NASA/TMm2000-209891, Vol. 44

Technical Report Series on the

Boreal Ecosystem-Atmosphere Study (BOREAS)

Forrest G. Hall and Jaime Nickeson, Editors

Volume 44

BOREAS RSS-2 Extracted Reflectance

Factors Derived from ASAS Imagery

C. Russell, SSAI

P. Dabney, Goddard Space Flight Center, Greenbelt, Maryland

W. Kovalick, D. Graham, and M. Bur, Raytheon ITSS

J. Irons and M. Tierney, Goddard Space Flight Center, Greenbelt, Maryland

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000

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NASA/TMm2000-209891, Vol. 44

Technical Report Series on the

Boreal Ecosystem-Atmosphere Study (BOREAS)

Forrest G. Hall and Jaime Nickeson, Editors

Volume 44

BOREAS RSS-2 Extracted Reflectance

Factors Derived from ASAS Imagery

C. Russell, SSAI

P. Dabney, Goddard Space Flight Center, Greenbelt, Maryland

W. Kovalick, D. Graham, and M. Bur, Raytheon ITSS

J. Irons and M. Tierney, Goddard Space Flight Center, Greenbelt, Maryland

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000
NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

Price Code: A17

Available from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Price Code: A10
BOREAS RSS-2 Extracted Reflectance Factors Derived from ASAS

Imagery

C. Russell, P. Dabney, W. Kovalick, D. Graham, M. Bur, J. Irons, M. Tierney

Summary

The BOREAS RSS-2 team derived atmospherically corrected bidirectional reflectance factor means

from multispectral, multiangle ASAS imagery for small homogeneous areas near several BOREAS

sites. The ASAS imagery was acquired from the C-130 aircraft platform in 1994 and 1996. The data

are stored in tabular ASCII files.

Table of Contents

1) Data Set Overview

2) Investigator(s)

3) Theory of Measurements

4) Equipment

5) Data Acquisition Methods

6) Observations

7) Data Description

8) Data Organization

9) Data Manipulations

10) Errors

11) Notes

12) Application of the Data Set

13) Future Modifications and Plans

14) Software

15) Data Access

16) Output Products and Availability

17) References

18) Glossary of Terms

19) List of Acronyms

20) Document Information

1. Data Set Overview

1.1 Data Set Identification

BOREAS RSS-02 Extracted Reflectance Factors Derived from ASAS Imagery

1.2 Data Set Introduction

Atmospherically corrected bidirectional reflectance factor means for small homogeneous areas from

several BOReal Ecosystem-Atmosphere Study (BOREAS) sites were derived from multispectral,

multiangle imagery acquired by the Advanced Solid-state Array Spectroradiometer (ASAS) aboard the

C-130 aircraft platform in 1994 and 1996.

At-ground reflectance factors (a mean value for small areas from the ASAS images) have been

derived for the Southern Study Area (SSA)-CAL (Airborne Visible InfraRed Imaging Spectrometer

(AVIRIS) calibration site), SSA-Old Black Spruce (OBS), SSA-Old Aspen (OA), SSA-Old Jack Pine

(OJP), SSA-Young Jack Pine (YJP), and SSA-Fen flux tower sites.

Page 1
1.3 Objective/Purpose

The purpose was to derive at-surface reflectance factors from airborne multiangle reflected radiance

data to study the bidirectional reflectance properties of boreal forest canopies.

1.4 Summary of Parameters

ASAS measures at-sensor radiance of surfaces as a function of spectral wavelength, view

geometry (combinations of view zenith angle, view azimuth angle, solar zenith angle, and solar

azimuth angle), and altitude. For these data, mean surface reflectance factors have been derived from

at-sensor radiances for small areas adjacent to scaffold towers at several flux tower sites and a soil

calibration target. Also included are C-130 flight information, date and time of observations, viewing

and solar geometry, image subset coordinates, and atmospheric conditions.

1.5 Discussion

The main objectives of BOREAS, conducted in Canada throughout 1994 and 1996, are to improve

process models that describe the exchanges of energy, water, carbon, and trace constituents between

the boreal forest and the atmosphere, and to develop methods for applying the process models over

large spatial scales using remote sensing and other integrative modeling techniques. The Remote

Sensing Science (RSS) group, of which ASAS is a part, is responsible for developing linkages

between optical and microwave remote sensing and boreal zone biophysical parameters at various

scales (leaf, canopy, and regional) using measurements from field, aircraft, and satellite sensors plus a

range of radiative transfer models.

Data tables described in this document were derived only from data acquired on 26-May-1994;

21-Jul-1994; and 20-Jul-1996. ASAS at-sensor radiance image data are available for other dates; see

the document for ASAS Level lb image data.

1.6 Related Data Sets

BOREAS RSS-01 PARABOLA Surface Reflectance and Transmittance Data

BOREAS RSS-02 Level-lb ASAS Imagery: At-sensor Radiance in BSQ Format

BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted Barnes MMR

BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted SE-590

BOREAS RSS- 18 Level- 1B AVIRIS Imagery: At-sensor Radiance in BIL Format

BOREAS RSS-19 Background Spectral Reflectance Data

2. Investigator(s)

2.1 Investigator(s) Name and Title

Dr. James R. Irons

2.2 Title of Investigation

Boreal Forest Bidirectional Reflectances Acquired by an Airborne Multispectral, Multiangle

Imaging Spectroradiometer

2.3 Contact Information

Contact 1:

Dr. James R. Irons

Code 923

NASA GSFC

Greenbelt, MD 20771

(301) 614-6657

(301) 614-6695 (fax)

James.R.Irons. l@gsfc.nasa.gov

Page 2
Contact 2:

Michael Bur

Code 923

NASA GSFC

Greenbelt, MD 20771

(301) 614-6661

(301) 614-6695 (fax)

bur@ gyrfalcon.gsfc.nasa.gov or

Michael.J.Bur. l@gsfc.nasa.gov

Contact 3:

Jaime Nickeson

Raytheon ITSS

NASA GSFC

Code 923

Greenbelt, Maryland 20771

(301) 286-3373

(301) 286-0239 (fax)

Jaime.Nickeson@ gsfc.nasa.gov

3. Theory of Measurements

ASAS is an airborne imaging spectroradiometer modified to point off-nadir by the National

Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) for the purpose

of remotely observing directional anisotropy of solar radiance reflected from terrestrial surfaces. The

instrument is capable of off-nadir pointing from approximately 70 degrees forward to 55 degrees aft

along-track (in the direction of flight). As the aircraft approaches and approaches and passes the

ground target, digital radiance measurements of the target are recorded for a discrete sequence of

fore-to-aft view zenith angles within this range. The terms "tilt," "look," or "view" angles are used

interchangeably when referring to the ASAS view zenith angles. For the BOREAS data collection

flights, ASAS imaged most study sites at eight different view zenith angles: +70, +60, +45, +26,

nadir, -26, -45, and -55 degrees.

Imaging of sites at the 70-degree off-nadir view angle is problematic, and this particular angle may

or may not be available in every data set. Data were acquired in 62 spectral bands ranging from

404-1023 nm with a spectral resolution of approximately 10 nm in each band.

See sections below for further details.

4. Equipment

4.1 Sensor/Instrument Description

The ASAS instrument employs a cooled 1024 x 1024 element silicon charged-coupled-device

(CCD) detector array to generate multispectral digital image data in a pushbroom mode. The first 324

rows of the CCD are masked. The next 186 rows are exposed to the output from the spectrometer. The

final 516 rows are masked and used for readout of the array. Two of the rows under the mask collect

smear data which are used to remove smear effects and dark current from the data.

During the BOREAS missions, the operating method of the array was to bin every 3 rows into one

spectral band, which resulted in 62 spectral channels. In addition, every 2 detectors within each row

were binned, resulting in 512 pixels (per row or line) in the output image data (Level lb).

In this configuration the spectral band centers, which range from 404 to 1023 nm, are spaced at

approximately 10 nm. Each spectral band has a full-width half-maximum (FWHM) of approximately

10 nm.

