ data.

Data Contributions

The SIMBIOS project funds numerous

investigators in order to obtain in situ optical and

pigment data for Case I (optically characterized solely

by phytoplankton) water characterization. Additional

investigators are also supported to develop new

algorithms or scientific approaches in accordance with

the goals of the SIMBIOS Project. As described

above, the data and information provided are used for

both internal analysis and satellite validation and to

populate the SeaBASS archive for future activities and

community use. Table 7 summarizes the data sets

which have been received from investigators during

the first year of funding. As shown in the table, the

majority of funded principal investigators provide

field data for the archive. However, some additional

investigators were funded solely to develop algorithms

or analysis techniques.

Future Plans

The SIMBIOS project has created an environment

by which in situ data may be archived, accessed and

analyzed to improve satellite retrievals through

scientific data validation. In its first year of operation,

the Project has implemented software and format

standards which should greatly aid in future satellite

efforts. Additionally, the Project’s focus on thorough

data documentation should aid in both current and

future research activities. Subsequent years will focus

on improving the usefulness of in situ data by

continuing to improve the data ingest and data

analysis approach.

Table 7. SIMBIOS supported data submitted to SeaBASS

Principle

Investigator

University

or Laboratory

Optics

Data

Pigment

Data

Documentation

Provided

Algorithm

Development

William Balch Bigelow Labs ÷ ÷ ÷

J. Brock / C. Brown USGS / NOAA ÷ ÷ ÷

Douglas Capone U. MD ÷ ÷ ÷

Ken Carder U. South Florida ÷ ÷ ÷

Francisco Chavez Mont. Bay ARI ÷ ÷

Glenn Cota ODU ÷ ÷ ÷

Tom Dickey UC SantaBarbara ÷ ÷

Dave Eslinger U. AK, NOAA/CSC ÷ ÷ ÷

Piotr Flatau Scripps, UCSD ÷ ÷

Robert Frouin UCSD / Scripps ÷ ÷

Robert Green JPL ÷ ÷

Watson Gregg GSFC ÷ ÷

Mark Miller BNL ÷ ÷

Rick Miller Stennis Space Ctr. ÷

Greg Mitchell Scripps, UCSD ÷ ÷ ÷ ÷

Jim Mueller San Diego St. U. ÷ ÷ ÷

Frank Müller-Karger U. South Florida ÷ ÷ ÷

John Porter U. Hawaii ÷ ÷

Dave Siegel UC Santa Barbara ÷ ÷ ÷ ÷

Knut Stamnes U. Alaska ÷ ÷ ÷

Ron Zaneveld OSU ÷ ÷ ÷
SIMBIOS Project Annual Report

23

4.2.4 Support Services

In an effort to improve the quality and quantity of

calibration and validation data sets, the SIMBIOS

Project offers several support services to field

investigators. These services include; scheduling of

on-board Local Area Coverage (LAC) recording for

SeaWiFS; overflight predictions for operational

sensors (currently SeaWiFS, MOS-B and OCI); near

real time SeaWiFS imagery for cruise locations; and

optical instrumentation from a pool of investigatorand project-owned instruments. These services may

be requested via the World Wide Web at

http://simbios.gsfc.nasa.gov.

In return for these services, the SIMBIOS Project

requests that the field investigators provide in situ

validation data to the Project's bio-optical archive,

SeaBASS. Since October of 1997, when these

services were initially offered, the SIMBIOS Project

has supported 81 cruises (Table 8).

SeaWiFS Scheduling

Since much of the worlds oceans are not covered

by a SeaWiFS High Resolution Picture Transmission

(HRPT) station, high-resolution data may be recorded

onboard the SeaWiFS sensor. As a service to the

science community, the SIMBIOS project in

conjunction with the SeaWiFS project can schedule

SeaWiFS onboard LAC for cruises that occur outside

HRPT coverage. SeaWiFS has the ability to record a

maximum of 10 minutes of high-resolution data per

downlink. Typically, a 30-second interval is allotted

for LAC target, which corresponds to 180 scan lines

or approximately 200 km along track at nadir.

Detailed information on LAC scheduling is available

on the SIMBIOS web site.

Overflight Predictions

For calibration and validation purposes, in situ

measurements should be made as close to the sensor

overflight time as is possible. To aid investigators in

determining when sampling should occur, the

SIMBIOS project offers overflight predictions for all

operational ocean color remote sensors. Currently,

the sensors supported are SeaWiFS and MOS-B.

With the successful launch of ROCSAT-1 on 26

January 1999, OCI is being added to this list. Detailed

information on overflight predictions is available on

the SIMBIOS web site.

Near-Real Time SeaWiFS Imagery

In addition to providing predictions for satellite

overflight times, the SIMBIOS project offers near real

time imagery of the operations SeaWiFS products in

JPEG format to cruises at sea. These images provide

field investigators with additional information with

which they may maximize in situ sampling of

transient oceanographic features. The default

specifications for the images provided include:

Available LAC, HRPT, and Global Area

Coverage (GAC);

Chlorophyll-a and pseudo-true color images;

2-degree box about a designated location or the

entire designated region;

Image Width: 600 pixels; and

Minimum percent valid chlorophyll pixels: 5% .

Images may be customized to best accommodate

individual investigators needs. Detailed information

on near real time imagery is available on the

SIMBIOS web site.

Table 8. Table of SIMBIOS supported cruises with services provided.

Cruise Location Begin Date End Date

On-board LAC

Over-flight

Prediction

Near Real Time

Imagery

Instrument Pool

Principal Investigator

Chesapeake Bay 09/28/1997 11/23/1997 ÷ Curt Davis

Black Sea 10/03/1997 10/13/1997 ÷ Oleg Kopelevich

Alaska 10/10/1997 10/17/1997 ÷ Glenn Cota

Gulf Of Maine 11/10/1997 11/21/1997 ÷ ÷ William Balch

Taiwan 11/23/1997 11/25/1997 ÷ ÷ Hsien-wen Li

Equatorial Pacific 09/27/1997 12/16/1997 ÷ ÷ Francisco Chavez

Ross Sea 10/01/1997 12/14/1997 ÷ ÷ ÷ Greg Mitchell

Equatorial Atlantic 11/14/1997 12/12/1997 ÷ ÷ ÷ C. Menkes

HOTS 12/01/1997 12/21/1997 ÷ ÷ John Porter
SIMBIOS Project Annual Report

24

Cruise Location Begin Date End Date

On-board LAC

Over-flight

Prediction

Near Real Time

Imagery

Instrument Pool

Principal Investigator

Jamstec / Kaiyo 12/07/1997 12/26/1997 ÷ ÷ ÷ Marlon Lewis

Southern Polar Front 10/19/1997 02/15/1998 ÷ ÷ Greg Mitchell

HOTS Cruise 01/09/1998 01/12/1998 ÷ ÷ John Porter

Jamstec / Mirai 01/31/1998 02/11/1998 ÷ ÷ ÷ Marlon Lewis

SeaWiFS Initialization Cruise 01/26/1998 02/12/1998 ÷ ÷ ÷ ÷ Dennis Clark

Florida Bay 01/25/1998 02/07/1998 ÷ ÷ Eurico D'Sa

Antarctic 02/10/1998 03/18/1998 ÷ ÷ ÷ Greg Mitchell

Azores / Canary Islands 03/02/1998 03/27/1998 ÷ ÷ Marcel Wernand

Gulf of California 03/05/1998 03/16/1998 ÷ ÷ ÷ ÷ Jim Mueller

Gulf Of Maine 03/14/1998 03/27/1998 ÷ ÷ ÷ Bruce Monger

Indian Ocean 02/28/1998 03/15/1998 ÷ ÷ John Morrison

East China Sea 03/16/1998 03/27/1998 ÷ ÷ ÷ Gwo-Ching Gong

Bahamas 04/1/1998 04/07/1998 ÷ ÷ ÷ Robert Steward

HOTS 04/14/1998 04/16/1998 ÷ ÷ Craig Motell

Sicily Channel 03/27/1998 04/20/1998 ÷ ÷ ÷ M. Ribera d'Alcala'

California Coast 04/02/1998 04/24/1998 ÷ ÷ B.G. Mitchell

Yellow Sea 04/03/1998 04/23/1998 ÷ ÷ ÷ Sonia Gallegos

Sea Of Cortez 04/17/1998 04/26/1998 ÷ ÷ ÷ Gene Feldman

SW Pacific 03/24/1998 04/30/1998 ÷ ÷ ÷ ÷ Ajit Subramaniam

North Sea 04/6/1998 05/01/1998 ÷ ÷ ÷ Marcel Wernand

Atlantic Meridional Transect 04/6/1998 05/01/1998 ÷ ÷ ÷ Stan Hooker

Equatorial Pacific 04/26/1998 05/2/1998 ÷ ÷ ÷ Peter Strutton

Subtropical North Pacific 04/21/1998 05/06/1998 ÷ ÷ ÷ Jeffrey Polovina

HOTS 05/11/1998 05/15/1998 ÷ ÷ John Porter

Atlantic Ocean - Baltic Sea 05/01/1998 05/18/1998 ÷ ÷ Roland Doerffer

Gulf Of Cadiz 05/09/1998 05/19/1998 ÷ ÷ Andreas Neumann

Baltic Sea 05/26/1998 06/03/1998 ÷ Peter Land

Atlantic Meridional Transect 05/14/1998 06/18/1998 ÷ ÷ ÷ Stan Hooker

Gulf Of Maine 06/01/1998 06/15/1998 ÷ ÷ ÷ Bruce Bowler

Equatorial Pacific 06/6/1998 06/16/1998 ÷ ÷ ÷ ÷ Peter Strutton

Massachusetts Bay 07/05/1998 07/10/1998 ÷ ÷ ÷ Ajit Subramaniam

Labrador Sea 06/22/1998 07/10/1998 ÷ ÷ ÷ Glenn Cota

East China Sea 06/27/1998 07/08/1998 ÷ ÷ ÷ Gwo-Ching Gong

South China Sea 06/28/1998 07/03/1998 ÷ ÷ Hsien-Wen Li

Gulf Of Mexico 06/27/1998 07/03/1998 ÷ Andrew Thomas

Arctic Ocean 06/18/1998 07/20/1998 ÷ ÷ Dariusz Stramski

Resolute Bay 07/28/1998 08/25/1998 ÷ ÷ ÷ Glenn Cota

Equatorial Atlantic 07/15/1998 08/15/1998 ÷ ÷ ÷ C. Menkes

Long Island Sound 07/20/1998 07/30/1998 ÷ S. Papanikolaou

Puget Sound 06/04/1998 06/25/1998 ÷ ÷ ÷ Ron Zaneveld

Puget Sound 07/29/1998 08/22/1998 ÷ ÷ ÷ Ron Zaneveld

Arctic Ocean 08/05/1998 08/07/1998 ÷ ÷ Sergey Shirshov

Puget Sound 07/24/1998 08/22/1998 ÷ ÷ ÷ M.J. Perry

Taiwan Straits 08/10/1998 08/20/1998 ÷ Ming-Xia HE
SIMBIOS Project Annual Report

25

Cruise Location Begin Date End Date

On-board LAC

Over-flight

Prediction

Near Real Time

Imagery

Instrument Pool

Principal Investigator

HOTS 08/08/1998 08/12/1998 ÷ John Porter

Gulf of Maine 08/14/1998 08/18/1998 ÷ ÷ ÷ Bruce Bowler

SE Bering Sea 08/15/1998 09/09/1998 ÷ ÷ ÷ Stephan Zeeman

South West U.S. 08/17/1998 09/25/1998 ÷ ÷ ÷ Edward Zalewski

South China Sea 09/11/1998 09/27/1998 ÷ ÷ ÷ Rick Miller

California Coast 09/13/1998 10/02/1998 ÷ ÷ Gregg Mitchell

North Pacific 08/30/1998 09/21/1998 ÷ ÷ ÷ ÷ Ron Zaneveld

HOTS 09/26/1998 09/30/1998 ÷ ÷ John Porter

North Pacific 10/01/1998 10/12/1998 ÷ ÷ ÷ Carrie Leonard

Atlantic Meridional Transect 9/14/1998 10/30/1998 ÷ ÷ ÷ Stan Hooker

Barents Sea 9/15/1998 10/10/1998 ÷ ÷ Oleg Kopelevich

U.S. East Coast 10/5/1998 10/13/1998 ÷ ÷ Stephan Howden

Gulf Of Maine 9/10/1998 10/31/1998 ÷ ÷ ÷ ÷ Bruce Bowler

HOTS 10/18/1998 10/20/1998 ÷ John Porter

East China Sea 10/15/1998 10/31/1998 ÷ ÷ ÷ Gwo-Ching Gong

Equatorial Pacific 10/23/1998 11/09/1998 ÷ ÷ ÷ Peter Strutton

HOTS 11/10/1998 11/12/1998 ÷ ÷ John Porter

South Atlantic Bight 10/27/1998 11/24/1998 ÷ ÷ ÷ Ajit Subramaniam

Gulf of California 11/25/1998 12/09/1998 ÷ ÷ ÷ ÷ Andrew Barnard

Gulf of Maine 12/02/1998 12/18/1998 ÷ ÷ Heidi Sosik

HOTS 12/13/1998 12/16/1998 ÷ ÷ John Porter

Indian Ocean 01/04/1999 02/23/1999 ÷ ÷ ÷ J. Le Fevre

Indian Ocean - INDOEX 01/14/1999 04/01/1999 ÷ ÷ ÷ Piotr Flatau

Southern Ocean 01/01/1999 04/01/1999 ÷ ÷ Steve Groom

California Coast 01/09/1999 01/31/1999 ÷ ÷ Greg Mitchell

Field Instrument Pool

The SIMBIOS project provided funding to

several of the science team members for the purchase

of in situ ocean optical instrumentation. The funding

was provided with the stipulation that these

instruments would be made available for three years to

an instrument pool to be maintained by the Project

Office. The Project augmented this instrument pool

with atmospheric instrumentation. Table 10

summarizes the instruments available.

4.3 SENSOR ENGINEERING AND

CALIBRATION

AERONET is a network of ground-based

automated sun photometers owned by national

agencies and universities. AERONET data provides

globally distributed, near-real time observations of

aerosol spectral optical depths, aerosol size

distributions, and precipitable water. These data allow

for algorithm validation of satellite aerosol retrievals

as well as characterization of aerosol properties. Such

validation and characterization are critical for

atmospheric correction of ocean color sensors. The

majority of the instruments within the AERONET

network are in continental locations. The CIMEL Sun

Photometer manufactured in France is the instrument

used for AERONET.

The SIMBIOS Project augmented his instrument

pool with atmospheric instruments by purchasing 12

MicroTops hand-held sun photometers, 2 PREDE

(Japanese built) sun photometers, one micro-pulse

lidar and the 12 CE318 CIMEL sun photometers.

Specifically, the 12 CIMEL instruments augment

the AERONET network with coastal and island

stations. These CIMEL instruments better withstand

the corrosive marine environment after undergoing a

robust re-engineering. These “hardened” CIMEL
SIMBIOS Project Annual Report

26

instruments are placed, with other instruments, at sites

near marine environments. Confirmed (delivered or

negotiated) CIMEL sites include Lanai-Hawaii (with a

backup in Honolulu), Ascension Island, Bahraine,

Tahiti, Wallops Island (Virginia), South Korea, and

Turkey (Black Sea).

CIMEL Re-engineering

In its normal configuration, the CIMEL Sun

Photometer is not suitable for use in a corrosive

marine environment. Meridian Engineering of

Hanover (Maryland) under Tom Riley’s guidance

hardened these instruments for placement in locations

where they may be subject to salt spray. The

modifications include:

Replacement of the base housing — The new

base housing is welded and has more weather

resistant connectors.

Replace motor housing — The new housing is

welded.

Replace instrument housing — Again the new

housing is welded.

Cable and connectors — Connectors were

replaced with military style connectors. Cables

replaced with ones rated for this environment.

The cables were then sealed with both 3M 2242

Linerless Electrical Rubber Splicing Tape and

then 3M Scotch Super 88 Vinyl Electrical Tape.

Hardened moisture sensor — The moisture sensor

cable and connector were replaced.

The following devices were added to allow

remote operation:

Electronic boxes — The two electrical boxes

(Control Box and Power Box) are now sealed

plastic NEMA boxes and are painted white.

Photovoltaic panel mount — The two

photovoltaic panels and the moisture sensor are

mounted on a fiberglass panel that is held to the

power box with stainless steel hardware.

Sun Shield — The Control Box also has a fiber

glass sun shield held one inch above the box and

has stainless steel hardware.

Mounting Plate — A heavy galvanized steel

mounting plate is now available.

Sun Photometer Calibration:

Non-Polarized Channels

The calibration consists of using a sun photometer

calibrated in high altitude conditions (Mauna Loa,

Hawaii) and transferring the calibration to the other

sun photometers by taking simultaneous sun direct

measurements from ground during a clear day. The

top of atmosphere (TOA) signals (V0) of the noncalibrated sun photometer are deduced from those of

the CIMEL sun photometer. This method is currently

applied to all the CIMEL sun photometers involved in

the AERONET network (Holben et al., 1998).

The processing steps for analyzing the calibration

measurements performed by a sun photometer are

described below and summarized in Diagram 1:

Download the raw signal of the uncalibrated sun

photometer [Vu (i)] and of the calibrated sun

photometer [Vr (i)].

Select the simultaneous measurements (time

difference lower than 36 seconds).

Compute for each channel, the TOA signals for

the un-calibrated sun photometer using the TOA

signals of the calibrated sun photometer (obtained

at Mauna Loa).

The TOA signals, computed for each

simultaneous event, are averaged

The comparison with the aerosol optical thickness

(AOT) retrieved from the calibrated sun photometer

allows for validation of the protocol. AOT are

retrieved using the same steps as in Diagram 2 except

for the Ozone retrieval. Total Ozone Mapping

Spectrometer (TOMS) measurements are used for the

computation of ozone contribution.

Currently, eight MicroTops, one SIMBAD and

two PREDE sun photometers have been successfully

transfer calibrated according to the inter-calibration

method. The TOA signals of the MicroTops #3773,

SIMBAD #972396 and PREDE #PS090063 are

summarized during several transfers of calibration

between August and December 1998 in Table 1.

Means and standard deviation are presented for each

channel of each instrument. The standard deviation of

the TOA signal is overall lower than 2%. The results

are especially good for the MicroTops and SIMBAD

sun photometers, considering the long period used, the

design (i.e., hand held) and affordable cost. The

accuracy of the CIMEL sun photometer TOA signals

(calibrated at Mauna Loa and used for our calibration

transfer) is 0.5 % for the channels between 440 and

1020nm (Holben et al., 1998). The accuracy of the

calibration transfer for the PREDE PS090063 is only

presented on Table 11. Another PREDE (#PS090064)

instrument, used between October and December

1998, is still under study.

Sun Photometer Calibration:

Polarized Channels

The polarized version of the CIMEL sun

photometers is composed of three channels at 870nm

mounted on the filter wheel. Three polarizing sheets

are located in front of the filters and are respectively

adjusted according to 0, -60 and +60 degrees.
SIMBIOS Project Annual Report

27

The polarization rate of the light is deduced from three

measurements in these three channels.

The calibration of the polarized version of the

CIMEL sun photometer is performed using a

calibration device designed by the Laboratoire

d’Optique Atmosphérique. The calibration device is

located ahead of a non-polarized source and allows the

polarization of the light in the output of the device.

The reading of the angular position of the two

SF11windows mounted inside the device allows for

the computation of the polarization rate of the light.

The calibration consists of plotting the computed

polarization rate versus the measured one and

determining the slope and the intercept of the trend

line.

The calibration have been performed on six

polarized instruments belonged to the AERONET

group. The results are summarized in Table 12. The

same calibration is scheduled for the SIMBIOS

polarized CIMEL sun photometers. The calibration is

performed for a polarization rate ranging between 0 to

65%, because of the dimensions of the device. The

linear squared fit determined for the calibration of the

six CIMEL sun photometers ranges between 0.9993 to

1.

Sun Photometer Data Processing

The data processing is applied to all SIMBIOS

sun photometers (i.e., CIMEL, PREDE, MicroTops II

and SIMBAD). The data processing principle is

described below and summarized in Diagram 2:

1. Download the raw signal Vi corresponding to the

measurements performed in the channel i.

2. Compute the ratio between the raw signal and the

top of Atmosphere (TOA) signal Vi0 provided by

the calibration of the sun photometer, Vi/Vi0.

3. Compute the ratio between the averaged SunEarth distance and the Sun-Earth distance of the

day, (d0/d).

4. Compute the air mass m, according to the day, the

date, the time and the location when/where the

measurements were taken.

5. Compute the total optical thickness in the channel

i, tot(i).

6. According to the location, compute and remove

from the total optical thickness the Rayleigh and

the ozone optical depth for each channel, R(i)

and O(i). The same equation and Dobson table is

used for the data processing of all the sun

photometers.

7. Compute the aerosol optical thickness (AOT),

A(i).

Several AOT measurements have been performed

on the roof of a building at GSFC (from August to

December 1998), from cruises during several

campaigns and from ground, allowed performance

comparisons with SeaWiFS sensor (Wang et al.,

1999).

Calibration Round Robin

NASA personnel carried out the first SeaWiFSSIMBIOS Intercalibration Round-Robin Experiment

(SIRREX-6) from August 1997 to February 1998.

SIRREX-6 was performed in a completely different

manner from SIRREX-1 through SIRREX-5. In those

tests, laboratory references were brought to a central

location and tested against one another. In SIRREX-6,

the same four common field instruments (e.g.,

Satlantic in-water radiometers) were taken to nine

separate laboratories and tested using the laboratories’

standards and procedures. Two of the sensors were

seven-channel radiance heads and two were sevenchannel irradiance heads. The calibration and data

reductions procedures used at each site followed that

laboratories’ normal procedures. The reference lamps

normally used for the calibration of these types of

instruments by the various laboratories were also used

for this experiment. NASA personnel processed the

data to produce calibration parameters from the

various laboratories for comparison. These tests

showed an overall agreement at better than the +/-2%

level. Test equipment, calibration procedures, data

reduction, and specific handling procedures have been

published in the Riley and Bailey (1998).

SXR-II

The first SeaWiFS Transfer Radiometer (SXR)

was built for the SeaWiFS Project to verify and

compare measurements of spectral radiance at six

discrete wave-lengths in the visible and near infrared

Johnson et al. (1998). In addition SXR is used to

compare these sources to standards of spectral

radiance maintained at the National Institute of

Standards (NIST). SIMBIOS project had a second

copy of the SeaWiFS Transfer Radiometer (SXR-II)

built for use in the calibration round robin. This unit

will supplement the first unit and is designed for

easier travel. The SXR-II is currently being

characterized and calibrated. It will be used in future

SIRREX round robin experiments.

Additional SQMs

NASA developed a portable optical calibration

source called the SeaWiFS Quality Monitor (SQM)

with NIST. Last year, NASA provided limited

financial support for the development of the SQM as a

commercial product. Two companies elected to take

advantage of the opportunity, Satlantic Instruments

and Yankee Environmental Systems, Inc. The

Satlantic version was evaluated by Dr. Stan Hooker.
SIMBIOS Project Annual Report

28

The Yankee Environmental Systems, Optical

Calibration Source prototype was evaluated at GSFC

by Tom Riley. Their computer interface is a

significant improvement over the earlier models. A

number of small problems were uncovered and

reported back to the manufacter who has taken

corrective action.

4.4 SIMBIOS COMPUTING

RESOURCES

The SIMBIOS computing facility contains many

different types of equipment (Diagram 3). The main

goal of the facility is to provide support for the

following areas: 1) routine bulk data processing, 2)

large scale analysis and match-up between sensors, 3)

focused analysis on data subsets, and 4) storage of

large sensor data sets.

To support these efforts, the facility has grown to

include two large server systems, a 6 terabyte tape

library, four desktop workstations, and numerous

personal computers and printers. Co-location of the

facility with the SeaWiFS Project has also made

available other resources such as high-quality color

printers, network equipment, and other supporting

equipment. Large scale tasks such as bulk data

processing and large scale analysis tasks are

performed by two Silicon Graphics (SGI) Origin 2000

servers. To prepare for increased workload, the

systems were upgraded to 6 processors each, and

approximately 3 gigabytes (GB) of RAM. The influx

of large data sets for additional sensors requires

increasing amounts of space, especially when

performing comparative analysis. The Data Processing

server has been increased to 98 GB of disk, and the

Data Analysis server has over 372 GB of total disk

space. Long term storage of data sets is handled by

the 6 terabyte (TB) tape library attached to the Data

Analysis server.

Silicon Graphics O2 workstations are used for

software development and more focused analysis

tasks. The sizing of the workstations varies with the

task requirements. One workstation has 320

megabytes (MB) of RAM and 28 GB of disk space, a

second workstation has 640 MB of RAM combined

with 72 GB of disk space. The third workstation has

640 MB of RAM and 50 GB of disk space.

Acquisition of a fourth workstation is planned for this

fiscal year.

SIMBIOS is connected to the Internet via a 100

megabit link, making network transfer of large data

sets more feasible. Internal connections are also 100

megabit for rapid transfer of data between the servers

and workstations. Data ingest for SIMBIOS is also

done via removable media. The Project can read a

wide variety of removable media including CD-ROM,

8 millimeter tape, 4 millimeter (DAT) tape, and DLT

media up through DLT 7000.

Table 10. SIMBIOS Pool Instruments

Instrument Quantity Description Manufacturer Custodian(s)

MicroTops II

Sunphotometer

w/GPS

12 5 channel handheld sun photometer

w/Garmin GPS-38

Solar Light

Company SIMBIOS Project

HISTAR Package 1

2 hyper-spectral absorption/beam attenuation

meters mounted on a cage with a SeaBird

CTD

WETLabs, Inc Zaneveld/Pegau

Hydroscat 6 3 Backscattering meter HOBILabs

Siegel

Carder

Mitchell

Pure Water System 3

Water purification system for calibration of

WETLabs AC-9 and HISTAR absorption and

attenuation meters

Barnstead Zaneveld/Pegau

AC-9 3 Absorption/beam attenuation meter WETLabs, Inc.

Cota

Capone

Muller-Karger

SIMBAD 2 5 channel radiometer and sun photometer Frouin

SeaWiFS

Multichannel

Profiling Radiometer

2

Free-fall profiling radiometer measuring Lu(z),

Ed(z), Es, Lu(1m) with cables, deck unit and

PC with data acquisition and processing

software

Satlantic, Inc. Capone

Chavez

Micropulse LIDAR 1 Continuous operation LIDAR system SESI SIMBIOS Project

Prede Sun

Photometer 2 Automated ship-board sun photometer Prede SIMBIOS Project

CE 318

CIMEL Sun

Photometer

12 Marine-hardened, automated sun photometer Cimel SIMBIOS Project
SIMBIOS Project Annual Report

29

Table 11. Top of Atmosphere signals (V0) of MicroTops, Simbad and Prede sun photometers determined by

transfer calibration from a calibrated CIMEL at GSFC between August and December 1998.

MicroTops #3773 440nm 500nm 675nm 870nm 940nm

08/20/98 – Cimel # 37 1236.95±0.78 980.63±1.37 1214.27±0.98 821.80±1.12 1419.70±1.22

08/21/98 – Cimel # 37 1243.64±1.92 989.01±1.48 1220.24±0.86 825.59±0.76 1420.55±1.80

10/16/98 – Cimel # 27 1216.46±0.91 970.49±0.89 1187.49±0.77 822.38±0.58 1400.10±0.55

11/24/98 – Cimel # 27 1219.75±0.45 976.43±0.46 1191.42±0.34 821.64±0.61 1401.36±0.75

MEAN 1229.20 979.14 1203.35 822.85 1410.43

STD % 1.07 0.79 1.35 0.22 0.79

Simbad #972306

08/20/98 – Cimel # 37 393564.40±1.89 482820.40±1.07 403245.16±0.35 420247.88±0.84 307582.92±0.59

08/21/98 – Cimel # 37 393525.05±3.13 481855.71±1.02 407705.35±0.41 423453.93±1.03 305498.45±0.56

10/16/98 – Cimel # 27 381894.63±1.25 469676.76±0.99 393682.49±1.82 409544.15±0.56 306692.23±0.98

11/24/98 – Cimel # 27 392974.50±0.89 477633.99±0.97 409380.37±1.16 412874.93±0.41 307275.49±0.17

12/14/98 – Cimel # 101 386234.51±0.95 471653.55±0.37 393092.41±0.21 409462.25±0.51 310487.83±0.22

MEAN 389638.62 476728.08 401421.16 415116.63 307507.39

STD % 1.36 1.24 1.91 1.54 0.60

Prede #PS090063

08/20/98 – Cimel # 37 1.52E-04±3.38 2.86E-04±1.43 3.59E-04±2.22 2.81E-04±0.36 2.84E-04±2.63

08/21/98 – Cimel # 37 1.48E-04±1.13 2.84E-04±1.45 3.57E-04±1.75 2.81E-04±0.45 2.92E-04±2.30

MEAN 1.50E-04 2.82E-04 3.58E-04 2.81E-04 2.88E-04

STD % 1.48 0.51 0.27 0.11 1.87

Table 12: Slope ( p), intercept (p0) and linear squared fit applied to the polarization rate given by the device

and plotted versus the polarization rate measured by six polarized CIMEL sun photometers.

