# Presentation: 196463

## The Continuity of Ocean Color Measurements from SeaWiFS to MODIS

- Bryan Franz
- Ocean Biology Processing Group
- NASA Goddard Space Flight Center
- SPIE Earth Observing Systems X
- 31 July - 4 August 2005

## Bryan A. Franz, Science Applications International Corporation
P. Jeremy Werdell, Science Systems and Applications Incorporated
Gerhard Meister, Future Tech Corporation
Sean W. Bailey, Future Tech Corporation
Robert E. Eplee Jr., Science Applications International Corporation
Gene C. Feldman, NASA Goddard Space Flight Center
Ewa Kwiatkowska, Science Applications International Corporation
Charles R. McClain, NASA Goddard Space Flight Center
Frederick S. Patt, Science Applications International Corporation
Donna Thomas, Future Tech Corporation

- P. Jeremy Werdell, Science Systems and Applications Incorporated
- Gerhard Meister, Future Tech Corporation
- Sean W. Bailey, Future Tech Corporation
- Robert E. Eplee Jr., Science Applications International Corporation
- Gene C. Feldman, NASA Goddard Space Flight Center
- Ewa Kwiatkowska, Science Applications International Corporation
- Charles R. McClain, NASA Goddard Space Flight Center
- Frederick S. Patt, Science Applications International Corporation
- Donna Thomas, Future Tech Corporation

**Authors**

## Introduction to Ocean Color

**Introduction to Ocean Color**

## Introduction

**As a component of NASA’s “Missions to Measurements” initiative, the OBPG was formed from the former SeaWiFS & SIMBIOS Projects to consolidate the processing and distribution efforts required to retrieve ocean color measurements from various spaceborne instruments.**
**CZCS, SeaWiFS, MODIS, NPP/VIIRS (MOS, OSMI, OCTS)**
**In February 2004 the OBPG assumed responsibility for MODIS ocean color processing and distribution. **
**This presentation will cover**
**Approach to multi-mission integration**
**Changes implemented to improve quality & consistency**
**Comparison of results**

## Multi-Mission “Measurement-Based” Processing

- Common software for Level-1 through Level-3
- eliminates potential for algorithm and implementation differences
- sensor-specific issues consolidated in i/o function and external tables
- Mission-independent, distributed processing system
- 200x global reprocessing for MODIS, 1600x for SeaWiFS
- mission-long test processing for calibration & algorithm evaluation
- Standard procedures for calibration and validation
- temporal calibration via On-Board Calibration system (OBC)
- vicarious calibration to MOBY (instrument + algorithm calibration)
- validation against SeaBASS *in situ* archive
- temporal trending analysis of Level-3 products

## Sensor Spectral Bands

## Sensor Spectral Bands

## nLw: MODIS vs SeaWiFS at OBPG Transition Deep-Water (global mean > 1000m)

**nLw: MODIS vs SeaWiFS at OBPG Transition ****Deep-Water (global mean > 1000m)**

**MODAPS**
**Aqua 003**

**MODAPS**
**Aqua 003**

**MODAPS**
**Terra 041**

**MODAPS**
**Terra 041**

**MODIS & SeaWiFS**

**MODIS / SeaWiFS**

## nLw: MODIS/Aqua vs SeaWiFS Deep-Water

- Concentrate on MODIS/Aqua (more stable than Terra)
- step 1: integrate MODIS processing into common (SeaWiFS) software
- step 2: update to best available instrument calibration from MCST
- step 3: apply standard vicarious calibration using MOBY *in situ* data
- Initial OBPG processing of MODIS/Aqua completed May 2004

**MODAPS**
**Aqua 003**

**MODAPS**
**Aqua 003**

**MODIS & SeaWiFS**

**MODIS / SeaWiFS**

## nLw: MODIS vs SeaWiFS Deep-Water

**nLw: MODIS vs SeaWiFS ****Deep-Water**

**OBPG**
**Aqua R0**

**OBPG**
**Aqua R0**

**MODAPS**
**Aqua 003**

**MODAPS**
**Aqua 003**

**MODIS & SeaWiFS**

**MODIS / SeaWiFS**

## nLw: MODIS vs SeaWiFS Deep-Water

**nLw: MODIS vs SeaWiFS ****Deep-Water**

**OBPG**
**Aqua R0**

**OBPG**
**Aqua R0**

**After Initial OBPG Processing of MODIS**
**10% peak-to-peak seasonal variability between MODIS/Aqua and SeaWiFS global mean nLw **

**MODIS & SeaWiFS**

**MODIS / SeaWiFS**

## Polarization Correction

- The atmospheric signal reaching the sensor is polarized.
- SeaWiFS has a polarization scrambler.
- MODIS has significant polarization sensitivity, especially in the blue.
- H. Gordon developed an algorithm to derive the polarization components of the atmospheric signal and correct for the polarization response, given the instrument polarization sensitivity.
- G. Meister (OBPG) reviewed the laboratory set-up and determined that the MODIS polarization sensitivty results had been misinterpreted in the original implementation (Collection 3 & OBPG R0).