Page 3
4.1.1 Collection Environment

TheASASinstrumentis mountedontheundersideof theplatformaircraftfuselagewith thesensor

opticseitherslightlyprotrudingintotheslipstreamorretractedintothefuselagepressurebox,

dependingontheview angle.As theaircraftapproachesthetargetsitefrom adistance,theASAS

instrumentispointedforward-looking.A videocamerabore-sightedwith theASASopticalheadrelays

apictureto anonboardmonitorscreenattheASASoperator'sstation.Thisenablestheoperatorto

identify thesiteandcontinuetrackingit througha sequenceof view anglesastheaircraftproceedsona

flight lineoverthesite.Whenthesitecomesintoview ontheforwardpoint,theoperatorbeginsdata

acquisition.Thesequenceis timedsuchthattheview is atnadirwhentheaircraftis overthesite,and

aft-lookingviewsaretakenafterpassingthesite.Determiningwhichviewsareforwardscatteror

backscatterrequiresexaminationof theaircraftheadingandthesolarazimuthangle.

During1994and1996BOREASmissions,multiangledataovertheflux towerswereusually

acquiredon3 separateflights in azimuthsparallel,perpendicularandobliqueto thesolarprincipal

plane.

As theplatformaircraftflies forward,eachrowof 512detectorbinsiselectronicallyscannedto

generate62spectralchannelsof digital imagedatain apushbroommode.Thesignalsgeneratedby the

CCDdetectorsaresampledatarateof 38framelinespersecondto producethealong-trackdimension

of theimagery(imagelines).Thesampledsignalfromeachdetectoris digitizedto 12bitsandthe

digitaldataarestoredonahigh-densityS-VHSformattapeusingabufferedVLDS datarecorder.

4.1.2 Source/Platform

NASA AmesResearchCenter(ARC)C-130EarthResourcesAircraft(1994)andNASA Wallops

Flight Facility (WFF) C-130Q(1996).

4.1.3 Source/Platform Mission Objectives

Themissionobjectiveswereto collectmultispectral,multianglebidirectionalreflectancedata

(acquiredasat-sensorradiances)overasoil field andflux towersitesfor studyof borealforest

canopies,andto simulateMulti-Angle ImagingSpectro-Radiometer (MISR)databy obtaining

measurementsatMISR view angles.At-groundreflectancefactorshavebeenderivedfor some(butnot

all) datasets.

4.1.4 Key Variables

ASASmeasuresat-sensorspectralradiancein thevisibleandnear-infraredportionof thespectrum

asafunctionof view geometry.At-groundspectralreflectancefor (a)asoil field usedasacalibration

targetand(b) smallareasadjacento thescaflbldtowersatflux towersiteshavebeenderivedusingthe

atmosphericorrectionalgorithmSecondSimulationof theSatelliteSignalintheSolarSpectrum(6S)

(seeSection17.1forreferences).

4.1.5 Principles of Operation

TheASASopticalheadis mountedin anopenportin theundersideof theC-130aircraft.A

complexpointingmechanismincorporatingagimbalenablesthesensortoview off-nadir,facilitating

movementin thehorizontal,vertical,rotationalforeandaft, andyawdirections.

As theaircraftapproachesthetargetsitefrom adistance,theASASinstrumentis pointed

forward-looking.A videocameramountedadjacento theASASopticalheadrelaysapictureto an

onboardmonitorscreenat theASASoperator'sstation.Thisenablestheoperatorto identify thesite

andcontinuetrackingit throughasequenceof view anglesastheaircraftproceedsonaflight line over

thesite.Whenthesitecomesintoview onthefirst forwardangle,theoperatorinitiatesdata

acquisition.Thesequenceistimedsuchthattheview is atnadirwhentheaircraftis directlyoverthe

site,andaft-lookingviewsaretakenafterpassingthesite.Yawcompensationcanbeperformedby the

operator(if necessary)to preventthesitefrom drifting outof thefield of view (FOV).

As theplatformaircraftflies forward,eachrow of 1024x 186arrayelementsareelectronically

scannedto generate62spectralchannelsof digital imagedatain apushbroommode.Thesignals

generatedby theCCDdetectorsaresampledatarateof 38framelinespersecondto producethe

along-trackdimensionof theimagery(imagelines).Thesampledsignalfrom eachdetectorisdigitized

Page4
to 12bitsandthedigitaldataarestoredonahigh-densityS-VHSformattapeusingabufferedVLDS

datarecorder.

4.1.6 Sensor/Instrument Measurement Geometry

Radiation incident on the ASAS aperture is focused onto an entrance slit by an f/1.4 objective lens

with a 57.2 mm focal length. The entrance slit is 50 _m wide across-track, and 23 _m wide

along-track. The lens focuses incoming energy through the entrance slit into a 1:1 relay with an

effective focal length of 76.3 mm in each half. In each half of the relay, a 90-degree mirror prism folds

the optical path to create a compact optical head. A transmission grating ruled at 75 lines per mm and

blazed at 530 nm is located between the two prisms to disperse the radiant energy into its wavelength

spectrum, which is in turn directed by the second prism onto the 186 rows of the array in the focal

plane, where the CCD is mounted.

The instantaneous field of view (IFOV) of an ASAS pixel is a function of optics, detector

dimensions, tilt angle (view angle), and aircraft altitude and attitude (pitch and roll). The optical system

includes an f/1.4 objective lens with a 57.2 mm focal length, providing a 0.33 rad (19.3 degree) total

angular across-track FOV. The individual angular resolution of the center detectors is 0.66 mrad

across-track. The along-track FOV is 0.44 mrad.

Each detector has dimensions of 19.0 micrometers spatially (across-track) and 19.0 micrometers

spectrally, however with a binning factor of 2 in the spatial dimension and 3 in the spectral dimension,

the resulting array pixel size is 38.0 micrometers in the spatial dimension and 57 micrometers in the

spectral dimension.

4.1.7 Manufacturer of Sensor/Instrument

The ASAS instrument evolved over a number of years. The original optics, built by TRW, were

part of the Scanning Imaging Spectroradiometer (SIS) constructed in the early 1970s for NASA's

Johnson Space Center (JSC). ASAS was created in 1981 when a charge-injection device (CID) silicon

detector array, made by GE, was incorporated with the optical system for a joint program involving

NASA JSC and the Naval Ocean Systems Center. In 1984, the sensor was transferred to NASA

GSFC, where the aircraft mounting bracket was modified for off-nadir pointing.

In late 1991, the pointing mechanism was upgraded by NASA GSFC to allow view angles of 70

degrees forward to 55 degrees aft, and to enable operator-controlled aircraft yaw compensation. In

1992, the CID was replaced with a Thomson CSF Model TH7896A (high speed version) CCD silicon

detector array. BOREAS data were acquired with this CCD array.

4.2 Calibration

Radiometric Calibration

Radiometric calibration data for the BOREAS experiment were acquired from two primary

calibration sources: 1) a 1.2 m diameter integrating hemisphere in the NASA GSFC calibration

laboratory, and 2) a 30 inch (0.76 m) diameter portable hemisphere that is owned and operated by

GSFC. The latter source was used for in situ calibration data acquisition since it could be positioned

directly under the aircraft-mounted instrument. The integrating hemisphere is operated and maintained

by the Sensor Development and Characterization Branch at NASA GSFC. Up to 12 levels of radiance

can be provided for calibration by turning the internal tungsten filament lamps on or off. The

hemisphere is calibrated on an absolute scale by comparison to the output from a National Institute of

Standards and Technology (NIST) traceable calibration lamp using a laboratory-based transfer

spectroradiometer. In a calibration run, ASAS is exposed to a 12-level sequence of spectral radiance

levels from the hemisphere. Dark current (the response of the instrument under conditions of no

incident radiation) is also acquired.

More detailed information about ASAS radiometric calibration can be found in the document for

ASAS Level lb images. See Section 1.6.

Page 5
Spectral Calibration

A McPhersonModel2850.5 m double monochromator serves as the spectral reference source for

ASAS. Light from the monochromator is collimated by a paraboloid mirror and directed to the ASAS

optics. Instrument output is sampled every 0.5 nm. The band centers have been computed by

determining the centroid of the area under the response curve for each band. FWHM was measured

directly from the response curves.