Instrument # p p0 R

2

92 1.1088 -0.1051 0.9996

25 1.2256 -0.0523 0.9977

111 1.0791 0.0476 1

45 1.0608x 0.2354 0.9998

43 1.1935x - 0.7816 1

14 1.1665 -11.179 0.9993
SIMBIOS Project Annual Report

30

Diagram 1. Sun photometer transfer calibration

Calibration Input

TOA signal of the calibrated sun photometer

Vr0(i)

TOA computation for the uncalibrated signal

Vu0(i)=Vr0(i)*(Vu(i)/Vr(i))

for the selected simultaneous measurements

Time difference<36 seconds

Sun photometer data processing

applied to all measurements

(see Diagram 2

except ozone computation)

Ozone content retrieved

using TOMS sensor

according to day and location

Aerosol optical thickness computation

A(i)

Raw signals (in V) or (in A) in the channel i

Vu(i) for the uncalibrated sun photometer

Vr(i) for the calibrated sun photometer

Date, Time, Longitude, Latitude

Diagram 2. Sun photometer data processing

Calibration Input

Top of Atmosphere signal Vi0

Earth-Sun distance computation

according to the averaged distance

d0/d

(Iqbal M., 1983)

airmass computation

m

(Kasten et al, 1989)

Total optical thickness computation

tot(i)=Ln[(Vi/Vi0)/(d0/d)^2]/m

Rayleigh optical thickness computation

R(i)

(Penndorf R., 1957)

Ozone optical thickness computation

O(i)

Lookup table by 5degrees of latitude

(London et al., 1976)

Rayleigh and Ozone correction

tA(i)=ttot(i)- R(i)- O(i)

Aerosol optical thickness computation

A(i)

Raw signals (in V) or (in A) in the channel i: Vi

Date, Time, Longitude, Latitude
SIMBIOS Project Annual Report

31

Diagram 3. SIMBIOS Analysis/Data Processing System
SIMBIOS Project Annual Report

32

Chapter 5

Validation of Surface Bio-optical Properties

in the Gulf of Maine as a Means for Improving

Satellite Primary Production Estimates

William M. Balch

Bigelow Laboratory for Ocean Sciences

West Boothbay Harbor, Maine

5.1 INTRODUCTION

There is a strong need to have sea-truth optical

data in order to evaluate remotely-sensed ocean color.

Our SIMBIOS contract is to use the M/S Scotian

Prince ferry as a ship of opportunity, running between

Portland, Maine and Yarmouth (NV). While the Gulf

of Maine is cloudy and foggy more than it is clear; the

climatology shows on average, about 1 in 4 days is

completely clear and clear days are slightly more frequent in the late summer and early fall months. A

ship of opportunity program (where one has choice of

the days of sampling) provides much better flexibility

to sample during clear periods with good satellite coverage. Measurements include continuous, surface,

along-track fluorescence, light scattering, absorption,

beam attenuation, above-water remote sensing reflectance, calcite-dependent light scattering, temperature,

and salinity. Expendable Bathythermograph (XBT)

drops allow acquisition of vertical temperature information, useful for defining isopycnal slope, which

affects primary production. These data are comparable to a previous program from early 1982, where a

Ship Of Opportunity Program (SOOP) was run on the

truck ferry, M/V Marine Evangeline, which ran along

the same transect (Boyd, 1985). These surface data

were combined with satellite-derived sea surface temperature fields to examine the Maine coastal current

(Bisagni et al., 1995). Unfortunately, this program

stopped in 1982. The ongoing SIMBIOS results will

dovetail nicely with the previous work (which also

had CZCS coverage) for looking at any long-term

changes in the Gulf of Maine hydrography or biooptics.

The Gulf of Maine is an ideal site for gathering

sea-truth optical data. It is a semi-enclosed basin with

an average depth of about 150m. Isopycnal slope (and

productivity) appears to be strongly topographically

driven, with the water column becoming isothermal at

the 60m isobath around Georges Bank. Integrated

productivity in the region varies seasonally by a factor

of 45x (0.1 to 4.4 gC m-2 d-1; O'Reilly, 1987), greater

than in the California Current (15x variability; 0.2-3.0

gC m-2 d-1). The Marine resources Monitoring Assessment and Prediction (MARMAP) database along

the eastern seaboard of the U.S. has been the equivalent to the California Cooperative Oceanic Fisheries

Investigation (CalCOFI) database (West Coast) in

terms of its sheer size and length of sampling. However, MARMAP does not maintain pigment or inherent optical property data. This SIMBIOS project attempts to provide this unique data for the region. 

5.2 RESEARCH ACTIVITIES

We participated in several field cruises to field

test equipment, and collect data. We have completed

the following field activities:

June '98-Second set of sea trials of sampling and

underway system in the Gulf of Maine and Georges Bank (11d cruise).

September-October '98-Eleven cruises aboard

M/S Scotia Prince completed.

Real time enumeration of coccolithophores is essential to this work (as well as cell counts done after

the cruise). We have an Olympus BH2 microscope

with epi-fluorescence and polarization optics which

allows us to quantify birefringent CaCO3 coccoliths,

empty coccospheres, and fluorescing, plated coccolithophore cells on board the ship. Due to limited time

at each station, only about two samples typically can

be enumerated. However, counts are recorded on

video, which provides an important record for postcruise comparison to the preserved counts, as well as

for any retrospective analyses. We take preserved cell

count samples at all stations (preserving with 4%

buffered formalin) and, after the cruise, measure the

concentration of detached coccoliths and plated coccolithophores (Utermöhl, 1931 and 1958).

The technique of Fernandez et al. (1993) is used

to measure CaCO3 concentrations. Briefly, samples

are filtered onto 0.4 m polycarbonate filters, and

rinsing first with filtered sea water, then borate buffer
SIMBIOS Project Annual Report

33

(pH=8) to remove seawater calcium chloride. Filters

are placed in trace metal free centrifuge tubes with 5

ml 0.5% Optima grade Nitric acid. Next, the Ca concentration is measured using graphite furnace atomic

absorption spectrometry. The sensitivity of the technique, after correction to the volume of seawater filtered, is about 2ng Ca l-1.

Particulate organic carbon and nitrogen are measured according to Sharp (1974; 1991). One liter sample bottles will be emptied via tygon tubing, through

in-line pre-combusted glass fiber filters. Low vacuum

will be maintained during filtration. These filters will

be placed in plastic petri dishes using clean forceps,

and stored at -20°C. Prior to running the samples, they

will be fumed over HCl to remove any carbonates,

then dried in a dessicator, and shipped on dry ice to

the Bermuda Biological Laboratory for analysis.

Chlorophyll is measured fluorometrically according to

Strickland and Parsons (1972) and modified according

to Joint Global Ocean Flux Study (JGOFS) (1996)

which involves filtering 200 ml seawater with Gelman

GFF filters, extracting overnight at 4oC in 10 ml of

90% acetone, and measuring fluorescence with a

Turner 111 fluorometer.

We locate high densities of coccolithophores in

the field with a flow-through system which estimates

suspended CaCO3 using an optical technique. A

Wyatt Technologies laser-light scattering photometer

(equipped with a flow-through cell) is used to measure

optical volume scattering at 18 angles. Integration of

this signal in the backward direction allows calculation of backscattering in real time. A pump injects

weak acid every 4 minutes to dissolve the CaCO3, and

then backscattering is re-measured. The difference

between the total bb and the acidified bb is called the

“acid-labile bb,” and is calibrated to suspended

CaCO3 concentrations. The acidified bb represents

backscattering due to organic matter (which can be

calibrated to CHN measurements). This value can be

converted to POC concentration using our POCspecific backscattering coefficients (Balch et al.,

1999). The system monitors chlorophyll fluorescence,

pH, temperature, salinity and 18-channel volume

scattering (with and without CaCO3). An AC-9 provides estimates of absorption and attenuation, which

by difference, also provides scattering. A Global Positioning System is interfaced, as well. The flowthrough system has been field-tested over carbonate

banks off of Florida, which provided data over 3 orders of magnitude in acid-labile bb

. Such high concentrations of suspended CaCO3 are found in the most

dense coccolithophore blooms that we have ever visited. During the Arabian Sea expedition, as well as 5

recent Gulf of Maine cruises, the instrument ran virtually flawlessly over thousands of kilometers, providing a wealth of data on the distribution of particulate

inorganic and organic carbon (Balch et al., 1999). The

final cruise of this year was completed in October; the

raw data have been worked up and distributed to the

NASA SIMBIOS Project. Discrete samples for suspended calcite, POC, PON, and coccolith counts were

also taken, and will be processed over the coming

months.

5.3 RESEARCH RESULTS

We completed 33 days at sea in 1998, with 11

trips aboard the M/S Scotia Prince ferry (Table 1).

Two of 11 trips were cloudy (82% were sunny). In

the Gulf of Maine, where 28% of the time it is sunny,

we have demonstrated that we take full advantage of

ferry as a ship of opportunity. For the year, we have

processed about 147 stations in the Gulf of Maine and

Georges Bank, and provided continuous underway

data along 5000 miles of ship track for SeaWiFS calibration. Below are summarized the main sampling

activities:

R/V Delaware 10-21 November 1997 R/V Delaware, Gulf of Maine and Georges Bank. Underway data analysis completed and submitted to SeaBASS database. Data collected: underway fluorescence, backscattering and calcite-dependent

backscattering (510 nm; Wyatt light scattering

photometer, absolutely calibrated with a glass

standard), absorption, scattering (AC-9; SeaWiFS

bands; recently calibrated), temperature, salinity.

Discrete measurements at 27 stations of suspended calcite, POC/PON, chlorophyll, coccolith

and coccolithophore concentration. Discrete cell

counts and analytical analyses are still being

processed.

R/V Albatross 3-12 June 1998, Gulf of Maine and

Georges Bank. Data collected: underway fluorescence, backscattering and calcite-dependent backscattering (510 nm), absorption, scattering (AC-9:

SeaWiFS bands), temperature, salinity, Lw and Ed

at SeaWiFS wavelengths measured with Satlantic

SAS system. Discrete measurements at 28 stations of suspended calcite, POC/PON, chlorophyll, coccolith and coccolithophore concentration.

M/S Scotia Prince on a total of 1l cruises (Table

1). Data collected: underway fluorescence, backscattering and calcite-dependent backscattering

(510 nm; Wyatt light scattering photometer, absolutely calibrated with a glass standard), absorption, scattering (AC-9; SeaWiFS bands; recently

calibrated), temperature, salinity. Lw and Ed at

SeaWiFS wavelengths measured with Satlantic

SAS system. Microtops sun photometer measurments performed for overpasses. Discrete measurements at stations of suspended calcite,

POC/PON, chlorophyll, coccolith and coccolitho-
SIMBIOS Project Annual Report

34

phore concentration. Discrete cell counts and

analytical analyses being processed.

5.4 WORK PLAN

Our contract calls for 20 ferry trips next year. We

anticipate no problem completing these trips since our

laboratory container and sample arm are already completed and ready.

Moreover, we anticipate no problems in timely

data work-up and submission as our processing software is now streamlined for post-cruise calibrations.

Table 1. Summary of cruises and in situ data collected.

Cruise Location

Cruise

Name Date

Fluorescence

Backscattering

Calcite-dependent

backscattering

Absorption

Scattering

Temperature

and salinity

MicroTops sun

photometer Stations Stations

Suspended

calcite

Chlorophyll

POC/PON

Coccolith and

Coccolithoph. Con.

Discrete cell count

Lw and Ed

(Satlantic SAS)

Delaware, Gulf of Maine and

George Bank

10d 10-21

 Nov 1997

÷ ÷ ÷ ÷ ÷ ÷ 27 ÷ ÷ ÷ ÷ ÷

Gulf of Maine and George Bank 11d 3-12

June 1998

÷ ÷ ÷ ÷ ÷ ÷ 28 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 1 10-11

Sept. 1998

÷ ÷ ÷ ÷ 2 ÷ ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 2 16-17

Sept. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 10 ÷ ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 3 17-18

Sept. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 9 ÷ ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 4 28-29

Sept. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 9 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 5 3-4

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 10 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

 Yarmouth (NV)

Ferry 6 4-5

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 10 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 7 11-12

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 10 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 8 12-13

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 8 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

 Yarmouth (NV)

Ferry 9 16-17

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 9 ÷ ÷ ÷ ÷ ÷ ÷

Portland, Maine and

Yarmouth (NV)

Ferry 10 17-18

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 9 ÷ ÷ ÷ ÷ ÷

Portland, Maine and

 Yarmouth (NV)

Ferry 11 18-19

Oct. 1998

÷ ÷ ÷ ÷ ÷ ÷ ÷ 8 ÷ ÷ ÷ ÷ ÷
SIMBIOS Project Annual Report

35

Chapter 6

OCTS and SeaWiFS Bio-Optical Algorithm and

Product Validation and Intercomparison in

U.S. Coastal Waters

Christopher W. Brown

NOAA/NESDIS, Camp Springs, Maryland

John C. Brock

USGS Center for Coastal Geology and Regional Marine Studies

St. Petersburg, Florida

6.1 INTRODUCTION

The launch of the National Space Development

Agency of Japan (NASDA) Ocean Color and Temperature Sensor (OCTS) in August 1996, and the

launch of Orbital Science Corporation’s (OSC)

SeaWiFS in August 1997 signaled the beginning of a

new era for ocean color research and application. The

ocean color data provided by these satellites promises

the ability to remotely evaluate and monitor 1) water

quality, 2) transport of sediments and adhered pollutants, 3) primary production, upon which commercial

shellfish and finfish populations depend for food, and

4) harmful algal blooms which pose a threat to public

health and economies of affected areas. Accordingly,

several US government agencies have recently expressed interest in using optical remote sensing in US

coastal waters for these purposes.

The goal of this project is to evaluate the performance of standard bio-optical algorithms and validate satellite ocean color products derived from OCTS

and SeaWiFS data in Case I and Case II coastal US

waters. To accomplish this goal, in situ bio-optical

observations were collected and analyzed. This

document briefly describes the methods used in sample collection and analysis, and presents preliminary

results obtained during the first year of the project. As

a result of the failure of the Japanese satellite on June

30, 1997, and the consequent termination of the OCTS

data stream, we have been unable to evaluate the performance of OCTS algorithms and data products.

6.2 RESEARCH ACTIVITIES

In-situ bio-optical data were collected during

eight cruises in diverse US Case I and Case II waters

along the Atlantic coast and in the Great Lakes since

OCTS became operational in November 1996 (Table

1). Optical instruments were deployed on cruises to

measure surface spectral downwelling irradiance, inwater spectral downwelling irradiance and upwelling

radiance. Deployment of other instruments and the

collection of bottle samples enabled additional measurements that included temperature, chlorophyll fluorescence, light scattering, quantum scalar irradiance,

total suspended solids concentration, chlorophyll and

pigment concentrations from fluorometric and High

Pressure Liquid Chromatography (HPLC) techniques,

and absorption coefficients of colored dissolved organic matter and particles. Although sampling

strategies and instrument packages varied between

cruises, a Biospherical Instruments Profiling Reflectance Radiometer (PRR) cage was typically deployed

off the stern of the boat in conjunction with a reference surface unit with matching channels. The PRR

cage contains a split PRR600s that measures seven

channels of downwelling irradiance, seven channels of

upwelling radiance, depth, tilt, roll, and temperature.

A reference surface unit PRR610 that measures seven

matched channels of surface downwelling irradiance

was also used. PRR600s channels 1 to 6 are narrow

band (10-nanometer [nm], full width half maximum

[FWHM]) centered at 380 nm, 412 nm, 443 nm, 490

nm, 510 nm, and 555 nm, while channel 7 on the

downwelling sensor and PRR610 measures broad

band Photosynthetically Available Radiation (PAR)

(400 to 700 nm). In addition, the PRR cage contains a

10-centimeter pathlength, 660 nm Light Emitting Diode (LED) -based SeaTech transmissometer, a Biospherical Instruments Quantum Scalar Profiling sensor

(QSP200), a SeaTech light scattering sensor (LSS),

and a WETLabs Wetstar chlorophyll fluorometer.

Water is drawn through the fluorometer using a SeaBird pump running at 2,000 revolutions per minute.

The data from these instruments are multiplexed

through the PRR600s such that each record contains a

depth and the parameters from every instrument.

In some cases, a Hydro-Optics, Biology, and Instrumentation Laboratories, Inc. (HOBI Labs) Hydro-
SIMBIOS Project Annual Report

36

Scat-6 spectral backscattering sensor was lowered by

hand following the deployment of the PRR cage.

Typically, an along-track system was used to measure

the position (latitude, longitude), time, course and

speed of the vessel, temperature, and salinity. In situ

temperature, salinity, and density were also measured

at some stations with a Conductivity-TemperatureDepth (CTD) instrument. Water samples for chlorophyll biomass, particulate, and dissolved absorption

were obtained from a separate cast using a Niskin array. Discrete water samples were collected following

the PRR cast, from just below the sea surface using a

Niskin bottle.

Bio-Optical Data Processing

The PRR optical data was processed using the

Bermuda Bio-Optics Project (BBOP) processing software (Siegel et al, 1995c). The data were separated

into upcast and downcast profiles and then binned to

0.5 meter bins. Spectral attenuation coefficients were

calculated for the optical channels over a five point

moving window. Subsurface downwelling irradiance

and upwelling radiance were extrapolated to just below the surface using data from the top 3 meters. The

HydroScat-6 data were processed using software provided by HOBI Labs, Inc. The data were despiked, in

two passes using a difference threshold, and a moving

average was calculated for these channels. These data

were also separated into upcast and downcast profiles

and then binned to 0.5-m bins.

For fluorometric chlorophyll a and HPLC pigment determinations, water samples are filtered

through glass fiber. The chlorophyll a samples are

cold extracted in 10 ml of 90% acetone (10% water)

for 24 hours in the dark, and the biomass is determined fluorometrically with a Turner Designs fluorometer using the method of Yentsch and Menzel

(1963). Filtered HPLC pigment samples are cut into

small pieces, ground, and extracted in a 1.5 ml microcentrifuge tube with 1.5 ml 90% acetone and are

placed in a freezer overnight. They are centrifuged at

0°C for 15 minutes, 0.5 ml is filtered through a Nalgene nylon syringe filter, the samples are diluted to

60% acetone with the addition of 0.25 ml water, and

0.5 ml is injected into the HPLC. A Hewlett-Packard

1050 Series HPLC with a Phenomonex Sphericlone

ODS (2) reverse-phase column (250 mm x 4.5 mm

with 5 μm particles) is used with a ternary gradient to

separate and identify the photosynthetic pigments

(Wright et al, 1991). On cruises that included alongtrack measurements, water from about one meter below the sea surface was pumped through a hose into a

bucket in which a Hydrolab Datasonde 3 Multiprobe

logger was immersed. The Datasonde was used to

measure temperature, specific conductivity, and salinity. Data from many of these cruises are made available via cruise reports (Culver et al. 1998, Subramaniam et al. 1997a, Subramaniam et al. 1997b, Subramaniam et al. 1997c, Subramaniam et al. 1998), and

also through a website at the NOAA Coastal Services

Center (http://www.csc.noaa.gov/crs/cruises/).

6.3 RESEARCH RESULTS

Our group has conducted eight cruises since the

beginning of October 1996, including six cruises in

the South Atlantic Bight (SAB), one in the Gulf of

Maine, and one in the vicinity of Nantucket Shoals.

Coverage of the SAB has been extensive due to productive collaboration with the NOAA Southeast Fisheries Science Center.

The SAB consists of a variety of environments

including near-coastal and continental shelf regimes,

the Gulf Stream, and the Sargasso Sea. Smooth transitions from low temperature waters with high pigment concentrations and attenuation coefficients, that

are typical of nearshore environments, to the higher

temperature waters with low pigment concentrations

and attenuation coefficients, that are typical of offshore environments, are often disrupted by Gulf

Stream eddies that appear on the continental shelf.

The variability in the biological and optical characteristics of these regimes complicates temporal or spatial

analyses of changes in, for example, phytoplankton

species composition, primary production rates, colored dissolved organic matter (CDOM) concentration,

suspended sediments, or temperature.

Coastal waters of the SAB can be classified as

optical Case II waters. Data from the MAY97OB

cruise (Subramaniam et al., 1998), on May 5, 1997

and May 8, 1997, indicate that the waters of Onslow

Bay and especially Pamlico Sound were sedimentdominated. Data from the May cruise suggest that the

OC2 algorithm (O’Reilly et al., 1998) over-estimated

chlorophyll and pigment concentrations in these waters by a factor of at least 1.5 and up to 15. Chlorophyll a and total suspended solids concentrations in

waters of the SAB during the APR98SAB cruise in

April 1998 were highly variable. Chlorophyll a concentrations tended to be higher nearshore, and total

suspended solids concentration showed no discernible

geographic pattern, with high and low concentrations

being measured at both nearshore and offshore stations. High attenuation coefficients for the blue

wavelengths indicated the presence of high concentration of colored dissolved organic material near the

coasts of South Carolina, Georgia, and Florida however, these high coefficients were not observed near

North Carolina. Overall, the OC2 version 2 algorithm

significantly over-estimated the chlorophyll a concentration by a factor of 4 and as much as a factor of

50, however, CZCS pigment concentration was estimated more successfully, with ratios of measured to

estimated pigment ranging from 1 to 5.
SIMBIOS Project Annual Report

37

Table 1. Summary of cruises.

Cruise Location Date Aircraft Ship Cruise Name

Southern California Bight 1/29/96 to 2/18/96 None Jordan JAN96CAL

Mid-Atlantic Bight 3/1/96 to 3/10/96 NASA P-3 Endeavour MAR96OMP

South Atlantic Bight 4/22/96 to 4/26/96 None Ferrel APR96FER

New York Bight 5/13/96 to 5/16/96 None Osprey MAY96NY

Gulf of Maine 5/18/96 to 5/24/96 None Gulf Challenger MAY96ME

Lake Erie 8/26/96 to 8/30/96 None R/V Bio Lab AUG96GL

Beaufort, North Carolina 3/13/97 to 3/13/97 None R/V Onslow Bay MAR97OCC

Coastal North Carolina 5/5/97 to 5/8/97 None R/V Onslow Bay MAY97OB

Gulf of Maine 6/3/97 to 6/10/97 None Gulf Challenger JUN97ME

South Atlantic Bight 9/6/97 to 9/24/97 None Cape Hatteras SEP97SAB

South Atlantic Bight 11/4/97 to 11/6/97 None R/V Palmetto NOV97SAR

South Atlantic Bight 4/5/98 to 4/27/98 NOAA Twin Otter Cape Hatteras APR98SAB

Nantucket Shoals 7/6/98 to 7/10/98 None Gulf Challenger JUL98NAN

South Atlantic Bight 10/28/98 to 11/25/98 None Cape Hatteras NOV98SAB

Figure 1. OC2 version 2 vs. fluorometric chlorophyll.

0.10

1.00

10.00

0.10 1.00 10.00

Measured ChlF (mg/m^3)

OC2 ver 2 (mg/m^3)

r

2

=0.83

Slope=0.8
SIMBIOS Project Annual Report

38

The results of cruise NOV97SAR (Culver et al,

1998), conducted from November 3 to 5, 1997, show

that the OC2 algorithm performs reasonably well at

stations well off-shore, although, in general the algorithm tends to over-predict chlorophyll concentrations

in coastal waters. Also, we found good agreement

between our in situ optical measurements of normalized water-leaving radiance and that measured by the

SeaWiFS sensor. We interpret this to mean that our in

situ measurements are of good quality, and that our

goal of validating satellite chlorophyll algorithms using these measurements is reasonable and tractable.

The consistent overestimation of chlorophyll a

concentration in the SAB by the standard algorithms is

likely due to the influence of sediments and CDOM

on ocean color. Preliminary analysis suggests that

sediment may be the dominant factor near North

Carolina, and CDOM may be the dominant factor for

the southern waters.

When these components do not covary with chlorophyll a, the algorithms will overestimate chlorophyll

a concentration. The agreement between our in situ

optical measurements of normalized water-leaving

radiance and that measured by the SeaWiFS sensor

indicate that a chlorophyll algorithm for these waters

is tractable, however, the coefficients will require adjustment to compensate for the effect of sediment and

CDOM on the radiance measurements. Overall, our

results show that it is necessary to establish empirical

bio-optical relationships for separate coastal regions,

such as the SAB.

There is a reasonable relationship between the

OC2 algorithm-derived chlorophyll concentration and

the fluorometrically measured chlorophyll concentration in the SAB (Figure 1). Small changes in the

power equation coefficients should yield a better regional algorithm for the SAB. The relationship between HPLC-derived chlorophyll a and the OC2 algorithm is not as robust and requires further study.

6.4 WORK PLAN

The project plans to complete three additional

cruises in the SAB during October 1998 through September 1999 in order to collect a more complete data

set using our established sampling protocol. Given

that analyses thus far have demonstrated that the OC2

Version 2 algorithm estimates of chlorophyll a concentration for SAB waters exceed acceptable error

limits, our project will strive to develop a regionspecific algorithm for SeaWiFS for these waters.

During the recent NOV98SAB cruise, in addition to

the deployment of the NOAA CSC PRR600, a Satlantic free falling profiler (SPMR), the SIMBAD, and an

above water hyperspectral Spectrex instrument were

used to obtain water leaving radiance data. This coincident multiple instrument data set will be used to

compare the efficacy of each instrument in coastal

Case II waters. In response to the observation that

erroneous negative radiances occur in SeaWiFS data

at 412 nm band, especially in late spring/early summer, sunphotometer data will be used to determine the

suitability of the standard atmospheric correction algorithms for the SAB.

ACKNOWLEDGMENTS

We sincerely thank Drs. A. Subramaniam and M.

Culver for their invaluable assistance in this project.

In addition to collection and analysis of the data, they

reviewed and suggested improvements in a previous

version of this Technical Memorandum.
SIMBIOS Project Annual Report

39

Chapter 7

Validation of Ocean Color Satellite Data Products

in Under-Sampled Marine Areas

Douglas G. Capone and Ajit Subramaniam

Chesapeake Biological Laboratory

Solomons, Maryland

Edward J. Carpenter

SUNY at Stony Brook, New York

7.1 INTRODUCTION

The marine diazotroph, Trichodesmium is a

planktonic cyanobacterium which occurs throughout

the tropical and sub-tropical oligotrophic seas. It can

form large blooms and is thought to be responsible for

the major fraction of N2 fixation in the pelagic zone of

world's oceans. The total rate of N2 fixation by this

organism has been thought to be about 10 Tg annually. However, estimates of Trichodesmium's contribution to total marine N2 fixation are relatively crude

and other independent estimates suggest a higher rate

of marine N2 fixation. The annual rate was derived by

scaling an average trichome N2 fixation rate with biomass abundance and distribution data largely taken

from historical plankton surveys. However, there are

unique difficulties in quantifying the biomass of a

buoyant, colonial alga such as Trichodesmium and the

quantitative accuracy of many of these surveys are

suspect. One of the most appealing prospects of using

satellites in biological oceanography has been the potential to derive flux estimates from inventories of

standing stock calculated from changes in optical

properties of the ocean. Using algorithms to estimate

global distributions of Trichodesmium biomass, we

can calculate nitrogen fixed by this organism, and

hence model its contribution to new production in the

world oceans. Towards this goal, we proposed to use

a previously developed hyperspectral optical model

for the Trichodesmium to construct sensor specific

biomass algorithms.

The goal of our proposed work was to develop

sensor specific algorithms to quantify the biomass of

Trichodesmium in the world oceans. The specific objectives of our proposal were to:

Use a hyperspectral optical model for Trichodesmium to derive sensor specific Trichodesmium

chlorophyll algorithms.

Constrain and validate these algorithms using

field measurements. Also use the field measurements to validate standard chlorophyll algorithms.

Estimate the error in using standard algorithms to

estimate chlorophyll in a Trichodesmium bloom.

Develop flags for switching algorithms if necessary.

We were required by our contract to acquire and

process data from at least one cruise per year. The

data included measurements of vertical profiles of

spectral downwelling irradiance, upwelling radiance,

spectral attenuation and remote-sensing reflectance

calculated from the profile data, photosynthetically

active radiation, primary productivity, and concentrations of chlorophyll a and other pigments. We were

required to purchase and make available to the instrument pool, an AC-9 instrument and a turnkey free-fall

profiling radiometer system. Here we outline our progress during the first year of our SIMBIOS project to

develop an algorithm for detection and quantification

of Trichodesmium biomass for the SeaWiFS sensor.

We also describe our field program for validating the

OC2 algorithm and obtaining in situ bio-optical data

in under-sampled marine areas.

7.2 RESEARCH RESULTS

The work detailed below is of an effort in progress and intended to provide an interim update to the

SIMBIOS project. Our initial approach was to derive

a Trichodesmium chlorophyll specific algorithm from

an optical model, and then constrain this algorithm

based on field data. Our optical model detailed in

Subramaniam et al. (1999) showed that at low concentrations, Trichodesmium does not have singular

enough optical properties to be uniquely identified

(Figure 1). But as the concentration of Trichodesmium

in the water column increases, its optical properties

dominate and it is possible to identify and quantify
SIMBIOS Project Annual Report

40

this organism (Figure 1). Therefore, we initially decided to develop a branching algorithm, where at low

Trichodesmium concentrations the algorithm produced

total chlorophyll (i.e. not Trichodesmium specific), but

at higher Trichodesmium concentrations the algorithm

resulted in Trichodesmium specific chlorophyll. We

formulated the algorithm as (R555-R490/R510) where

R555, R490, R510 are the SeaWiFS remote sensing reflectance corresponding to bands 3, 4 and 5 respectively. We parameterized this formulation by fitting a

power equation to the results of the previously developed remote-sensing reflectance based hyperspectral

optical model for Trichodesmium. However, we were

not satisfied by the results of this formulation and

have been working on other approaches and band

combinations.

Although the branching algorithm approach is

very attractive for producing global maps of Trichodesmium abundance based on a sound theoretical

model, it is essential to characterize the chlorophyll

concentration threshold where the algorithm results in

Trichodesmium specific chlorophyll concentration.

