# Introduction  {#introduction .aHeading1}

The Office of Earth Science (OES) of the National Aeronautics and Space
Administration (NASA), the National Oceanic and Atmospheric
Administration's (NOAA) National Environmental Satellite, Data, and
Information Service (NESDIS) Integrated Program Office (IPO), have
agreed to jointly implement a mission called the NPOESS Preparatory
Project (NPP). NPP has the objectives listed below.

1.  Demonstrate and validate:

    a.  A global imaging radiometer and a suite of two sounding
        instruments, associated algorithms, and data processing

    b.  An ozone mapping and profiling instrument, associated
        algorithms, and data processing

    c.  A NPP Command, Control and Communications Segment (C3S), an
        Interface Data Processing Segment (IDPS), an Archive and
        Distribution Segment (ADS), and a Science Data Segment (SDS).

2.  Provide continuity of systematic, global, calibrated, validated and
    geo-located Earth science imaging radiometry, sounding observations,
    and ozone mapping and profiling observations for NASA Earth Science
    research.

This document specifies the requirements and concept of operations for
the NPP Ocean PEATE (Product Evaluation and Test Element) that will be
managed and developed by NASA. As defined in NASA's NPP Level 1
Requirements (see Appendix 1), the role of the SDS is principally
directed to assessment and verification of NPP product quality, where
those products are identified as Raw Data Records, Sensor Data Records,
and Environmental Data Records (RDRs, SDRs, and EDRs, respectively). For
the Ocean products, these will be generated exclusively using data from
the Visible and Infrared Imager/Radiometer suite (VIIRS). In executing
its responsibilities for assessment and verification, the SDS functions
will be performed principally by a distributed and interoperable
architecture of Climate Analysis Research Systems (CARS).

-   Acquire RDRs, SDRs, and Ocean EDRs from the SDS

-   Assess the quality of the NPP Ocean EDRs for accomplishing NASA's
    climate research requirements

-   Provide suggested algorithm improvements to the IDPS via the Project
    Science Working Group (PSWG)

-   Process selected data subsets in support of Evaluation and
    Validation activities

-   Support field programs and other research activities of the Ocean
    Science Community.

# Interfaces  {#interfaces .aHeading1}

The NPP Ocean PEATE will support interfaces with the following
facilities and organizations:

1.  SDS Data Delivery Depository (SD3) Component

The Ocean PEATE will acquire VIIRS RDRs, SDRs and Ocean EDRs from the
SD3. Prior to the NPP launch, these will be either simulated data sets
for algorithm testing, or test data sets from instrument or spacecraft
tests. Following launch, these will be data routinely transmitted from
the IDPS. All RDRs will be acquired as they are made available at the
SDS interface, while selected SDRs and EDRs will be acquired on request.

2.  SDS Integration and Test System (I&TS)

The Ocean PEATE will interact with the I&TS for processing code
deliveries and updates. The I&TS will provide the latest version of the
operational SDR and Ocean EDR processing code to the Ocean PEATE. The
PEATE will provide proposed code and algorithm updates to the I&TS.

3.  NASA NPP Characterization Support Team (NCST)

The Ocean PEATE will interact with the NCST in support of VIIRS
calibration. The NCST will provide calibration LUTS for evaluation,
which may utilize more recent calibration measurements than the
operational LUTS provided by the IDPS. The Ocean PEATE will provide the
results of calibration evaluations to the NCST.

4.  NASA VIIRS Ocean Science Team (NVOST)

The Ocean PEATE will be co-located with the NVOST leader and will be the
primary facility for analyses and evaluations performed by the NVOST.
The NVOST will provide deliveries of science code, proposed algorithm
improvements and evaluation processing requests to the PEATE, and will
serve as the primary liason between the NASA Ocean researcher community
and the Ocean PEATE. The PEATE will provide operational processing code,
standard SDRs and EDRs acquired from SD3, and SDRs and EDRs generated
from evaluation processing, to the NVOST.

5.  Ancillary Data Providers

### The Ocean PEATE will acquire ancillary data products needed for EDR processing from various providers. The current ancillary data sets consist of TOMS and TOVS ozone data and NCEP meteorological data (wind speed, atmospheric pressure and humidity). The sources and providers of ozone and meteorological data will be reviewed and revised as needed. {#the-ocean-peate-will-acquire-ancillary-data-products-needed-for-edr-processing-from-various-providers.-the-current-ancillary-data-sets-consist-of-toms-and-tovs-ozone-data-and-ncep-meteorological-data-wind-speed-atmospheric-pressure-and-humidity.-the-sources-and-providers-of-ozone-and-meteorological-data-will-be-reviewed-and-revised-as-needed. .unnumbered}

# Requirements  {#requirements .aHeading1}

The NPP Ocean PEATE will meet the following requirements.