4.2.1 Specifications

ASAS spectral band centers and FWHM applicable to 1994 and 1996 BOREAS data sets are as

follows:

Band

i

2

3

4

5

6

7

8

9

i0

ii

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

3O

31

Center FWHM Band Center FWHM

(nm) (nm) (nm) (nm)

404 3

413 7

423 2

432 4

441 7

451 4

460 9

470 5

480 3

490 2

500 0

509 7

519 6

529 7

539 9

549 8

559 6

569 4

579 4

589 7

600 0

610 2

620 3

630 4

640 7

650 9

661 1

671 4

681 5

691 6

701 7

9 5

9 5

9 5

i0 0

i0 0

i0 0

i0 0

i0 0

i0 5

i0 5

i0 0

i0 5

i0 0

i0 5

i0 5

i0 5

i0 0

i0 5

i0 5

ii 0

i0 5

ii 0

i0 5

i0 5

ii 0

i0 5

ii 0

i0 5

ii 0

ii 0

ii 0

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

5O

51

52

53

54

55

56

57

58

59

60

61

62

711 9

722 1

732 3

742 6

752 9

763 2

773 5

783 8

794 1

804 5

814 9

825 3

835 7

846 0

856 4

866 8

877 2

887 6

897 9

908 3

918 7

929 0

939 5

949 9

960 3

970 7

981 1

991 5

i001 9

1012 2

1022 7

ii 0

ii 0

ii 0

ii 0

ii 0

ii 0

ii 0

ii 5

ii 0

ii 0

ii 0

ii 5

ii 0

ii 0

ii 0

ii 0

ii 5

ii 5

ii 0

ii 0

ii 0

ii 0

i0 5

ii 0

ii 0

ii 0

ii 0

i0 5

i0 5

i0 5

i0 5

4.2.1.1 Tolerance

Information on spectral radiometric resolution factors and periodic horizontal striping (relevant to

ASAS Level lb images) is presented in this section in the document on ASAS Level lb images. See

Section 1.6.

Page 6
4.2.2 Frequency of Calibration

In general, ASAS acquires radiometric calibration data at least twice for each mission, with one

calibration set acquired prior to the mission, followed by a postmission calibration after the instrument

arrives back at GSFC. Radiometric calibration data were also acquired during each BOREAS field

campaign using the portable integrating hemisphere described elsewhere in this document. For dates of

calibration data used to calibrate BOREAS field data, see this section in the document for ASAS Level

lb images.

Laboratory spectral calibrations of ASAS were performed both before and after the 1994 BOREAS

field season. The spectral stability was also checked once in the middle of the field season using a

portable helium neon laser. It has been determined that the spectral calibration results from

13-Oct-1994 are most appropriate for all 1994 and 1996 BOREAS data sets.

4.2.3 Other Calibration Information

None.

5. Data Acquisition Methods

The ASAS instrument is mounted on the underside of the platform aircraft fuselage with the sensor

optics either slightly protruding into the slipstream or retracted into the fuselage pressure box,

depending on the view angle. As the aircraft approaches the target site from a distance, the ASAS

instrument is pointed forward-looking. A video camera bore-sighted with the ASAS optical head relays

a picture to an onboard monitor screen at the ASAS operator's station. The operator identifies the site

and tracks it through a sequence of view angles as the aircraft proceeds on a flight line over the site.

When the site comes into view on the forward point, the operator begins data acquisition. The

sequence is timed such that the view is at nadir when the aircraft is directly over the site, and

aft-looking views are taken after passing the site. Determining which views are forwardscatter and

backscatter requires examination of the aircraft heading and the solar azimuth angle, given in the ASAS

American Standard Code for Information Interchange (ASCII) header.

During 1994 and 1996 BOREAS missions, data were acquired as follows: flux towers at multiple

view zenith angles on view azimuths parallel, perpendicular, and oblique to the solar principal plane.

As the platform aircraft flies forward, each row of 512 detector bins is electronically scanned to

generate 62 spectral channels of digital image data in a pushbroom mode. Signals generated by the

CCD detectors are sampled at a rate of 38 frame lines per second to produce the along-track dimension

of the imagery (image lines). The sampled signal from each detector is digitized to 12 bits and the

digital data are stored on a high-density S-VHS format tape using a buffered VLDS data recorder.

6. Observations

6.1 Data Notes

None.

6.2 Field Notes

ASAS operators do not make extensive notes about field conditions during missions. ASAS

usually is not flown if atmospheric conditions are not sufficiently clear. Any observations noted by

ASAS operators are made at altitude, and if considered pertinent to the data, are included in the ASAS

header (of Level lb images) COMMENTS field.

Page 7
7. Data Description

7.1 Spatial Characteristics

7.1.1 Spatial Coverage

At-ground reflectance factors (a mean value for small areas from the ASAS images) have been

derived for the SSA-CAL (AVIRIS calibration site), SSA-OBS, SSA-OA, SSA-OJP, SSA-YJP, and

SSA-Fen flux tower sites. At-sensor radiance images (ASAS Level lb) are available for more sites in

the SSA and for sites in the NSA. See the document on ASAS Level lb images. The North American

Datum of 1983 (NAD83) coordinates for the sites are:

Site Latitude Longitude

SSA FEN

SSA OA

SSA OBS

SSA OJP

SSA YJP

SSA AVIRIS CAL

53 801 °

53 629 °

53 988 °

53 916 °

53 876 °

53 24 °

N 104

N 106

N 105

N 104

N 104

N 105

619 ° W

198 ° W

i19 ° W

690 ° W

647 ° W

69 ° W

7.1.2 Spatial Coverage Map

Not available.

7.1.3 Spatial Resolution

Across-track direction (x):

ASAS spatial resolution in the x-direction is a function of the across-track FOV, view angle, and

the altitude of the platform aircraft. Across-track pixels do not overlap. The across-track pixel size (in

meters) is given in the header of each ASAS Level lb image, however this information is not retained

in the at-ground reflectance factor tables.

Approximate ASAS pixel sizes are given below (the platform aircraft flew at slightly different

altitudes in the two different years):

Tilt angle 1994 x pixel size 1996 x pixel size

(degrees) (meters) (meters)

+70 i0

+60 7

+45 5

+26 4

00 3

-26 4

-45 5

-55 6

7 9

3 6

2 4

1 3

6 3

1 3

2 4

4 5

.0

2

4

4

1

4

4

4

Along-track direction (y):

The along-track spatial resolution of an ASAS image pixel is more complicated. For a detailed

explanation, see the document for ASAS Level lb images.

All ASAS data sets are oversampled in the along-track direction. This means that each image line

somewhat overlaps the previous line, making the images appear more elongated than in reality. This

frame or line overlap is not corrected for during operational processing. Essentially, the along-track

pixel size is determined by the aircraft ground speed divided by the data frame rate, and this represents

the smear distance portion of each pixel in the y-direction. For both 1994 and 1996 ASAS BOREAS

data, this along-track (y) pixel size was approximately 3 m in all tilt angles.

Page 8
TheASASmultiangleimageshavenotbeengeoregistered,andthoughthesampledareasare

selectedcarefully,theyarenotguaranteedto representtheexactsameareain eachimage.

7.1.4 Projection

Not applicable.

7.1.5 Grid Description

Not applicable.

7.2 Temporal Characteristics

7.2.1 Temporal Coverage

The data cover various dates over the period of 26-MAY-94 to 20-JUL-96.

7.2.2 Temporal Coverage Map

Current coverage for at-ground reflectance factor tables:

DATE SITE FLIGHT LINES

26-May-1994 SSA CAL 1

21-Jui-1994 SSA OBS 3

SSA OA 3

SSA OJP 3

SSA YJP 1

SSA FEN 1

20-Jui-1996 SSA FEN 1

7.2.3 Temporal Resolution

ASAS site passes may vary slightly in time duration, depending on the length of the flight line and

the aircraft speed. Typically one multiangle pass over a site has a time duration of about 5 minutes.

At-ground reflectance factor tables have been generated for three dates only at this time:

26-May- 1994; 21-Jul- 1994; and 20-Jul- 1996.