The optical model suggested that this threshold was

about 0.5 mg/m3 Trichodesmium Chl a. While we did

not encounter such high concentrations of Trichodesmium during the Trichonesia cruise, preliminary

analysis of field data from a cruise in the South Atlantic Bight shows that this threshold is probably much

higher – around 3 mg/m3

. We need more field data

with Trichodesmium cell counts to characterize this

threshold. In the meantime we have developed a flag

to study global occurrence of Trichodesmium blooms.

This flag is based on the combination of high reflectance at 555 nm, and absorption at 490 nm. We are

comparing this to climatological data on Trichodesmium occurrence - in regions and seasons where

Trichodesmium is known to occur historically. We

think we are very close to completing an initial

Trichodesmium chlorophyll algorithm and will communicate it to the SIMBIOS office as soon as we are

satisfied with it.

Our 1998 field campaign was a 35-day research

cruise in the South Western Pacific ocean. We left

Lyttleton, New Zealand on the 24 March 1998 and

arrived in Suva, Fiji on the 30 April 1998. We had

requested cruise time in January-February when the

organism is most abundant in this region. However,

due to ship availability, our cruise was pushed to

April. This, in combination with the effects of the ElNino, resulted in our encountering lower Trichodesmium populations than we had anticipated. After our

port call in New Caledonia on 30 March, we had to

head north to avoid Cyclone Zumann. Thus we were

under overcast skies during the portion of the cruise

with some of the highest chlorophyll concentrations.

In total, we occupied 51 stations and made 33 optics

deployments including 2 diel deployments for Inherent Optical Property measurements. The in situ optical

data, chlorophyll concentrations, and carbon and

nitrogen fixation rates have been submitted to

SeaBASS.

We acquired a Wetlabs AC-9 in January 1998.

This instrument was field tested during a SIMBIOS

cruise (CALCOFI 9802) and recalibrated after that

cruise. This instrument was used on the Trichonesia

cruise and is now available at CBL.

A Satlantic SeaWiFS Profiling Multispectral Radiometer (SPMR) with a matched SeaWiFS Multispectral Surface Reference (SMSR) was procured in

March 1998. The SPMR is a 13 channel free falling

profiler that measures in situ downwelling irradiance

(Ed-

) and upwelling radiance (Lu-) at 340, 380, 412,

443, 490, 510, 520, 555, 565, 619, 665, 670, and 683

nm. The SMSR is a floating reference that measures

downwelling irradiance (Ed+

) just above water and

upwelling radiance (Lu-

) 70 cm below the surface.

The SPMR includes a 300-m power telemetry cable, 2

axis tilt sensors, and external temperature and conductivity sensors. The SMSR includes a 100-m power

telemetry cable and 2 axis tilt sensors. The package

includes a deckbox with computer interface and power

supply, data logging and display software, and a Hitachi pentium laptop computer with an extra PCMCIA

serial card and cables.

The SPMR was used on the Trichonesia cruise in

March-May, on NOAA cruises in July and November,

and a CALCOFI cruise in September. Initially there

were problems with gain switching and some data

from the Trichonesia cruise and JUL98NAN cruise

were compromised because of this. This has been

subsequently fixed by Satlantic. The instrument has

been recalibrated twice at Satlantic and twice at UC

Santa Barbara since March 1998. It has been shipped

to the Indian Ocean for use in the Indian Ocean Experiment (INDOEX).

7.3 WORK PLAN

We will continue to work on refining the Trichodesmium algorithm. Specifically we will analyze the

field data collected during the Trichonesia (1998) and

INDOEX (1999) cruises to define the Trichodesmium

specific chlorophyll concentration that can be detected

by the algorithm and test the sensitivity of the algorithm. We will work on algorithms specific to the

OCTS, the MOS, and the MODIS sensors. We will

participate in the INDOEX cruise in March 1999 and

a cruise off northern Australia in October 1999.
SIMBIOS Project Annual Report

41

Figure 1. Optical model of Trichodesium remote sensing reflectance for a) 0.1 mg Chl/m3, b) 1.0 mg

Chl/ m3, and c) 10.0 mg Chl/ m3.

Wavelength (nm)

400 450 500 550 600 650 700 750

% Remote sensing reflectance

0.000

0.005

0.010

0.015

0.020

0.025

Seawater

Trichodesmium colonies

Mixture of colonies and trichomes

Average phytoplankton

Synechococcus

Trichomes only

Colonies - modeled backscatter

1

1

2

2

3

3

4

4

5

5

6

6

7

7

Wavelength

400 450 500 550 600 650 700 750

0.000

0.005

0.010

0.015

0.020

0.025

Seawater

Trichodesmium colonies

Mixture of colonies and trichomes

Average phytoplankton

Synechococcus

Trichomes only

Colonies - modeled backscatter

Low Gilvin 1

2

1

2

3

3

4 4

5 5

6

6

7 7

400 450 500 550 600 650 700 750

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Seawater

Trichodesmium colonies

Average phytoplankton

Synechococcus

Colonies - modeled backscatter

% Remote sensing Reflectance
SIMBIOS Project Annual Report

42

Chapter 8

Stray Light and Atmospheric Adjacency Effects for

Large-FOV, Ocean-Viewing Space Sensors

Kendall L. Carder

University of South Florida,

St. Petersburg, Florida

8.1 INTRODUCTION

The radiance of dark targets (e.g. oceans and

lakes) when measured by large-field imagers such as

MODIS and SeaWiFS can be enhanced by stray light

within the sensor and by radiance atmospherically

scattered from bright, adjacent targets. One of the

goals of this project is evaluation of this stray light

and estimation of its effect on derived products of

remote color imagery.

8.2 RESEARCH ACTIVITIES

The first year of this project focused on collecting

field data to evaluate the performance of SeaWiFS.

To assure field data quality, a significant effort was

expended in characterizing and calibrating field instruments as well as standardizing field methodology.

Field sites were selected where adjacency artifacts

would be likely. One site is a deep ocean canyon surrounded by bright carbonate banks, the Tongue of the

Ocean (TOTO); another is Lake Okeechobee, Florida

where dark water is surrounded by bright vegetation.

With funding from other sources, additional field experiments were applied to this study and help with

evaluation of SeaWiFS performance. These included

sampling on Tampa Bay, the West Florida Shelf,

Exuma Sound, the San Juan Islands in Puget Sound,

and Lake Tahoe.

8.3 RESEARCH RESULTS

The degradation of SeaWiFS infrared bands,

which are used to evaluate the type and amount of

aerosol path radiance, caused a perturbation in the

type of aerosol correction to be made by the SeaWiFS

atmospheric correction scheme. This resulted in over

estimation of the blue-richness of the aerosol scattering. Furthermore, high cirrus clouds have a tendency

to exaggerate this effect, due to enhanced aerosol absorption in the oxygen band near 762 nm. To obviate

the worst effects of both problems, we developed an

aerosol-typing algorithm using bands 6 and 8 over

clear waters. This approach forced the calibration of

band 6 relative to band 8 to provide normalized waterleaving radiance values at band 6 consistent with the

Gordon and Clark (1981) for scenes with known aerosol type. For scenes of unknown aerosols, the new 6-8

band combination delivered appropriate aerosol types

with SEADAS. This prevented blue exaggeration of

the aerosol type and prevented excessive removal of

blue radiance from the scene, which otherwise would

have resulted in blue-poor water-leaving radiance values. This approach provided atmospherically corrected

scenes that did not became negative at blue wavelengths for gelbstoff-rich (blue-absorbing) areas. This

approach also provided clear water, normalized waterleaving radiance values at 555 nm consistent with

Gordon and Clark (1981) using the calibration factors

distributed by the SeaWiFS Project on 6 January

1998. Furthermore, it provided a data distribution for

clear waters using ratios of bands 1 and 2 versus bands

2 and 5 that are consistent with those found by Carder

et al. (1999) using the SeaBASS in situ data set.

Using the above calibration scheme, SeaWiFS

images of the TOTO, the West Florida Shelf, and regions between were compared to field data using the

default NASA chlorophyll algorithm and the Carder et

al. (1999), MODIS-like, semianalytic chlorophyll algorithm. For these spring scenes, the pigments were

somewhat packaged with little in the way of photoprotective pigments. Both algorithms performed

similarly (within 5%) for Case 1 waters. When

gelbstoff absorption overwhelmed the pigment absorption, however, the semianalytic algorithm delivered chlorophyll values within 25% of measured values; while the default NASA algorithm overestimated

chlorophyll by as much as a factor of 4. These scenes

will be re-evaluated with the new calibrationdegradation curves of SEADAS 3.2 during the next

contract year, but the new results are not expected to

deviate significantly from these results using the 6-8

band combination except for turbid waters.

In terms of evaluating atmospheric adjacency and

stray light effects due to infrared radiance emanating

from the bright foliage surrounding Lake Okeechobee
SIMBIOS Project Annual Report

43

or blue-green light reflected from the bright shallow

banks surrounding TOTO, our preliminary findings

suggest the following:

Lake Okeechobee has so much horizontal variability in the water-leaving radiance field at infrared wavelengths that it is at times an impractical

site at which to evaluate stray infrared light from

its surrounds. It does offer, however, so much

gelbstoff absorption at 412 nm that we are considering performing atmospheric corrections

based upon the blue end of the spectrum.

Data we collected at the Friday Harbor Laboratory in the San Juan Islands suggest that this site

provides a viable alternative to Lake Okeechobee

for evaluation of stray infrared light and/or atmospheric adjacency effects. Hyperspectral

Imager for Low Light Spectroscopy (PHILLS)

aircraft data Curtis Davis (NRL) suggests that one

can find a red-edge effect (exaggerated infrared

light) in the water near sunlit tree lines in data

collected at 10,000 feet and with visibility in excess of 50 km. These data will be evaluated next

year along with SeaWiFS data collected at high

resolution over Griffin Bay (San Juan Island)

which is surrounded by forest land.

Chlorophyll values farther than 2 pixels offshore

and east from bright, shallow banks of the TOTO

were not significantly different than those found

farther offshore. Extreme caution must be taken,

however, to avoid misinterpreting conditions

where gelbstoff- and particle-laden waters from

the shallows are transported offshore. Next year

an evaluation of the electronic over-shoot, and/or

hysteresis on the west sides of bright targets will

also be evaluated on the eastern edge of the

TOTO. More accurate calibration of the

SeaWiFS sensor will help in this effort.

A recently published paper by Reinersman et al.

(1998) on calibration of aircraft and small footprint, spacecraft sensors using cloud shadows was

dependent upon the development of a Monte

Carlo model of radiance from single spherical

clouds. This model is being modified to permit

evaluation of atmospheric adjacency effects of

clouds on radiance values received by a space

sensor when viewing the ocean through an opening (elliptical cylinder) in a cloud bank. Algorithms that are more immune to the adjacency effects of clouds will be sought. Much of the light

scattered into the sensor from clouds will be from

molecules and stratospheric aerosols and thin cirrus clouds. A strategy using the effect of the oxygen absorption line on band 7 versus results from

bands 6 and 8 may provide an indication of the

effective height of any aerosol scattering for

SeaWiFS, whereas MODIS has a cirrus discriminator built into its data processing scheme

8.4 WORK PLAN

The main goal of the project will remain the

same, to evaluate stray light effects on derived products from ocean color imagery. Since MODIS and

OCTS will not be available, the effort will be concentrated on SeaWiFS, Advanced Visible and Infrared

Imaging Spectrometer (AVIRIS), and PHILLS.

The TOTO site will be visited in mid-April. It is

planned to use PHILLS overflights of Griffin Bay,

Tampa Bay, and the West Florida Shelf. The aircraft

data will be used to refine techniques to detect atmospheric adjacency effects and bright infrared reflectance due to vegetation.
SIMBIOS Project Annual Report

44

Chapter 9

Bio-Optical Measurements at Ocean Boundaries

in Support of SIMBIOS

Francisco P. Chavez

Monterey Bay Aquarium Research Institute

Moss Landing, California

9.1 INTRODUCTION

This project consists of a mooring program and

supporting cruise-based measurements aimed at quantifying the spectrum of biological and chemical variability in the equatorial Pacific. The mooring program

was designed to obtain continuous time series of biological and chemical properties on a time scale that is

equivalent to measurements of currents, local winds

and temperature structure.The project has the following general objectives:

to understand the relationships between physical

forcing, primary production, nutrient supply and

the exchange of carbon dioxide between ocean

and atmosphere in the equatorial Pacific;

to describe the biological and chemical responses

to climate and ocean variability;

to describe the spatial, seasonal and interannual

variability in near surface plant pigments, primary

production, carbon dioxide and nutrient distributions, and

to obtain near real-time bio-optical measurements

to ground-truth satellite measurements of ocean

color.

9.2 RESEARCH ACTIVITIES

Moorings

Bio-optical and chemical sensors were deployed

on two moorings of the TAO array in the equatorial

Pacific at 0°, 155°W and 2°S, 170°W. The following

sensors formed the core set:

A Biospherical PRR-620 located 3m above the

water surface, to measure downwelling irradiance

at 412, 443, 490, 510, 555, 656nm and PAR.

A pCO2 system to measure the difference in

partial pressure of CO2 between ocean and atmosphere (supported by NOAA).

Two Satlantic OCR-100s located approximately

1.5m below the surface, to measure upwelling radiance at 412, 443, 490, 510, 555, 670 and

683nm.

Two Wetlabs miniature fluorometers at approximately 1.5m and 20m below the surface to measure stimulated in vivo fluorescence.

Two Biospherical MCP-200s located at 10m and

30m below the surface to measure downwelling

irradiance at 490nm.

A Biospherical PRR-600 located 20m below the

surface to measure downwelling irradiance at

412, 443, 490, 510, 555, 670nm and PAR, plus

upwelling radiance at 412, 443, 490, 510, 555,

670 and 683nm.

Daily noon-time bio-optical data were delivered

via service ARGOS in near real time to MBARI, and

then via automated FTP to the SeaBASS database,

after some processing and quality control. Higher frequency, publication-quality data (10 or 15-minute

intervals) were recovered at approximately six month

intervals, and sent to the SeaBASS database after

processing and quality control. Some derived products, such as OC2V2 chlorophyll from surface upwelling radiances, and mean chlorophyll over the upper 20m of the water column (Morel, 1988) were included in these data files. Using simple algorithms

derived from optical profile data the upwelling radiances measured by the moored radiometers have been

converted to normalized water-leaving radiances

(Lwn), for the SeaWiFS calibration/validation effort.

In addition to the two mooring installations described above, MBARI has also maintained smaller

bio-optical packages at four sites in the equatorial Pacific: 2°N, 180°; 2°S, 140°W; 2°N, 140°W and 2°N,

110°W. These bio-optical packages produced measurements of downwelling incident irradiance at

490nm, upwelling radiance from ~1.5m depth at 412,

443, 490, 510, 555, 670 and 683nm, plus stimulated in

vivo fluorescence. Data, including derived Lwn (see

above) were delivered in near real time to MBARI and

the SeaBASS database. A bug in the original software

precluded collection of significant data prior to March

of 1998.
SIMBIOS Project Annual Report

45

In situ measurements

All cruises were undertaken aboard the NOAA

ship Ka’imimoana, with the exception of GP6-98-RB

aboard the NOAA ship Ronald H. Brown (Table 1).

Essentially, the cruise-based measurements consisted

of chlorophyll (using the fluorometric method described by Chavez et al., 1995) and nutrient profiles (8

depths, 0-200m) obtained at CTD stations between

8°N and 8°S across the Pacific from 95°W to 165°E.

On selected cruises (primarily the 155°W and 170°W

meridional transects), primary productivity measurements and optical profiles, using the Satlantic Profiling Multispectral Radiometer, were also performed.

These data were archived at MBARI and the chlorophyll and optical profile measurements provided to

NASA’s SeaBASS database.

9.3 RESEARCH RESULTS

Chavez et al. (1998) describe the biologicalphysical coupling observed in the central equatorial

Pacific during the onset of the 1997-98 El Niño. Figure 1 shows the time series of chlorophyll, SST and

pCO2 from the mooring located at 0°, 155°W for the

time period covering the peak of the 1997-98 El Niño

and the subsequent recovery of the phytoplankton

community. Our data from the four smaller bio-optical

packages describe the physical and biological effects

of the passage of Tropical Instability Waves. While

the corresponding SeaWiFS data in large part agree

closely with the mooring-derived chlorophyll concentrations, there are time periods where this is not the

case. This may in part be due to the spatio-temporal

averaging that is inherent in the SeaWiFS 9km/8-Day

data. We have performed SeaWiFS chlorophyll comparisons with extracted chlorophyll concentrations for

all of the 1998 equatorial Pacific cruises, with good

agreement between the two data types.

9.4 WORK PLAN

During 1999 data collection will continue as for

1998. The two major mooring installations at 0°,

155°W and 2°S, 170°W are now operating well after

some initial problems with damage and loss of instruments. The smaller bio-optical packages at four additional locations across the Pacific are also performing

well and data collection at those sites, as described

above, will also continue. The program of cruisebased measurements of chlorophyll, nutrients, primary

productivity and bio-optical profiles will continue on

up to eight equatorial Pacific cruises during 1999,

with scheduled SeaWiFS LAC where possible, to enhance the probability of obtaining valid matchups.

The major data processing objective for 1999 is to

automate the near real-time data provision to the SeaBASS database as much as possible to aid in the calibration/validation effort. In addition we aim to improve our data processing routines for the high resolution data that are downloaded from the 0°, 155°W and

2°S, 170°W moorings at approximately 6 month intervals. This should decrease the lag time between

data download and provision of products to the SeaBASS database.
SIMBIOS Project Annual Report

46

Table 1. Summary of cruises during which in situ data have been obtained by MBARI in support of SIMBIOS. All cruises were undertaken aboard the NOAA ship Ka’imimoana, with the exception of GP6-98-RB

aboard the NOAA ship Ronald H. Brown. Meridional transects indicate the lines occupied by the ship. Along

each line, CTD stations were performed approximately every degree of latitude from 8°N to 8°S. Measurements

consisted of extracted chlorophyll (Chl) plus nitrate, phosphate and silicate (Nutrients) at 8 depths between 0 and

200m. On selected cruises, primary productivity (PP) measurements were also made using 14C incubation techniques, and daily optical profiles with the Satlaintic Profiling Multispectral Radiometer (SPMR) were obtained.

During GP7-98-KA, a SIMBAD radiometer was also used, on loan from the SIMBIOS instrument pool.

Cruise ID Dates Meridional transects Measurements

GP6-97-KA 27-Sep-97 to 30-Oct-97 125°W and 140°W Chl, PP, Nutrients, SPMR

GP7-97-KA 06-Nov-97 to 17-Dec-97 155°W, 170°W and 180° Chl, PP, Nutrients, SPMR

GP1-98-KA 05-Feb-98 to 13-Mar-98 95°W and 110°W Chl, Nutrients

GP2-98-KA 18-Apr-98 to 20-May-98 125°W and 140°W Chl, Nutrients

GP3-98-KA 02-Jun-98 to 03-Jul-98 155°W and 170°W Chl, PP, Nutrients, SPMR

GP4-98-KA 07-Jul-98 to 03-Aug-98 165°E and 180° Chl, Nutrients

GP5-98-KA 05-Sep-98 to 09-Oct-98 125°W and 140°W Chl, Nutrients

GP6-98-RB 11-Oct-98 to 13-Nov-98 95°W and 110°W Chl, Nutrients

GP7-98-KA 19-Oct-98 to 13-Nov-98 155°W and 170°W Chl, PP, Nutrients, SPMR

GP8-98-KA 18-Nov-98 to 12-Dec-98 180° and 170°W Chl, Nutrients

GP1-99-KA 22-Jan-99 to 24-Feb-99 125°W and 140°W Chl, Nutrients

Figure 1. Time series of Sea Surface Temperature (SST – heavy shaded line), chlorophyll a averaged over

the upper 20m of the water column from moored spectroradiometer data (heavy solid line) SeaWiFS OC2V2

chlorophyll (closed triangles) and pCO2 (thin solid line).

-0.25

0

0.25

0.5

0.75

1

1.25

1.5

Dec-96 Mar-97 Jun-97 Sep-97 Dec-97 Mar-98 Jun-98 Sep-98

Date

Chl a [ug l-1] / pCO2 [uatm/100]

22

24

26

28

30

32

Temperature [°C]

in-situ chl

SeaWiFS

pCO2/100

SST
SIMBIOS Project Annual Report

47

Chapter 10

Remote Sensing of Ocean Color in the Arctic:

Algorithm Development and Comparative Validation

Glenn F. Cota

Old Dominion University

Norfolk, Virginia

10.1 INTRODUCTION

The Optical Research Consortium of the Arctic

(ORCA) is a collaborative project between G.F. Cota

of Old Dominion University (ODU), T. Platt and

W.G. Harrison of the Bedford Institute of Oceanography (BIO), S. Sathyendranath of Dalhousie University

and S. Saitoh of Hokkaido University. ORCA initiated bio-optical data collections in August, 1994 and

has conducted 10 high latitude cruises in the Bering

Sea (7/95 = Ber95, 7/96 = Ber96), the Labrador Sea

(10-11/96 = Lab96, 5-6/97 = Lab97, 6-7/98 = Lab 98),

the Gulf of Alaska (10/97 = Goa97), and in the

Northwest Passage near Resolute Bay, NWT, Canada

(8/94 = Res94, 8/95 = Res95, 8/96 = Res96, 8/98 =

Res98). ORCA has now collected almost 500 inwater optical profiles and most of them have been

submitted to NASA’s SeaBASS database.

The ORCA program depends upon coordination

and cooperation between international co-investigators

with support from NASA, NASDA and Canadian

sources. ODU has had primary responsibility for biooptical and biogeochemical data collection with assistance from all collaborators. ODU has been responsible for data processing, distribution and submission to SeaBASS. Data analyses are being conducted

by all co-investigators. Modeling is being done primarily by BIO and Dalhousie. Our algorithm development efforts encompass most of the potential data

products listed for SeaWiFS, MODIS and GLI, and

addresses product validation for a specific area of

concern, i.e. high latitudes and coastal waters.

Observational suites depend primarily on field

program duration, the sampling time, berths and personnel available. Longer, dedicated field programs

(i.e. Resolute) include more comprehensive observations. Core observations always include in-water

spectroradiometer profiles for apparent optical properties (AOPs) and discrete profiles of fluorometric

chlorophyll. Absorption spectra for particulate, extracted particulates, and soluble materials are also

available from most cruises. The observational suites

for Resolute and the Labrador Sea are typically more

comprehensive with in situ inherent optical property

(IOPs) profiles (AC-9, Hydroscat-6: Resolute only),

above-water spectral remote sensing reflectance

Rrs( ), spectrophotometric and/or HPLC pigments,

primary production and/or photosynthesis versus irradiance, inorganic nutrients, 15N-nutrient uptake, particulate organic carbon and nitrogen.

10.2 RESEARCH ACTIVITIES

From May, 1997 through August, 1998 four

SIMBIOS validation cruises for OCTS or SeaWiFS

were conducted with one on an early-start supplemental contract (Labrador Sea 5-6/97) and three under

the main contract (Gulf of Alaska 10/97, Labrador Sea

6-7/98, and Resolute Bay 8/98). Our scheduled

August, 1997 Resolute field program was cancelled

because OCTS had failed and SeaWiFS was not yet

operational.

Bio-optical, biogeochemical and experimental observations were made as frequently as logistical and

weather considerations permitted. Data collections

and processing for biogeochemical and optical observations conform closely to Joint Global Ocean Flux

Studies (JGOFS, 1991) and SeaWiFS protocols

(Mueller and Austin 1992, 1995).

Water column profiling consisted of a bottle or

pump cast for discrete samples preceded or followed

by optical casts. Discrete water samples were collected from standard depths and depths corresponding

to features of particular interest such as fluorescence,

beam attenuation and/or density maxima. Biogeochemical observations included fluorometric chlorophyll and phaeopigments, spectrophotometric (Resolute) or HPLC (Labrador Sea) pigments, absorption

spectra of particulates, methanol-extracted particulates, and dissolved colored organic material

(CDOM), inorganic nutrients, particulate organic carbon and nitrogen, and selected other observations such

as total suspended matter and cell count samples.

Experimental observations at Resolute and the Labrador Sea included 14C and 13C primary production and

15N-nutrient uptake of nitrate and ammonium.

Optical stations include hand-held sun photometry and photographs of sea and sky conditions. In-
SIMBIOS Project Annual Report

48

water optical observations were made with a Satlantic

SeaWiFS Profiling Multichannel Radiometer (SPMR)

and SeaWiFS Multichannel Surface Reference

(SMSR). Downwelling irradiance Ed(0-, ) and upwelling radiance Lu(0-

, ) were measured just below

the sea surface at 13 wavebands with the SMSR sensors mounted on a floating, tethered buoy with an umbilical cable for power and data transmission. The

SPMR also has 13 channels for vertical profiles of

downwelling irradiance Ed(z, ) and upwelling radiance Lu(z, ), and was deployed in a free-fall mode

with a kevlar cable for power and data transmission.

The SPMR includes sensors for tilt and pitch, pressure, conductivity and temperature (Ocean Sensors),

and fluorescence (WETLabs WetStar). The SMSR

and SPMR measurements were always made concurrently and the sensors were deployed 20-100 m from

the vessel to avoid ship-shadow effects. Above-water

reflectance measurements of the sea surface were

made with an Analytical Spectral Devices (ASD) Personal Spectrometer II (350-1050 nm, 1.4 nm bandpass,). Incident spectral irradiance Ed(0+

, ) was estimated with a gray Spectralon card (10% reflectance)

and water-leaving radiance Lu(0+, ) was corrected for

reflected sky light (K. Carder and C. Davis, pers.

Comm.). Spectrometers have been calibrated 1-2

times per year depending upon the number of field

campaigns. Profiles of IOPs were measured with 1-2

WET Labs AC-9 absorption and beam attenuation

meters with 9 channels and 25 cm path lengths for

total and/or soluble constituents <0.2um. A HOBI

Labs Hydroscat-6 was used to measure backscatter in

6 spectral bands. The latter three types of measurements were only made at Resolute.

AOPs, fluorometric chlorophyll and absorption

spectra data from all cruises have been submitted to

SeaBASS, except the Lab98 data set. The downwelling irradiance Ed sensor malfunctioned during Lab98,

and the data processing will require modifications of

Satlantic software or estimation of normalized waterleaving radiance Lwn from models. Additional ancillary data are also being submitted as they become

available from our lab and collaborators.

10.3 RESEARCH RESULTS

High northern latitude waters have unique biooptical properties compared with temperate data and

models (Sathyendranath et al. 1999b). These waters

have a large dynamic range of biomass, which must be

considered in algorithm development.

 Results to date reveal that diatoms usually dominate phytoplankton assemblages, but prymenesiophyte

blooms may alter bio-optical signatures (Sathyendranath et al. 1999a). The relatively large diatom cells

are highly packed with high chlorophyll-specific attenuation in the blue. Regional differences have been

found in soluble attenuation with the highest values in

the Canadian Arctic Archipelago. Blue-green band

ratio algorithms provide reasonable chlorophyll and

net daily primary production retrievals when properly

tuned for high latitudes. However, the current

SeaWiFS OC2 chlorophyll algorithm underestimates

biomass at moderate to high concentrations (Figure 1).

Solar-induced fluorescence should provide reasonable

instantaneous estimates of primary production with

robust backscatter corrections. The universality of

any algorithms requires extensive evaluation and validation.

10.4 WORK PLANNED

Cruise plans for 1999 are not yet finalized, but

should include a spring (May-June) Labrador Sea

cruise and one more to be determined. With

NOAA/NDBC, a time-series of bio-optical observations from the Chesapeake Light Tower is being initiated. As proposed ORCA is conducting 1-3 cruises

per year, and contributing critical core observational

data as well as a variety of ancillary bio-optical and

biogeochemical data.

Core observations have been delivered within 90

days and include profiles of AOPs made with our

Satlantic profiling spectroradiometer, fluorometric

chlorophyll, and normally particulate and dissolved

absorption spectra. Additional observations for which

ODU has primary responsibility for are being delivered within 12 months, while contributions from international collaborators are submitted as they become

available.

Our goal is to make raw data and derived products generally available via the web but our site is still

under construction. Efforts in 1999 will concentrate on

data analyses, modeling, and publication of results.

Two manuscripts have been submitted and several

more are in preparation.
SIMBIOS Project Annual Report

49

Figure 1. The current best-fit line of our high latitude data (minus Lab98) versus the current SeaWiFS OC2

chlorophyll algorithm.
SIMBIOS Project Annual Report

50

Chapter 11

High Frequency, Long-Time Series Measurements from

the Bermuda Testbed Mooring in Support of SIMBIOS

Tommy Dickey, S. Zedler and D. Sigurdson

University of California at Santa Barbara,

Santa Barbara, California

11.1 INTRODUCTION

The primary goal of the present activity is to provide high frequency, long-term time series bio-optical

data from the Bermuda Testbed Mooring (BTM) in

support of SIMBIOS (Dickey et al., 1998). The site is

located about 80km southeast of Bermuda at ~31° 43'

N, 64° 10' W in waters of ~4530m depth.

The BTM study, which is funded by NASA, NSF,

ONR, and NOPP, supports a variety of scientific research including SIMBIOS calibration and validation

activities. Our study contributes to the development

of methodologies and capabilities for synthesizing

data derived from several satellite ocean color missions (Esaias et al., 1995), particularly SeaWiFS. Key

NASA supported BTM optical measurements (every

15min during daylight) presently include: surface

downwelling spectral irradiance (7 's, SeaWiFS

matched) and subsurface (nominal depths of 14 and

32m) downwelling spectral irradiance and upwelling

spectral radiance (7 's for each, SeaWiFS matched).

