# Presentation: 202739

## On-orbit Vicarious Characterization of MODIS-Terra

- Bryan Franz, Ewa Kwiatkowska, Gerhard Meister
- and the
- NASA Ocean Biology Processing Group

- Ocean Color Research Team Meeting, 1 May 2008, College Park, MD

## Issues and Limitations with MODIS-Terra

- Overheating event in pre-launch testing "smoked" the mirror
- pre-launch characterization may not adequately represent at-launch configuration (mirror-side ratios, RVS, polarization sensitivities)

## MODIS Temporal Degradation at 412 nmLunar and Solar Calibration Trends

- 40%

- 5%

- MODIS Temporal Degradation at 412 nmLunar and Solar Calibration Trends

- 30%

- 20%

- 10%

- 50%

-   0%

## Issues and Limitations with MODIS-Terra

- Substantial temporal degradation of instrument response
- degradation varies with mirror-side and scan-angle
- temporal change in polarization sensitivity, RVS

- Overheating event in pre-launch testing "smoked" the mirror
- pre-launch characterization may not adequately represent at-launch configuration (mirror-side ratios, RVS, polarization sensitivities)

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

## MODIS-Aqua Residual RVS - Lwn(412)

- Scan Pixel

- -10%

- +10%

- MS1

- MS2

## MODIS-Terra Residual RVS - Lwn(412)

- Scan Pixel

- -10%

- +10%

- MS1

- MS2

## MODIS-Terra Residual RVS - Lwn(412)

- Scan Pixel

- -10%

- +10%

- MS1, Det 1-10

- MS2, Det 1-10

## Issues and Limitations with MODIS-Terra

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

- scan-dependent error in nLw of MODIS-Terra suggests
- instrument RVS may be in error, or
- polarization sensitivity may be incorrect, or
- both

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

## nLw(’)

- nLw(’)

- gas

-  glint

-  whitecap

-  air

-  aerosol

- LI() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg()

- water

- ’  ,   (0,0,0)  (0,,)
- Morel model, f/Q, etc.

- SeaWiFS
- 9-day mean

- from MODIS NIR
- assumes MCST NIR band characterization

- MODIS – vicarious TOA radiance (unpolarized)

- Vicarious Characterization of Instrument RVS and Polarization

## LI() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg()

- MODIS – vicarious TOA radiance (unpolarized)

- gas

-  glint

-  whitecap

-  air

-  aerosol

- LI() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg()

- water

- Lt() = M11LI() + M12LQ() + M13LU()

## Lt() - [M11LI() + M12LQ() + M13LU()]

- MODIS – vicarious TOA radiance (unpolarized)

- gas

-  glint

-  whitecap

-  air

-  aerosol

- LI() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg()

- water

- Lt() - [M11LI() + M12LQ() + M13LU()]

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

## MODIS-Terra Vicarious Characterization (MS1)

- M11

- M12

- M13

- 412

- + 5%

- -15%

- October 2007

- March 2000

- M13 fixed to pre-launch

- 443

- 488

## MODIS-Terra Vicarious Characterization (MS2)

- M11

- M12

- M13

- + 5%

- -15%

- October 2007

- March 2000

- M13 fixed to pre-launch

- 412

- 443

- 488

## MODIS-Terra Vicarious Characterization

- M11

- M12

- M13

- 412

- 531

- 678

- M11

- M12

- M13

- 443

- 488

- 551

- 667

- _Mirror-Side 1, Detector 4_

- _Mirror-Side 2, Detector 4_

## MODIS-Terra Residual RVS in nLw

- 412

- 443

- After Vicarious Characterization

- 488

- 412

- 443

- 488

- Before Vicarious Characterization

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

- After Vicarious Characterization

- Before Vicarious Characterization

## 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 nLw.
- Results show significant improvement in agreement between MODIS-Terra and MODIS-Aqua nLw 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.

## Thank You

## backup

## Lt() = M11LI() + M12LQ() + M13LU()

- Lt() = M11LI() + M12LQ() + M13LU()

- where M11, M12, M13 represents the instrument response
- per  and aoi on mirror (scan angle)

## Lt() = M11LI() + M12LQ() + M13LU()_x0003_

- Vicarious calibration:
- given Lwn() and radiant path geometry, we can predict
- LI, LQ, LU
- Global optimization:
- find best fit M11, M12, M13 to relate predicted and observed Lt() over wide range of viewing geometry and

- Lt() = M11LI() + M12LQ() + M13LU()_x0003_

- Vicarious Characterization of Instrument RVS and Polarization

- where M11, M12, M13 represents the instrument response model per  and aoi on mirror (scan angle)

## Detector Ratios at 412nm Derived FromLunar Observations  and Vicarious Characterization

## Temporal Trends in Global Mean Water-Leaving Radiance

- Aqua - solid line Terra - dashed line

- MODIS Terra & Aqua Global Deep-Water Means

## Temporal Trends in Global Mean Water-Leaving Radiance

- Terra/Aqua Ratios in Global Deep-Water Means

- - 20%

- + 5%

## MODIS-Terra Residual RVS - Lwn(412)

## Deep-Water Seasonal Anomaly in nLw

- MODIS-Terra

- 412

- SeaWiFS

## Deep-Water Seasonal Anomaly in Chlorophyll

## Pre-launch M13

**Pre-launch M13**

## Assessment of Residual RVS, Mirror-Side, and Detector Striping

- Assessment of Residual RVS, Mirror-Side, and Detector Striping

## MODIS-Terra Vicarious Characterization (MS1)

- M11

- M12

- M13

- 412

- 443

- 488

- +9%

- -2%

## Polarization   fp()

**I****t** – Stokes vector exiting the TOA
- Mueller matrix **M** – polarization sensitivity of the instrument
- ** **- rotation angle
**I****m** – Stokes vector measured by a sensor
**	****	****	****I****m** =  **M** **R**() **I****t**

- Detectors respond only to the total incident radiation
- Im = M11It + M12(Qtcos2 – Utsin2) + M13(Qtsin2 + Utcos2)