1.  Acquire RDRs, SDRs, and Ocean EDRs from the SDS

The Ocean PEATE will require access to the Visible and Infrared
Imager/Radiometer suite (VIIRS) RDRs, SDRs, and Ocean EDRs. The Ocean
EDRs are Ocean Color (40.7.6) and Sea Surface Temperature (SST) 40.2.4).
(The SST requirements are TBD pending a decision by NASA Headquarters.)

The Ocean PEATE will ingest the full stream of VIIRS RDRs as they are
made available at the SDS interface.

The Ocean PEATE will ingest selected subsets of the SDRs and EDRs as
specified by the NVOST, for assessment and validation.

The Ocean PEATE will provide storage for VIIRS RDS, SDRs and EDRs as
follows:

-   One full-mission set of RDRs

-   Approximately 10% of SDRS

-   Two full-mission sets of Ocean EDRs.

-   All prelaunch test data sets.

    1.  Assess the quality of the NPP Ocean EDRs for accomplishing
        NASA's climate research needs.

The Ocean PEATE will support the NVOST in performing the following
assessments of the Ocean EDRs:

-   Ground truth validation using match-ups with in situ radiometry and
    chlorophyll data sets

-   Cross-comparisons with concurrent satellite data sets (e.g., MODIS
    Aqua) (if possible)

-   Comparisons with the climatological data sets from past missions
    (e.g., SeaWiFS)

-   Assessments of internal consistency (e.g., analysis of interannual
    repeatability in clear-water and deep-water regions; assessments of
    short-term stability).

-   Assessments of the effectiveness of flagging and masking algorithms
    (e.g., clouds, glint, stray light, zenith angle limits, turbidity).

-   Prelaunch assessment of algorithm functionality and implementation
    using simulated TOA radiances in the SDR format.

In order to fully evaluate the quality of the EDRs, the Ocean PEATE will
also support the NVOST in performing the following assessment of the
SDRs:

-   Assessment of the long-term radiometric stability of the VIIRS Ocean
    bands

-   Assessments of the instrumental corrections (e.g., temperature, RVS,
    polarization.)

-   Analysis of prelaunch test results and instrument characterization
    data sets.

    1.  Provide suggested algorithm improvements to the IDPS via the
        PSWG.

The Ocean PEATE will provide algorithm and software updates to the SDS
I&TS, when algorithm improvements are recommended by the NVOST for the
Ocean EDRs.

2.  Process selected data subsets in support of Evaluation, Validation
    and Algorithm improvement activities

The Ocean PEATE will provide the capability to process any desired set
of VIIRS data, up to and including the full mission data set, from RDRs
to Ocean EDRs. This is required in order to support the NVOST in
developing and assessing algorithm improvements for the Ocean EDRs.

The Ocean PEATE will acquire the operational SDR and Ocean EDR
processing software from the SDS I&TS.

The Ocean PEATE will provide the capability to process RDRs to SDRs
using the operational software. This will include the capability to
accept alternative LUTs, either provided by the NCST or generated
locally by the NVOST.

The Ocean PEATE will provide the capability to process SDRs to Ocean
EDRs using the operational Ocean algorithms, software and LUTS.

The Ocean PEATE will provide the capability to process SDRs to Ocean
EDRs using the operational Ocean algorithms and software, and
alternative LUTS generated locally by the NVOST. These may include, for
example, vicarious gains, flag thresholds, optical properties, or
aerosol models.

The Ocean PEATE will provide the capability to process SDRs to Ocean
EDRs using alternative algorithms, software and LUTS provided by the
NVOST, to evaluate potential algorithm improvements and additional
products.

The Ocean PEATE will support cataloging, searching, ordering and
distributing of all internally processed data products.

3.  Support field programs and other research activities of the Ocean
    Science Community. (Note: this activity will make use of NPP/VIIRS
    data but is not an NPP requirement nor is the funding requested from
    the NPP Project for this activity.)

The Ocean CARS will support the field programs of the Ocean Science
Community by providing satellite overpass predictions and near real time
image support.