Products include: radiance and irradiance ratios,

spectral attenuation coefficients, and upwelling spectral radiances just beneath the surface (0-). These data

provide necessary links to and interpolation of radiometric data for remotely sensed observations of ocean

color (suite of satellite color imagers) which can be

used to estimate biomass and primary productivity

globally.

Our newly developed telemetry system is now

providing near real-time radiometric data to our lab.

We are in the process of developing system software

which will make key data available to the SIMBIOS

project on a daily basis.

Highly complementary, value-added optical, meteorological, and physical data products are provided

through our complementary NSF BTM study (e.g.,

Dickey et al., 1998). Our comprehensive measurements can be used to relate bio-optical signals to inherent optical properties and to biogeochemical measurements and to test interdisciplinary models of phytoplankton biomass and productivity and carbon flux.

11.2 RESEARCH ACTIVITIES

A major objective of the SIMBIOS program is to

estimate normalized spectral water-leaving radiance,

Lwn, by using in situ measurements. Our approach is

to utilize moored instruments to obtain high temporal

resolution measurements of fundamental radiometric

variables to estimate upwelled spectral radiance just

beneath the ocean surface, Lu(0-), which can be used

to determine Lwn.

The mooring methodology, which allows for collection of very high temporal resolution, long-term

data, has several advantages including the ability to

obtain high numbers of "match-up" data for comparisons with SeaWiFS (e.g., Mueller and Austin, 1992).

However, the use of moorings for obtaining optical

data is a relatively new approach and has been used by

very few groups (e.g., Dickey. 1991; Smith et al.,

1991; Clark et al., 1997; Dickey et al., 1998).

Moored optical observations are more challenging

than their ship-based counterparts for several reasons

(e.g., less frequent calibration, biofouling, etc.). Thus,

it is desirable to intercompare fundamental radiometric data and derived products based on nearly concurrent, co-located data from moored and ship-based instrumentation. We have been collaborating with Dr.

David Siegel (UCSB), who has been collecting comparable vertical profile data during approximately

monthly (every other week in springtime) shipboard

cruises near the BTM site.

Our BTM data products are being intercompared

with ship-based data collected as part of Dr. Siegel's

Bermuda Bio-optical Program (BBOP) program (Siegel et al., 1995a,b; Siegel and Michaels, 1996). It

should be noted that the BTM and BBOP measurements are displaced in space and to a lesser extent in

time. In addition, there are several other significant

differences. Thus, correlations between the BTM and

BBOP data sets should not necessarily be expected to

be great.

The BTM Deployment 7, 8, and 9 (May 3, 1997 -

March 31, 1998) data sets encompass periods when 1)

only the Japanese ocean color imager (OCTS) was

collecting data, 2) neither OCTS nor SeaWiFS was
SIMBIOS Project Annual Report

51

collecting data, and 3) when only SeaWiFS was collecting data. The time series of meteorological, physical, and optical data are described in Dickey et al.

(1998). Time series measurements of surface and near

surface optical properties were made using moored

optical radiometer systems. Measurements include

surface spectral downwelling irradiance (Ed (0+, ) at

 = 412, 443, 490, 510, 555, 665, and 683nm (10nm

bandwidth at half power) at 6Hz for 20sec every

15min during daylight and at midnight. Subsurface

(nominal depths of 14 and 32m) downwelling irradiance (Ed (z, ) and upwelling radiance, Lu (z, ) data

at = 412, 443, 490, 510, 555, 665, and 683nm are

collected following the same regimen.

Our work is demonstrating that moored radiometric instrumentation can be used to provide a large

number of in situ match-up data for comparisons with

SeaWiFS observations in near real-time. The present

approach uses a multi-purpose mooring, the BTM, and

is relatively inexpensive. The use of such moorings

for optical measurements is relatively new, and thus

several complicating issues need to be considered and

evaluated. We are working with data from the BTM

and are doing statistical comparisons of data obtained

from the BTM and those obtained nearly concurrently

by the BBOP program. Despite several complicating

factors, generally favorable correlations have been

obtained for fundamental radiometric variables. Results including estimates of Lu(0-) have been transferred to the SeaBASS system. More detailed analyses and comparisons will continue to be done in the

future. Particular areas of investigation will include

calibration, sampling issues (e.g., BBOP spatial vs.

BTM temporal), and biofouling. In addition, it is

noteworthy that our near real-time data telemetry system has been functioning during the present Deployment 10. Lu(0-) estimates for this deployment have

also been transferred to SeaBASS.

11.3 WORK PLAN

It is our intention to place an additional radiometer at 5-7m depth for a future deployment to determine

if our estimates of Lu (0-) can be improved significantly. Deployment 10 full bandwidth data will be

recovered in March 1999 and Deployment 11 will be

initiated.

ACKNOWLEDGMENTS

We wish to thank David Siegel and Margaret

O'Brien for sharing the BBOP data used for intercomparisons and for their assistance.
SIMBIOS Project Annual Report

52

Chapter 12

The High-latitude Intercomparison and

Validation Experiment (HIVE)

Dave L. Eslinger

Institute of Marine Science, University of Alaska Fairbanks

(Present affiliation: NOAA, Charleston, South Carolina)

12.1 INTRODUCTION

The HIVE project is a three-year series of cruises

in both the Bering Sea and Prince William Sound/Gulf

of Alaska. Both locations are at similar latitudes

(~60°N) and have similar planktonic communities;

however, the physical environments are dramatically

different. These locations provide excellent test sites

to determine the performance of bio-optical algorithms at high latitudes. We are making measurements

of pigments (fluorometric and HPLC), radiometric

profiles, total suspended matter, and ocean aerosols.

The HIVE project builds on additional funding from

the Japanese ADEOS program and the EXXON Valdez Oil Spill Trustee Council, which are supporting

research projects in the Bering Sea and Prince William

Sound, Alaska, respectively.

We are contracted to perform two or more cruises

per year in the Gulf of Alaska, Prince William Sound,

and/or Bering Sea depending on availability of sampling opportunities on US and Japanese vessels. In

1997, we received additional funding from the NASA

SIMBIOS program to participate in a collaborative

Japanese cruise in the Bering Sea prior to the start of

the actual SIMBIOS project. In the first year of the

SIMBIOS contract, we participated in three cruises,

two in Prince William Sound and one in the Bering

Sea. This technical memorandum reports on all four

HIVE cruises to date.

The goal of the HIVE project is to validate highlatitude, satellite data products derived from imagery

from different ocean color sensors. This goal is to be

accomplished through meeting the following objectives:

Make accurate measurements of in situ data fields

of potential ocean color data products in northernhemisphere, high-latitude waters.

Compare measured data fields with data fields

determined from ocean color satellites.

Intercompare data fields retrieved from different

ocean color satellites.

Intercompare data fields retrieved from the same

satellite at different times of day.

The failure of the ADEOS spacecraft precluded

us from getting any match-up OCTS data during our

1997 cruise, which was prior to the SeaWiFS launch.

In 1998, clouds, fog and poor weather have prevented

any match-ups with the SeaWiFS data sets. Therefore

poor weather and the ADEOS failure have prevented

us from making any progress towards objectives 2 and

4. However, we have been successful in making field

measurements, even under less-than-ideal conditions.

12.2 RESEARCH ACTIVITIES

We are making field measurements of phytoplankton pigments using both fluorometric and HPLC

techniques, profiles of upwelling radiance and downwelling irradiance, total suspended matter, and ocean

aerosols. These activities are described in detail below. We describe our activities in four cruises. The

first occurred in July, 1997, in the Bering Sea, aboard

the Japanese training ship Oshoro Maru and has a

cruise identifier of OS97. The second was in June,

1998 was in Prince William Sound, AK, aboard a 58-

foot charter vessel, the M/V Auklet and has a cruise

identifier of AUK9806. The third was in July and was

back to the Bering Sea aboard the T/S Oshoro Maru

and has a cruise identifier of OS98. The fourth HIVE

cruise was in August, again in Prince William Sound

aboard the M/V Auklet, and has identifier AUK9808.

On all cruises, water samples were collected from

6 depths in the upper water column using Niskin bottles. During AUK9806, samples were taken from the

surface and 5, 10, 15, 25 and 50 meter depths. During

the OS97, OS98, and AUK9808 cruises, sampling

depths were selected based on standard light levels

and were generally taken at the depths corresponding

to1, 10, 20, 36, 50, and 95% of surface light. Depths

were altered when the water column was too shallow

to permit sampling to the one-percent light level. Surface samples generally came from one-meter depth,

but were occasionally deeper under rough sea conditions, when necessary to avoid firing bottles above the

surface.
SIMBIOS Project Annual Report

53

Phytoplankton Pigments

Water samples were filtered under low vacuum

onto GF/F filters, followed by freezing in liquid nitrogen for HPLC, and by grinding and extraction in 90%

acetone for immediate fluorometric analyses. Chlorophyll and phaeophytin concentrations were measured

in the acetone extracts aboard the ship immediately

after centrifugation using the technique of Strickland

and Parsons (1972). HPLC samples were shipped in

liquid nitrogen back to Fairbanks, where they were

stored. Our group does not have the necessary facilities to perform HPLC analyses, therefore, after storage, samples from the first three cruises were shipped

via FedEx to the Grice Marine Lab, Charleston, SC,

for analysis. A combination of inadequate packing

and shipment delays in both pick-up and transit led to

the samples arriving in Charleston at room temperature. HPLC analysis of a subset of these filters indicated significant degradation of pigments had occurred and the samples were discarded. The filters

from the fourth cruise remain in Fairbanks, in liquid

nitrogen, while we determine exactly where the delays

in handling and timing occurred and how to prevent

them in the future.

Total Suspended Mater Concentrations

Water samples were taken for determination of

total suspended matter (TSM) according to the JGOFS

procedures (JGOFS, 1991) as outlined in the SeaWiFS

protocols (Mueller and Austin, 1995). A modification

of this was to use pre-combusted glass fiber filters.

Filtered samples were dried and returned to Fairbanks

for weighing on a precision analytical balance.

Weighed dry filters were then recombusted and

reweighed to give both total suspended matter and

organic and inorganic fractions.

Radiance and Irradiance Profiles

For OS97, we were able to borrow a Biospherical

Instruments MER-2048 system from the NOAA

Coastal Services Center. Using this MER, we made

measurements of Ed at 340, 380, 395, 412, 443, 455,

490, 510, 532, 555, 565, and 671 nm. Eu and Lu profiles measurements were made at 380, 412, 443, 490,

510, 555, and 683 nm. For surface reference, Es was

measured at 340, 380, 395, 412, 443, 490, 510, 555,

565, 671, 780, and 875 nm. Temperature was also

measured during these profiles.

For AUK9806 cruise Satlantic loaned us an

SPMR system (serial # 022). The profiler measured

ED at 405.4, 411.9, 435.6, 442.8, 455.4, 489.6, 510.4,

531.9, 554.8, 590.5, 665.6, 669.6, 700.4 nm and Lu at

405.1, 411.9, 435.1, 443.5, 456.3, 489.4, 510.3, 531.5,

554.3, 590.5, 665.3, 670.2, and 700.3 nm. The surface

reference measured Ls at 406.5, 412.2, 435.3, 443.4,

455.9, 489.9, 510.4, 531.6, 554.6, 590.3, 665.1, 670.0,

and 700.6 nm and Es 405.1, 412.4, 435.6, 442.9,

456.1, 489.3, 510.4, 531.5, 554.5, 590.4, 664.8, 670.0,

and 700.6 nm. This system was only used for the

AUK9806 cruise. Due to failure of a PCMCIA serial

port card, both the profiler and surface reference could

not be used simultaneously. Instead, we made a

measurement of Es and Ls, did three profiles, and then

repeated the surface reference measurements. Given

the heavy overcast conditions during this cruise, we

do not expect the surface light values to have varied

significantly during the time we were profiling.

For the OS98 and AUK9808 cruises, we used our

newly purchased SPMR system, which simultaneously

measured Ed, Lu, Es temperature, conductivity, and in

vivo fluorescence profiles. Ed was measured at 412.3,

443.1, 490.7, 510.0, 555.1, 665.6 and 682.4 nm. Lu

was measured 412.3, 442.1, 490.9, 510.1, 554.9,

665.4, and 682.9 nm. Es was measured at 412.3,

442.6, 490.3, 510.2, 554.4, 665.0, and 683.8 nm.

Instrument Calibration

All instruments have been calibrated as required

by the SeaWiFS protocol and SIMBIOS contract.

Calibration files have been submitted with the biooptical data to SeaBASS.

12.3 RESEARCH RESULTS

Table 1 summarizes the cruise time, location, station, and measurement data. All cruises had complete

overcast at almost every station. Although these high

latitudes are generally cloudy, this was an exceptionally bad year for our cruises. In 1994 through 1996

cruises, we had much better weather at these times and

expected similar intermittent clouds these last two

years.

12.4 WORK PLAN

This last year we participated in three cruises instead of only the two in which we were contracted to

participate. Next year, we plan to consolidate our two

5-day Prince William Sound cruises into one 10-day

cruise. By increasing our at-sea time to ten days, we

hope to get the satellite match-ups that we have

missed up to the present time. At the present, we plan

to schedule the cruise for middle to late April, to capture the high, spring-bloom phytoplankton concentrations. However, we will review the previous years

AVHRR data to try and determine if expecting cloudfree days during this time period is realistic. We will

still plan to participate in the T/S Oshoro Maru cruise

in July.
SIMBIOS Project Annual Report

54

Table 1. Summary of cruises and in situ data collected.

Cruise ID Location Cruise Dates Number

of Stations

Non-optical

measurements*

OS97 Bering Sea 18 July –2 Aug.1997 20 Pigments (fluor),

TSM, T

AUK9806 Prince William

Sound

5 –9 June 1998 21 Pigments (fluor),

TSM, T

OS98 Bering Sea 18 July –1 Aug. 1998 17 Pigments (fluor),

TSM, T, S, Fluor

AUK9808 Prince William

Sound

8 Aug. – 2 Sept., 1998 15 Pigments (fluor &

HPLC), TSM, T, S,

Fluor

* TSM = Total Suspended Matter, T = temperature profile, S = Conductivity profile, Fluor = in vivo fluorescence profile
SIMBIOS Project Annual Report

55

Chapter 13

Satellite Ocean Color Validation Using Merchant Ships

Robert Frouin and David L. Cutchin

Scripps Institution of Oceanography

University of California San Diego, La Jolla, California

Pierre-Yves Deschamps

Laboratoire d'Optique Atmospherique

Universite des Sciences et Technologies de Lille, Villeneuve d'Ascq, France

13.1 INTRODUCTION

The usual approach to satellite ocean color validation is to organize dedicated experiments at sea, e.g.

in regions that are likely to cause atmospheric correction errors, and to measure concomitantly waterleaving radiance and aerosol optical properties at the

time of satellite overpass (Clark et al., 1997). The data

are necessary not only to compare satellite estimates

with in situ measurements, but also to interpret the

differences and, eventually, adjust atmospheric correction algorithms. These experiments, unfortunately,

are expensive; they cannot be carried out over the full

range of expected atmospheric and oceanic conditions.

Furthermore, because of cloud cover only a few

match-ups are generally obtained during a campaign,

making the approach even less cost-effective.

A complementary approach --and the focus of the

present project-- is to use ships of opportunity, in particular, merchant ships traveling routes in the world's

oceans. For the approach to be cost-effective, the ships

must participate on a volunteer basis or at a very small

cost, and the measurement program must not interfere

with the ship’s activities. Importantly, the ship should

not be required to stop, i.e. one should be able to collect the data en route, while the ship is steaming. Because of these limitations, one cannot expect to measure the full set of ocean-color variables using ships of

opportunity. Still, to be useful the measurement program should meet the basic requirements for satellite

ocean color validation.

It is in this context, and also according to a study

of the measurements required for satellite ocean-color

validation (Schwindling et al., 1998), that the SIMBAD concept was developed. SIMBAD is a portable

radiometer designed for use onboard ships of opportunity. It measures normalized water-leaving radiance

(or diffuse marine reflectance) and aerosol optical

thickness in typical spectral bands of satellite ocean

color sensors. Knowledge of both variables is needed

and generally sufficient to evaluate atmospheric correction algorithms (Schwindling et al., 1998). The

instrument is easy to operate, so that any ordinary

crew can learn quickly how to make measurements.

To achieve adequate sampling, i.e. acquire data in a

wide range of oceanic and atmospheric conditions, a

series of ten radiometers was built for use in two complementary networks of ships/routes, one operated by

the Scripps Institution of Oceanography, the other by

the University of Lille.

13.2 RESEARCH ACTIVITIES

The SIMBAD radiometer was designed and built by

the Laboratoire d’Optique Atmospherique (LOA) of

the University of Lille. It measures water-leaving radiance from above the surface as opposed to below the

surface the usual way. This eliminates constraints associated with deploying underwater instruments at

sea, e.g. stopping the ship. Viewing of the ocean surface is made from the side of the ship lit by the sun,

outside the glitter region, at a nadir angle of 45 degrees. A vertical polarizer reduces the skylight reflected by the surface in the instrument’s field-ofview. The best location to operate the instrument is

generally the bow, making it easy to avoid shipgenerated foam. The radiometer also measures aerosol

optical thickness, by viewing the sun like a standard

sun photometer. The same optics (2.5 degree field-ofview) and detectors are used in both ocean- and sunviewing modes, but at different electronic gain.

The radiometric measurements are made simultaneously in five spectral bands centered at 443, 490,

560, 670, and 865 nm. These bands are not exactly

those of the ocean color sensors that are flying or

scheduled to fly, but result from a compromise. They

constitute, however, a basic set of bands for atmospheric correction and bio-optical algorithms. Viewing

of the ocean and sun is made sequentially, but the

non-simultaneity of the measurements is not limiting.

SIMBAD does not measure incoming solar irradiance,

a variable that must be known to normalize water-
SIMBIOS Project Annual Report

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leaving radiance. It is calculated accurately in clear

sky conditions or when the sky is partly cloudy

(<30%) with the sun not obscured by clouds. This

defines the sky conditions under which SIMBAD

should be operated. In addition to radiometry, SIMBAD automatically acquires viewing angles (using a

magnetometer and two inclinometers), time and geographic location (using a GPS), pressure, and temperature. It requires about 15 minutes to collect a

complete data set (ocean, sun, optical zero), including

deploying the instrument and logging ancillary data

(wind speed, sea state, cloud cover, etc.). Internal

memory and batteries allow for 3 months of operations in normal mode (typically 5 sets of measurements per day). At the end of the campaign or voyage,

after the ship returns to port, the data are downloaded

onto computer disk and diskette and the radiometer is

calibrated. In the case of long campaigns, the data are

mailed from selected ports along the ship’s route, allowing for a more rapid data turnover.

Justification and Verification

The principle of the SIMBAD radiometer, in particular its ability to reduce reflected skylight with the

help of a vertical polarizer, has been justified theoretically and verified experimentally (Fougnie et al.,

1999b). Theoretical calculations show that, for a nadir

angle of 45 degrees and a relative azimuth angle between solar and viewing directions of 135 degrees, the

recommended geometry, reflected skylight is reduced

to typically 10-3 in reflectance units at 443 nm. This

represents 2 to 10% of the diffuse marine reflectance,

the signal of interest. Furthermore, the effects of surface roughness on skylight reflection and, hence, uncertainties in sea state (wind speed) are minimized.

Taking into account typical uncertainties in wind

speed and geometry, the residual reflected skylight are

correctable to a few 10-4 in reflectance units. For most

oceanic waters, the resulting error on the diffuse marine reflectance in the blue and green is less than 1%.

The theoretical results have been verified experimentally at the Scripps Institution of Oceanography pier,

by viewing the ocean surface with a scanning polarization radiometer (Fougnie et al., 1999b). The various

angular and spectral effects predicted by theory have

been evidenced in the measurements.

Since the water body polarizes incident sunlight

(e.g., Ivanoff, 1975, Frouin et al., 1994), the measured

polarized radiance differs from the total radiance. For

the recommended geometry, the underwater scattering

angle varies only between 148 and 158 degrees, and

the maximum polarization factor varies between 0.83

and 0.92 (Fougnie et al., 1999b). One should be able

to correct the polarization effects to within 5% relative

accuracy, which compares with other errors, such as

those due to bi-directional effects and radiometric

calibration.

The SIMBAD radiometer was evaluated at sea,

during California Cooperative Fisheries Investigation

(CalCOFI) cruises in the southern California Bight.

The diffuse marine reflectance measured by the radiometer was compared with that measured by an underwater MER optical system. The agreement between the two types of measurements was good, to

within 1.6 10-3 in reflectance units. Aerosol optical

thickness measured by the SIMBAD radiometer also

compared well with that measured by sun photometers

during the October-November 1996 CalCOFI cruise

(Nakajima et al., 1999) and during the Second Aerosol

Characterization Experiment (ACE-II).

The SIMBAD radiometer proved useful to check

vicariously the radiometric sensitivity of the Polarization and Directionality of the Earth’s Reflectance

(POLDER) instrument onboard ADEOS (Fougnie et

al., 1999a). The satellite radiance was compared with

that computed for the same geometry using a radiation-transfer model. SIMBAD measurements of aerosol optical thickness and marine reflectance at the time

of satellite overpass were used as input to the model.

The accuracy of the vicarious calibration coefficients

was estimated to be better than 3%. A large decrease

of the POLDER instrument response was found in the

blue, confirming the results previously obtained using

alternative calibration techniques.

Data Format

The SIMBAD data sets are fairly complete

for satellite ocean color validation. They include nearconcurrent values of spectral aerosol optical thickness

and diffuse marine reflectance, necessary variables for

checking radiometric calibration and evaluating atmospheric correction algorithms. They also include

fractional cloud coverage and wind speed (useful to

estimate whitecap reflectance). The data sets can be

accessed at the following web addresses:

http://genius.ucsd.edu/~frouin/ and http://www-loauniv-lille1.fr/~poteau/.

13.3 RESEARCH RESULTS

Since the launch of the SeaWiFS in September

1997 and until December 1998, SIMBAD measurements have been made during 12 research cruises and

9 merchant ship voyages (Table 1). A total of 156

SIMBAD data sets have been collected under clear or

mostly clear sky (fractional cloud coverage less than

0.2) within a few hours of satellite overpass. A variety

of oceanic and atmospheric conditions have been

sampled, but no data have been acquired in the South

Atlantic and Indian Oceans. The research cruises and

merchant ship voyages are listed below in chronological order with location or route, date, name of the

SIMBAD operator, and network (SIO or LOA).
SIMBIOS Project Annual Report

57

Table 1. SIMBAD cruise measurements from 9/1997 to 12/1999

CalCOFI 9709, Southern California Bight, 09/20/98-10/08/98, Wieland, SIO.

M/V Asian Challenger, Valparaiso-Auckland, 10/12/98-10/18/98, Cutchin, SIO.

R/V Melville, San Diego-Acapulco-Callao-Valparaiso-Easter-Papeete-Honolulu, 11/02/97-06/07/98,Comer, SIO.

M/V Nacre, Honolulu-Coronel, 12/20/98-01/02/98, Cutchin, SIO.

CalCOFI 9802, Southern California Bight, 01/23/98-02/10/98, Subranamian, SIO.

CalCOFI 9804, Southern California Bight, 04/02/98-04/24/98, Mitchell, SIO.

R/V Revelle, Eastern Tropical Pacific Ocean, 04/09/98-04/27/98, Dupouy, LOA.

M/V Toucan, Le Havre-Cayenne-le Havre, 05/04/98-05/23/98, Poteau, LOA.

M/V Chevron Mississippi, Honolulu-Valdez, 05/18/98-05/23/98, Cutchin, SIO.

M/V Toucan, Le Havre-Cayenne-le Havre, 06/08/98-06/20/98, Poteau, LOA.

CalCOFI 9807, Southern California Bight, 07/09/98-07/27/98, Wieland, SIO.

ATMARA 9807, English Channel, 07/21/98-08/06/98, Wartel, LOA.

NAN 9807, Cape Cod, 07/06/98-07/10/98, Shieber, SIO.

M/V Mokihana, Oakland-Guam-Taiwan-Japan-Oakland, 07/20/98-08/15/98,Bousseloub, SIO.

CalCOFI 9809, Southern California Bight, 09/13/98-10/01/98, Wieland, SIO.

BREST 9809, Northeastern Atlantic Ocean, 09/25/98-10/01/98, Gohin, LOA.

M/V Mokihana, Oakland-Guam-Taiwan-Japan-Oakland, 08/25/98-09/08/98, Bousseloub, SIO.

M/V Micronesian Navigator, California-Micronesia-Philippines-California,08/25/98-10/28/98, Sumogat, SIO.

R/V Cape Hatteras, Beaufort-Jacksonville, 10/21/98-12/01/98, Subranamian, SIO.

M/V Micronesian Navigator, California-Micronesia-Philippines-California, 10/30/98-12/31/98, Sumogat, SIO.

R/V Ka’imimoana, Honolulu-Fiji-Honolulu, 10/19/98-12/11/98, Strutton, SIO.

13.4 WORK PLAN

A collaborative LOA-SIO measurement program

for satellite ocean color validation based on ships of

opportunity has been developed. This has been accomplished in a series of successive, logical steps.

First, a study of validation requirements was performed, indicating that measurements of spectral water-leaving radiance and aerosol optical thickness at

the time of satellite overpass are generally sufficient to

evaluate satellite-derived ocean color (Schwindling et

al., 1999). Second, in view of the study and limitations

of dedicated validation experiments at sea, the SIMBAD radiometer was designed, for use of ships on

opportunity such as merchant ships traveling regular

routes in the world’s oceans. Third, the instrument’s

innovative principle (use of a vertical polarizer to reduce skylight reflection) was verified experimentally

at the Scripps Institution of Oceanography pier (Fougnie et al., 1999b). Fourth, the instrument was tested at

sea, on station and en route, during various oceanographic campaigns (Fougnie, 1998, Nakajima et al.,

1999). Fifth, suitable merchant ships and routes in the

Pacific and Atlantic Oceans were identified and selected officers were trained. Some of the ships, for

example M/V Micronesian Navigator (SIO network)

and M/V Toucan (LOA network), are now providing

SIMBAD data routinely. Sixth, SIMBAD data were

used to check vicariously the radiometric calibration

of the POLDER instrument onboard ADEOS (Fougnie

et al., 1999a).

Regarding measurement opportunities, the program’s focus has been on research campaigns during

which water-leaving radiance and/or aerosol optical

thickness were measured by other instrumentation

(e.g., CalCOFI campaigns), so that comparisons could

be made. Although more evaluation of the SIMBAD

data is necessary, and should be done on a continuous

basis, in order to increase the number of surface/satellite match-ups the focus should be shifted to

ships that do not carry out the same type of measurements as the SIMBAD radiometer (e.g., more merchant ships). The program also needs to be extended

to ships traveling in other oceanic regions, in particular the southern Oceans and the Indian Ocean, to complement the present coverage. There are many possibilities, and the demand for SIMBAD radiometers has

been increasing. The realization of a new series of

radiometers is envisioned, with the instruments available for the next generation of satellite ocean color

sensors.

ACKNOWLEDGMENTS

The authors wish to thank all the officers and scientists that have collected SIMBAD data, P. Lecomte

and M. Verwaerde of the University of Lille for realizing the SIMBAD radiometer, B. Fougnie, J.

McPherson, and A. Poteau for processing the data.

This work has been supported by the National Aeronautics and Space Administration under Contract

NAS-97135 (to R. Frouin), the Centre National

d’Etudes Spatiales, the Centre National de la Recherche Scientifique, and the Region Nord-Pas de Calais.
SIMBIOS Project Annual Report

58

Chapter 14

High Attitude Measurements of Radiance at High Spectral

and Spatial Resolution for SIMBIOS Sensor

Calibration, Validation and Intercomparisons

Robert Green and Thomas G. Chrien

NASA, Jet Propulsion Laboratory

Pasadena, California

14.1 INTRODUCTION

The successful combination of data from different

ocean color sensors depends on the correct interpretation of signal from each of these sensors. Ideally, the

sensor measured signals are calibrated to geophysical

units of spectral radiance, and sensor artifacts are removed and corrected. The calibration process resamples the signal into a common radiometric data

space so that subsequent ocean color algorithms that

are applied to the data are based in physical processes

and inherently sensor independent. The objective of

this SIMBIOS effort: “High Altitude Measurements of

Radiance at High Spectral and Spatial Resolution For

SIMBIOS Sensor Calibration, Validation, and Intercomparisons is to conduct a series of direct calibration

comparisons using the NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS),” is to

assess the calibration of the satellite sensors which

participate in SIMBIOS.

The AVIRIS sensor flies at 20 km altitude on a

NASA ER-2 near the top of the absorbing and scattering portions of the atmosphere. AVIRIS measures

the solar reflected spectrum from 370 nm to 2500 nm

through 224 contiguous 10 nm wide spectral channels.

Data are acquired as images of 11 by up to 800 km

extent with 20 m spatial resolution. The stability and

repeatability of AVIRIS calibration has been and continues to be validated through a series of inflight calibration experiments. With pre and post flight calibrations of AVIRIS, coupled with the on-board calibrator, calibration accuracy of better than 2% spectral,

3% radiometric and 3% spatial have been achieved.

The activities and results presented here are primarily for SeaWiFS. However, related work has been

carried out for ADEOS OCTS. In the future, it is

planned that AVIRIS will underfly EOS.