7.3 Data Characteristics

7.3.1 Parameter/Variable

The parameters contained in the data files on the CD-ROM are:

Reference File

Column Name

SITE NAME

SUB SITE

DATE OBS

TIME

C130 LINE NUM

C130 RUN NUM

PLATFORM ALTITUDE

C130 TRUE HEADING

RELATIVE SOLAR POSITION

SOLAR ZEN ANG

SOLAR AZ ANG

CENTER VIEW ZEN ANG

CENTER VIEW AZ ANG

Page 9
RELATIVE VIEW AZ ANG

ASAS EXTRACTION START LINE

ASAS EXTRACTION START SAMPLE

ASAS EXTRACTION END LINE

ASAS EXTRACTION END SAMPLE

COLUMN WATER VAPOR 6S

OZONE CONTENT 6S

INTERP AEROSOL OPT THICK 550

EST BELOW PLATFORM WATER VAPOR

EST BELOW PLATFORM OZONE

EST BELOW PLATFORM AOT 550

CRTFCN CODE

REVISION DATE

Data File

Column Name

SITE NAME

SUB SITE

DATE OBS

TIME

WAVELENGTH

ASAS CHANNEL NUM

CENTER VIEW ZEN ANG

MEAN RADIANCE

SDEV RADIANCE

MEAN SURF RAD

SDEV SURF RAD

MEAN SURF REFL

SDEV SURF REFL

DIRECT DOWN SOLAR IRRAD

DIFFUSE DOWN SOLAR IRRAD

ENV DOWN SOLAR IRRAD

CRTFCN CODE

REVISION DATE

7.3.2 Variable Description/Definition

The descriptions of the parameters contained in the data files on the CD-ROM are:

Reference File

Column Name Description

SITE NAME

SUB SITE

The identifier assigned to the site by BOREAS,

in the format SSS-TTT-CCCCC, where SSS identifies

the portion of the study area: NSA, SSA, REG,

TRN, and TTT identifies the cover type for the

site, 999 if unknown, and CCCCC is the identifier

for site, exactly what it means will vary with

site type.

The identifier assigned to the sub-site by

BOREAS, in the format GGGGG-IIIII, where GGGGG is

the group associated with the sub-site

instrument e.g. HYD06 or STAFF, and IIIII is the

identifier for sub-site, often this will refer to

Page 10
DATE OBS

TIME

C130 LINE NUM

C130 RUN NUM

PLATFORM ALTITUDE

C130 TRUE HEADING

RELATIVE SOLAR POSITION

SOLAR ZEN ANG

SOLAR AZ ANG

CENTER VIEW ZEN ANG

CENTER VIEW AZ ANG

RELATIVE VIEW AZ ANG

ASAS EXTRACTION START LINE

ASAS EXTRACTION START SAMPLE

ASAS EXTRACTION END LINE

ASAS EXTRACTION END SAMPLE

COLUMN WATER VAPOR 6S

OZONE CONTENT 6S

an instrument.

The date on which the data were collected.

The Greenwich Mean Time (GMT) when the data were

collected.

The number of the C130 line in its flights over

the BOREAS area as given in the flight logs.

Zero values are given for non-"official" C130

missions and for data between C130 sites or

lines.

The number of the C130 run in its flights over

the BOREAS area as given in the flight logs.

Zero value is given for non-"official" C130

missions and data between C130 sites, lines or

runs.

The nominal altitude of the data collection

platform above the target.

The nominal azimuthal direction, measured

clockwise from North, along which the center line

of the C-130 aircraft was aligned during the

flight.

The relative position of the aircraft flight line

to the solar position, the values being either

parallel, perpendicular, or oblique.

The angle from the surface normal (straight up)

to the sun during the data collection.

The azimuthal direction of the sun during data

collection expressed in clockwise increments from

North.

At the center of the scene, the angle from the

surface normal (straight up) to the observing

instrument.

The azimuthal direction in which the radiant

energy was traveling when collected by the

instrument and expressed in clockwise increments

from North.

The azimuthal angle at which the radiant energy

was traveling when measured by the sensor,

relative to the solar azimuth. The relative view

azimuth angle increases in a clockwise direction

from the solar position.

The starting line in the ASAS image from which

values were extracted to derive BRDF estimations.

The starting sample in the ASAS image from which

values were extracted to derive BRDF estimations.

The ending line in the ASAS image from which

values were extracted to derive BRDF estimations.

The ending sample in the ASAS image from which

values were extracted to derive BRDF estimations.

The modeled amount of precipitable water in the

total vertical column of air with a cross-section

of 1 centimeter squared output from the 6S

atmospheric model.

The modeled total column abundance of ozone,

output from the 6S atmospheric model.

Page 11
INTERP AEROSOL OPT THICK 550 The aerosol optical depth interpolated to 550

nanometers, used in the atmospheric correction.

EST BELOW PLATFORM WATER VAPOR The estimated amount of precipitable water

EST BELOW PLATFORM OZONE

EST BELOW PLATFORM AOT 550

CRTFCN CODE

REVISION DATE

within a vertical column of air between the

ground and the aircraft, with a cross-section of

1 centimeter squared (modeled) .

The estimated column abundance of ozone below

the aircraft (modeled).

The estimated aerosol optical depth for the air

column below the aircraft (modeled).

The BOREAS certification level of the data.

Examples are CPI (Checked by PI), CGR (Certified

by Group), PRE (Preliminary), and CPI-??? (CPI

but questionable).

The most recent date when the information in the

referenced data base table record was revised.

Data File

Column Name Description

SITE NAME

SUB SITE

DATE OBS

TIME

WAVELENGTH

ASAS CHANNEL NUM

CENTER VIEW ZEN ANG

MEAN RADIANCE

SDEV RADIANCE

MEAN SURF RAD

SDEV SURF RAD

MEAN SURF REFL

SDEV SURF REFL

DIRECT DOWN SOLAR IRRAD

The identifier assigned to the site by BOREAS,

in the format SSS-TTT-CCCCC, where SSS identifies

the portion of the study area: NSA, SSA, REG,

TRN, and TTT identifies the cover type for the

site, 999 if unknown, and CCCCC is the identifier

for site, exactly what it means will vary with

site type.

The identifier assigned to the sub-site by

BOREAS, in the format GGGGG-IIIII, where GGGGG is

the group associated with the sub-site

instrument e.g. HYD06 or STAFF, and IIIII is the

identifier for sub-site, often this will refer to

an instrument.

The date on which the data were collected.

The Greenwich Mean Time (GMT) when the data were

collected.

Spectral wavelength at which measurement was

acquired.

The ASAS designation for channel number,

sequential from 1 to 62.

At the center of the scene, the angle from the

surface normal (straight up) to the observing

instrument.

The mean at-sensor radiance.

The standard deviation of at-sensor radiance.

The mean atmospherically corrected surface

radiance

The standard deviation of atmospherically

corrected surface radiance

The mean surface reflectance factor

(atmospherically corrected).

The standard deviation of atmospherically

corrected surface reflectance factor

Downwelling solar spectral irradiance from 6S

Page 12
DIFFUSE DOWN SOLAR IRRAD

ENV DOWN SOLAR IRRAD

CRTFCN CODE

REVISION DATE

model; direct component reaches surface on first

sun-surface path without scattering.

Downwelling solar spectral irradiance from 6S

model; diffuse component is the scattered flux

on the first sun-surface path, independent of

surface properties.

Downwelling solar spectral irradiance from 6S

model; environmental component has been scattered

between the surface and atmosphere and thus is

dependent on surface albedo.

The BOREAS certification level of the data.

Examples are CPI (Checked by PI), CGR (Certified

by Group), PRE (Preliminary), and CPI-??? (CPI

but questionable).

The most recent date when the information in the

referenced data base table record was revised.