The Ocean CARS will provide access to local data archives by the Ocean
Science Community to support the assessment of alternative algorithms
and non-standard data products.

# Operations Concept {#operations-concept .aHeading1}

The Ocean PEATE operations concept is built on the highly successful
Ocean Discipline Processing System (ODPS), originally developed for
SeaWiFS and enhanced for MODIS. Although operational processing of
standard data products is not a PEATE function, the requirements given
in Section 3 map perfectly into the ODPS approach. The basic elements of
this are:

-   An integrated, cohesive team supporting all activities, including
    systems, software, data processing, calibration, validation, and
    distribution;

-   Substantial reprocessing capacity, to support rapid, multiple
    evaluations of potential algorithm improvements;

-   Rapid turnaround on critical test data sets, during prelaunch
    testing, initial on-orbit checkout and commissioning, and
    significant operational changes;

-   Management of a local archive of in situ ocean data for vicarious
    calibration and validation, in the SeaWiFS Biological Archive and
    Storage System (SeaBASS);

-   Maintenance and development of a highly capable data analysis and
    display package, the SeaWiFS Data Analysis System (SeaDAS), utilized
    for in-house analysis and freely available to the public; and

-   Close cooperation with the scientific community in algorithm and
    product evaluation and in situ data collection.

The following sections summarize the activities to be performed in
support of VIIRS EDR assessment at the Ocean PEATE, followed by a
summary of facilities to be provided.

4.1 VIIRS Ocean EDR Assessment

Assessment of a satellite-based ocean color sensor, such as VIIRS,
should be both global and regional in scope. It commences well before
launch, with the analysis of instrument test data sets and the
verification of algorithms, software and procedures using simulated
data. It must be a continuing process throughout the life of a satellite
mission, particularly if the data products are to be used in a
long-term, multi-sensor time series. For VIIRS, continuous validation is
necessary for the assessment of the accuracy of the calibration across
platforms.

1.  VIIRS Data Acquisition and Management

The complete set of VIIRS RDRs will be acquired as made available from
the SD3. The timeliness of these data is critical for support of
prelaunch test data evaluation, initial postlaunch instrument checkout,
and field programs (see below). Selected SDRs and EDRs will be acquired
as needed for calibration and data product assessment. The fraction of
data to be acquired is still TBD. The facilities for storing and
managing the acquired data are described in Section 4.2.

2.  Prelaunch and Early Mission Testing and Verification

The Ocean PEATE will support several critical activities during the
prelaunch phase of NPP. These include: verification of the science
algorithm and operational processing code; evaluation of test versions
of the EDRs, produced by the IDPS from simulated data and transmitted to
the SD3; and quick-response processing of instrument test data sets, as
soon as they are acquired from the SD3.

The processing code will be acquired and installed in the ODPS to
support verification and testing. The initial versions are expected to
be the science algorithm code, which will be obtained by the NVOST and
provided to the PEATE. As operational software becomes available on the
I&TS, it will be acquired directly by the PEATE. The prelaunch versions
of the software will be tested and verified using simulated data sets,
either SDRs or RDRs. In order to fully exercise the logic of the Ocean
EDR algorithms, high-fidelity simulated data with realistic radiances
over water and clouds and geographically correct land pixels will be
required.

These same data sets, along with sample EDRs produced by IDPS, will also
be used to test the EDR evaluation procedures to be used during the
mission. The types of evaluations to be performed are described in other
sections, below.

Finally, these capabilities in the PEATE will be used to acquire and
process the prelaunch instrument test data sets for analysis by the
NVOST. The test data sets will be acquired from the SD3 as they become
available, immediately processed as needed (i.e., RDR to SDR) and made
available to the NVOST. This quick turnaround will be absolutely
critical during instrument testing, to allow feedback from the NVOST to
the VIIRS test team while the tests are still in progress. By analyzing
test results during the actual testing, the NVOST will determine whether
tests need to be rerun, either in original or modified form, to achieve
the required instrument characterization result.

4.1.3 Evaluation Processing

To evaluate the efficacy of changes to the VIIRS SDR processing and the
cross-calibration with MODIS/Aqua, we will develop the capability to
process VIIRS RDRs, in the ODPS to produce level-2 water-leaving
radiance and chlorophyll EDRs. We will use this capability to process
limited amounts of VIIRS data for in situ validation, and larger amounts
of VIIRS data for global, long time-series analyses. This will enable
evaluation of multiple versions of the VIIRS mission data, similar to
that which was performed for all SeaWiFS and MODIS reprocessings..