14.2 RESEARCH ACTIVITIES

On the 2nd of October 1997 AVIRIS under flew

the SeaWiFS sensor of the coast of Southern California near latitude 35° and longitude 127°. The

SeaWiFS sensor was tilted to the Northeast to avoid

sun glint. In order for the AVIRIS spectral images to

overlap the area, the azimuth, and the zenith angles of

the SeaWiFS measurements, AVIRIS was flown in a

circle beneath SeaWiFS. The AVIRIS scan angle (±

15 degrees) plus the aircraft roll angle (20 degrees)

assured overlap of both area and observation geometry. The AVIRIS data from the 2nd of October 1997

flight were spectrally, radiometrically and spatially

calibrated through the AVIRIS data system algorithms. The SeaWiFS data and the SEADAS processing software were requested and received. Both

the AVIRIS and the SEAWIFS data sets include the

position and pointing information at the time of acquisition. The simultaneous acquisition of the AVIRIS

and SeaWiFS with overlapping observation geometry

provides the essential data set to complete the calibration objective.

14.3 RESEARCH RESULTS

Determination of the areas of the SeaWiFS and

AVIRIS images with the same observation geometries

requires projection of the data based on the position

and pointing knowledge of the sensor. A set of algorithms were developed to accept the SeaWiFS position

and point information and calculate the azimuth and

zenith angles for the 2nd of October SeaWiFS data.

All angles were calculated from the perspective of the

surface. The observation geometry at the surface is

the correct geometry for calibration comparison.

AVIRIS receives and records both Global Positioning

System (GPS) and Inertial Navigation System (INS)

information from the ER-2 aircraft. The GPS provides latitude, longitude and altitude information,

while the INS provides roll, pitch, and yaw information. These position and pointing data were used with

an analogous set of algorithms to calculate the

AVIRIS spectral image azimuth and zenith angles

were calculated. With both the AVIRIS and SeaWiFS

image azimuth and zenith angles determined, the target area of overlapping observation geometry was

identified.
SIMBIOS Project Annual Report

59

This area contains the AVIRIS spectra and SeaWiFS

multi spectral data of the same area on the surface

with the same observation azimuth and zenith (Table

1).

The average AVIRIS spectrum from the area of

observational and temporal coincidence was extracted.

A correction factor was applied to the AVIRIS spectra for the transmittance from the 20 km AVIRIS altitude to the top of the atmosphere. This correction

factor was calculated with the MODTRAN radiative

transfer code using Ozone values from the TOMS

total ozone archive for the area.

The SeaWiFS multi spectral band data were extracted directly for this target. A graphical comparison

of the AVIRIS spectrum and SeaWiFS bands showed

good agreement. In order to quantitatively compare

the AVIRIS and SeaWiFS data, a convolution algorithm was developed to convolved the AVIRIS spectra

to the SeaWiFS bands. The algorithm was applied to

the AVIRIS spectra for the target area and the

AVIRIS predicted radiances compared to the

SeaWiFS reported radiances (Table 2). These results

are preliminary. A review of the version of SEADAS

used to process the SeaWiFS data is underway. A

high priority activity has begun to review and compare

the absolute radiometric standard used for SeaWiFS

calibration and AVIRIS calibration.

The primary objective of this SIMBIOS effort has

been achieved. On the 2nd of October 1997, AVIRIS

underflew the SeaWiFS sensor. The data set was acquired such that the observation geometries of

SeaWiFS and AVIRIS could be match for direct comparison of measured radiance. A set of algorithms

were developed to calculate the surface azimuth and

zenith angles for both the SeaWiFS and AVIRIS data

sets.

These algorithms required as input position and

pointing information for the two sensors. The initial

graphical comparison of the AVIRIS spectrum and

SeaWiFS bands showed good agreement for the ocean

target of overlapping observation geometry. An additional set of algorithms were developed to convolved

the AVIRIS spectra to the SeaWiFS spectral bands.

Direct comparison of the AVIRIS measured and

SeaWiFS measured radiance shows the agreement is

best for SeaWiFS bands 3,4,5, and 6 and least good

for SeaWiFS bands 1, 2, 7, and 8. These are initial,

preliminary results and additional review and uncertainty analysis is required to strengthen the basis of

comparison. Never-the-less, these initial results validate the objective, approach, and activities of this

SIMBIOS Project.

14.4 WORK PLAN

In 1999 three additional underflights of

SEAWIFS are planned. The first underflight is

planned for the Spring of 1999 from the west coast. A

second underflight will be attempted from the east

coast in the late Spring or early Summer. The third

underflight is planned for the west coast in the late

summer early fall time frame. Each underflight will

include two flight circle acquisitions to assure a match

to the SeaWiFS viewing geometry. The first flight

circle will be timed to coincide with the satellite overpass. The second flight circle acquisition enables investigation of the time sensitivity of the measurements. Efforts will be made to coordinate all underflights with other participating SIMBIOS investigators. Following each successful underflight, the

AVIRIS runway calibration standard will be used to

place the maximum accuracy on the AVIRIS radiometric calibration for the SeaWiFS underflight. In

April of 1999, the new SIMBIOS SXR-II transfer

radiometer will be used at JPL to further compare the

SIMBIOS and AVIRIS radiometric standards. Results

of all the 1999 activities of this project will be provided to SIMBIOS. Work will proceed on writing up

the 1998 and 1999 results for publication.

ACKNOWLEDGMENTS

This research was carried out at the Jet Propulsion

Laboratory / California Institute of Technology, Pasadena, California, under contract with the National

Aeronautics and Space Administration.
SIMBIOS Project Annual Report

60

Table 1. Preliminary results of AVIRIS and SeaWiFS radiance comparison.

BAND SeaWiFS AVIRIS AVIRIS Difference

Radiance Radiance Uncertainty

1 7.800 6.791 5.1% 12.9%

2 6.852 6.311 3.5% 7.9%

3 4.899 4.861 2.1% 0.8%

4 3.995 3.972 2.5% 0.6%

5 2.753 2.711 2.9% 1.5%

6 1.248 1.193 2.3% 4.5%

7 0.641 0.601 3.6% 6.2%

8 0.449 0.412 3.5% 8.3%

The units of radiance are microWatts/cm2/nm/sr.

Table 2. Website locations for AVIRIS SeaWiFS match up example

1 First AVIRIS flight circle. ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic01.jpg

2 Corresponding SeaWIFS image ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic04.jpg

3 SeaWIFS azimuth ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic05.jpg

4 SeaWIFS zenith ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic06.jpg

5 AVIRIS azimuth ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic07.jpg

6 AVIRIS zenith ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic08.jpg

7 AVIRIS and SeaWIFS data measured within 5 seconds.

 ftp://makalu.jpl.nasa.gov/pub/rog/seawifs/pic09.jpg
SIMBIOS Project Annual Report

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Chapter 15

Merging Ocean Color Data from Multiple Missions

Watson W. Gregg

NASA/Goddard Space Flight Center

Greenbelt, Maryland

15.1 INTRODUCTION

In response to the potential importance of phytoplankton in the global carbon cycle and the lack of

comprehensive data, the National Aeronautics and

Space Administration (NASA) and the international

community have established high priority satellite

missions designed to acquire and produce high quality

ocean color data. Seven of the missions are routine

global observational missions: the Ocean Color and

Temperature Sensor (OCTS), the Polarization and

Directionality of the Earth's Reflectances sensor

(POLDER), SeaWiFS, Moderate Resolution Imaging

Spectrometer-AM (MODIS-AM), Medium Resolution

Imaging Spectrometer (MERIS), Global Imager

(GLI), and MODIS-PM. In addition, there are several

other missions capable of providing ocean color data

on smaller scales.

Any individual ocean color mission is limited in

ocean coverage due to sun glint and clouds. For example, one of the first proposed missions, the

SeaWiFS, can provide about 45% coverage of the

global ocean in four days and only about 15% in one

day (Gregg and Patt, 1994).

The proliferation of missions suggests that better

ocean coverage can be obtained in less time if the data

are combined. In addition to improved, and faster

coverage, data can be taken from different local times

of day if the missions are placed in different orbits,

which they are. This can potentially lead to information on diel variability of phytoplankton abundances.

We propose to investigate, develop, and test algorithms for merging ocean color data from multiple

missions. We seek general algorithms that are applicable to any retrieved ocean color data products, and

that maximize the amount of information available in

the combination of data from multiple missions. Most

importantly, we will investigate merging methods that

produce the most complete coverage in the smallest

amount of time, nominally, global daily coverage. We

will also assess the ability to produce fuller coverage

in larger time increments, including 4-day, 8-day

(weekly), monthly, seasonal and annual. Secondarily,

we will investigate the ability of the missions to produce coverage at different times of day, for diel variability and dynamical evaluations, and develop algorithms to produce this information.

15.2 RESEARCH ACTIVITIES

Work in the first two years has focused on: a)

defining the problems and opportunities provided by

the existence of multiple sensors; b) analysis of past

sensors to provide insights into the characteristics,

drawbacks, and advantages of individual sensor responses in the context of merging; and c) analysis,

development, and testing of candidate merger algorithms.

a) Defining the Problems

First we assessed the global coverage improvements possible by the six global missions. These results show that significant scientific advantages can

accrue from assembling and merging data from the

multiple satellite platforms proposed for ocean color

in the next decade. The principal advantages are increased ocean coverage in less time, and new observations of the daily dynamics of phytoplankton abundances, resulting from different observation times of

co-located ocean areas. Data from three satellites as

opposed to one, can increase ocean coverage by 58%

for one day, and 45% for four days. Additional satellites produce diminishing returns, however. This latter

point is not necessarily an adverse finding, since each

mission has a limited life expectancy and in-flight

problems are, unfortunately, still not rare in the satellite business. Using observations from pairs of missions, as much as 14 hour time differences at colocated points can be realistically achieved at high

latitudes, even considering the distribution of land

masses and ice cover. Smaller time differences are

observed at lower latitudes, but 5 to 7 hour differences

are still available. Furthermore, massive numbers of

these co-located pairs are available, suggesting that

routine scientific studies of diel phytoplankton variability can be supported (Gregg et al., 1998). More

detailed analyses emphasized seasonal and regional

coverage improvements and was limited to the

SeaWiFS/MODIS combination, since these are the

two missions planned for next launch. The results

showed that the launch of EOS AM-1 provides an

opportunity to improve ocean color observations by

combining data from the SeaWiFS and MODIS mis-
SIMBIOS Project Annual Report

62

sions. The sensors have different scanning characteristics and are flying on different platforms in different

orbits. The results suggested that very large improvements in coverage frequency (daily to four-day)

can be obtained by combining data from both sensors:

40-47% increases in global coverage over SeaWiFS

alone in one day, and > 100% in areas near the solar

declination. Four-day increases are slightly smaller

for global coverage, 29-35%, but meridional percent

increases are similar to the one-day case. These differences are due to reduced sun glint contamination

obtained by tilting (SeaWiFS), and scanning away

from the maximum glint region (MODIS),due to its

10:30 AM equator crossing time, and due to the large

scan width of MODIS. The results show that

SeaWiFS and MODIS are very complementary ocean

color missions that can provide more complete observations of ocean processes at high frequency if data

are combined (Gregg and Woodward, 1998). A more

detailed paper with more fully defined results was

published as a NASA TM (Woodward and Gregg,

1998). Third, assessed potential capability for improving ocean color observations by selecting complementary mission orbits. Considering that observations are severely hampered by cloud cover and sun

glint, a possibility exists for using multiple missions to

improve the coverage of the oceans in shorter time

scales. In fact, only about 10-18% of the oceans are

observed in a single day, even by so-called global

observational missions, due to these two ocean color

contaminants. Analysis of a 7-day period of cloud

cover from the International Satellite Cloud Climatology Project (ISCCP), show that 12% new surface area

is available for viewing each day. This translates to

an increase of about 0.5% per hour of separation in

viewing times. Thus if the ocean could be viewed by

2 different satellites 4 hours apart, 2% more ocean

area could be observed. This represents a coverage

increase of about 13%. If 2 satellites were placed in

Earth orbit with equator crossing times 4 hours apart,

the improvement in coverage by these 2 satellites over

a single one is about 60%. Furthermore, by managing

the orbits of the 2 satellites, nearly complete sun glint

avoidance can be achieved, further improving the

ocean coverage. The best improvements can be made

by 2 satellites in the same node, whose orbital positions are adjusted to view the sun glint contaminated

areas of the other. If scan edges are useful for quantitative ocean color observations (the validity of which

is unknown at this time), then only 2 polar-orbiting

satellites are necessary. If not, a third satellite is necessary, preferably in a low inclination orbit where

losses in coverage in the tropics by the polar orbiters

can be best compensated (polar orbiters overlap coverage at high latitudes, and the scan edges are necessary only near the equator). However, the best configuration is 3 geostationary satellites, which provide

complete global coverage routinely with a viewing

time separation that can maximize cloud and sun glint

avoidance, with a single polar orbiter to provide high

latitude coverage (Gregg, 1999a).

b) Analysis of Past Sensors

We continued investigations into OCTS data.

These investigations began before the failure of

ADEOS, in an effort to characterize OCTS data for

use with a merging activity with SeaWiFS. The loss

of data from the sensor precludes its use in merging,

but the similarity of some aspects of sensor design

with MODIS suggests that significant understanding

of the capabilities and deficiencies of MODIS data can

be facilitated through a thorough analysis of OCTS

data. In fact, we have found this to be true. Initial

observations just after failure of OCTS suggested 6

problem areas: band registration, image striping, cloud

noise, navigation, calibration, and bright target response. Analysis of the first three led to solutions that

improved imagery substantially (Gregg, 1998; Gregg,

1999b). Particularly the methods for reducing image

striping is a useful method for a problem expected to

occur in MODIS imagery. Analysis of geolocation,

radiometric stability and accuracy, and bright target

responses were characterized and submitted for publication (Gregg et al.,1999). The results here also have

implications for MODIS.

c) Merging Algorithms

 Efforts have began on developing merging algorithms. We are investigating 4 possible approaches: a)

simple splicing, where 1 data set is deemed superior

and the other is patched into gaps, b) sensor weighting, where specific dependences and deficiencies are

identified and co-located observations are merged

using different weighting functions for the sensors, c)

the Conditional Relaxation Analysis Method, where

the best data are selected as interior boundary conditions into a merged set using Poisson's equation (Reynolds, 1988), and d) optimum interpolation, where

merging occurs by weighting individual sensor data to

minimize spatial covariance function. The Conditional Relaxation Analysis Method (CRAM) was implemented and tested using CZCS data and in-situ

data. Although these results were funded by separate

grant, the results enabled us to begin to understand the

strengths and weaknesses of the method and its potential use for satellite data (Gregg and Conkright, 1999).

Several modifications are required before effective use

with in-situ data, but it is not clear at this time whether

these modifications will be necessary for merging of

multiple satellite data, since data paucity may not be

an issue. It may be an issue, however, if significant

deficiencies are identified.
SIMBIOS Project Annual Report

63

Chapter 16

Validation of Bio-optical Properties in Coastal

Waters: a Joint NASA - Navy Project

Richard L. Miller

NASA, Stennis Space Center, Mississippi

16.1 INTRODUCTION

This project is a joint effort between NASA’s

Earth System Science Office and the Naval Oceanographic Office (NAVOCEANO) at the John C. Stennis Space Center, MS. The collaboration reflects a

partnership developed by NASA and NAVOCEANO

over six years to share resources and expertise in the

collection of ocean optics, hydrographic, biological,

and remotely sensed data to support each agency’s

goals in coastal research. NAVOCEANO provides

ship time, instrumentation, and operational support

during oceanographic surveys while NASA provides

expertise in data collection, computer programming

and modeling, and data processing and analysis. This

SIMBIOS project was established to provide data

collected in the South China Sea, Gulf of Thailand and

adjacent coastal waters. This project is designed to

provide NASA with cost-effective access to in-water

optics and ancillary data in coastal waters representing

diverse turbid environments, and if successful, will

help provide an effective mechanism for interagency

cooperation and data exchange.

16.2 RESEARCH ACTIVITIES

NAVOCEANO hydrographic surveys 260797 (27

April - 19 May) and 260897 (23 May - 16 June) were

completed in the South China Sea, and the Gulf of

Thailand / South China Sea, respectively. The SIMBIOS project investigators comprise the optics team

of these surveys, one of three primary operations: optics, bioluminescence, and basic hydrography. Vertical

profiles were acquired by each operations team at a

dense grid of selected stations. In addition, XBTs were

dropped at regular intervals along the cruise track

between the profiling stations. Three optics packages

were deployed. These were designated as the day

(IOPs and radiometer), night (IOPs), and the Satlantic

system. The day and night packages (Table 1) used the

Mermaid II data acquisition system (Miller et al.,

1995). System power and communications network

for the day and night packages were provided by

MODAPS (Wet Labs, Inc.).

Vertical Profiles and IOP

Several power and communication problems were

encountered with the MODAPS deck and subunits of

each package. Power delivery from the subunit to the

MER 1032 failed after 11 profiles and hence the combined package was abandoned. The subunit for the

IOP package could not establish communications with

the Seabird CTD. The CTD was disconnected from

the MODAPS system and was deployed in standard

profiling mode (internal data collection). CTD Data

were downloaded independently following each cast.

Unfortunately, this approach decoupled the CTD and

AC-9 data streams. A program was developed and

used to interactively merge AC-9 and CTD profiles

during preprocessing and quality control. Two AC-9s

were on the IOP package. The inflow tubes of one

AC-9 were fitted with 0.2 m inline filters at several

stations to partition the total spectral absorption and

beam attenuation into dissolved and particulate fractions. At these stations, total (unfiltered) and dissolved

(filtered) a and c profiles were obtained. A comparision / calibration of the AC-9s were performed when

both AC-9s were unfiltered. The IOP package was

deployed at 54 stations (111 profiles) and 120 stations

(248 profiles), during survey 260797 and survey

260897, respectively. Two PC-based programs were

written in IDL 5.0 (castDisplay, castMapper) to apply

quality control checks and routine data correction and

display. Temperature, salinity and scattering corrections were applied to all AC-9 data. Scattering corrections used either Method 1 of the Zaneveld Method

(AC-9 User Guide, Wet Labs, Inc). A branching algorithm was used based on the a715 nm / b715 nm ratio

to select which scattering method was applied.

Method 1 was used for ratios greater than 0.35. The

Zaneveld Method was used for ratio values <= 0.35.

The castDisplay and castMapper (a geographic contouring package for vertical profiles) will be used on

subsequate surveys for near-realtime processing and

analysis. All data have been translated to SeaBASS

format.
SIMBIOS Project Annual Report

64

Satlantic Profiles

A SeaWiFS Profiling Multichannel Radiometer

(SPMR) and a SeaWiFS Multichannel Surface Reference (SMSR) instrument were deployed at 42 and 36

stations during survey 26079 and 260897, respectively. In general, three profiles were acquired at each

station. The central wavelengths for the SMPR and

SMSR channels were: 405.3, 412.9, 435.1, 443.8,

456.2, 490.9, 509.1, 532.7, 555.2, 590.5, 665.8, 683.8,

and 700.4 nm. Satlantic’s Prosoft 4.0 (revision f) was

used to produce derived products of K, Reflectance,

Rrs, Lwn, and modeled pigments. The Satlantic system

performed without problems.

Discrete Water Samples

At most stations, discrete water samples were

collected at select depths (based on profiling transmissometer and fluorometer data) using Niskin Bottles

mounted on the hydrographic CTD rosette. These

water samples were filtered for analysis of fluorometric chlorophyll a and phaeopigments, HPLC pigments,

CDOM absorption, particle absorption (QFT), and

total suspended mater. All samples were collected and

processed following the procedures of Mueller and

Austin (1995). HPLC pigments determined were chlorophyll a, chlorophyll b, peridinin, fucoxanthin, 19

hex, prasinoxanthin, alloxantin, lutein, zeaxanthin,

diadinoxanthin, canthaxantin, and -carotene. Absorption spectra were determined for total, detrital,

and phytoplankton components following the hotmethanol extraction technique (Kishino et al., 1985).

Corrections for path-elongation were performed following the method of Mitchell (1990). CDOM absorption spectra were collected using a Perkin-Elmer

Lambda 3 spectrophotometer. The number of samples

collected for each analysis were (Survey 260797;

260897): HPLC (71; 100), fluorometic chl a (86; 149),

total suspended mater (50; 50), CDOM absorption (5;

20), and particle absorption (0; 61).

16.3 RESEARCH RESULTS

The project was able to follow the proposed work

plan with regards to data collection and processing. In

general, instrument calibration and data collection

followed the guidelines provided by the proposal with

the exception that the MER 1032 needed to be phased

out of the instrument suite. The problems with the

MODAPS created unexpected delays in preprocessing

and analysis. In addition to collection problems and

limitations, considerable effort was invested to develop a reliable and robust method to merge CTD and

AC-9 data. Raw and intermediate data products were

created for most profiler data. The volume of data

collected at sea exceeded our expectations. This resulted in a significant increase in the time required to

process data. The NAVOCEANO provide operational

support to the US fleet by conducting military surveys

worldwide. These surveys are conducted under the

provisions of military ordinances, and as such, do not

require diplomatic permission from local governments.

The data collected during this project were mostly

obtained in the Exclusive Economic Zone (EEZ) of

several countries. Therefore, as a consequence of

“The Law of the Sea”, these data are currently restricted to DOD and DOD contractors use only.

Hence, specific results and findings can not be presented at this time.

Members of the project team at NASA and NAVOCEANO are actively engaged in determining how

these data may be made available to the SIMBIOS

project office. It is the project’s intent to establish a

precedent for the release and use of this data for civilian projects without compromising the Navy’s international agreements and mandates. If successful, this

project may establish the means by which an important resource of oceanographic data may be made

available to the research community.

16.4 WORK PLAN

The project will follow the proposed project plan

with the exceptions that above water estimates of Rrs

( ) will be obtained using a GER (Geophysical Environmental Research, Inc.) 1500 hand-held spectroradiometer (300 -100 nm, effective 1 nm bandwidth)

and the MER 1032 will not be used.

A survey to the South China Sea and Gulf of

Thailand is planned for the summer 1999. A duplicate

Satlantic system has been purchased to provide system

redundancy. A Wet Labs WetStar profiling fluorometer will be configured on a profiling package to direct

the selection of depths for discrete water samples.

SeaWiFS LAC data will be requested during filed

activites and upon processing using SeaDAS will be

compared with in situ observations.

 The project has acquired a AC-9 to ensure calibration history and performance for project deployments. A MicroTops II sun photometer will be used

during future cruises. Increased effort will be devoted

to secure the release of the data for SIMBIOS project

use.
SIMBIOS Project Annual Report

65

Table 1. Profiling Instrument Packages.

INSTRUMENTS MEASUREMENTS

Day Package

MER 1032 In-water Radiometer1Spectral Upwelled and Downwelled Irradiance, and Spectral Upwelled Radiance

MER 21 Deck Radiometer1b Surface Incident Irradiance

AC-92Spectral absorption and beam attenuation coefficients

LS-6000 Light Scattering Sensor3 Light scattering at 880 nm

Sea-Bird SBE 19 CTD4 Conductivity, temperature, and depth

PSA-900 Sonar Altimeter5 Height (m) of package above bottom

Night Package

AC-92 (x2) Spectral absorption, beam attenuation, backscattering coefficients

LS-6000 Light Scattering Sensor3 Light scattering at 880 nm

Sea-Bird SBE 19 CTD4 Conductivity, temperature, and depth

PSA-900 Sonar Altimeter5 Height (m) of package above bottom

Remote - Tethered Package

SeaWiFS Profiling Multichannel Radiometer6Spectral Upwelled Radiance, Spectral Downwelled Irradiance

SeaWiFS Multichannel Surface Reference6Downwelled Spectral Surface Irradiance

1Biospherical Instruments, Inc.; 1bBiospherical Instruments, Inc., MER 21 is a deck-mounted sensor;

2WET Labs, Inc. (Western Environmental Technology Laboratories, Inc); 3

Sea Tech, Inc.;

4

Sea-Bird Electronics, Inc.;

5Datasonics, Inc.; 6

Satlantic, Inc.
SIMBIOS Project Annual Report

66

Chapter 17

Bio-Optical Measurement and Modeling

of the California Current and Polar Oceans

B. Greg Mitchell and Piotr Flatau

Scripps Institution of Oceanography

University of California San Diego, La Jolla, California

17.1 INTRODUCTION

This SIMBIOS project contract supports in situ

oceanic optical observations in the California Current

and Southern Ocean. The principal objectives of this

research are to validate standard or experimental

products through detailed bio-optical and biogeochemical measurements, and to combine ocean optical

observations with advanced radiative transfer modeling to contribute to satellite vicarious radiometric

calibration and algorithm development.

Our sampling efforts have been directed towards

obtaining measurements in both the California Current

and Antarctic polar waters, with the purpose of generating a high-quality, methodologically consistent data

set encompassing a wide-range of oceanic conditions.

The combined data base includes stations which cover

the clearest oligotrophic waters to highly eutrophic

blooms and red-tides, and provides a coherent set of

observations to validate bio-optical algorithms for

pigments and primary production. This unique and

comprehensive data is utilized for development of

experimental algorithms (e.g. high-low latitude pigment transition; phytoplankton absorption, photosynthesis, cDOM.

17.2 RESEARCH ACTIVITIES

The Southern California Bight region, from San

Diego to just north of Point Conception, has one of the

longest, most comprehensive time-series of marine

observations; the California Cooperative Oceanic

Fisheries Investigation (CalCOFI). This region experiences a large dynamic range of coastal and open

ocean trophic structure, and has been extensively

studied with respect to its regional optical properties

in an effort to develop regional ocean color algorithms

(e.g. Smith and Baker 1978, Mitchell and Kiefer 1988,

Sosik and Mitchell 1995). During the first year of our

contract, we participated in 4 quarterly cruises in the

California Current region as part of the CalCOFI program.

The Southern Ocean is a large, remote region

which plays a major role in global biogeochemical

cycling. Despite evidence that bio-optical relationships in these waters can diverge significantly from

lower-latitude waters (e.g. Mitchell and Holm-Hansen

1991), Antarctic waters have not been represented in

the databases (e.g. SeaBAM) used to formulate and

test modern ocean color algorithms. During the past

year, we participated in 3 cruises to the Southern

Ocean as part of the US JGOFS program. One cruise

was located within the Ross Sea Polyna during the

annual spring phytoplankton bloom, with two subsequent cruises covering the region of Antarctic Polar

Front Zone along 170° W.

On all cruises, an integrated underwater profiling

system was used to collect optical data and to characterize the water column. The system included an underwater radiometer (Biospherical Instruments MER2040 or MER-2048) measuring depth, downwelling

spectral irradiance (Ed) and upwelling radiance (Lu) in

13 spectral bands. A MER-2041 deck-mounted reference radiometer (Biospherical Instruments Inc) provided simultaneous measurements of above-surface

downwelling irradiance. Details of the profiling procedure, characterization and calibration of the radiometers, data processing and quality control are described in Mitchell and Kahru (1998). The underwater radiometer was also interfaced with 25 cm transmissometers (SeaTech or WetLabs), a fluorometer,

and SeaBird conductivity and temperature probes.

When available, additional instrumentation integrated

onto the profiling package included AC9 absorption

and attenuation meters (Wetlabs Inc.), and a Hydroscat-6 backscattering meter (HobiLabs).

In conjuction with in situ optical measurements,

discrete water samples were collected from a CTDRosette immediately before or after each profile for

additional optical and biogeochemical analyses. Pigment concentrations were determined flurometrically

and with HPLC. Spectral absorption coefficients

(300-800 nm) of particulate material were estimated

by scanning particles concentrated onto Whatman

GF/F (Mitchell 1990) in a dual-beam spectrophotometer (Varian Cary 1). Absorption of soluble material was measured in 10cm cuvettes after filtering

seawater samples through 0.2 um pore size polycarbonate filters.
SIMBIOS Project Annual Report

67

17.3 RESEARCH RESULTS

Validation of satellite-retrieved normalized waterleaving radiances (LWN) was done by comparing

SeaWiFS images with in situ data collected concurrently (± 4 hours). Satellite data received at the Monterey Bay Research Institute, the University of California Santa Barbara (CalCOFI region) and McMurdo

Station, Antarctica (Southern Ocean region) were

processed to LWN using SeaDAS 3.2 software (Fu et

al. 1998). A total of 16 matching sets of LWN were

found between 2-Oct-1997 and 21-Apr-1998 for the

CalCOFI region. Because of persistent cloud cover in

the Southern Ocean, only 3 matchups were possible in

the Ross Sea region (all on 1-Dec-1997). Satellite

values were derived as averages over 3 x 3 pixel areas

centered at the in situ measurement.

In both regions, these comparisons reveal significant under-estimation of the SeaWiFS-retrieved LWN

compared to in situ measurements. The differences

were generally smallest in the 555 nm band, and largest at shorter wavelengths. The magnitude of underestimation in the shorter wavlength bands increases at

high Chl concentration.

O’Reilly et al. (1998) describe the Ocean Color 2

(OC2) chlorophyll algorithm that is used by NASA in

the operational processing of SeaWiFS data (Fu et al.

1998). This algorithm uses the ratio of remote sensing

reflectances (Rrs) at 490 and 555 nm to estimate chlorophyll a concentration, with the coefficients derived

by a statistical fit to a data set of 919 bio-optical

measurements comprising the SeaBAM data set.

More recently (August 1998), NASA announced a

revised version of the OC2 (OC2-v2) which was intended to reduce the drastic over-estimation of Chl in

high biomass waters produced by the original OC2

algorithm.

Figure 1 compares the performance of the OC2-

v2 algorithm with our present data base of measurements from CalCOFI and the Southern Ocean. When

applied to the CalCOFI data, this algorithm overestimates chl a at very high chl a and underestimates

elsewhere (with the exception of the extreme low chl

a). A similar pattern is seen with the Southern Ocean

data, although in general the degree of underestimation is greater and the transition to overestimation

occurs at lower Chl. These results underscore the

eventual need for specific regional empirical algorithms to obtain more accuate estimates of Chl and

primary production from ocean color remote sensing.