7.3.3 Unit of Measurement

The measurement units for the parameters contained in the data files onthe CD-ROM are:

Reference File

Column Name Units

SITE NAME [none]

SUB SITE [none]

DATE OBS [DD-MON-YY]

TIME [HHMMSS GMT]

C130 LINE NUM [none]

C130 RUN NUM [none]

PLATFORM ALTITUDE [meters]

C130 TRUE HEADING [degrees]

RELATIVE SOLAR POSITION [none]

SOLAR ZEN ANG [degrees]

SOLAR AZ ANG [degrees]

CENTER VIEW ZEN ANG [degrees]

CENTER VIEW AZ ANG [degrees]

RELATIVE VIEW AZ ANG [degrees]

ASAS EXTRACTION START LINE [none]

ASAS EXTRACTION START SAMPLE [none]

ASAS EXTRACTION END LINE [none]

ASAS EXTRACTION END SAMPLE [none]

COLUMN WATER VAPOR 6S [millimeters]

OZONE CONTENT 6S [Dobson units]

INTERP AEROSOL OPT THICK 550 [unitless]

EST BELOW PLATFORM WATER VAPOR [millimeters]

EST BELOW PLATFORM OZONE [Dobson units]

EST BELOW PLATFORM AOT 550 [unitless]

CRTFCN CODE [none]

REVISION DATE [DD-MON-YY]

Page 13
Data File

Column Name Units

SITE NAME

SUB SITE

DATE OBS

TIME

WAVELENGTH

ASAS CHANNEL NUM

CENTER VIEW ZEN ANG

MEAN RADIANCE

SDEV RADIANCE

MEAN SURF RAD

SDEV SURF RAD

MEAN SURF REFL

SDEV SURF REFL

DIRECT DOWN SOLAR IRRAD

DIFFUSE DOWN SOLAR IRRAD

ENV DOWN SOLAR IRRAD

CRTFCN CODE

REVISION DATE

[none]

[none]

[DD-MON-YY]

[HHMMSS GMT]

[micrometers]

[none]

[degrees]

[Watts] [meter^-2] [steradian^-l] [micrometer^-l]

[Watts] [meter^-2] [steradian^-l] [micrometer^-l]

[Watts] [meter^-2] [steradian^-l] [micrometer^-l]

[Watts] [meter^-2] [steradian^-l] [micrometer^-l]

[percent]

[percent]

[Watts] [meter^-2] [micrometer^-l]

[Watts] [meter^-2] [micrometer^-l]

[Watts] [meter^-2] [micrometer^-l]

[none]

[DD-MON-YY]

7.3.4 Data Source

The sources of the parameter values contained in the data files on the CD-ROM are:

Reference File

Column Name Data Source

SITE NAME

SUB SITE

DATE OBS

TIME

C130 LINE NUM

C130 RUN NUM

PLATFORM ALTITUDE

C130 TRUE HEADING

RELATIVE SOLAR POSITION

SOLAR ZEN ANG

SOLAR AZ ANG

CENTER VIEW ZEN ANG

CENTER VIEW AZ ANG

RELATIVE VIEW AZ ANG

ASAS EXTRACTION START LINE

ASAS EXTRACTION START SAMPLE

ASAS EXTRACTION END LINE

ASAS EXTRACTION END SAMPLE

COLUMN WATER VAPOR 6S

OZONE CONTENT 6S

INTERP AEROSOL OPT THICK 550

[Assigned by BORIS Staff]

[Assigned by BORIS Staff]

[ASAS data system (recorded with data ]

[ASAS data system (recorded with data ]

[ASAS flight logs]

[ASAS flight logs]

[C130 navigation information]

[C130 navigation information]

[ASAS data system (recorded with data ]

[Calculated by ASAS software]

[Calculated by ASAS software]

[ASAS data system (recorded with data ]

[Calculated by ASAS data system software]

[Calculated by ASAS data system software]

[Obtained in image analysis software]

[Obtained in image analysis software]

[Obtained in image analysis software]

[Obtained in image analysis software]

[Modeled and output by 6S]

[Modeled and output by 6S]

[Interpolated from BORIS RSSll and RSSI2

data sets, then input to 6S]

EST BELOW PLATFORM WATER VAPOR [Modeled and output by 6S]

EST BELOW PLATFORM OZONE [Modeled and output by 6S]

EST BELOW PLATFORM AOT 550 [Modeled and output by 6S]

CRTFCN CODE [Assigned by BORIS Staff]

REVISION DATE [Assigned by BORIS Staff]

Page 14
Data File

Column Name Data Source

SITE NAME

SUB SITE

DATE OBS

TIME

WAVELENGTH

ASAS CHANNEL NUM

CENTER VIEW ZEN ANG

MEAN RADIANCE

SDEV RADIANCE

MEAN SURF RAD

SDEV SURF RAD

MEAN SURF REFL

SDEV SURF REFL

DIRECT DOWN SOLAR IRRAD

DIFFUSE DOWN SOLAR IRRAD

ENV DOWN SOLAR IRRAD

CRTFCN CODE

REVISION DATE

[Assigned by BORIS Staff]

[Assigned by BORIS Staff]

[ASAS data system (recorded with data)]

[ASAS data system (recorded with data)]

[ASAS spectral response files]

[ASAS software]

[Calculated by ASAS data system software]

[Calculated by image analysis software]

[Calculated by image analysis software]

[6S output]

[ASAS software that runs 6S]

[6S output]

[ASAS software that runs 6S]

[6S output]

[6S output]

[6S output]

[Assigned by BORIS Staff]

[Assigned by BORIS Staff]

7.3.5 Data Range

The following table gives information about the parameter values found in the data files on the

CD-ROM.

Reference File

Column Name

Minimum Maximum Missng Unrel Below

Data Data Data Data Detect

Value Value Value Value Limit

Data

Not

Cllctd

SITE NAME

SUB SITE

DATE OBS

TIME

C130 LINE NUM

C130 RUN NUM

PLATFORM ALTITUDE

C130 TRUE HEADING

RELATIVE SOLAR

POSITION

SOLAR ZEN ANG

SOLAR AZ ANG

CENTER VIEW ZEN ANG

CENTER VIEW AZ ANG

NSA-FEN-FLXTR

RSS02-BRF01

26-MAY-94

153838

i01

1

5130

19

oblique

33.5

117.9

.3

18.2

RELATIVE VIEW AZ ANG .244

ASAS EXTRACTION 22

START LINE

ASAS EXTRACTION 22

START SAMPLE

ASAS EXTRACTION END 36

LINE

ASAS EXTRACTION END 38

SAMPLE

SSA-YJP-FLXTR None None None None

RSS02-BRF01 None None None None

20-JUL-96 None None None None

211436 None None None None

703 None None None None

2 None None None None

6177 None None None None

340 None None None None

perpendicular None None None None

46

229 4

7O

351 2

359 925

1809

489

1823

5O4

None None None None

None None None None

None None None None

None None None None

None None None None

None None None None

None None None None

None None None None

None None None None

Page 15
COLUMN WATER VAPOR 14.2 14.2 None None None None

6S

OZONE CONTENT 6S 340 340 None None None None

INTERP AEROSOL OPT .054 .09 None None None None

THICK 550

EST BELOW PLATFORM 10.45 12.16 None None None None

WATER VAPOR

EST BELOW PLATFORM i0 i0 None None None None

OZONE

EST BELOW PLATFORM .05 .086 None None None None

AOT 550

CRTFCN CODE CPI CPI None None None None

REVISION DATE 19-JAN-99 19-JAN-99 None None None None

Data File

Column Name

Minimum Maximum Missng Unrel Below Data

Data Data Data Data Detect Not

Value Value Value Value Limit Cllctd

SITE NAME NSA-FEN-FLXTR SSA-YJP-FLXTR None None None None

SUB SITE RSS02-BRF01 RSS02-BRF01 None None None None

DATE OBS 26-MAY-94 20-JUL-96 None None None None

TIME 153838 211436 None None None None

WAVELENGTH .4043 1.0227 None None None None

ASAS CHANNEL NUM 1 62 None None None None

CENTER VIEW ZEN ANG .3 70 None None None None

MEAN RADIANCE 1.806 128.437 None None None None

SDEV RADIANCE .19 40.753 None None None None

MEAN SURF RAD 0 130.893 None None None None

SDEV SURF RAD 0 41.955 None None None None

MEAN SURF REFL 0 67.9 None None None None

SDEV SURF REFL 0 25.1 None None None None

DIRECT DOWN SOLAR 214.688 1212.9 None None None None

IRRAD

DIFFUSE DOWN SOLAR 7.84 293.149 None None None None

IRRAD

ENV DOWN SOLAR IRRAD 0 20.063 None None None None

CRTFCN CODE CPI CPI None None None None

REVISION DATE 15-JAN-99 15-JAN-99 None None None None

Minimum Data Value -- The minimum value found in the column.

Maximum Data Value -- The maximum value found in the column.

Missng Data Value -- The value that indicates missing data. This is used to

indicate that an attempt was made to determine the

parameter value, but the attempt was unsuccessful.

Unrel Data Value -- The value that indicates unreliable data. This is used

to indicate an attempt was made to determine the

parameter value, but the value was deemed to be

unreliable by the analysis personnel.

