# Presentation: 562553

## MODIS Solar Diffuser (SD) Earth Shine Analysis

**MODIS & SeaWiFS ****Calibration Meeting**
**Feb. 11, 2004 (revised)**
- Robert Wolfe
- NASA GSFC Code 922,
- Raytheon ITSS

##  Xiong, X., J. Sun, J. Esposito, X. Liu, W. L. Barnes, and B. Guenther, “On-Orbit       Characterization of a Solar Diffuser’s Bi-Directional Reflectance Factor Using Spacecraft              Maneuvers,” Proceedings Earth Observing Systems VIII, W. L. Barnes, ed., SPIE 5151  (2003). 

** ****Xiong, X., J. Sun, J. Esposito, X. Liu, W. L. Barnes, and B. Guenther, “On-Orbit ****      Characterization of a Solar Diffuser’s Bi-Directional Reflectance Factor Using Spacecraft  ****            Maneuvers,” Proceedings Earth Observing Systems VIII, W. L. Barnes, ed., SPIE *****5151*****  (2003).**

- R. Wolfe, Feb. 11, 2004

## Understanding SD measurement variation – What is the Earth shine contribution?

- R. Wolfe, Feb. 11, 2004

## Simplified SD Geometry

- Direct Light  - full illumination

- Earth Shine (reflected light)  - partial illumination  - atmospheric attenuation  - clouds and shadows  - sun glint  - varying albedo  - complicated BRDF

- R. Wolfe, Feb. 11, 2004

## MODIS Solar Diffuser Geometry

- To Sun

- Solar Diffuser

- Internal Baffle

- Front of instrument

- Lowest angle seen by SD (37o)

- Nominal SD angles (10-17o)

- 18o

- SD Port

- Solar specular Refl. (29o)

- To Scan Mirror

- Max. Earth glancing angle (27o)

- Sweet Spotcenter (12.5o)

- R. Wolfe, Feb. 11, 2004

## MODIS Solar Diffuser Stray Light Analysis

- Analysis program
- Fortran with IDL display logic
- Uses Two Line Element ephemeris
- can easily be run for additional cases
- Estimates:
- location of stray light from Earth’s surface
- sub-satellite point
- solar specular reflection point
- Separately calculates stray light within normal SD left-to-right view and for full view left-to-right extent
- angles estimated from instrument drawings

- R. Wolfe, Feb. 11, 2004

## Solar Diffuser Stray Light from Earth Surface (1 of 3)

- 2000/059.0435.91 (14.205o) – Start of “sweet spot”

- R. Wolfe, Feb. 11, 2004

## Solar Diffuser Stray Light from Earth Surface (2 of 3)

- 2000/059.0436.92 (10.824o) – End of “sweet spot”

- R. Wolfe, Feb. 11, 2004

## Solar Diffuser Stray Light from Earth Surface (3 of 3)

- 2000/059.0435.91 and 0436.92 (14.205o and 10.824o)

- 14.205o

- 10.824o

- R. Wolfe, Feb. 11, 2004

## L1B Data from 2000/059.0440

- Specular reflection

- start

- end

- R. Wolfe, Feb. 11, 2004

## Purpose: study effects of stray light (earth-shine) on MODIS Solar Diffuser (SD) results
Analysis notes:
only non-saturated non-thermal bands shown
data is from 15 orbits starting with 2003/183.2010 – first data after SD door anomaly
background/bias (from space view) subtracted
all values are band averages for all SD samples in a scan
both mirror sides used – smoothing performed (3 scans, triangular weighting)
corrected for SD/sun cosine angle and SD BRF
additional smoothing performed in scan direction (21 scans, triangular weighting)
no temperature correction

- Analysis notes:
- only non-saturated non-thermal bands shown
- data is from 15 orbits starting with 2003/183.2010 – first data after SD door anomaly
- background/bias (from space view) subtracted
- all values are band averages for all SD samples in a scan
- both mirror sides used – smoothing performed (3 scans, triangular weighting)
- corrected for SD/sun cosine angle and SD BRF
- additional smoothing performed in scan direction (21 scans, triangular weighting)
- no temperature correction