We have recently developed an improved empirical

chlorophyll algorithm for the California Current

(CAL-P6), which utilizes a sixth order polynomial of

the ratio of LWN at 490 and 555nm (Kahru and

Mitchell, 1999).

17.4 WORK PLAN

Our participation in the quarterly CalCOFI

cruises in the California Current will continue

throughout the next period. We are also initiating

field programs in the Indian Ocean (INDOEX) and the

Sea of Japan (JES) to increase the regional scope of

our data base. Modeling efforts include the pursuit of

regional bio-optical algorithms for in water optical

properties and their relationship to biogeochemical

parameters, as well as the development of semianalytical models for the retrieval of inherent optical

properties from satellite data. We anticipate that these

efforts will lead to an improved understanding of the

variability observed in empirical satellite algorithms.

We will also initiate analyses to determine the elements of the SeaWiFS processing that lead to the underestimates of Lwn, which is of particular concern

for high chlorophyll waters.
SIMBIOS Project Annual Report

68

Figure 1. A comparison of the OC2-v2 algorithm (solid line in left panels) with in situ measurements of

chlorophyll a from CalCOFI and the Southern Ocean. The right panels illustrate quantile-quantile plots of the

differences between modeled and measured chlorophyll a.
SIMBIOS Project Annual Report

69

Chapter 18

SIMBIOS Normalized Water Leaving Radiance

Calibration and Validation: Sensor Responses,

Atmospheric Corrections, Stray Light and Sun Glint

James L. Mueller

Center for Hydro-Optics and Remote Sensing

 San Diego State University, San Diego California

18.1 INTRODUCTION

The objectives of research under this contract are

to improve the uncertainty budgets and protocols for

normalized water leaving radiances LwN( ) and remote sensing reflectance RrsN( ) determined from in

situ measurements, and to apply in situ reflectance

measurements to validate LwN( ) and RrsN( ) determined from radiances measured by the SIMBIOS ensemble of orbiting ocean color sensors (i.e. SeaWiFS,

MODIS, GLI, POLDER and others). Our approach to

these objectives includes protocol experiments to

evaluate uncertainties in reflectances derived from

above-water and in-water radiometry, field expeditions to acquire in situ radiometric, optical and biological ground truth data for validating SIMBIOS satellite ocean color sensors and match-up analyses,

combining the in situ data with satellite radiometric

data and derived parameters for vicarious radiometric

calibration, and for evaluating sun glint effects and

stray light artifacts in the image data.

18.2 RESEARCH ACTIVITIES

There is a general consensus that poorly understood optical variability associated with surface waves

contributes strongly to the persistently significant discrepancies between remote sensing reflectances determined from above-water and underwater radiometric measurements. In above-water radiance measurements, wave roughness modifies the surface reflectance relative to a flat surface. Wave roughening

also widens the effective field-of-view of reflected

skylight components of the measured signal, and thus

may incorporate angular variability in skylight which

is not quantified by measurements using current protocols (Mueller and Austin, 1995). Finally, wave

slope variations repolarize reflected skylight in ways

which may not be properly accounted for using these

and proposed alternative protocols.

In underwater radiometric profiles near the sea

surface, surface waves radomly focus and defocus

incident radiance and introduce “noise” which increases exponentially with proximity to the surface.

Additional uncertainties result from strong waveinduced accelerations on an underwater radiometric

package, which accelerations also increase exponentially with proximity to the surface and introduce

quasi-random, difficult to measure fluctuations in

sensor orientation. It is very difficult to separate these

wave-related sources of uncertainty in comparing reflectances calculated from in-water and above-water

measurements. It is correspondingly difficult, therefore, to partition the overall observed uncertainty

between the two types of measurement. We are

working towards comparative outdoor tank and field

measurements which attempt to separately quantify

near-surface in-water and above-water wave related

uncertainties under semi-controlled conditions.

To support the difficult measurements associated

with these protocol experiments, we are developing a

unique hyperspectral above-water and profiling spectroradiometer and inherent optical property (IOP)

system. The system is designed to allow repeated

radiometric and IOP profiling at controlled ascent and

descent rates, concurrent with measurements of

above-water irradiance and radiance. The profiler

package is built around a tethered variable buoyancy

Autonomous Profiling Vehicle (APV) manufactured

by Ocean Sensors Inc. of San Diego. In addition to

the APV’s built-in Conductivity, Temperature and

Depth (CTD) sensors, sensors are attached to the profiler package to measure irradiance Ed( ,z), radiance

Lu( ,z), absorption a( ,z), beam attenuation c( ,z)

and chlorophyll a fluorescence. Ed( ,z) and Lu( ,z)

are measured at 3.3 nm intervals from approximately

380 to 800 nm using radiometers based on Zeiss

miniature fiber-optic spectrometers. Chlorophyll a

fluorescence is measured using a WETSTAR fluorometer, and a( ,z) and c( ,z) are measured at 3.3 nm

intervals using a HISTAR underwater spectrophotometer – both instruments are manufactured by

WETLABS of Philomath, Oregon. (The WETSTAR

and HISTAR are obtained under a ONR/ECOHAB

research grant at CHORS.) Additional radiometers
SIMBIOS Project Annual Report

70

are being integrated into the system for above-water

measurements of irradiance Es( ,z), total waterleaving radiance Lsfc( ,z) and sky radiance Lsky( ,z).

Validation Field Experiments

We are acquiring in situ data for validating

SeaWiFS (and in the future MODIS and other ocean

color sensors) data during field expeditions aboard the

Mexican Research Vessel Francisco de Ulloa (FdU)

in the Gulf of California (GoCAL). The GoCAL

cruises are in collaboration with Drs. Ron Zaneveld

and Scott Pegau of Oregon State University (SIMBIOS contract NAS5-97129) and Mexican scientists

(Drs. Helmut Maske, Ruben Lara-Lara, Saul AlvarezBorrego, and their students) at CICESE (an oceanography PhD granting postgraduate university in Ensenada, BC, Mexico).

The FdU is owned and operated by CICESE, and

they have thus far contributed ship time for cruises in

October 1997 (GoCal-97), March 1998 (GoCal-98A)

and Nov-Dec 1998 (GoCal-98B). Measurements on

each cruise include profiles of Ed( ,z) and Lu( ,z) at

SeaWiFS wavelengths, fluorometric chlorophyll a,

and HPLC pigments. IOP measurements are made by

the OSU investigators, and additional bio-optical and

ancillary measurements are contributed by CICESE.

The next GoCal cruise aboard the FdU (GoCal-99A)

is tentatively scheduled for 21 April – 2 May 1999.

All radiometric, optical and phytoplankton pigment measurement and data analysis procedures follow protocols in Mueller and Austin (1995). Radiometric profiles are analysed to obtain Es( ,0+

),

Ed( ),0+), and Lu( ,0+), using the integral method of

Mueller (1995), as implemented using the CHORS

interactive Kfit routine.

We are also planning to acquire validation data

during day-cruises near San Diego and other California coastal sites using a small research boat. We have

recently ordered and will outfit a trailerable research

boat (a Parker-25 sport-fishing boat) to support this

and other research projects at CHORS. Electronic

equipment will be installed in the boat’s enclosed pilothouse and forward cabin, while water sampling/filtering stations will be installed aft of the pilothouse under a permanent awning. Costs (acquisition, maintenance, and operating) associated with the

CHORS research boat will be shared between this

contract, other CHORS research projects using the

boat, and SDSUF cost-sharing funds.

Calibration and Characterization

To support these experiments and analyses,

CHORS carries out calibrations and characterizations

of radiometers used in this project, including those of

our collaborators at OSU and CICESE. NIST traceability of CHORS calibrations is maintained through

tertiary standards (Optronics, Inc) and assured

through participation in SIRREX and independent

comparisons with other laboratories calibrating SIMBIOS instruments.

18.3 RESEARCH RESULTS

Radiometric data from GoCal-97 and GoCal-98A

(including the results of the CHORS KFIT analysis of

OSU’s SPMR profiles) have been processed, analysed

and archived in SeaBASS. Pigment data analyses and

quality control have recently been completed for these

two cruises, and the data will be archived in SeaBASS

after appropriate reformatting and insertion of metadata. Processing and analysis of data from GoCal-98B

(24 Nov through 8 Dec 1998) are in progress.

18.4 WORK PLAN

During the current contract year we will complete

work in progress including:

data processing, analysis and SeaBASS archival/documentation of data from GoCal-98B;

Analysis and publication, in collaboration with

investigators from CICESE and OSU, of data

from completed GoCal cruises in 1995, 1996,

1997, 1998A and 1998B, (including SeaWiFS

data for the 1997 and 1998 periods);

Integration, laboratory characterization and calibration, and field-testing of the CHORS hyperspectral radiometric and IOP profiling and reflectance system;

Continued routine calibrations of radiometers

used by CHORS and our collaborators (OSU and

CICESE) in this project.

During the current contract year, planned field campaigns include:

GoCal-99A aboard the FdU in the Gulf of California between 20 April and 2 May 1999; and

Day cruise, clear-sky validation sorties (within 20

nautical miles of the California coast) aboard the

CHORS research boat ( circa June 1999).

Reflectance protocol experiments will include

tank and field in-water versus above-water reflectance

measurement comparisons, as well as experimental

evaluations of plaque reflectance versus direct measurements of incident irradiance and instrument selfshading tests.
SIMBIOS Project Annual Report

71

Chapter 19

Validation of Carbon Flux and Related Products for

SIMBIOS: the CARIACO Continental Margin

Time Series

Frank Müller-Karger

Department of Marine Science

University of South Florida

Ramon Varela

Fundacion La Salle de Ciencias Naturales

Punta de Piedras, Estado Nueva Esparta, Venezuela

19.1 INTRODUCTION

This SIMBIOS investigation focuses on validating

ocean color satellite products from waters near continental margins. Specifically, our program focuses on

collecting monthly observations within a coastal upwelling site, and seasonal extreme measurements

within the plume of the Orinoco River, which is classified as having the third largest discharge in the world.

Initial focus of this project has been on setting up

the logistics for field data collection and initiating

routine observations. The program incorporates an

effort to validate SeaWiFS products and products from

the future MODIS (AM and PM), MISR, MERIS,

GLI, and ROCSAT missions. Our goals are to evaluate algorithms used to compute biological and geophysical data products, develop new products aimed at

assessing carbon flux, estimate the spatial and temporal errors in these products, and identify strategies that

will help minimize such errors and eliminate possible

biases between data sets from different missions.

19.2 RESEARCH ACTIVITIES

The core of this SIMBIOS project is an established oceanographic time series stations in the

CARIOCO basin. In November 1995, the U.S. National Science Foundation, in collaboration with the

Consejo Nacional de Investigaciones Cientificas y

Tecnologicas (CONICIT) of Venezuela, implemented

a comprehensive program of continuous observations

in the Cariaco Basin, which is located in the southeastern Caribbean Sea. This multidisciplinary program is

referred to as the CArbon Retention In A Colored

Ocean (CARIACO) program. Specifically, the program conducts monthly observations at a station located at 10.5 N, 64.67 W.

The importance of the Cariaco Basin as a natural

laboratory to study seasonal upwelling, sediments and

anoxic effects has been appreciated for over 40 years.

The CARIACO Program seeks to define a budget

which assesses the total CO2 upwelled with deep,

nutrient-rich water with respect to the annual export of

organic carbon from surface waters along this continental margin. This basin is ideal for a carbon flux

study because it is a large depression on a continental

shelf which experiences vigorous wind-driven upwelling, and oligotrophic conditions at different times

of the year. As the circulation below 200 m in this

basin is restricted, it forms a natural sediment trap.

The Cariaco Basin is the only permanently anoxic

oceanic basin, and as such serves as an oceanic analog

of the Black Sea.The series station is located at 10.50

N, 64.66 W and consists of:

1 to 3 monthly cruises with a fully-equipped,

modern oceanographic vessel;

Mooring with 4 sediment traps (200, 400, 800,

1200 m; capturing bi-weekly sample integrations);

Varved (laminated) sediment core analyses.

The monthly oceanographic cruises provide information on:

Composition, levels, and light absorption properties of organic particulate and dissolved matter;

Pigments, HPLC, taxonomy of phytoplankton and

general classification of bacteria;

Biological productivity (phytopl. and bacteria);

The physical/chemical characteristics of the water,

including nutrient and oxygen levels;

Carbonate system.
SIMBIOS Project Annual Report

72

Shore-based, continuous meteorological and tide

gauge observations are available, and we are trying to

obtain these in collaboration with the local Air Force,

Navy, and Environment Ministries. This project incorporates subsurface and above-surface spectral radiance, irradiance, and aerosol optical thickness measurements to the CARIACO series. The in situ biooptical observations are all done following the

SeaWiFS protocols. We have also participated in

other SIMBIOS activities, including the first SIMBIOS PI meeting in Salomon's Island and a cal/val

cruise to the Bahamas organized under Ken Carder's

SIMBIOS program.

19.3 RESEARCH RESULTS

Each month since December 1995, bio-optical

measurements have been part of the suite of measurements made at the CARIACO site. These observations

were initially limited to above-water hyperspectral

reflectance measurements. MER casts were performed

only a few months out of this period because there was

no continuous access to such an instrument.

Since October 1997, our suite of observations has

included MER subsurface radiance/irradiance profiles.

The optical measurements are used to validate

SeaWiFS. The measurements are scheduled around

the time of the SeaWiFS overflight. The monthly

cruises last about 2 days each.

During each cruise, we collect bio-optical measurements using the underwater profiling Biospherical

Instruments MER2048 in conjunction with a

MER2041 Deck Cell. Above water measurements are

made with a Photo Research Hyperspectral Colorimeter Model PR650, which is a calibrated, hand-held

radiometer (8 nm resolution). Derived products include Lw (Water-Leaving Radiance), Rrs (Remotesensed reflectance) and K (attenuation coefficient). In

addition, a full suite of measurements is made which

includes: particulate material and pigment absorption,

HPLC, fluorometric determinations of Chl concentration, pH, Alkalinity, Primary Productivity, POC, DOC

absorption and concentration, nutrients, sun photometry, oxygen, and salinity.

Cruise reports for each cruise starting in September 1997, have been submitted to the SIMBIOS Project. Approximately two years of bio-optical data have

been submitted to the SeaBASS archive.

Preliminary results suggest marked seasonal

changes in optical properties occur in this basin as

phytoplankton concentration increases and decreases

in response to coastal upwelling. Figure 1 shows the

seasonal variation in surface hyperspectral remote

sensing reflectance at the Cariaco station. A clear progression is seen from clear water conditions during

boreal summer to blue-poor reflectances during boreal

winter-spring, the time of upwelling. The decrease in

blue reflectance is accompanied by a marked increase

at 683 nm, clearly defining the signal of solarstimulated fluorescence. We plan to examine this feature in relation to the primary productivity data collected concurrently during our CARIACO cruises.

We also find that there is a close correlation between phytoplankton specific absorption coefficients,

primary productivity, and chlorophyll a. These data

clearly are preliminary and need to be examined closely

to understand variations from season to season.

The Orinoco River Plume

Above-water spectral remote-sensing reflectance

(Rrs 380-700 nm) was measured including corrections

for sky-radiance. We also conducted underwater

measurements of remote sensing reflectance at 7

wavelengths (412, 443, 455, 475, 490, 510, 532, 560,

589, 625, 671, 683, and 700 nm) using submersible

MER2048 instrumentation (Biospherical Instr.). Some

observations were conducted away from the coast,

where the color of the plume is influenced by colored

dissolved organic matter as well as phytoplankton, but

where suspended terrestrial material is expected to be

minimal. We also collected data very close to the

coast where the plume is extremely turbid. As of February 1, 1999, we are currently submitting bio-optical

data collected during the first and second 1998 Orinoco plume cruises to SeaBASS

The Orinoco Plume data span a very broad range of

remote sensing reflectance values. The river plume

data are also being used by Joe Salisbury and Charles

Vorosmarty at the University of New Hampshire for

automated modeling of river water impact off the continent of South America, in a model linked to terrestrial

hydrology.

19.4 WORK PLAN

We will continue to occupy the CARIACO station on a monthly basis. In addition, we plan to conduct two cruises to the Orinoco River plume, specifically in February and October 1999. Analysis of data

and samples will continue. We are currently finalizing

a manuscript that describes the seasonal cycle in hydrographic properties, phytoplankton biomass and

productivity, and vertical carbon flux at the

CARIACO station. We will now initiate work on a

manuscript that summarizes the bio-optical data from

this location.

ACKNOWLEDGMENTS

This work was supported by the National Science

Foundation (NSF Grant OCE 9216626), the National

Aeronautics and Space Administration (NASA Grants

NAG5-6448 and NAS5-97128), and the Consejo Na-
SIMBIOS Project Annual Report

73

cional de Investigaciones Cientificas y Tecnologicas

(CONICIT, Venezuela). Many people have contributed substantially to the success of this program, and

if they are not mentioned here it is by plain oversight

on the author's part. We are indebted to the personnel

of the Fundacion La Salle de Ciencias Naturales/Estacion de Investigaciones Marinas Isla Margarita

(FLASA/EDIMAR) for their enthusiasm and professional support. In particular we thank FLASA's Director, Dr. Hermano Gines, for his confidence in our

activities and the crew of the R/V Hermano Gines

(FLASA) for their able support at sea. Field biooptical measurements were conducted primarily by

Natasha Rondon and John Akl of FLASA. They, and

Yrene Astor and Ana Lucia Odriozola have processed

the majority of the data to satisfy the seabass report

formats. Jonathan Garcia (also at FLASA) has processed the samples for particulate and dissolved absorption coefficients. Juan Capelo and Javier Gutierrez (FLASA) have assisted with the primary production observations. Robert Thunell and Eric Tappa (U.

South Carolina) maintain the sediment trapping program and process our particulate samples (POC,

PON). Mary Scranton and Gordon Taylor (SUNY)

conduct bacteria productivity studies. Dissolved Organic Carbon samples were processed by Ed Peltzer

(formerly at the Woods Hole Oceanographic Institution and currently at the Monterrey Bay Aquarium

Research Institute), and lately by David J. Hirschberg

of State University of New York at Stony Brook.

Seasonal Remote Sensing Reflectance

0.0000

0.0010

0.0020

0.0030

0.0040

0.0050

0.0060

0.0070

380 480 580 680 780

Wavelength [nm]

Rrs

May '96

Sep '96

Oct '96

Nov '96

Dic '96

Jan '97

Feb '97

Mar '97

Apr '97

May '97

Figure 1. Remote sensing reflectance at the Cariaco station over the course of one year.
SIMBIOS Project Annual Report

74

Chapter 20

Bermuda Bio-Optics Program (BBOP)

David Siegel

University of California at Santa Barbara,

Santa Barbara, California

20.1 INTRODUCTION

The Bermuda BioOptics Project (BBOP) is a collaborative effort between the Institute for Computational Earth System Science (ICESS) at the University

of California at Santa Barbara (UCSB) and the Bermuda Biological Station for Research (BBSR, D. A.

Siegel [UCSB] and N. B. Nelson [BBSR] P.I.'s). This

research program is designed to characterize light

availability and utilization in the Sargasso Sea and in

doing so, provide an optical link by which biogeochemical observations may be used to evaluate biooptical models for pigment concentration, primary

production, and sinking particle fluxes from satellitebased ocean color sensors.

20.2 RESEARCH ACTIVITIES

The Bermuda Bio-Optics Program (BBOP) collects detailed profiles of AOPs and IOPs in conjunction with the US JGOFS Bermuda Atlantic Timeseries Study (BATS) at 31°

50' N, 64°10' W in the

mesotrophic waters of the Sargasso Sea. There are up

to 16 cruises per year, conducted monthly with additional cruises during the spring bloom period, January

through May.

Continuous profiles of apparent optical properties

(AOPs) are collected in the upper 200m using a Multispectral Environmental Radiometer (MER2040/2041, Biospherical Instruments Inc., San Diego

CA; Smith et al., 1984). The primary optical measurements are downwelling vector irradiance and upwelling radiance, Ed(z,t, ) and Lu(z,t, ), respectively. The instrument samples these properties at 12

wavebands (including SeaWiFS wavelengths) plus

broadband natural fluorescence. The BBOP sampling

package also includes sensors for temperature and

conductivity (SeaBird, Bellevue WA) chlorophyll

fluorescence and red beam transmission (SeaTech,

Corvallis OR) and a second mast-mounted spectroradiometer (MER-2041) with wavebands similar to

those on the underwater instrument for measuring

incident downwelling vector irradiance, Ed(0+,t, ).

Instrument deployments are planned to optimize

match-ups with the BATS primary production incubations and, when possible, with SeaWiFS overpasses.

The BBOP group also collects several measurements of inherent optical properties (IOPs). Continuous profiles of spectral beam absorption and attenuation, a(z, ) and c(z, ), are measured using the WET

Labs AC-9 (Brody, 1998), and discrete samples for

determining the absorption spectra of particulates,

aph(z, ) and ad(z, ), and CDOM (ag(z, )) are collected according to Nelson et al (1998). Spectral

beam absorption measurements have been hampered

by the fact that the baseline absorption of Sargasso

Sea water is nearly the same as that of the deionized

water used for the calibration. Particulate absorption

spectra are determined using the quantitative filter

technique (Mitchell, 1990) and CDOM absorption

according to Nelson et al (1998). In 1997, we initiated the collection of above water R+

rs(l) spectra using

the Analytical Spectral Devices FieldSpec spectrometer (ASD, Boulder Colorado). We are currently

comparing this data set with values of R+

rs(l) calculated from MER data to evaluate its usefulness for

SIMBIOS.

The profiling radiometers are calibrated three

times per year at UCSB and have demonstrated remarkable calibration stability for several years, allowing the use of long-term averages for calibration

coefficients (O’Brien et al., 1999). This stability,

combined with streamlined procedures for data analysis, has made it possible for us to report many of our

derived products with ~98% reliability in near-real

time, including profiles of remote sensing reflectance

(Rrs(z, ) = Lu(z, )/Ed(z, )), and down- and upwelled attenuation coefficients (Kd(z, ), Ku(z, )).

Our analysis procedures are fully documented in Siegel et al. (1995b). In addition to radiometer data,

samples for fluorometric chlorophyll-a are collected

before dawn and near noon (local time) and results are

delivered to the SIMBIOS project with the AOP data,

usually within one week after a cruise. Table 1 contains a list of data products collected by BBOP and/or

BATS, which are relevant to SIMBIOS. A total of

472 AOP, 16 IOP and 36 pigment profiles were deliv-
SIMBIOS Project Annual Report

75

ered from the start of this contract (July 1997) through

1998.

20.3 RESEARCH RESULTS

Since its inception in 1992, BBOP has made a

number of important contributions toward the scientific understanding of the relationship between light

and ocean biogeochemistry. The Sargasso Sea near

Bermuda is mesotrophic, characterized by both eutrophic and oligotrophic conditions during different times

of the year. Although low chlorophyll a stocks and

primary production rates prevail for the most of the

year, there is a short spring bloom characterized by

somewhat higher concentrations and rates which is

controlled by winter mixing and the associated nutrient influx.

Our research has shown that the BATS/BBOP site

has an interesting and important ocean color signal

associated with its colored dissolved organic material

(CDOM) content. We have found that CDOM may

comprise up to 50% of the light attenuation budget

(Kd( )) at 410 nm (Siegel et al. 1995a, Siegel and

Michaels 1996) and that CDOM concentrations can be

determined from in situ ocean color spectra (Garver

and Siegel, 1997). The ratio of Kd(410) to Kd(488)

can be used as an index of CDOM concentration to

illustrate its time-depth dynamics (Siegel et al. 1995a,

Siegel and Michaels 1996). During the summer,

CDOM is simultaneously produced within the seasonal pycnocline and photo-oxidized in the surface

mixed layer (Figure 1c). Fall and winter mixing homogenizes the profile. The seasonal distribution of

CDOM is unrelated to the those of chlorophyll or dissolved organic carbon, however it may be that the

summer CDOM source is microbial (Siegel and

Michaels 1996, Nelson et al. 1998). Since CDOM is a

significant source of light attenuation in the Sargasso

Sea that varies independently of chlorophyll, it appears that the optical definition of Case I waters which

is based solely on chlorophyll should be reconsidered.

Table 1. A partial list of measurements made by BBOP and BATS

Direct Measurements:

Ed(z, ) Downwelling vector irradiance (410,441,465,488,510,520,555,565,589,625,665 & 683 nm)

Ed(0+, ) Incident irradiance (340,390,410,441,465,488,520,545,565,589,625,665 & 683 & 350-1050 nm)

Lu(z, ) Upwelling radiance (410,441,465,488,510,520,555,565,589,625,665 & 683 nm)

a(z, ) In situ absorption spectrum using WetLabs AC-9 (410,440,490,520,565,650,676&715 nm)

c(z, ) In situ beam attenuation spectrum (same 's as above)

atp( ) Particulate absorption spectrum by QFT

ad( ) Detrital particle absorption spectrum by MeOH extraction

ays( ) Colored dissolved absorption spectrum

Eo(z, ) Scalar irradiance at 441 and 488 nm

Ff(z) Natural chlorophyll fluorescence using a broadband upwelled radiance sensor

chl-fl(z) Chlorophyll fluorescence with a SeaTech fluorometer

c(z,660) Beam attenuation coefficient at 660 nm with SeaTech 25 cm transmissometer

T(z) & S(z) Temperature and conductivity with SeaBird probes

chl-a(z) Discrete chlorophyll a determinations via Turner fluorometry (for next day delivery)

Primary Derived Products:

LwN( ) Normalized water leaving radiance (410,441,465,488,510,520,555,565,589,625,665 & 683 nm)

RRS(0-, ) In-water remote sensing reflectance (410,441,465,488,510,520,555,565,589,625,665 & 683nm)

RRS(0+, ) Above-water remote sensing reflectance (350 to 1050 nm)

aph( ) Phytoplankton absorption spectrum (= ap( ) - adet( ))

Kd(z, ) Attenuation coefficient for Ed(z, ) (410,441,465,488,510,520,555,565,589,625,665 & 683 nm)

KL(z, ) Attenuation coefficient for Lu(z, ) (410,441,465,488,510,520,555,565,589,625,665 & 683 nm)

<PAR(z)> Daily mean photosynthetically available radiation at depths of the in situ C14 incubations

b(z, ) Spectral scattering coefficient (= c(z, ) - a(z, ))
SIMBIOS Project Annual Report

76

Figure 1. A-C: Time-depth contours of a) Chlorophyll-a (HPLC), b) Kd(z,t,490), c) the ratio of

Kd(z,t,410):Kd(z,t,490) and D) time series of remote-sensing reflectance spectra (Rrs(t,0-, )). 
SIMBIOS Project Annual Report

77

Chapter 21

SIMBIOS Data Product and Algorithm Validation

with Emphasis on the Biogeochemical

and Inherent Optical Properties

J. Ronald V. Zaneveld and Andrew H. Barnard

Oregon State University

Corvallis, Oregon

21.1 INTRODUCTION

The purpose of the SIMBIOS program is to provide routine, long-term ocean color data from the

various international ocean color missions. Our

funded component of this program is to address and

quantify the relative accuracies of the products from

the international missions by means of product and

algorithm validation. Our long-term objectives are to

a) collect optical and biochemical data in oceanic and

coastal regions including a cooperative international

bio-optical monitoring program in the Gulf of California; b) provide collected data to the NASA database,

SIMBIOS project office, and other interested users;

and c) determine spatial and temporal error fields for

the biological and geophysical data products from the

various ocean color missions.

21.1 RESEARCH ACTIVITIES

Over the past 4 years we have been involved in a

multi-national research effort focused on determining

the physical and biogeochemical variability in the

Gulf of California. This research is done in coordination with Drs. J. Mueller and C. Trees from San Diego

State University (SDSU), Drs. S Alvarez Borrego, R.

Lara-Lara, G. Gaxiola and H. Maske from the Centro

de Investigacion Cientifica y de Educacion Superor de

Ensenada (CICESE), Ensenada, Mexico, and Dr. E.

Valdez from the University of Sonora, Hermosillo,

Mexico. Our component has been to measure the inherent and apparent optical properties as well as the

traditional CTD parameters on vertical scales less than

0.5 m. We have completed 5 cruises in the Gulf of

California, with 3 of these cruises occurring in the last

year and half during our SIMBIOS contract period.

Optical data collected during these cruises are currently being used to validate SeaWiFS algorithms.

We have also completed a cruise of opportunity offshore of Oregon in September 1998. Data from this

cruise is currently being processed and analyzed.

Two sampling platforms are typically used during

these cruises; a SLOW Descent Rate Optical Profiler

(SLOWDROP) to measure the inherent optical properties as well as the physical parameters, and a profiling radiometer system to measure the downwelling

irradiance and upwelling radiance. Typically,

SLOWDROP and radiometer profiles are made within

an hour of each other at the same location.

The SLOWDROP platform is free-falling and

slightly negatively buoyant and provides 10-20 cm

scale vertical resolution. A typical instrument configuration includes a SeaBird SBE-25 CTD for measuring physical parameters, a fluorometer, and two

WETLabs ac-9 (9 wavelength absorption and attenuation meters) for measuring particulate and dissolved

component of the inherent optical properties (IOP).

CTD and IOP data are collected simultaneously during a single profile using a Wet Labs, Inc. MODAPS

system for data collection and integration. Calibrations of the ac-9 instruments were performed several

times during the contract period. Field calibrations of

the ac-9 meters were typically done once per sampling

day using a clean water standard produced using a

Barnstead nanopure water system according to the

SIMBIOS protocols for this instrument.

A Satlantic Inc. SPMR system is used to measure

profiles of the apparent optical properties (AOP) including downwelling irradiance and upwelling radiance at 412, 444, 490, 533, 555, 590, and 684 nm.