Below Detect Limit -- The value that indicates parameter values below the

instruments detection limits. This is used to

indicate that an attempt was made to determine the

parameter value, but the analysis personnel determined

Page 16
Data Not Cllctd

Blank --

N/A --

None --

that the parameter value was below the detection

limit of the instrumentation.

-- This value indicates that no attempt was made to

determine the parameter value. This usually

indicates that BORIS combined several similar but

not identical data sets into the same data base table

but this particular science team did not

measure that parameter.

Indicates that blank spaces are used to denote that type of value.

Indicates that the value is not applicable to the respective column.

Indicates that no values of that sort were found in the column.

7.4 Sample Data Record

The following are wrapped versions of data record from a sample data file on the CD-ROM.

Reference File

SITE NAME, SUB SITE, DATE OBS,TIME,CI30 LINE NUM, CI30 RUN NUM, PLATFORM ALTITUDE,

C130 TRUE HEADING, RELATIVE SOLAR POSITION, SOLAR ZEN ANG, SOLAR AZ ANG,

CENTER VIEW ZEN ANG,CENTER VIEW AZ ANG,RELATIVE VIEW AZ ANG,

ASAS EXTRACTION START LINE,ASAS EXTRACTION START SAMPLE,ASAS EXTRACTION END LINE,

ASAS EXTRACTION END SAMPLE,COLUMN WATER VAPOR 6S,OZONE CONTENT 6S,

INTERP AEROSOL OPT THICK 550,EST BELOW PLATFORM WATER VAPOR,

EST BELOW PLATFORM OZONE,EST BELOW PLATFORM AOT 550,CRTFCN CODE REVISION DATE

'SSA-999-CALIB', 'RSS02-BRF01',26-MAY-94, 172628, 601,2, 6038.0,322 0, 'parallel',

36.7,142.0,45.0,143.3,181.27,199,210,294,255,14.2,340.0, .085,11 29,10.0, .081,

'CPI', 19-JAN- 99

'SSA-999-CALIB', 'RSS02-BRF01' 26-MAY-94,172655,601,2,6038 0,322 0, 'parallel',

36.7,142.1,26.0,143.9,181.806 191,204,292,266,14.2,340.0, 085,11.29,10.0, .081,

'CPI', 19-JAN- 99

'SSA-999-CALIB', 'RSS02-BRF01',26-MAY-94, 172717, 601,2, 6038 0,322.0, 'parallel',

36.7,142.3, .9,223.2,260.884 197,198,292,267,14.2,340.0, .085,11.29,10.0, .081,

'CPI', 19-JAN- 99

Data File

SITE NAME, SUB SITE, DATE OBS TIME, WAVELENGTH,ASAS CHANNEL NUM, CENTER VIEW ZEN ANG,

MEAN RADIANCE,SDEV RADIANCE MEAN SURF RAD,SDEV SURF RAD,MEAN SURF REFL,

SDEV SURF REFL,DIRECT DOWN SOLAR IRRAD,DIFFUSE DOWN SOLAR IRRAD,

ENV DOWN SOLAR IRRAD,CRTFCN CODE,REVISION DATE

'SSA-FEN-FLXTR', 'RSS02

0.0,0.0,717.179,280.86

'SSA-FEN-FLXTR', 'RSS02

0.0,0.0,805.467,279.03

'SSA-FEN-FLXTR', 'RSS02

0.0,0.0,806.568,259.51

'SSA-FEN-FLXTR', 'RSS02

0.0,0.0,815.609,237.90

-BRF01',21-JUL-94,203607, .4043,1,70.0,4.195,2.127,0.0,0.0,

3,0.0, 'CPI',I5-JAN-99

-BRF01',21-JUL-94,203607, .4137,2,70.0,8.755,1.224,0.0,0.0,

4,0.0, 'CPI',I5-JAN-99

-BRF01',21-JUL-94,203607, .4232,3,70.0,15.941,i.345,0.0,0.0,

5,0.0, 'CPI',I5-JAN-99

-BRF01',21-JUL-94,203607, .4324,4,70.0,22.857,1.212,0.0,0.0,

3,0.0, 'CPI',I5-JAN-99

Page 17
8. Data Organization

8.1 Data Granularity

The smallest unit of data tracked by the BOREAS Information System (BORIS) was the data

collected at a given site on a given date.

8.2 Data Format(s)

The Compact Disk-Read-Only Memory (CD-ROM) files contain ASCII numerical and character

fields of varying length separated by commas. The character fields are enclosed with single apostrophe

marks. There are no spaces between the fields.

Each data file on the CD-ROM has four header lines of Hyper-Text Markup Language (HTML)

code at the top. When viewed with a Web browser, this code displays header information (data set

title, location, date, acknowledgments, etc.) and a series of HTML links to associated data files and

related data sets. Line 5 of each data file is a list of the column names, and line 6 and following lines

contain the actual data.

9. Data Manipulations

9.1 Formulae

Not applicable.

9.1.1 Derivation Techniques and Algorithms

See references for 6S (Section 17.1).

9.2 Data Processing Sequence

9.2.1 Processing Steps

The processing of raw ASAS data to at-sensor radiances is explained in detail in the document for

ASAS Level lb images. Processing beyond the at-sensor radiances to produce the at-ground

reflectance tables was as follows:

• ASAS multiangle images were displayed using Interactive Data Language (IDL) software.

• From each tilt angle image, roughly the same small image area was delineatedusing IDL

software.

• View angle information and radiance statistics were extracted for the sampled polygon in each

tilt angle image.

• 6S corrected the mean at-sensor spectral radiances for atmospheric effects and directly output

table parameters.

9.2.2 Processing Changes

Not applicable.

9.3 Calculations

See 6S references (Section 17.1).

9.3.1 Special Corrections/Adjustments

See 6S references (Section 17.1).

9.3.2 Calculated Variables

Calculated (derived) variables: at-ground radiance, at-ground reflectance factor.

9.4 Graphs and Plots

Not applicable.

Page 18
10. Errors

10.1 Sources of Error

Potential sources of uncertainty associated with ASAS spectral radiance and at-ground reflectance

factors include the following: spectral radiance from the integrating hemisphere, spectral radiance from

the portable hemisphere, transfer of spectral radiance to ASAS detector elements, spectral calibration of

ASAS detector elements, and the atmospheric correction algorithm. Other factors such as polarization

sensitivity, signal cross-talk between detectors, and stray light may contribute to the uncertainty, but

these factors have not been evaluated.

10.2 Quality Assessment

10.2.1 Data Validation by Source

ASAS Level lb Image Data: During processing, frequency histograms of selected channels for

each view angle are plotted and examined manually for anomalies. Images are also displayed and

visually analyzed for target coverage, data dropouts, saturation, and other potential problems.

Derived Reflectance Factors: ASAS atmospherically corrected reflectance factors are compared to

reflectances acquired on the ground at the same sites when available; in most cases, ASAS reflectance

factors have compared well to ground observations especially for the spectral range from 490 to 860

rim.

10.2.2 Confidence Level/Accuracy Judgment

The uncertainty associated with ASAS spectral radiance values is approximately 6%. This number

is the root-sum-square of the uncertainties contributed by the following factors: spectral radiance from

the integrating hemisphere (5% uncertainty); transfer of spectral radiance to ASAS detector elements

(2% uncertainty); and spectral calibration of the ASAS detector elements (1% uncertainty). The

uncertainty associated with the radiance of the portable hemisphere has not been determined; however,

it is probably similar to that of the integrating hemisphere. Other factors such as polarization

sensitivity, signal cross-talk between detectors, and stray light may contribute to the uncertainty, but

these factors have not been evaluated. Uncertainty in the 6S atmospheric algorithm has not been

evaluated.

10.2.3 Measurement Error for Parameters

None given.

10.2.4 Additional Quality Assessments

Spectral response curves for selected training areas are plotted and examined for known

atmospheric absorption features. These plots are also compared to similar measurements made by other

instruments, if data are available.

10.2.5 Data Verification by Data Center

BORIS staff reviewed the data files submitted by the RSS-02 team for content and consistency

with the provided documentation.

Page 19
1 1. Notes

11.1 Limitations of the Data

The ASAS multiangle images have not been georegistered, and though the sampled areas are

selected carefully, they are not guaranteed to represent the exact same area in each image.