4.1.4 Global and Regional Comparative Time Series Analyses

We will perform global and regional comparative time-series analysis
between VIIRS and MODIS/Aqua standard, archived level-3 products, and
repeat the entire analysis following any VIIRS reprocessings. For
periods beyond the life of the Aqua mission, we will perform clear-water
and deep-water mission trend analyses. This work will establish the
interannual consistency of the VIIRS radiometry.

4.1.5 In situ Matchup Comparison

The ODPS has already developed an automated system for validation of
MODIS, SeaWiFS, and other sensors against the SeaBASS in situ radiance,
chlorophyll and aerosol optical thickness (AOT) holdings. We will
perform the in situ validation of the standard VIIRS Ocean EDRs,
extending the analysis as additional VIIRS data or in situ data becomes
available, and regenerating the match-up comparison following any VIIRS
reprocessing. The methodology for performing the validation of VIIRS is
consistent with that which we have developed and successfully applied to
SeaWiFS and MODIS. Using a consistent methodology across missions and
platforms will aid in developing a consistent long-term, multimission,
ocean color data set.

4.1.6 Scientific Community Involvement

The SeaWiFS and SIMBIOS Projects maintained an outstanding record of
involvement by the scientific community. From the first major SeaWiFS
Project review in 1992, through the fourth reprocessing (Feldman and
Patt, 2003), all SeaWiFS activity was conducted so as to maximize
opportunities for scientific input, evaluation, and commentary by the
community. This has included continual posting of the latest Project
plans, analysis results, and evaluation products on the Web, and holding
workshops to facilitate the exchange of ideas. The SIMBIOS Project
maintained this philosophy from its inception in 1996 through 2003, with
regular team meetings and wide dissemination of data and results. This
approach was initiated for the MODIS Ocean team in 2004 with the
selection of the new MODIS Science team.

We propose to follow this approach for our VIIRS Ocean calibration and
validation activity. We will hold workshops at NASA GSFC, which will be
open to all interested members of the community. These will follow the
same general format as previously used for the SeaWiFS workshops and the
SIMBIOS and MODIS team meetings.

We will maintain a public Web site for all of our VIIRS activities. This
will include results and proceedings of the workshops; descriptions of
proposed algorithm changes and calibration methodologies; results of
data analyses, processing tests and product evaluations; and sample
products for outside evaluation.

4.1.7 Near Real-Time Field Support

For calibration and validation purposes, in situ measurements should be
made as close as possible to the sensor overflight time. The SIMBIOS
Project offered overflight prediction services for MODIS (Terra and
Aqua), as well as SeaWiFS and other sensors. We will continue this
service and implement the capability to provide near real-time images
from VIIRS level-1 and level-2 data, as is currently being done with
SeaWiFS and MODIS data. These images provide useful information in
oceanographic cruise planning, both prior to and during cruises. The
ability to perform near-real-time image support with VIIRS will be
limited by the turn-around time between observation and availability of
the VIIRS RDRs.

4.1.8 SeaBASS Maintainance

Validation of remotely-sensed ocean color data is essential for
determining how well the satellite-derived values reflect true
conditions. This is best achieved through a comparison of coincidentally
measured satellite and in situ observations, collected under the widest
possible range of conditions. A comprehensive, spatially and temporally
diverse in situ data set with measurements covering a wide range of
oceanographic conditions is essential for such an effort. The SeaBASS
database developed by the SeaWiFS and SIMBIOS Projects was designed with
this goal in mind (Hooker et al., 1994; Werdell and Bailey, 2002). The
in situ data archived in SeaBASS and used for validation purposes were
collected using a consistent protocols (Mueller et al., 2002) and
processed using a well-defined quality control procedures, as
recommended by Hooker et al. (2001). We will continue the maintenance of
the SeaBASS archive, soliciting voluntary contributions from the ocean
color community at large to ensure the widest possible geographic and
oceanographic coverage.