The Satlantic radiometer is calibrated at SDSU by

Drs. Mueller and Pegau following NIST protocols and

calibrated twice a year by Satlantic Inc. The optical

filters on this radiometer were upgraded by the manufacturer (Satlantic) over the past year.

One meter binned profiles of all of the data, are

provided to the SeaBASS database within 90 days of

completion of each cruise. Also provided are the calibration histories of the ac-9's and the radiometer, and a

detailed logbook. In the future we plan to make these

data sets available via the web.

The dates of each cruise and the number of profiles made using each system are listed in Table 1.
SIMBIOS Project Annual Report

78

Cruises in 1997 and 1998 were SIMBIOS supported.

Figure 1 shows the station locations sampled during

each cruise. Data collected during the fall cruise in

1998 is currently being processed and quality controlled. As is such, the locations of the profiles are not

shown on Figure 1. Currently, we are receiving all of

the SeaWiFS HRPT Level 1A data for the West Coast

of North America including the Gulf of California

from the DAAC. This data is being archived and

processed to various levels for use in the validation of

ocean color products. We have been contracted to

maintain an optical profiling system for use in the

SWIMBIOS instrument pool. The system contains

two hyperspectral absorption and attenuation meters

(WET Labs Histars), a CTD (SeaBird Electronics 25),

a data acquisition system (WET Labs MODAPS+),

cage, and necessary cabling. We have assembled the

above system and have been testing the system in

various local environments. Currently there are still

some issues to be resolved as to the HiStar measurements in comparison to the ac-9 measurements, which

at this point seems to be calibration dependent. We

are currently working closely with WET Labs to resolve these issues. A full time technician has been

hired to accompany this system, to assist users in deployment and operation and to process the data. We

also maintain 3 deionizing water filtration systems

(Barnstead Nanopure) which are for use by the SIMBIOS authorized users. These systems are used to

produce a clean water standard for ac-9 and HiStar

field calibrations. These systems are currently in hand

and each has been tested and is ready for general use.

We expect that the calibration issues with the profiling

package will be fully addressed and the system ready

for general usage by the SIMBIOS authorized users by

late February 1999.

21.3 RESEARCH RESULTS

Over the past contract period, we have begun

analyzing our field data collected over the past 4

years. Data collected in the Gulf of California as well

as other locations were used to examine the spectral

relationships between the inherent optical properties in

Barnard et al. (1998). The results of this research

were used to compare and contrast the inherent optical

properties observed in the Gulf of California. In the

shallow northwest region of the Gulf, Case II waters

are consistently observed due to the resuspension of

sediments. In the central portion of the Gulf, the largest variability in optical properties is associated with

coastal upwelling. Away from the coasts the spectral

optical properties are fairly constant. Validation of the

normalized water leaving radiance measured by

SeaWiFS in the Gulf of California during the 1997

and spring 1998 cruises was examined. The results of

this research indicated that atmospheric correction was

problematic, often causing negative water leaving

radiances at 412 nm.

In coordination with our SeaWiFS funding, we

have undertaken the development of a new remote

sensing algorithm involving the triple ratio of the remote sensing reflectance. We have also compared the

in situ radiance with the upwelling radiance resolved

by the OCTS sensor off the northeastern U.S. coast.

21.4 WORK PLAN

We will be participating in two research cruises in

the Gulf of California during 1999, tentatively planned

for the spring and fall. We anticipate participating in

other cruises in the next year, as the opportunity

arises. We will also be working on the installation of

an in-line fluorometer on the trans-Gulf ferry to provide a monthly transect of chlorophyll fluorescence

and beam transmission data in the Gulf of California.

In the next year, we anticipate that the hyperspectral profiling package will receive a high amount

of usage by the authorized users. We plan to maintain

these systems as well as provide technical support to

the users. Again we anticipate that this system will be

available for general use by the end of February 1999.

We plan to continue to investigate the inherent and

apparent optical properties of the Gulf of California,

as well as continuing our work with ocean color algorithm validation and development. We will also be

addressing issues of atmospheric correction over the

Gulf of California, which have been found to be

problematic.

Table 1 Dates and number of profiles made during each of the Gulf of California cruises.

Cruise Name Dates # IOP profiles # AOP profiles

GOC95fall 11/25/95 to 12/6/95 28 69

GOC96fall 10/30/96 to 11/7/96 25 25

GOC97fall 10/16/97 to 10/29/97 39 24

GOC98spring 3/6/98 to 3/16/98 27 7

GOC98fall 11/27/98 to 12/6/98 45 11
SIMBIOS Project Annual Report

79

Figure 1. Map of the Gulf of California with sampling locations. The circles denote sampling locations

during the 1995 cruise, the stars the 1996 cruise, the triangles the 1997 cruise, and the squares are for the spring

1998
SIMBIOS Project Annual Report

80

Chapter 22

Validation of the SeaWiFS Atmospheric Correction

Scheme Using Measurements of

Aerosol Optical Properties

Mark A. Miller, R. Michael Reynolds and M. J. Bartholomew

Brookhaven National Laboratory

Upton, New York

22.1 INTRODUCTION

The focus of the research described below is

comparisons between surface and satellite measurements of aerosol optical properties as a medium for

validating the assumptions made in the aerosol models

used in the retrieval of water-leaving radiance. Two

research projects are being conducted as part of the

SIMBIOS contract: The first project is to develop a

Marine Fast Rotating Shadow-band Spectral Radiometer (MFRSSR) that can be used for continuous,

ship-board measurements of the spectral aerosol optical depth and the spectral direct-normal and spectral

diffuse irradiance. The second project is to measure

and interpret aerosol properties in regions under surveillance by an ocean color satellite, thereby providing

a data set from which to evaluate the atmospheric correction algorithm. This second project entails the use

of AERONET and ship-board photometers and radiometers. Progress toward the completion of each of

these projects and work planned for the next period is

described in the subsections below.

22.2 RESEARCH ACTIVITIES

MFRSSR

There are two primary techniques used to measure the aerosol optical depth: sun photometry and rotating shadow-band radiometry. Just as sun photometers must be accurately oriented toward the sun, an

obvious pitfall at sea, conventional shadow-band radiometers have required exact orientation. The development of fast-rotating, shadow-band radiometers, a

hybrid form of the original shadow-band technique,

has removed orientation requirement, whereupon

shipboard use of shadow-band radiometers has been

encouraged. As compared to land-based units, shipboard fast-rotating shadow-band radiometers require

much faster rotation of the occulting arm, fastresponse silicon detectors, higher data sampling rates,

and more sophisticated data analysis. As part of a

multi-agency effort between the Department of Energy (DOE) and NASA SIMBIOS, the Brookhaven

National Laboratory has developed an MFRSSR. It

measures spectral global and spectral diffuse irradiance, which are used to calculate the spectral direct-normal irradiance as a function of solar zenith

angle. From these data, the aerosol optical thickness

can be computed during clear periods using the Langley regression technique, or continuously if high

quality extraterrestrial calibration coefficients are

known.

Initial data comparisons of optical depths from

hand held sunphotometers have been encouraging and

an example of a time series of optical depth from the

MFRSSR and MicroTops is shown in Figure 1. In

this case, a well-defined decrease in the optical depth

during a 9-hour measurement period was observed by

both instruments. Periods of noisy optical thickness

are the result of clouds, which have not been filtered

in this plot. The MFRSSR is designed to operate for

long periods with minimal attention and it is scheduled, along with two new units, to be at sea for a total

of 7-8 months during 1999. During this period measurements will be taken over three oceans aboard the

R/V Ron Brown and other ships, and from an island in

the Tropical Western Pacific. At the conclusion of

these cruises, all three units will spend several weeks

at Mauna Loa for calibration. An important element

of the MFRSSR design philosophy is automated operation and timely data analysis. Toward this end,

efforts have been made to develop a cloud-filtering

algorithm that can be used to identify cloud-free conditions. The initial version of this algorithm was

based on the work of Long et al. (1999), but it has

since been modified for more efficient use in a marine

environment.

AERONET SeaWiFS Comparisons

Another approach to validating the atmospheric

correction algorithms is to use land-based sunphotometers deployed in coastal locations, such as

AERONET. These systems make a full range of

measurements that can be used to compute the atmos-
SIMBIOS Project Annual Report

81

pheric correction parameters defined by Gordon et al.

(1980). It is not possible, with current instrumentation, to measure the full range of variables necessary

to compute the atmospheric correction parameters at

sea. One drawback of the land-based approach, however, is that near-shore measurements may not faithfully represent conditions further from the coast,

whereupon an approach that combines ship-board and

AERONET measurements is probably the best alternative. Both approaches are part of this study.

The AERONET and SeaWiFS optical properties

for some selected locations are being compared using

the SeaWiFS/AERONET match-up code developed at

NASA GSFC. The initial form of this code selects

dates and times of coincident SeaWiFS and

AERONET measurement and extracts the aerosol optical depth from the respective data files, providing the

following are true: (1) AERONET data that have

passed a cloud filter algorithm are available during the

two-hour period centered on the satellite overpass

time, and (2) the SeaWiFS data in each individual

pixel in a scene pass all quality control checks.

The match-up code identifies coincident SeaWiFs

and AERONET measurement times at several locations and detailed examinations of these data are in

progress. There are several points to be made. At present, we have analyzed the matchup data for the following locations: Dry Tortugas, Bermuda, San

Nicholas Island, Lanai, Kaashidoo, and Bahrain. Preliminary results suggest that the pixel-to-pixel variability in the aerosol optical thickness at most of the

sites is unrealistically large, perhaps due to an inadequate cloud filtering algorithm applied to the

SeaWiFs data. The best match-up data sets analyzed

to date are from Bermuda, Bahrain, and Kaashidoo.

Comparing Bermuda and Kaashidoo, both island sites,

the aerosol optical thickness as measured by both

AERONET and satellite suggests that the aerosol optical thickness is generally higher at Kaashidoo, which

lies in the Indian Ocean, and it tends to be more variable than at Bermuda. In general, more data tend to

pass the SeaWiFs quality control algorithms at

Kaashidoo, which may reflect less cloudiness more

than any other single factor. The data suggests that

the comparison between the SeaWiFS and AERONET

is somewhat better at Bermuda than at Kaashidoo.

The reason for the less favorable comparison data at

Kaashidoo is under investigation, but some evidence

suggests that the AERONET sunphotometer calibration may have impacted this result. Before this analysis is complete, however, the wind vector must be

considered in match-up pixel selection. If the wind

speed is greater than a few meters per second, the current two-hour sunphotometer data averaging period

suggests that pixels outside the scene area may need to

be considered for an appropriate comparison. Conversely, the sunphotometer averaging window could

be reduced, although it is likely that this problem is

not a factor in many of the analyses.

The largest amount of match-up data available is

from the Dry Tortugas. After extensive analysis of the

Dry Tortugas data, there appear to be some problems

with data quality, most likely the result of AERONET

sunphotometer calibration or filter decay. This problem may be corrected in the latest match-up data set.

In general, data from Bermuda suggest that the aerosol

optical thicknesses measured by AERONET and

SeaWiFs are highly compatible. In contrast, match-up

data from Kaashidoo suggest potential problems with

either the AERONET or SeaWiFS aerosol optical

thickness measurements, or perhaps both. It is reasonable to conclude on the basis of these results that

the atmospheric correction algorithm is highly suspect

in the vicinity of Kaashidoo. Data from other matchup locations are being analyzed and preliminary results suggest that SeaWiFS tends to measure a higher

aerosol optical thickness at almost all locations than

the AERONET. Additional ship and satellite aerosol

optical thickness comparisons await a more extensive

match up data base, which should be in place by the

end of this year.

23.3 WORK PLANNED

There are still some issues to be addressed in the

design of the MFRSSR. Controlled experiments need

to be conducted on a motion simulator. The required

equipment for these tests has been assembled and the

experiments will be conducted when a second

MFRSSR under construction for DOE is complete. In

addition, pitch and roll information need to be incorporated into the data processing algorithms used to

process MFRSSR, especially when the instrument is

deployed on small ships.

 Data from the R/V Ron Brown’s 7-month cruise

for INDOEX and DOE Nauru-99 campaigns will be

used to facilitate match-ups with SeaWiFS and submitted to SeaBASS. In addition, two new MFRSSR

units will be deployed in support of Nauru-99: one on

the Japanese R/V Mirau and the other on the island of

Nauru in the Tropical Western Pacific. These data

will include over 200 measurement days aboard the

R/V Ron Brown and additional 90 measurement days

from the Mirai and Nauru. Several quality match-ups

are anticipated from a variety of geographic locations

and aerosol regimes. At the conclusion of INDOEX

and Nauru-99, in August, all three MFRSSR units (the

original and the two new units) will be offloaded at

Hawaii and taken to Mauna Loa for a three week calibration, along with the microtops used in these experiments. Before shipment back to Brookhaven National Laboratory, one MFRSSR will be used in a

collaborative cruise with Dr. John Porter at the University of Hawaii. Hence, over 300 ship-board meas-
SIMBIOS Project Annual Report

82

urement days are planned this fiscal year and, once

these data have been processed, satellite match-ups

will be made. The AERONET/SeaWiFS matchup

analysis is continuing. Data from all of the match-up

sites will be analyzed. Particular emphasis will be

placed on interpreting the match-up data from locations, such as Kaashidoo, where the analysis suggests

problems with the atmospheric correction algorithm.

In addition, attempts will be made to interpret the

AERONET- SeaWiFS match-up data in the context of

the full set of atmospheric correction parameters as

described by Gordon et al. (1980).

Figure 1. Spectral optical thickness measurements made with the MFRSSR at 415 nm, 500 nm, 610 nm,

660 nm, and 862 nm on January 27, 1999 over the Atlantic Ocean near the equator. Indicated in the boxes are

instantaneous hand-held sun photometer measurements at 440 nm, 500 nm, 670 nm, and 870 nm.
SIMBIOS Project Annual Report

83

Chapter 23

Measurements of Aerosol, Ocean and Sky Properties

at the HOT Site in the Central Pacific

John N. Porter and Ricardo Letelier

Hawaii Institute of Geophysics and Planetology,

University of Hawaii, Honolulu, Hawaii

23.1 INTRODUCTION

Monthly cruises have been made to the Hawaii

Ocean Time Series (HOT) site (~100 km north of

Oahu) since October 1988. The goal of these cruises is

to make hydrography, chemistry, and biology observations (PI: Dave Karl and Roger Lucas). Measurements are typically made at a near coastal station

(Kahe) on the first day to test the equipment and to

obtain coastal shallow water (~1500m) observations.

The second and third days are spent at the HOT site.

On the morning of the fourth day, measurements are

made at the HOT site and noon time measurements

are made at the Hale-Aloha station near the mooring

before returning to port by early the next morning.

The locations of the three stations are: 

Kahe (21.34o N, 158.27o W)

HOT (22.75o N, 158.0oW)

Hale-ALOHA buoy (22.43oN, 158.0oW).

The routine HOT measurements are available

during the summer following the year of the observations. The 1998 measurements will therefore become

available during the summer of 1999. The data sets

can be obtained at the National Oceanographic Data

Center (NODC) or from the Hawaii HOT web site

(www.hahana.soest.hawaii.edu/hot/hot_jgofs.html).

Selected parts of this data set will be submitted to the

SeaBass archive as the data comes on line.

23.2 RESEARCH ACTIVITIES

Microtops Sun Photometers

Beginning with the HOT89 cruise, aerosol optical

depth measurements were made with two Microtops

sun photometers. Examples of the data sets collected

are shown in Figure 1. Aerosol optical depth measurements were made at 380, 440, 500, 675, 870 and

1020 nm. Column integrated water vapor and ozone

concentrations were also derived. These measurements have been submitted to the SeaBass archive. In

general we find the aerosol optical depths to be

roughly the same (~0.05) at all wavelengths for typical

trade wind conditions where sea salt dominates. Asian

dust periods also have a flat spectral aerosol optical

depth but can have optical depths of 0.1 and higher.

Under VOG (volcanic smog) conditions, the shorter

wavelengths have larger optical depths such as the

case shown in Figure 1 (left panel). Calibration has

been a major concern and numerous calibration efforts

have been carried out at Mauna Loa and Haleakala.

The results of these calibrations are good and they are

reported in a technical report submitted to SIMBIOS.

The same report goes into detail on calibration problems, measurement problems, and suggested protocols

for using the Microtops hand held sun photometers.

Comparisons between the ship sun photometer measurements and the SeaWiFS aerosol optical depths at

870 are shown in Figure 2. In general the agreement is

about 0.04 with the exception of two corrisponding

cases which had flat spectral optical depths higher

than 0.06, suggesting Asian dust may have been present. For VOG we found a systematic under-prediction

of the aerosol optical depth by about 20%.

Marine Shadowband Radiometer

During the past year we have been working on a

marine shadowband radiometer which will measure

aerosol optical depths and downwelling irradiance at

~20 wavelengths. This system uses a gimbaled cosine

response detector and a rotating shadowband arm

which shadows the detector. A CVI Laser spectrometer is used to collect the light and a PC104 computer is

used to collect the data. The system has been tested on

several cruises and the gimbal works well. An algorithm has been written to collect the total and diffuse

light and the direct solar component is obtained from

the difference. A cloud screening algorithm has also

been developed which detects clouds by the variation

in the downwelling irradiance just before and after the

detector is shadowed. Although we believe we have

made significant progress in many areas, we still have

not resolved the cosine response problem as we would

like near perfect cosine response with the cosine response known to 0.1%. We have tried diffusers made
SIMBIOS Project Annual Report

84

of teflon, flashed opal, ground glass, spectralon, and

integrating spheres. We now believe that the integrating sphere or the spectralon offer the best performance. Several new designs are being machined.

Radiometric Calibration Facility

In the past we have carried out radiance calibration of our systems at the Moby calibration facility

(thanks to Dennis Clarke). Now we have purchased a

NIST traceable irradiance lamp and integrating sphere

from Optronics. These systems were set up in a dark

room at the University of Hawaii for optical calibration. Our plans are to maintain this facility with routine checks. Unfortunately, during a SIRREX comparison, we found our calibration was approximately

5.5% too low. We could not understand this difference. Therefore we have purchased a shunt resistor

which was recently calibrated by a NIST traceable

calibration facility. We will soon use this calibrated

resistor to check the current output of our power supply. The Optronics power supply is the first suspect as

it had a transistor failure which was replaced prior to

our SIRREX comparison. We expect this problem will

soon be solved.

In Water Optics Measurements

As part of this SIMBIOS effort, in water PRR

(Profiling Reflectance Radiometer) and TSRB (Tethered Spectral Radiometer Buoy) measurements were

begun on HOT90 cruise (Dec. 1997). PRR measurements are made by Karl et al. and processed by Ricardo Letalie. Calibration of this instrument was carried out and the coefficients have been submitted to

the SeaBASS archive. A description of the data and

calibration is available at

http://picasso.oce.orst.edu/users/jasmine/ORSOO/.

Aerosol Phase Function Measurements

As part of our initial SIMBIOS proposal, we proposed to develop a polar nephelometer which could

measure the aerosol phase function. Throughout the

past year we have been developing this system and

have recently collected our first measurements from

this prototype instrument. Our design follows the system described by Winchester Jr. (in Optical Engineering, 1983, pg. 40). Our first measurements were

made at Bellows beach directly downwind of small

breaking waves. We have recently purchased a pulsed

laser which will allow for phase function measurements at 3 wavelengths (1064, 532, 355 nm). The

system is being designed to install in the door of a

light aircraft and we expect to hope to make column

aerosol phase function measurements in the future.

Sky and Surface Radiometer

We are developing a hand radiometer to sky radiance and above surface upwelling radiance. The sky

radiance will be used to derive aerosol size distribution information and the surface radiance will be used

to validate satellite measurements and to study the

diffuse reflectance problem. This system uses a wide

angle camera and a tilt meter to determine the viewing

geometry and a spectrometer to measure the sky or the

aureole. The scattering angle is derived from the position of the sun in the camera image and a tilt meter.

The system will be in a weather proof enclosure using

a PC/104 computer to control the two axis motor, the

camera, and the spectrometer. We had expected to

have a prototype system working by now but delays

have pushed it back to Spring 1999.

23.3 WORK PLAN

We have three goals: 1) continue collection of

existing measurements on the HOT cruises, 2) finishing the construction of new instruments (shadowband

radiometer, polar nephelometer, and sky radiometer),

and 3) carry out modeling efforts. The modeling effort

will focus on developing new algorithms to derive

column aerosol properties from surface measurements

and estimating the impact of aerosol on upwelling

radiance at the top of the atmosphere.
SIMBIOS Project Annual Report

86

Chapter 24

Assessment of the Contribution of the Atmosphere to

Uncertainties in Normalized Water-Leaving Radiance:

a Combined Modelling and Data Analysis Approach

Knut Stamnes and Bingquan Chen

Geophysical Institute

University of Alaska Fairbanks, Fairbanks, Alaska

24.1 INTRODUCTION

Atmospheric correction, i.e. the process of deriving the normalized water-leaving radiances from satellite-measured imagery of the oceans, has been established as one sub-goal of the SIMBIOS program

for which the main purpose is to provide routine, long

term ocean color data from a variety of international

ocean color missions. Our research for the SIMBIOS

program is focused on the study of atmospheric correction. The overall objective is to use a sophisticated,

state-of-the-art radiative transfer model for the coupled atmosphere-ocean system, with existing and

planned algorithms, and in conjunction with data

taken by other investigators in the SIMBIOS program,

to help quantify the uncertainties in the water-leaving

radiance due to inadequacies in atmospheric corrections applicable to OCTS, POLDER, SeaWiFS,

MODIS, and other ocean color sensors.

Efficient radiative transfer codes for the atmosphere-ocean system are not generally available, and

the popular and intuitively appealing Monte Carlo

method (Morel and Gentili, 1991) is too timeconsuming to be used in routine retrieval algorithms.

To solve the radiative transfer equation for the coupled atmosphere-ocean system, we employ the discrete-ordinate method (Jin and Stamnes, 1994). This

model for computing the transfer of radiation in the

coupled atmosphere-ocean system is reliable and efficient. It has the accuracy of the Monte Carlo method,

but overcomes its computational inefficiency.

24.2 RESEARCH ACTIVITIES

Water-leaving Radiance at NIR Wavelengths

The main goal of this study is to assess the uncertainty or error incurred in atmospheric correction

by ignoring the water-leaving radiance caused by

scattering from particles in the near-surface water at

NIR wavelengths between 660-870 nm. Aerosol multiple scattering is included in the forward modeling to

provide realistic simulations of the atmospheric contribution to the TOA radiance. We also employ a biooptical model of ocean water with ocean particle concentrations of 1.5, 5.0, and 10.0 mg/m3

, respectively,

and we employ phase functions for phytoplankton

particles (i.e., cyanobacteria and algae, Volten et al.,

1998) in the simulations conducted in this study.

Forward modeling is used to simulate or predict

radiances that ocean color sensors would measure.

From the deviation between the TOA radiances predicted by a model of the coupled atmosphere-ocean

system (Jin and Stamnes, 1994) and the same model in

which scattering by ocean particles (and hence waterleaving radiances) at NIR wavelengths has been ignored, one can determine under what conditions the

water-leaving radiance at NIR wavelengths can be

ignored in atmospheric corrections. For each sensor

channel we use forward modeling simulations to accurately predict the impact of both atmospheric aerosols and biogenic constituents in the ocean on TOA

radiances for any desired sun-satellite geometry, solar

zenith angle 0, sensor viewing polar angle , and

relative azimuthal angle with respect to the sun.

To describe scattering by particles in the ocean

we employ the Henyey-Greenstein phase function pHG

(Henyey and Greenstein, 1941):

This phase function has the desirable feature that

it yields complete forward scattering when the asymmetry factor g=1, isotropic scattering when g=0, and

complete backward scattering when g=-1. The linear

combination

is sometimes used to simulate a phase function with

both a forward and a backward scattering component

(g>0 and g'<0). Here is the scattering angle, b is the

fraction of forward-scattered light (0<b<1), and g and

( )

3/ 2

2 cos 21

2

1

( , cos )

+

=

g g

g

g HG p

p(cos ) = bp (g, cos ) + (1 b) p (g', cos ) HG HG
SIMBIOS Project Annual Report

87

g' are usually different. Based on laboratory measurements by Volten et al. (1998), we have used equation

(2) with different values of g, g', and b to simulate

phase functions corresponding to ocean waters with

different types of particles.

The measurements by Volten et al. (1998) were

carried out at 633 nm. Lacking better information we

assume for our present purpose that they can be used

to approximate the phase functions at wavelengths

between 630 nm and 870 nm. Previous studies show

that far from sources of pollution and/or sources of

desert aerosols the aerosol optical depth at 865 nm

over the Pacific Ocean lies in the range between 0.08

and 0.11 (Villevalde et al., 1994). In this study we

employ a Tropospherical aerosol model with relative

humidity of 80% (Shettle and Fenn, 1979) and use a

Mie code to calculate the aerosol optical properties.

From forward-modeling results based on these synthetic phase functions we conclude that:

The TOA radiance deviation depends on the

scattering phase function of particles in the nearsurface water.

As the aerosol optical depth decreases, the TOA

radiance deviation increases. When the aerosol

optical depth is large (e.g. a=0.2), TOA radiances, predicted by a model in which waterleaving radiances at NIR wavelengths are ignored, do not deviate significantly from those

obtained when including scattering by ocean particles. Thus, at large aerosol optical depths, we

may ignore water-leaving radiances at some NIR

bands (e.g. 865 nm) without introducing significant errors.

The TOA radiance deviation increases with increasing ocean particle concentration. When the

ocean particle concentration is large and the aerosol optical depth is low, water-leaving radiances

at NIR wavelengths contribute substantially to

TOA radiances and should not be ignored.

The TOA radiance deviation that results from

neglecting water-leaving radiances depends on

the sun-satellite geometry.

The TOA radiance deviation at =765 nm is

larger than that at =865 nm.

The TOA radiance deviation at =665nm is

much larger than that at =865nm. Since the 665

nm wavelength has been used in atmospheric correction for CZCS, this deviation can have led to

significant uncertainties in ocean color retrievals

from the CZCS measurements.

To avoid the uncertainties incurred by ignoring

water-leaving radiances at NIR wavelengths retrievals

and atmospheric corrections in ocean color imagery

should be based on a radiative transfer model for the

coupled atmosphere-ocean system (Jin and Stamnes,

1994).

Atmospheric Correction Algorithm

The existing atmospheric correction algorithm is

mainly based on the approximate exponential relationship of the single scattering aerosol reflectance over

the range 412-865 nm. Two types of lookup tables for

N selected aerosol models then constitute the main

part of the algorithm. The first type of lookup table is

for the coefficient ss ( , 865) which relates the single

scattering aerosol reflectance at wavelength to that

at 865 nm. The second type of lookup table is for the

coefficient k[ , as ,)] which makes a correction for

multiple scattering. For each type of lookup tables,

about twelve candidate aerosol models are employed;

and table entries are computed for each of these models for solar zenith angles between 0°and 80° in increments of 2.5°, for 33 values viewing zenith angles,

and for eight values of the aerosol optical depth between 0.05 and 0.8. The total number of separate solutions to the radiative transfer equation used in the

preparation of these lookup tables exceeds 33,000

(Gordon, 1996). Thus, the computational effort involved in the construction of these lookup tables is

very large.

Based on a state-of-the-art radiative transfer

model for the coupled atmosphere-ocean system, we

simulate the process of atmospheric correction. Using

four types of aerosol models (Tropospheric, Maritime,

Coastal and Urban with RH = 50, 80 and 98 %, = 7°)

we find that there exists an approximate exponential

relationship of the aerosol reflectance over the range

412-865 nm not only in the single scattering case, but

also in the multiple scattering case. Thus, a simple and

efficient algorithm for atmospheric correction is proposed and discussed by comparing it with the existing

algorithm. In our algorithm, the aerosol contribution

in the visible in the multiple scattering can be extrapolated directly from that in the near-infrared by

use of the approximate exponential relationship.

Therefore it is not necessary to construct lookup tables

for the coefficient [ , as ( )]. The new coefficient 

ms ( , 865), which represents the ratio of the multiple

scattering aerosol reflectance at to that at 865 nm, is

introduced in the new algorithm instead of ms ( ,

865) used in the existing algorithm. Future testing of

this algorithm will be carried out by use of satellite

data and field measurements. The most important conclusion of this study is that one should examine

whether or not water-leaving radiances at NIR wavelengths can be ignored when developing algorithms

either for the retrieval of atmosphere-ocean parameters or for atmospheric corrections. Otherwise, erroneous results can be obtained if such algorithms are applied to satellite-received data, even for open oceans.

A simple and efficient algorithm for atmospheric correction is also proposed and compared with the existing algorithm.
SIMBIOS Project Annual Report

88

Chapter 25

Validation of the Water-Leaving Radiance Data Product

Oleg V. Kopelevich

Ocean Optics Laboratory

P.P. Shirshov Institute of Oceanology, Moscow, Russia

25.1 INTRODUCTION

The overall objective of the research is to assess

an accuracy of retrieval of the water-leaving radiance

from satellite ocean color data. Specific goals include

an assessment of accuracy of the atmospheric correction algorithms for variety of meteorological and

oceanological conditions, effects of the rough sea surface reflectance and of the small-scale spatial inhomogeneities in the subsurface layer (sub-pixel variability), an accuracy of the water-leaving radiance

values obtained from in situ measurements. Combined

approach is used which includes direct comparison

between the values of water-leaving radiance derived

from satellite data and in situ measurements, computer

simulation, theoretical analysis.