11.2 Known Problems with the Data

Image Data and Derived Products:

• ASAS data acquired over the SSA calibration target (a soil field) were atmospherically

corrected and compared to ground measurements. The results show ASAS to agree very well

with the ground observations between 490 and 870 nm. Below 490 nm and above 870 nm,

the ASAS response falls below the expected level. Extreme ASAS channels have much lower

signal to noise ratios.

• Though a specific sequence of view angles from +70 to -55 degrees was attempted for each

flightline over the flux tower sites, not all look angles were achieved every time. Often the

70-degree oft-nadir view missed the site or contained too much distortion for inclusion in the

data set. Other angles may be missing as well.

Reflectance Factor Tables:

• In general, atmospheric correction by 6S effectively removes the scattered path radiance in the

visible, and diminishes the dips caused by gaseous absorption. However, a plot of reflectance

factor vs. wavelength may show, for some data sets, that some dramatic dips and spikes still

exist in the atmospherically corrected data. These result from either overcorrection or

undercorrection due to the difficulty of estimating the effect of absorption bands of varying

widths. See Brown de Colstoun et a1.(1995) for a discussion of this issue.

11.3 Usage Guidance

At present, the reflectance factor tables originated from ASAS images which were not georectified

or geolocated. Georegistered images may be available in the future. Contact ASAS staff or check the

ASAS homepage (http://asas.gsfc.nasa.gov/) for updates on available data.

Use special caution (or avoid) working with data from channels below 490 nm or above 870 nm

(see Section 11.1).

It is strongly suggested that you plot reflectance factor vs. spectral band number or band center and

view each data set for unusual dips and spikes. Affected bands should be avoided, and/or some

smoothing algorithm should be applied to the data before use.

11.4 Other Relevant Information

None.

None given.

12. Application of the Data Set

None given.

13. Future Modifications and Plans

14. Software

Page 20
14.1 Software Description

The IDL data analysis and visualization software package was used.

14.2 Software Access

IDL is available from:

Research Systems, Inc.

2995 Wilderness Place

Boulder, CO 80301

(303) 786-9900

http://www.rsinc.com/

15. Data Access

The reflectance factor data are available from the Earth Observing System Data and Information System

(EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

15.1 Contact Information

For BOREAS data and documentation please contact:

ORNL DAAC User Services

Oak Ridge National Laboratory

P.O. Box 2008 MS-6407

Oak Ridge, TN 37831-6407

Phone: (423) 241-3952

Fax: (423) 574-4665

E-mail: ornldaac@ornl.gov or ornl@eos.nasa.gov

15.2 Data Center Identification

Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory

(ORNL) Distributed Active Archive Center (DAAC) for Biogeochemical Dynamics

http://www-eosdis.ornl.gov/.

15.3 Procedures for Obtaining Data

Users may obtain data directly through the ORNL DAAC online search and order system

[http://www-eosdis.ornl.gov/] and the anonymous FTP site [ftp://www-eosdis.ornl.gov/data/] or by

contacting User Services by electronic mail, telephone, fax, letter, or personal visit using the contact

information in Section 15.1.

15.4 Data Center Status/Plans

The ORNL DAAC is the primary source for BOREAS field measurement, image, GIS, and

hardcopy data products. The BOREAS CD-ROM and data referenced or listed in inventories on the

CD-ROM are available from the ORNL DAAC.

16.1 Tape Products

None.

16. Output Products and Availability

Page 21
16.2 Film Products

None.

16.3 Other Products

These data are available on the BOREAS CD-ROM series.

17. References

17.1 Platform/Sensor/Instrument/Data Processing Documentation

Kovalick, W. and D. Graham. 1991. ASAS Programmer's Manual. Hughes STX, Code 923, NASA

GSFC, Greenbelt, MD (in-house document).

Tanre, D., J.L. Deuze, M. Herman, R. Santer, and E. Vermote. 1990. Second simulation of the

satellite signal in the solar spectrum - 6S code [abs]. In Proceedings of the 10th Annual Geoscience

and Remote Sensing Symposium, vol. I, p. 187, IEEE Int. Geosci. and Remote Sens., New York.

Vermote, E.F., D. Tanre, J.L. Deuze, M. Herman, and J.J. Morcrette. 1997. Second simulation of

the satellite signal in the solar spectrum: an overview. IEE Trans. Geosci. Remote Sens.

The 6S User Guide and code can be obtained via anonymous ftp on kratmos.gsfc.nasa.gov.

Information on ASAS data and the ASAS sensor can be obtained on the world-wide web at:

http://asas.gsfc.nasa.gov/

17.2 Journal Articles and Study Reports

Many of the following articles describe data from the first-generation CID array (prior to 1991).

Radiometric resolution factors and spectral band centers differ among the various ASAS data sets. A

more complete bibliography can be found in the documentation for ASAS Level lb images.

Abuelgasim, A.A. and A. Strahler. 1994. Modeling bidirectional radiance measurements collected by

the Advanced Solid-state Array Spectroradiometer (ASAS) over Oregon Transect conifer forests.

Remote Sens. Environ. 47:261-275.

Brown de Colstoun, E.C., C.L. Walthall, C.A. Russell, and J.R. Irons. 1995. Estimating the fraction

of absorbed photosynthetically active radiation (fAPAR) at FIFE with airborne bidirectional spectral

reflectance data. Journal of Geophysical Research, Vol. 100:25,523-25,535.

Deering, D.W., E.M. Middleton, J.R. Irons, B.L. Blad, E.A. Walter-Shea, C.J. Hays, C.L.

Walthall, T.F. Eck, S.P. Ahmad, and B.P. Banerjee. 1992. Prairie grassland bidirectional reflectances

measured by different instruments at the FIFE site. Journal of Geophysical Research

97:18,887-18,903.

Guinness, E.A., R.A. Arvidson, J.R. Irons, and D.J. Harding. 1991. Surface scattering properties

estimated from modeling airborne multiple emission angle reflectance data. Geophys. Res. Letters

18(11):2051-2054.

Hall, D.K., J.L. Foster, J.R. Irons, and P.W. Dabney. 1993. Airborne bidirectional radiances of

snow covered surfaces in Montana, USA. Annals of Glaciology 17:35-40.

Irons, J.R., K.J. Ranson, D.L. Williams, R.R. Irish, and F.G. Huegel. 1991. An off-nadir pointing

imaging spectroradiometer for terrestrial ecosystem studies. IEEE Trans. on Geoscience and Remote

Sensing 29(1):66-74.

Page 22
Johnson,L.F. 1994.Multiple view zenithangleobservationsof reflectancefrom ponderosapine

stands.Int. J.RemoteSens.15:3859-3865.

Lawrence,W.T., D.L. Williams, K.J. Ranson,J.R.Irons,andC.L. Walthall. 1994.Comparative

analysisof dataacquiredbythreenarrow-bandairbornespectroradiometersoversubborealvegetation.

RemoteSens.Environ.47:204-215.

Newcomer,J.,D. Landis,S.Conrad,S.Curd,K. Huemmrich,D. Knapp,A. Morrell, J.Nickeson,

A. Papagno,D. Rinker,R.Strub,T. Twine,F. Hall, andP.Sellers,eds.2000.CollectedDataof The

BorealEcosystem-AtmosphereStudy.NASA. CD-ROM.

Ranson,K.J., J.R.Irons,andD.L. Williams. 1994.Multispectralbidirectionalreflectanceof northern

forestcanopieswith theAdvancedSolid-stateArray Spectroradiometer(ASAS).RemoteSens.Env.

47:276-289.

Russell,C.A., C.L. Walthall, J.R.Irons, andE.C.Brown deColstoun.1995.Comparisonof

airborneandsurfacespectralbidirectionalreflectancefactors,spectralhemisphericalreflectanceand

spectralvegetationindices.Journalof GeophysicalResearch,Vol. 100:25,509-25,522.

Russell,C.A.,J.R.Irons,andP.W.Dabney.1997.Bidirectionalreflectanceof selectedBOREAS

sitesfrom multiangleairbornedata.Journalof GeophysicalResearch102(D24):29,505-29,516.

Schaaf,C..B. andA.H. Strahler.1994.Validationof bidirectionalandhemisphericalreflectances

from ageometric-opticalmodelusingASASimageryandpyranometermeasurementsof aspruce

forest.RemoteSens.Env.49:138-144.

