# Presentation: 756930

## MODIS-Terra cross-calibrationfor ocean color bands

- Ewa Kwiatkowska
- Bryan Franz, Gerhard Meister
- Ocean Biology Processing Group
- 13 May 2008
- MODIS Science Team Meeting

## MODIS calibration changes since launch 

**band 8  412nm **

- SD door permanently opened

- B side electronics

- A side electronics

- pre-launch
- damage to mirror coating, MS2

**Terra**

- SD – Solar Diffuser
-      frame 979, mirror AOI 50.30
- SV – Space View
-      frame 23, mirror AOI 11.40
- MS1 – Mirror Side 1
- MS2 – Mirror Side 2

## MODIS trends in ocean color products

**MODIS trends in ocean color products**

- Terra/Aqua ratios
- normalized water-leaving radiances Lwn
-     Lwn(412nm) band 8
-     Lwn(443nm) band 9
-     Lwn(488nm) band 10
-     Lwn(531nm) band 11
-     Lwn(551nm) band 12

- SD door permanently opened

## MODIS-Terra ocean color RVS 

**band 8  412nm **

- Terra response versus scan angle (RVS)
- in terms of
- normalized water-leaving radiances Lwn
- Lwn(412nm) band 8
- Mirror side 1 MS1
- Mirror side 2 MS2

- -10%

- +10%

- per detector

## Issues and limitations with MODIS-Terra

- On-board calibration (lunar or solar) CANNOT assess
- changes in RVS “shape”
- changes in polarization sensitivities

- Temporal and scan-dependent trend in Lwn of MODIS-Terra suggests
- instrument RVS may be in error
- polarization sensitivity may be changing
- on-board calibration capabilities may be degrading (SD, SDSM)

- OBPG developed a vicarious approach for on-orbit Terra characterization
- RVS
- polarization sensitivity

## SeaWiFS

- gas

- glint

-  whitecap

-  air

-  aerosol

- Lt(λ) = [ Lr(λ) + La(λ) + tLf(λ) + TLg(λ) + td(λ)Lw(λ) ] · tg(λ)

- water

**SeaWiFS**
**9-day mean**

- from MODIS NIR
- assumes MCST NIR band characterization

- λ’ → λ
- fit based on bio-optical models

**Modeling of TOA Stokes vector over oceans**

## Vicarious TOA MODIS total signal

- Lm(λ) = M11Lt(λ) + M12Qt(λ) + M13Ut(λ)

## TOA sensor cross-calibration

- Lm(λ) – M11Lt(λ) + M12Qt(λ) + M13Ut(λ)

-   minimize over global distribution of path geometries
-   find best M11, M12, M13 per band, detector, and mirror-side
-   M11, M12, M13 = f (mirror AOI)
-   do this for one day per month over the mission lifespan

- MODIS measured TOA radiance, _polarized_

- m

## Polarization of the atmosphere

- degree of atmospheric polarization dp
- air molecule (Rayleigh) and glint scattering

- polarization correction fp
- pre-launch MODIS characterization

- MODIS Terra
- swath
- 412nm band 8

- Lm

- Lt

- fp =

## RVS = 1/M11

**Blue band temporal trends**

- Mirror side 2

- Detector 4

- Mirror side 1

- Space View (lunar) frame
- Nadir frame
- Solar Diffuser frame

**RVS = 1**/**M**11

- 412

- 443

- 488

## Blue band RVS & polarization sensitivity MS1

- M13 fixed to pre-launch

- 412

- 443

- 488

- Detector 4

**Blue band RVS & polarization sensitivity MS1**

## Blue band RVS & polarization sensitivity MS2

- M13 fixed to pre-launch

- 412

- 443

- 488

- Detector 4

## MODIS-Terra vicarious characterization

- RVS

- M12

- M13

- 412

- 531

- 678

- RVS

- M12

- M13

- 443

- 488

- 551

- 667

- MS1, Detector 4

- MS2, Detector 4

## MODIS Terra and Aqua comparison

**MODIS Terra and Aqua comparison**

- RVS

- M12

- M13

- 412

- 531

- 678

- RVS

- M12

- M13

- 443

- 488

- 551

- 667

_**Terra**_ MS2, Detector 4

_**Aqua**_ MS2, Detector 4

## Comparison of MODIS-Terra and MODIS-Aqua Lwn

- After Vicarious Characterization

- Before Vicarious Characterization

- Lwn(412nm) band 8
- Lwn(443nm) band 9
- Lwn(488nm) band 10
- Lwn(531nm) band 11
- Lwn(551nm) band 12

## MODIS-Terra residual RVS in Lwn

**MODIS-Terra residual RVS in L****wn**

- 412

- 443

- After Vicarious Characterization

- 488

- 412

- 443

- 488

- Before Vicarious Characterization

- MS1
- MS2

## MODIS-Terra temporal anomalies

- After Vicarious Characterization

- Before Vicarious Characterization

- Lwn(488nm)
- band 10

- chlor_a

- Lwn(488nm)
- band 10

- chlor_a

## Summary

- MODIS-Terra shows evidence of residual error in instrument response versus scan-angle and/or changes in polarization sensitivity.
- The MODIS on-board calibration system can not assess changes in RVS “shape” or changes in polarization; these characteristics are restricted to our pre-launch knowledge, which itself may be in error.
- The OBPG developed a vicarious on-orbit characterization for visible band polarization and RVS changes over time, using SeaWiFS Lwn.
- Results show significant improvement in agreement between MODIS-Terra and MODIS-Aqua Lwn over the combined mission lifetime.
- Future work will focus on vicarious characterization of the NIR.

- Franz, B.A., E.J. Kwiatkowska, G. Meister, and C.R. McClain (2008). Moderate Resolution Imaging Spectroradiometer on Terra: limitations for ocean color applications*. J. Appl. Rem. Sens.*, in press.