25.2 RESEARCH ACTIVITIES

Field Methods and Data

 The instrumental set constructed in the

P.P.Shirshov Institute of Oceanology Russian Academy of Sciences (SIO RAS) for field studies comprises deck and floating spectroradiometers and

monitor photometer. The deck spectroradiometer is a

modification of the device described before (Goldin et

al. 1983); the floating spectroradiometer and the

monitor photometer are new instruments (Artemyev et

al., 1999). The floating spectroradiometer measures

the upwelling radiance and downwelling irradiance in

the spectral range 390-700 nm with spectral resolution

2.5 nm; the upwelling radiance is measured just beneath the sea surface and the downwelling irradiance

just above the sea surface at a distance about 50 m

from ship; thus the difficulties connected with influence of sun glints, correction for light reflected at the

sea surface, influence of ship shadow are precluded.

The monitor photometer is designed to check calibration of irradiance at 554 nm and measure continuously

the surface irradiance at this wavelength during spectral measurements by the spectroradiometers. The

radiometric accuracy of the deck and floating spectroradiometers and the monitor photometer is respectively 10%, 5% and 3%. The field testing of the floating spectroradiometer were carried out on the oceanografic platform of the Marine Hydrophysical Institute

NASU in Katsiveli, September 1996. They showed an

ability of the instrument to work under bad weather

conditions (strong wind, cloudiness) when measurements by the deck radiometer are impracticable.

 The field studies under satellite ocean color sensors

SeaWiFS and MOS-IRS were performed during the

scientific cruise of RV Akvanavt in the Black and Aegean Seas, October 6-24, 1997 (Artemyev et al.,

1999). Along with measurements of spectral upwelling radiance and surface irradiance by the deck and

floating radiometers, the studies included measurements of vertical profiles of nadir upwelling radiance

and downwelling irradiance by means of the submersible radiometer MER-2040 (these measurements

were performed by specialists from the Polish Institute

of Oceanology, Sopot); determination of the atmospheric spectral optical thicknesses by means of the sun

photometer; measurements of vertical profiles of the

seawater beam attenuation coefficient by the submersible transmissometer; sampling and conservation

of water samples for determination of phytoplankton

pigment concentration. Five drift stations were carried

out during the cruise, three in the Black Sea and two

in the Aegean Sea. The information on the stations is

given in Table 1.

 Absolute radiometric calibration of the radiance

and irradiance channels was performed before the

expedition. During the cruise, intercalibration of the

floating spectroradiometer and MER-2040 was carried

out; an example of intercalibration is shown in Fig. 1.

Discrepancy between values of Lu and Ed measured by

these two instruments was mainly in limits of 5%.

 In August-September 1998 the field studies in the

eastern part of the Barents Sea were carried out during

the 13th and 14th scientific cruises of R/V Akademik

Sergey Vavilov. They included the measurements

listed above, excluding measurements by MER-2040,

and additionally measurements of the diffuse attenuation coefficient at wavelength 530 nm by the Kd -

meter and also determinations of the particulate matter

concentration, primary production, dissolved organic

carbon concentration, CTD profiles. The information

on the stations with optical measurements is given in

Table 2.
SIMBIOS Project Annual Report

89

25.3 RESEARCH RESULTS

The validation cruise of RV Akvanavt in the

Black and Aegean Seas

 The validation of the SeaWiFS atmospheric correction algorithm was performed with measured data

from Station 2 and Station 4 where the measurements

were carried out under appropriate weather conditions.

Before validation, an agreement of the values of the

top-of-the-atmosphere radiance Lt(li) measured by

SeaWiFS sensor and calculated by a Monte Carlo

technique with in situ data on r(li) and ta(li) was

checked. The procedure developed for the Monte

Carlo calculation is described elsewhere (Kopelevich

et al. 1998; Burenkov et al., 1999). The results of

comparison between the measured and calculated values of Lt(li) are given in Table 3. As it is seen, the

agreement is quite well for Station 2; it should be

borne in mind that the observed discrepancies result

not only from errors of the measurements but from

also some assumption taken for the calculation. The

agreement is worse for Station 4; it can be explained

by some atmospheric inhomogeneity due to the

proximity of the cloud edge to the pixel with this station.

 The SeaWiFS atmospheric correction algorithm

was validated by comparison of the LWN(li) and ta(li)

values derived from SeaWiFS data and from in situ

measurements. The results of comparison are given in

Table 4. As it is seen, the agreement is quite satisfactory both for the LWN(li) and ta.

 The SeaWiFS algorithm for retrieving chlorophyll

concentration and the analytic algorithm developed by

the specialists of SIO RAS were validated by comparison of retrieved and measured data. The SeaWiFS

algorithm overestimates significantly the chlorophyll

concentration for Case-2 waters with predominance of

absorption by yellow substance; the analytic algorithm

results to reasonable agreement in all cases (Burenkov

et al. in press).

The Akademik Sergey Vavilov Cruises in the

Barens Sea

 The preliminary analysis revealed some cases of

incorrect SeaWiFS data products; an example is given

in Figure 2. The negative values of LWN(443) are seen

over most part of the image (left); the chlorophyll

concentration derived from SeaWiFS data agree reasonably with the measured values only in open part of

the Barent Sea and differ drastically (by a factor 20

and more) in the Pechora Basin (right image).

 The measured spectral dependences of the radiance

reflectance exhibit a wide variety of forms (Figure 3):

the spectra measured in the north-eastern part of the

Barents Sea have the maximum near 420 nm and the

ratio LWN(490)/LWN(555) about 3 (St.1209), whereas in

the southern part of the Pechora Basin they are respectively near 580 nm and less than 0.5 (St.1095).

According to the SeaWiFS data, the chlorophyll concentration varies over a wide range of values: from

less than 0.5 mg×m

-3 in the northern part to more than

20 mg×m

-3 in the Pechora Basin (Figure 2, right image). The in situ data show much more narrow range

of its changes. The further analysis is planned to establish the reasons for the revealed errors resulted

from the SeaWiFS algorithms.

Effects of the Sub-pixel Variability

 The mathematical simulation of effects of the

small-scale inhomogeneities in the subsurface layer

(sub-pixel variability) on the retrieval results from

satellite data has been performed. The horizontal distribution of chlorophyll concentration with the sharp

change was assumed, and the averaged spectral upwelling radiance was calculated. Then the averaged

spectra were used to retrieve the values of chlorophyll

concentration. Comparison between the obtained and

true mean values has shown that discrepancies between them are no more 5 % if the amplitude of

change is less 50%, but they increase up to 15% with

the twofold change and 45% with the fourfold. Such

sharp changes are real in the coastal waters, and potential errors should be taken into account.

25.4 WORK PLAN

The further analysis of data obtained during the

13th and 14th cruises of R/V Akademik Sergey

Vavilov in the Barent Sea, August-September

1998.

Preparation of the scientific equipment for work

in the 15-th cruise of R/V Akademik Sergey Vavilov in the Norwegian and Greenland Seas.

The field studies in the 15th cruise of R/V

Akademik Sergey Vavilov in the Norwegian and

Greenland Seas, May-June 1999.

Analysis of data obtained during the 15th cruise of

R/V Akademik Sergey Vavilov in the Norwegian

and Greenland Seas, May-June 1999.

Validation of the SeaWiFS algorithm for retrieving the chlorophyll concentration in the Black Sea

by comparison of the satellite and available in situ

data.
SIMBIOS Project Annual Report

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Figure 1. Results of intercalibration between the floating spectroradiometer and MER-2040 at St.2; upper

curves - surface irradiance, lower - upwelling radiance; - floating spectroradiometer, - MER-2040.

Figure 3. Spectra of the water radiance reflectance measured in different parts of the Barents Sea during

the 13-th and 14-th cruises of R/V Academik Sergey Vavilov: St.1209 - the north-eastern part of the Barents Sea;

St.1088 and St.1095 - the northern and southern parts of the Pechora Basin (see Table 2).
SIMBIOS Project Annual Report

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Figure 2. Spatial distributions of values of LWN (443) and Chl a in the eastern part of the Barents Sea on

August 25, 1998
SIMBIOS Project Annual Report

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Table 1. The information on the stations of Akvanavt’97.

Date St. Coordinates (degrees)

at the measurement

moments

Local

time

Difference with

GMT, h

10/07/97 1 * 42.5 N, 39.5 E 09:20 - 14:40 +3

10/08/97 2 *,** 43.0 N, 35.6 E 10:05 - 15:40 +3

10/09/97 3 42.9 N, 31.6 E 10:48 - 15:11 +3

10/11/97 4 *, ** 39.3 N, 25.1 E 11:30 - 14:55 +3

10/16/97 5 ** 39.6 N, 25.8 E 10:19 - 14:58 +3

* - under SeaWiFS; ** - under MOS-IRS.

Table 2. The information on the stations of R/V “Akademik Sergey Vavilov” 13 and 14 cruises.

Date St. Coordinates (degrees)

at the measurements

 moments

Local time Difference with

GMT, h

08/11/98 1088 70.42 N, 47.58 E 10:20 - 14:55 +4

08/12/98 1090* 70.18 N, 52.42 E 13:40 - 15:00 +4

08/14/98 1095 68.97 N, 58.47 E 08:15 - 10:30 +4

08/14/98 1097 69.07 N, 58.42 E 16:20 - 17:30 +4

08/15/98 1099 69.10 N, 58.03 E 09:00 - 10:30 +4

08/19/98 1112* 69.09 N, 58.29 E 11:30 - 12:50 +4

08/19/98 1112* 69.09 N, 58.29 E 13:55 - 14:25 +4

08/23/98 1123 69.06 N, 58.16 E 07:00 - 10:00 +4

08/23/98 1125* 69.50 N, 57.25 E 13:10 - 14:20 +4

08/23/98 1126 69.67 N, 57.24 E 16:25 - 17:30 +4

08/24/98 1131* 69.77 N, 56.28 E 14:10 - 16:00 +4

08/25/98 1133 70.33 N, 55.30 E 10:00 - 14:40 +4

08/29/98 1150 69.33 N, 50.12 E 08:10 - 09:30 +4

08/30/98 1154* 69.62 N, 50.57 E 10:30 - 14:50 +4

08/31/98 1157* 70.54 N, 52.79 E 12:30 - 14:30 +4

09/02/98 1164 68.40 N, 50.70 E 08:20 - 10:20 +4

09/10/98 1174 69.25 N, 41.00 E 08:40 - 10:40 +4

09/11/98 1183 71.50 N, 41.00 E 09:00 - 11:00 +4

09/12/98 1190 73.25 N, 41.00 E 10:00 - 12:00 +4

09/13/98 1196 74.75 N, 41.00 E 09:30 - 11:30 +4

09/15/98 1209 78.00 N, 41.00 E 10:20 - 13:00 +4

09/27/98 1281 76.00 N, 42.27 E 10:20 - 12:40 +4

* - under SeaWiFS

Table 3. Comparison between the SeaWiFS measured and Monte Carlo calculated values of the

top-of-the-atmosphere-radiance Lt(li); D is the relative discrepancy.

Station 2 Station 4

,

nm

Lt SeaWiFS,

W cm-2 sr-1 nm-1

Lt MC,

W cm-2 sr-1 nm-1

,

%

Lt SeaWiFS,

W cm-2 sr-1 nm-1

Lt MC,

W cm-2 sr-1 nm-1

,

%

412 7.40 7.42 0.3 8.10 7.89 2.6

443 6.52 6.57 0.7 7.24 6.86 5.0

490 4.84 4.83 0.2 5.35 5.16 3.5

510 4.12 4.08 1.0 4.50 4.21 6.4

555 2.93 2.80 4.4 3.18 2.96 6.9

670 1.25 1.16 7.2 1.55 1.44 7.1

765 0.55 0.59 7.2 0.77 0.73 4.8

865 0.36 0.33 8.3 0.55 0.43 22
SIMBIOS Project Annual Report

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Table 4. Comparison between values derived from SeaWiFS and in situ data for the normalized

water-leaving radiance LWN(li) and the aerosol optical thickness ta(865); D is the relative discrepancy.

Station 2 Station 4

, nm LWN SeaWiFS,

W cm-2 sr-1 nm-1

LWN measured,

W cm-2 sr-1 nm-1

,

%

LWN SeaWiFS,

W cm-2 sr-1 nm-1

LWN measured,

W cm-2 sr-1 nm-1

,

%

412 0.536 0.492 9 0.770 0.732 5

443 0.752 0.708 6 0.886 0.891 0.6

490 1.036 0.998 4 0.882 0.784 6

510 0.991 0.925 7 0.592 0.537 10

555 0.770 0.772 0.3 0.271 0.272 0.4

a(865) 0.065 0.095 31 0.160 0.142 13
SIMBIOS Project Annual Report

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Chapter 26

OCI Data Validation in the Waters Adjacent to Taiwan

Hsien-Wen Li, Chung-Ru Ho and Nan-Jung Kuo

Department of Oceanography

National Taiwan Ocean University, Keelung, Taiwan

26.1 INTRODUCTION

Taiwan successfully launched her first experimental satellite, ROCSAT-1, on January 27 1999. It is

a three-axis stabilized, low-earth orbit satellite with a

35° inclination. ROCSAT-1 is designed to carry out

three scientific experiments: ocean color imaging,

ionospheric plasma and electrodynamics, and Ka-band

communication.

The payload instrument for ocean color imaging

on ROCSAT-1 is called Ocean Color Imager (OCI).

OCI is a multi-spectral push-broom imager, which is

designed to map six reflected spectral radiances from

ocean surfaces. The six spectral bands are identical to

the six of the eight spectral bands on SeaWiFS. The

band characteristic comparison of OCI and SeaWiFS

is listed in Table 1.

In order to have successful operation of OCI,

there are two scientific groups under the OCI project,

the Science Team (ST) and the Science Data Distribution Center (SDDC). The purposes of the ST are to

calibrate the sensor, to correct for the atmospheric

influence, to develop bio-optical algorithms, and to

calibrate and validate OCI data. The SDDC at National Taiwan Ocean University (NTOU) is responsible for processing OCI data and then distributing it to

users.

OCI will perform imaging at any time between

9:00 and 15:00 local time. The normal mission operation of OCI is to map ocean surface pigments whenever weather permits.

Ideally, OCI will acquire ocean surface pigment

data when cloud coverage is less than 50% of the area

along the track. The actual OCI operation will ultimately be decided by the OCI-ST. A preliminary operation priority has been established based on geographic locations, request sequences, weather conditions, and cross calibration and field validation areas.

For calibration and validation purposes, images

are schedule to be taken when the OCI tracks overlap

with SeaWiFS, or the calibration buoy location or

location of the experimental cruises.

26.2 RESEARCH ACTIVITIES

It is believed that the OCI calibration at each

wavelength will change in some unpredictable manners as a function of time. Experience with previous

sensors, such as Coastal Zone Color Scanner (CZCS),

has shown that it is very difficult to determine a sensor’s calibration once it has been launched (Mueller

and Austin, 1992). Unlike the SeaWiFS instrument,

OCI has no on-board solar calibrator. Therefore, a

cross-calibration program with SeaWiFS will be performed after OCI is available. To validate OCI and

SeaWiFS data, field measurements of optical properties are carried out with a Tethered Spectral Radiometer Buoy (TSRB-II) and a SeaWiFS Profiling

Multi-channel Radiometer (SPMR) made by Satlantic

Company. TSRB-II is an optical buoy, which can

measure the in-water upwelling radiance just beneath

the sea surface (0 ,l) Lu and the incident spectral

irradiance above the sea surface (l) Es

. SPMR is a

profiling radiometer that can measure the in-water

upwelling radiance L (Z,l)

u and downwelling

spectral irradiance E (Z,l)

d with depth Z.

To obtain (l) Lw that is measured by the OCI it

is necessary to propagate (0 ,l) Lu upward through

the sea surface as

( )

1 ( , )

( ) (0 , )

2

l

r l q

l l

w

w u

n

L = L (1)

where r(l,q ) and (l) nw are the Fresnel reflectance at the solar zenith angle and the refractive index

for seawater, respectively. In order to remove the influence of view angle, sun angle and the solar irradiance, the water-leaving radiance is generally transferred to normalized water-leaving radiance Lwn as

( )

( )

( ) ( )

0

l

l

l l

s

wn w

E

F

L = L (2)
SIMBIOS Project Annual Report

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where ( ) F0 l denotes the mean extraterrestrial solar

irradiance (Neckel and Labs,1984). For calculating the

remote sensing reflectance just above the sea surface

(0 ,l)

+ Rrs the following equation was used

(0 , l) 0.54 (0 ,l) / (l) Rrs Lu Es

+

= (3)

Since the band characteristics of OCI are similar

to those of SeaWiFS, some of bio-optical algorithms

from the SeaWiFS Bio-optical Algorithms MiniWorkshop (SeaBAM) are evaluated using the data sets

that are collected in the water adjacent to Taiwan. The

evaluated algorithms are listed in Table 2. We have

collected a total of 29 in situ data including optical

properties and water samples in order to derive the

relationship between optical properties and chlorophyll a concentration. All samples, except the surface

seawater, were collected by Go-Flo 2.5/5 L sampler

which was attached on the rosette multi-sampler. Surface seawater was collected with a bucket. One liter of

seawater was immediately filtered by Whatman GF/F

(25 mm) filter, under pressure (<0.2 bar). To determine the chlorophyll a concentration, the filtered

sample was frozen in liquid nitrogen on board, while

in the laboratory the N, N-dimethylformamide (DMF)

extracting solvent was added in darkness at -20°.

Compared with the acetone extracting solvent, DMF

has some advantages (Suzuki and Fujita, 1986; Porra

et al., 1989; Suzuki and Ishimaru, 1990) and was

therefore used in this study. The measurement of chlorophyll a was undertaken in the laboratory according

to the fluorescence method described by Strickland

and Parsons (1972).

26.3 RESEARCH RESULTS

A total of 29 bio-optical data were made in the

time period of 1998 in the Kuroshio region near Taiwan for testing the SeaBAM algorithms. The field

measurements include (l) Es

, L (Z,l)

u ,

E (Z,l)

d , and water sample for determining the

chlorophyll a concentration. The Lwn is computed

using Eqs. (1), and (2). The Rrs is obtained from Eq.

(3). Most of the water samples were taken in the Case

I water. The range of measured chlorophyll a concentration is from 0.08 ug/l to 1.25 ug/l in this data set.

The statistical results between calculated chlorophyll a

concentration using some of SeaBAM algorithms and

measured chlorophyll a concentration from water

samples are listed in Table 3. The results show that R2

of Aiken-C, CalCOFI 2-band linear, CalCOFI 2-band

cubic, Morel 2, and SeaWiFS algorithms are higher

than 0.8. The RMS is smaller than 0.015 for these

methods. This suggests that the SeaWiFS algorithm is

also suitable for the waters adjacent to Taiwan.

26.4 WORK PLAN

In situ measurements of optical properties and

chlorophyll a concentration will be continuous in the

waters adjacent to Taiwan, especially in Taiwan Strait

and East China Sea. The schedule for normal operation of OCI is from April 1999. Therefore the intercomparison between SeaWiFS and OCI will be the

most important plan for next period. Some of

SeaWiFS project members will also take bio-optical

data for validating OCI data. OCI data will be available in April 1999.

ACKNOWLEDGMENTS

Many thanks go to captains and crew of R/V

Ocean Researcher II and R/V Ocean Researcher III for

shipboard assistance. We appreciate the assistance of

the GSFC/DAAC of NASA for providing the

SeaWiFS data. This work is supported by the National

Space Program Office (NSPO) of Taiwan under grants

NSC83-NSPO-A-RDD-019-002, NSC84-NSPO-(A)-

OCI-001-02, NSC85-NSPO-(A)-OCI-019-02, NSC86-

NSPO-(A)-OCI-019-01, NSC86-NSPO-(A)-OCI-019-

02, NSC87-NSPO-(A)-OCI-019-01, NSC87-NSPO-

(A)-OCI-019-02, NSC88-NSPO-(A)-OCI-019-01, and

NSC88-NSPO-(A)-OCI-019-02.

Table 3. Summary of statistical results of algorithm evaluations.

Method 1 2 3 4 5 6 7 8 9

R

2 0.859 0.833 0.816 0.772 0.825 0.769 0.794 0.792 0.848

RMS 0.012 0.014 0.015 0.019 0.015 0.020 0.017 0.018 0.013
SIMBIOS Project Annual Report

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 Table 1. A Comparison of characteristics between SeaWiFS and OCI.

SeaWiFS OCI

Inclination 98.25° 35°

Altitude (km) 705 600

Period (min) 98.9 96.6

Orbital repeat time (days) 16 52

Spectral bands (nm) B1 402-422

B2 433-453

B3 480-500

B4 500-520

B5 545-565

B6 660-680

B7 745-785

B8 845-885

B1 433-453

B2 480-500

B3 500-520

B4 545-565

B5 660-680

B6 845-885

B7 545-565

 Nadir pixel (m2)

1130 x 1130 800 x 800

 Swath width (km) 2801 702

 Redundancy No 555 nm

 Color sensing Scanner push broom

 Crossing equator time

 (local time)

12:00 9:00 ~ 15:00

 Bits 10 12

 Tilt -20°, 0°, 20° No

 Launch date (year/month) 1997/8 1999/1

Table 2. Bio-optical algorithms performed for the data taken in the waters adjacent to Taiwan.

Method Algorithms Band ratio(R), Coefficient(s)

1. Aiken-C C=EXP(a0+a1*ln(R))

C=(R+a2)/(a3+a4*R)

R=Lwn490/Lwn555

a=[0.464,-1.989,-5.29,0.719,-4.23]

2. CalCOFI 2- band Linear C=10^(a0+a1*R) R=log(Rrs490/Rrs555)

a=[0.444,-2.431]

3. CalCOFI 2- band Cubic C=10^(a0+a1*R+a2*R^2+a3*R^3) R=log(Rrs490/Rrs555)

a=[0.450,-2.860,0.996,-0.3674]

4. Morel 1 C=10^(a0+a1*R) R=Log(Rrs443/Rrs555)

a=[0.2492,-1.768]

5. Morel 2 C=EXP(a0+a1*R) R=Ln(Rrs490/Rrs555)

a=[1.077835,-2.542605]

6. Morel 3 C=10^(a0+a1*R+a2*R^2+a3*R^3) R=Log(Rrs443/Rrs555)

a=[0.20766,-1.82876,0.75885,-0.73979]

7. Power law model C=EXP(a0+a1*R) R=Ln(Lwn443/Lwn555)

a=[-0.0177,-1.233]

8. Carder Ratio Log(C)=a0+(a1+a2*log(R))*log(R) R=Rrs490/Rrs555

a=[0.0469,-1.0129,-0.7416]

9. SeaWiFS C=10^(a0-a1*R+a2*R^2+a3*R^3)+a4 R=log(Rrs490/Rrs555)

a=[0.2974,-2.2429,0.8358,-0.0077,-0.0929]
SIMBIOS Project Annual Report

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GLOSSARY

ACE Aerosol Characterization Experiment

ADEOS Advanced Earth Observation Satellite

(Japan)

AERONET Aerosol Robotic Network

AM-1 Not a acronym, used to designate the

morning platform of EOS

AOP Apparent Optical Properties

AOT Aerosol Optical Thickness

APV Autonomous Profiling Vehicle

ARGOS Not an acronym, but the name given to

the data collection and location system

on the NOAA Operational Satellites.

ASCII American Standard Code for Information

Interchange

AVHRR Advanced Very High Resolution

Radiometer

AVIRIS Advanced Visible and Infrared Imaging

Spectrometer

BATS Bermuda Atlantic Time-series Study

BBOP Bermuda Bio-Optics Profiler

BBSR Bermuda Biological Station for Research

BNL Brookhaven National Laboratory

BTM Bermuda Test Mooring

Cal/Val Calibration and Validation

CalCOFI California Cooperative Oceanic

Fisheries Investigation

CALVAL Calibration Validation

CARICO Carbon Retention in a Colored Ocean

Case-1 Water whose reflectance is determined

by absorption.

Case-2 Water whose reflectance is significantly

influenced by scattering.

CCD Charge-Coupled Device

CDOM Chromophoric Dissolved Organic Matter

CHN Carbon, Hydrogen and Nitrogen

CHORS Center for Hydro-Optics and Remote

Sensing (San Diego State University)

CICESE Centro de Investigation Cientifica y de

Edcacion Superior de Ensenada

(Mexico)

CIMEL The name of a sun photometer manufacturer

CNES Centre National d’Edudes Spatialle

CONICIT Consejo Nacional de Investigaciones

Cientifica y Technologicas (Venezuela)

CRAM Conditional Relaxation Analysis Method

CTD Conductivity-Temperature-Depth

CZCS Coastal Zone Color Scanner

DAAC Distributed Active Archive Center

DLR Deutshe Forshungsanstalt f r Luft-und

Raumfarhrt (German Aerospace Center)

DMF Dimethylformamide

DOC Dissolved Organic Carbon

DoD Department of Defense

DOE Department of Energy

ECOHAB Ecology of Harmful Algal Blooms

EEZ Exclusive Economic Zone

EORC Earth Observation Research Center

EOS Earth Observing System

FFP Firm-Fixed Price

FOV Field of View

ftp File transfer protocol

FWHM Full Width Half Maximum

GAC Global Area Coverage, coarse resolution

satellite data with a nominal ground resolution at nadir of approximately 4 Km

GB Gigabyte, or about one billion bytes

GF/F Not an acronym, but a specific type of

glass fiber manufactured by Whatman.

GLI Global Imager

GoCal Gulf of California

GPS Global Positioning System
SIMBIOS Project Annual Report

98

GSFC Goddard Space Flight Center

HIVE High-Latitude Intercomparison and

Validation Experiment

HOBI Hydro-Optics, Biology and

Instrumentation

HOT Hawaii Ocean Time series

HPLC High Performance Liquid

Chromatography

HQ Headquarters

HRPT High Resolution Picture Transmission

ICESS Institute for Computational Earth

Science System

IDL Interactive Data Language

INDOEX Indian Ocean Experiment

IOCCG International Ocean Color Coordinating

Group

IOP Inherent Optical Properties

IR Infrared

IRS Indian Remote Sensing Satellite

ISCCP International Satellite Cloud

Climatology Project

ISPO Interim SIMBIOS Project Office

JGOFS Joint Global Ocean Flux Study

JPL Jet Propulsion Laboratory

LAC Local Area Coverage, fine resolution

satellite data with a nominal ground resolution at nadir of approximately 1Km

LIDAR Light Detection and Ranging Instrument

LED Light Emitting Dicode

LOA Laboratorie d’Optique Atmospherique

MARMAP Marine Resources Monitoring, Assessment and Prediction

MBARI Monterey Bay Aquarium Research Institute

MB Megabyte, or about one million bytes

MER Multispectral Environmental Radiometer

MERIS Medium Resolution Imaging Spectrometer

MFRSSR Marine Fast Rotating Shadow-band

Spectral Radiometer

MISR Multi-angle Imaging SpectroRadiometer

MOBY Marine Optical Buoy

MODAPS Modular Ocean Data and Power System

MODIS Moderate Resolution Imaging

Spectroradiometer

MOS Modular Optoelectronic Scanner

MSl12 Multi-Sensor level-1B to level-2 code

MTPE Mission to Planet Earth

NASA National Aeronautics and Space

Administration

NASDA National Space Development Agency

of Japan

NAVOCEANO Naval Oceanographic Office

NDBC National Data Buoy Center

NIMBUS Not an acronym, but a series of NASA

experimental weather satellites containing a wide variety of atmosphere, ice,

and ocean sensors.

NIST National Institute of Standards and

Technology

NOAA National Oceanic and Atmospheric Administration

NODC National Oceanographic Data Center

NOPP NIMBUS Observation Processing System

NRA NASA Research Announcement

NSF National Science Foundation

NSPO National Space Program Office

NTOU National Taiwan Ocean University

OCI Ocean Color Imager

OCTS Ocean Color and Temperature Sensor

ONR Office of Naval Research

ORCA Optical Research Consortium
SIMBIOS Project Annual Report

99

of the Arctic

OSC Orbital Sciences Corporation

OSU Oregon State University

PAR Photosynthetically Available Radiation

PHILLS Hyperspectral Imager for Low Light

Spectroscopy

PI Principal Investigator

PM-1 Not a acronym, used to designate the

afternoon platform of EOS

POLDER Polarization Detecting Environmental

Radiometer (France)

PRR Profiling Reflectance Radiometer

R&D Research and Development

R/V Research Vessel

ROCSAT Republic of China (Taiwan) Satellite

platform for the OCI sensor.

RR Round-Robin

SAB South Atlantic Bight

SBE Sea-Bird Electronics

SCOR Scientific Committee on Oceanic Research

SDDC Science Data Distribution Center

SeaOPS SeaWiFS Optical Profiling System

SeaBAM SeaWiFS Bio-optical Algorithms Miniworkshop

SeaBASS SeaWiFS Bio-optical Archive and Storage System

SeaDAS SeaWiFs Data Analysis System

SeaWiFS Sea-viewing Wide Field-of-view Sensor

SIMBAD The name of a sun photometer

SIMBIOS Sensor Intercomparison and Merger for

Biological and Interdisciplinary Oceanic

Studies

SIO Scripps Institution of Oceanography

SGI Silicon Graphics, Inc.

SIRREX SeaWiFS Intercalibration Round-Robin

Experiment

SLOWDROP Slow Descendent Rate Optical Profiler

SMSR SeaWiFS Multispectral Surface

Reference

SOOP Ship of Opportunity Program

SOW Statement of Work

SPMR SeaWiFS Profiling Multi-channel

Radiometer

SQM SeaWiFS Quality Monitor

ST Science Team

TB Terabytes

TOA Top of the Atmosphere

TOMS Total Ozone Mapping Spectrometer

TOTO Tongue of the Ocean

TSM Total Suspended Matter

TSRB-II Tethered Spectral Radiometer Buoy - II

XBT Expendable Bathythermograph

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