4.1.9 SeaDAS VIIRS Processing

We will integrate, within the current SeaDAS infrastructure, the
capability to process VIIRS data to EDRs. There has been a need in the
user community to be able to process data for the purposes of algorithm
testing, regional and high latitude processing. Integrating VIIRS
processing into SeaDAS would fill this need, without requiring a massive
investment in systems and resources. It would also allow the users the
flexibility to download RDR files, which can then be processed to any
level, and reprocessed as soon as new calibration or software updates
become available. As the MODIS/Aqua mission nears the end of its
lifespan, researchers will have to make the transition to working with
VIIRS data. Most of these users are already using SeaDAS and IDL, so the
integration of VIIRS processing into SeaDAS would make this transition
much easier for the ocean color community. Furthermore, both existing
and new ocean color researches will benefit from the continuation of the
well-established user support provided by the SeaDAS group.

4.2 Systems and Facilities

The systems and facilities of Code 970.2 Ocean Color Group provide the
optimal environment to perform the assessment of NPP VIIRS Ocean data.
By using an existing infrastructure developed specifically for this type
of work, NASA will receive the maximum benefit for a minimum of cost.
The group has significant network, processing, storage and software
resources, in addition to its demonstrated expertise in characterizing a
wide range of ocean color instruments. Using MODIS and SeaBASS data as a
reference to validate the VIIRS data will require access to a large
amount of data on a regular basis. Adding functionality to SeaDAS to
support VIIRS data requires direct access to the developers and
maintainers of SeaDAS. The facility is co-located with the ODPS, the
SeaBASS archive, and the SeaDAS development team. In addition to access
to data and staff, the group has access to the ODPS computing resources.
The ODPS is a high-capacity, production-proven system that has been
providing high-quality science products to the ocean color community
daily for nearly 7 years. Data, software, and processing capabilities
from that effort will be applied to a VIIRS EDR assessment effort.

4.2.1 Data Acquisition and Distribution

The systems are currently sized to acquire/process/archive and
distribute SeaWiFS and MODIS data (Terra and Aqua) on a daily basis
through both access the the near real-time data flow via the EDOS/NOAA
bent pipe data feed and a data subscription with the Goddard DAAC. The
data is sent to our dedicated file server via Goddard\'s high
performance Science and Engineering Network (SEN). Data travels from
Building 32 to Building 28 over the campus ATM backbone at 622 megabits
per second, giving ample throughput to acquire the large data sets
generated by MODIS. The file server receives data through its gigabit
Ethernet interface, preventing bottlenecks at the destination. The
connection to the SEN provides access to Internet2, a 2 gigabit per
second network that can be used for collaboration and data transfer to
other Internet2-connected sites. Available bandwidth for MODIS data
transfers is maximized by routing all other network activity through the
GSFC CNE network. The facility\'s servers are connected locally via a
private gigabit Ethernet network, minimizing file transfer time within
the project. Analyst workstations communicate via Fast Ethernet.
Mechanisms for sharing data with the scientific community are already in
place, requiring no additional expenditures or set-up time. The facility
includes dedicated web, FTP, and mail servers. The long-established
\"ocean-color\" mailing list is hosted there and has become a
significant source for distributing ocean color information to
researchers around the world.

4.2.2 Development

Software development for calibration and validation in a production
environment requires a wide range of tools to be successful and easily
maintained. The facility already has a rich programming environment in
place, supporting development on IRIX, Linux, and Solaris. The
environment includes all the necessary compilers, libraries, debuggers,
and version control software. Additional development tools include IDL,
Purify, GUI builders such as UIM/X and BX Pro, and SGI\'s ProDev
development package including CaseVision and WorkShop. Maintenance
contracts are in place for the commercial packages. Our group has the
infrastructure, knowledge, and experience to support code development
for VIIRS calibration and validation activities. Furthermore, the
modular design of the ODPS system allows developers to easily add steps
to the processing mix without affecting the control functions of the
system.

4.2.3 Physical Facilities

The GSFC code 970.2 team has a well-supported facility located in
Building 28 of Goddard\'s Greenbelt campus. The servers reside in a 900
square foot raised floor computer area. All the critical infrastructure
required to operate a large computer facility is already in place. The
room is supported by dual air conditioning systems, and has 54 KVA of
UPS power to keep the servers operational 24x7. Environmental monitoring
is active 24x7 as well. All hardware and software maintenance contracts
are in place and kept up to date. Data security is maintained via
automated backups to the backup server. The network equipment, critical
to a distributed system design, is fully functional. The facility has a
NASA-compliant IT security infrastructure, ensuring the safety of the
data and the Project\'s computing resources. The systems are supported
by staff located on site.