Sellers,P.andF.Hall. 1994.BorealEcosystem-AtmosphereStudy:ExperimentPlan.Version

1994-3.0,NASA BOREASReport(EXPLAN 94).

Sellers,P.andF.Hall. 1996.BorealEcosystem-AtmosphereStudy:ExperimentPlan.Version

1996-2.0,NASA BOREASReport(EXPLAN 96).

Sellers,P.,F. Hall, andK.F. Huemmrich.1996.BorealEcosystem-AtmosphereStudy:1994

Operations.NASA BOREASReport(OPSDOC94).

Sellers,P.,F. Hall, andK.F. Huemmrich.1997.BorealEcosystem-AtmosphereStudy:1996

Operations.NASA BOREASReport(OPSDOC96).

Sellers,P.,F. Hall, H. Margolis,B. Kelly, D. Baldocchi,G. denHartog,J.Cihlar, M.G. Ryan,B.

Goodison,P.Crill, K.J.Ranson,D. Lettenmaier,andD.E. Wickland. 1995.Theboreal

ecosystem-atmospherestudy(BOREAS):anoverviewandearlyresultsfrom the1994field year.

Bulletinof theAmericanMeteorologicalSociety.76(9):1549-1577.

Sellers,P.J.,F.G.Hall, R.D.Kelly, A. Black, D. Baldocchi,J. Berry, M. Ryan,K.J. Ranson,P.M.

Crill, D.P.Lettenmaier,H. Margolis,J.Cihlar, J.Newcomer,D. Fitzjarrald,P.G.Jarvis,S.T.

Gower,D. Halliwell, D. Williams, B. Goodison,D.E.Wickland, andF.E.Guertin.1997.BOREAS

in 1997:ExperimentOverview,ScientificResultsandFutureDirections.Journalof Geophysical

Research102(D24):28,731-28,770.

CD-ROM Collections with ASAS Data

Angelici, G.L., J.W. Skiles, and L.Z. Popovici. 1992. OTTER: Oregon Transect Ecosystem Research

Project. Collected Data, Volume 1, Version 1, Satellite, aircraft and ground measurements, CD-ROM

USA_NASA_PLDS_OT_0001, NASA ARC.

Page 23
Arvidson, R.E.,M.A. Dale-Bannister,E.A. Guinness,S.H.Slavney,andT.C. Stein. 1991.Archive

of GeologicRemoteSensingFieldExperiment,Data-Release1.0.CD-ROMVolume

USA_NASA_PDS_GR_001,NASA PlanetaryDataSystem,JPL,Pasadena,CA.

Strebel,D.E.,D.R. Landis,J.A. Newcomer,B.W. Meeson,P.A. Agbu, andJ.M.P. McManus.

1992.CollectedDataof theFirstISLSCPFieldExperiment,Volume4:ASAS& PBMRImagery

1987& 1989.CD-ROM USA_NASA_PLDS_FIFE_0004, NASA/GSFC.ASASreflectancefactor

tablesfor selectedsitescanbefoundin Volume1:SurfaceObservationsandNon-ImageDataSets

(underGrabBagcategory).

17.3 Arehive/DBMS Usage Documentation

None.

None.

18. Glossary of Terms

6S

AGL

ARC

ASAS

ASCII

AVIRIS

BOREAS

BORIS

BRDF

CCD

CD-ROM

CID

DAAC

EOS

EOSDIS

FFC-T

FOV

FWHM

GIS

GMT

GSFC

HDR

IDL

IFC

IFOV

JSC

MISR

NAD83

NASA

NIST

NSA

OA

OBS

19. List of Acronyms

- Second Simulation of the Satellite Signal in the Solar

- Above Ground Level

- Ames Research Center

- Advanced Solid-state Array Spectroradiometer

- American Standard Code for Information Interchange

- Airborne Visible InfraRed Imaging Spectrometer

- BOReal Ecosystem-Atmosphere Study

- BOReas Information System

- Bidirectional Reflectance Distribution Function

- Charge-Coupled Device

- Compact Disk - Read-Only Memory

- Charge-Injection Device

- Distributed Active Archive Center

- Earth Observing System

- EOS Data and Information System

- Focused Field Campaign - Thaw

- Field of View

- Full-Width Half-Maximum

- Geographic Information System

- Greenwich Mean Time

- Goddard Space Flight Center

- Header

- Interactive Data Language

- Intensive Field Campaign

- Instantaneous Field of View

- Johnson Space Center

- Multi-Angle Imaging Spectro-Radiometer

- North American Datum of 1983

- National Aeronautics and Space Administration

- National Institute of Standards and Technology

- Northern Study Area

- Old Aspen

- Old Black Spruce

Spectrum

Page 24
OJP

ORNL

PANP

RSS

SIS

SPP

SSA

URL

WFF

YJP

- Old Jack Pine

- Oak Ridge National Laboratory

- Prince Albert National Park

- Remote Sensing Science

- Scanning Imaging Spectroradiometer

- Solar Principal Plane

- Southern Study Area

- Uniform Resource Locator

- Wallops Flight Facility

- Young Jack Pine

20. Document Information

20.1 Document Revision Date

Created: 30-Jun- 1997

Revised: 15-Sep- 1999

20.2 Document Review Date(s)

BORIS Review: 14-Jan-1998

Science Review: 25-Feb- 1998

20.3 Document ID

20.4 Citation

When using these data, please include the following acknowledgment as well as citations of

relevant papers in Section 17.2:

The ASAS data were provided by James R. Irons and Philip W. Dabney (NASA Goddard Space

Flight Center)

If using data from the BOREAS CD-ROM series, also reference the data as:

Irons, J.R., "Boreal Forest Bidirectional Reflectances Acquired by an Airborne Multispectral,

Multiangle Imaging Spectroradiometer." In Collected Data of The Boreal Ecosystem-Atmosphere

Study. Eds. J. Newcomer, D. Landis, S. Conrad, S. Curd, K. Huemmrich, D. Knapp, A. Morrell, J.

Nickeson, A. Papagno, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers. CD-ROM. NASA,

2000.

Also, cite the BOREAS CD-ROM set as:

Newcomer, J., D. Landis, S. Conrad, S. Curd, K. Huemmrich, D. Knapp, A. Morrell, J.

Nickeson, A. Papagno, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers, eds. Collected Data of

The Boreal Ecosystem-Atmosphere Study. NASA. CD-ROM. NASA, 2000.

20.5 Document Curator

20.6 Document URL

Page 25
REPORT DOCUMENTATION PAGE FormApproved

OMB No. 0704-0188

Public reporting burden for this collection of informationis estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

July 2000 Technical Memorandum

4. TITLE AND SUBTITLE

Technical Report Series on the Boreal Ecosystem-Atmosphere Study (BOREAS)

BOREAS RSS-2 Estracted Reflectance Factors Derived from ASAS Imagery

6. AUTHOR(S)

C. Russell, P. Dabney, W. Kovalick, D. Graham, M. Bur, J. Irons

and M. Tierney

Forrest G. Hall and Jaime Nickeson_ Editors

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS (ES)

Goddard Space Flight Center

Greenbelt, Maryland 20771

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS (ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

5. FUNDING NUMBERS

923

RTOP: 923-462-33-01

8. PEFORMING ORGANIZATION

REPORT NUMBER

2000-03136-0

10. SPONSORING / MONITORING

AGENCY REPORT NUMBER

TM--2000-209891

Vol. 44

11. SUPPLEMENTARY NOTES

C. Russell: SSAI; W. Kovalick, D. Graham, M. Bur, and J. Nickeson: Raytheon ITSS

12a. DISTRIBUTION / AVAILABILITY STATEMENT

Unclassifie_Unlimited

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Report available from the NASA Center for AeroSpace Information,

7121 Standard Drive, Hanover, MD 21076-1320. (301) 621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The BOREAS RSS-2 team derived atmospherically corrected bidirectional reflectance factor means

from multispectral, multiangle ASAS imagery for small homogeneous areas near several BOREAS

sites. The ASAS imagery was acquired from the C-130 aircraft platform in 1994 and 1996. The data

are stored in tabular ASCII files.

14. SUBJECT TERMS

BOREAS, remote sensing science, ASAS imagery.

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