## Polarization Correction

**Solid line = OBPG,  Dashed line = original correction**

## nLw Ratio: MODIS/Aqua vs SeaWiFS 50N-40N, 150W-170W

**Before Polarization Correction**

**After Polarization Correction**

**improved spectral consistency**

**straylight**

## MODIS Straylight Masking

**MODIS Straylight Masking**

- SeaWiFS already includes correction & masking for straylight.
- Modeled point-spread function (PSF) for MODIS indicates significant sensitivity to straylight from adjacent sources.
- 7 x 5-pixel masking around bright pixels removes significant contamination.
- Fixes AOT discrepancy (excess NIR radiance) between sensors.

**Before SL Masking**

**After SL Masking**

**MODIS Band 16 PSF**

**MODIS & SeaWiFS Deep-Water AOT Comparison**

## Bidirectional Reflectance at Surface

- Each sensor views the same location on earth from different view angle and at different time of day (solar angle).
- The angular distribution of upwelling radiance varies with solar illumination angle and the scattering properties of the water body.
- A. Morel developed a correction for this effect, which was incorporated into the common processing software for both sensors.

**Before BRDF**

**After BRDF**

**Residual Scan Dependence in MODIS nLw(443)**

## Reprocessing

- MODIS Reprocessing 1 completed February 2005
- SeaWiFS Reprocessing 5 completed March 2005

## Results from ReprocessingComparison with Field Data

**MODIS/Aqua R1**

**Results from Reprocessing****Comparison with Field Data**

## Results from ReprocessingSensor-to-Sensor nLw ComparisonDeep-Water Trends

- Sensor agreement to within 7% for global mean deep-water nLw retrieval.
- Some long-term trend, bias is still evident.

**MODIS & SeaWiFS**

**MODIS / SeaWiFS**

## Results from Reprocessing Sensor-to-Sensor nLw Ratios, Latitudinal Effects

**Results from Reprocessing**** ****Sensor-to-Sensor nLw Ratios, Latitudinal Effects**

- Seasonal, latitudinally-dependent differences reduced.

**35 North**

**25 North**

**15 North**

**nLw Ratios, Zonal Pacific, 150W-170W**

## Results for ReprocessingConsistency in Annual Cycle of nLw

**MODIS/Aqua R1**

**SeaWiFS R5**

## Multi-Mission Browse & Distribution

**Multi-Mission Browse & Distribution**

## Back-up Slides

## The Ocean Biology Processing Group (OBPG) at NASA’s Goddard Space Flight Center is responsible for the processing and validation of oceanic optical property retrievals from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). A major goal of this activity is the production of a continuous ocean color time-series spanning the mission life of these sensors from September 1997 to the present time. This paper presents an overview of the calibration and validation strategy employed to optimize and verify sensor  performance for retrieval of upwelling radiances just above the sea surface.  Substantial focus is given to the comparison of results over the common mission lifespan of SeaWiFS and the MODIS flying on the Aqua platform, covering the period from July 2002 through December 2004.  It will be shown that, through consistent application of calibration and processing methodologies, a continuous ocean color time-series can be produced from two different spaceborne sensors.

**Abstract**

## Atmospheric Correction Equation

*L**t** = L**r** + L**a** + tL**wc** + TL**g** + t L**w*
*L**w** *is the quantity we wish to retrieve at each wavelength.
*TL**g** *is Sun glint, the direct reflectance of the solar radiance from the sea surface. This effect is avoided through tilting.
*tL**wc** *is the contribution due to "white"-capping, estimated from statistical relationship with wind speed.
*L**r** *is* *the contribution due to molecular (Rayleigh) scattering, which can be accurately computed.
*L**a** *is the contribution due to aerosol and Rayleigh-aerosol scattering, estimated in NIR from measured radiances and extrapolated to visible using aerosol models.

## Deep-Water Chlorophyll Images

**Deep-Water Chlorophyll Images**
- common-bin 12-day composite, Winter 2002

**0.01-1 mg/m^3**

**SeaWiFS**
**R5**

**MODIS/Aqua**
**R1**

## Effect of BRDF Correction to MODIS/SeaWiFS Ratios

**Deep Water nLw Ratio**
**MODIS/SeaWiFS**

**After BRDF**

**Southern Pacific nLw Ratio**
**MODIS/SeaWiFS**

**Before BRDF**