VIIRS Product Evaluation at the Ocean PEATE

Frederick S. PattGene C. Feldman

IGARSS 2010

July 27, 2010

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Introduction

• The NPP Mission will support the continuation of climate records generated from NASA sensors and missions.

• The VIIRS instrument will generate (among with many other products) the Ocean Color and Chlorophyll (OCC) and Sea Surface Temperature (SST) Environmental Data Records (EDRs).

• The NASA Science Teams will perform evaluation of the NPP data products generated by the Interface Data Processing Segment (IDPS) and recommend improvements to the algorithms.

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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SDS and the PEATEs

• The NASA Science Data Segment (SDS) is a distributed facility that will support the product evaluation activities of the Science Teams.

• The Product Evaluation and Analysis Tool Elements (PEATEs) support data acquisition and archive, data processing, tool development and algorithm testing for the Science Teams.

• The Ocean PEATE is supported within the Ocean Biology Processing Group (OBPG) at NASA Goddard Space Flight Center (GSFC), using the existing Ocean Data Processing System (ODPS).

Product Evaluation Strategies

• Comparisons between the VIIRS Ocean EDRs and current OBPG products will be performed in stages, in order to isolate the causes of differences.

• The primary source of “truth” products will be the MODIS instrument on the Aqua satellite.

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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VIIRS EDR Evaluation – Step 1

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VIIRS EDRVIIRS EDR MODISLevel-2MODISLevel-2

COMPARE

If SAME = OK

L1B (SDR) or Level-2 (EDR) Processing ProblemL1B (SDR) or Level-2 (EDR) Processing Problem

If Different

VIIRS EDR Evaluation – Step 2

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VIIRS EDRVIIRS EDR MODISLevel-2MODISLevel-2

Bin to Global Grid

VIIRS Level-3VIIRS Level-3 MODIS Level-3MODIS Level-3

COMPARE

If SAME = OK

If Different

L1B (SDR) or Level-2 (EDR) Processing ProblemL1B (SDR) or Level-2 (EDR) Processing Problem

VIIRS EDR Evaluation – Step 3

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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VIIRS SDRVIIRS SDR MODISLevel-1bMODISLevel-1b

L2Gen

VIIRS L1B (SDR) Processing ProblemVIIRS L1B (SDR) Processing Problem

VIIRS Level-2VIIRS Level-2 MODIS Level-2MODIS Level-2

COMPARE

If SAME = If Different

EDR Processing ProblemEDR Processing Problem

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Evaluation Vs. Product Level

• Level-1 (SDR) Evaluations– Onboard calibration analyses– Vicarious calibration

• Level-2 (EDR) Evaluations– Matchup analyses– Residual detector (striping) and scan (RVS) dependence

• Level-3 Product Evaluations– Sensor cross-comparisons– Algorithm comparisons– Temporal anomaly evaluations

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Onboard Calibration Analyses

• NICSE has primary responsibility for radiometric calibration of VIIRS.

• The VIIRS Ocean Science Team will provide supplemental analyses of onboard calibrator (solar diffuser and lunar) data to achieve radiometric accuracy needed for Ocean products.

• Temporal radiometric stability has been achieved for SeaWiFS over the nearly 10 year mission using lunar calibrations.

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Vicarious Calibration

• Vicarious calibration using surface measurements (e.g., MOBY) gives constant gain correction to TOA radiances over the mission

• Analyses of calibration results provide insight into temporal and geometric sources of variation.

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Matchup Analysis

• Ocean data granules in ODPS catalog are automatically matched with in situ data

• SeaWiFS Bio-optical Archive and Storage System (SeaBASS) stores and manages in situ holdings from field programs and supported investigators.

• Ocean staff acquire, QC and analyze new data samples.

• Over 60,000 in situ profiles stored covering SeaWiFS/ MODIS time frame.

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Matchup Process Flow Chart

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Residual Detector Dependence

• Level-3 multi-day products (same or different sensor) are resampled to generate values at Level-2 resolution.

• Comparisons are performed by detector and mirror side to evaluate residual detector response errors

July 27, 2010 VIIRS Product Evaluation at the Ocean PEATE

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Residual Scan Dependence

• Level-3 multi-day products (same or different sensor) are resampled to generate values at Level-2 resolution.

• Comparisons are performed by pixel number and mirror side to evaluate residual RVS errors

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Level-3 Product Generation

• Sensor cross-comparisons and interannual comparisons require Level-3 binned (equal-area) products.

• The Ocean PEATE has implemented software to process VIIRS EDRs to Level 3 binned products in current OBPG (SeaWiFS-like) format.

• This will automatically provide the additional capabilities to produce multi-temporal composites, standard mapped image (SMI) products and Level-3 browse files.

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Sensor/Algorithm Cross-Comparisons

• Level-3 parameters (e.g., nLw) compared for common spectral bands

• Common bins extracted and compared over the period of overlap between the sensors

• Comparisons are performed globally (deep water, oligotrophic, mesotrophic, eutrophic), zonally and for specified regions.

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Zonal Cross-Comparisons

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Chlorophyll Image Comparisons

SeaWiFS Deep-Water Chlorophyll 2002 193

SeaWiFS Deep-Water Chlorophyll 2006 365

MODIS Deep-Water Chlorophyll 2002 193

MODIS Deep-Water Chlorophyll 2006 365

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Temporal Anomaly Evaluations

• Level-3 global averages for the entire mission are fit to a periodic function to remove natural annual variability.

• The differences between the global averages and the annual cycle are then plotted over the mission.

• The results show both geophysical variations and any unexpected changes due to uncharacterized instrument effects or algorithm artifacts.

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Temporal Anomaly Example

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Conclusion

• The Ocean PEATE will be supported using the proven capabilities of the ODPS, which will support EDR evaluation strategies successfully employed on current missions.

• Our approach provides progressive stages of evaluation for Level-1B (SDR), Level-2 (EDR) and Level-3 products.

• Evaluation methodologies and tools are already established for data sets cataloged within the ODPS.

• The hierarchy of methods will provide for rigorous evaluation of the VIIRS Ocean products.