- MODIS/Terra Stray Light Analysis

- R. Wolfe, Feb. 11, 2004

## MODIS/Terra SD Values for Selected Bands 2003/183.2010 (o1: first orbit) to 2003/184.1915 (o15: last orbit)

- MODIS/Terra SD Values for Selected Bands 2003/183.2010 (o1: first orbit) to 2003/184.1915 (o15: last orbit)

- Sweet spot (14.2 to 10.8 degrees)

- R. Wolfe, Feb. 11, 2004

## MODIS/Terra Sweet Spot Values and Ratios for Ocean Bands2003/183.2010 (first orbit: 1) to 2003/184.1915 (last orbit: 15)

- MODIS/Terra Sweet Spot Values and Ratios for Ocean Bands2003/183.2010 (first orbit: 1) to 2003/184.1915 (last orbit: 15)

- R. Wolfe, Dec. 10, 2003

- R. Wolfe, Feb. 11, 2004

## Earth shine features are visible 
see bands 12 & 19
Effect in sweet spot is small (during this one-day period)
at SD radiances +/- 0.2 %
largest effect is for band 8
More analysis of stray light on SDSM needed

- see bands 12 & 19
- Effect in sweet spot is small (during this one-day period)
- at SD radiances +/- 0.2 %
- largest effect is for band 8
- More analysis of stray light on SDSM needed

- Sweet Spot Summary

- R. Wolfe, Feb. 11, 2004

## 	Spacecraft Altitude: 374 km	Sun Elevation Angle: -22o

- Limb images courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center (http://eol.jsc.nasa.gov)

- Image STS092-316-24
- Date:  16:28:12Z 10/24/2000
- Nadir Point: 48.0N, 39.2E
- At nadir point:
- 	Sun Azimuth: 277o
- 	Spacecraft Altitude: 374 km	Sun Elevation Angle: -22o
- 	Orbit Number: 200

## MODIS vs. Shuttle/Space Station Geometry

- MODIS

- Shuttle

- Sun

*(not to scale)*

- R. Wolfe, Feb. 11, 2004

## Pacific Ocean     09/12/1995  STS069-725  398 km Alt.

- Frame 24  Time: 14:01:23Z  Nadir Sun El: -08

- R. Wolfe, Feb. 11, 2004

## Atmospheric Limb     10/20/2003  ISS007E  383 km Alt.

- R. Wolfe, Feb. 11, 2004

## Pacific Ocean     07/21/2003  ISS007E  377 km Alt.

- R. Wolfe, Feb. 11, 2004

## SD Spectral Response Asymmetry

- SD analysis for areas during partial illumination can be used to estimate degree of SD Earth-shine contamination
- Some detectors primarily see the top half of the SD (detectors 6-10) and others the bottom half (detectors 1-5)
- During ramp up from partial (50% or more) to full illumination, spectral differences in the ratio of the top half vs. bottom half (T/B) are partially due to Earth-shine contamination of the SD top half
- Other effects may include (expected to be small):
- SD BRF
- Non-linear gain
- Residual bias
- Before analysis the following effects must be removed:
- Sample times of different bands (because of focal plane location)
- Individual detector gain differences
- Band-to-band registration

- R. Wolfe, Feb. 11, 2004

## SD illumination

- 50% illumination

- Full illumination

- Not  illuminated

- Earth shine and direct illumination

- Direct illumination

- Earth shine and direct illumination

*(notional)*

- R. Wolfe, Feb. 11, 2004

## SD response from partial to full illumination

- R. Wolfe, Feb. 11, 2004

## Spectral Contamination

- Absolute contamination is not as important as the relative variation in the sweet spot. This latter effect is only +/- 0.2% (B8 over a single day)
- 		Lsd = Lsun + Learth
- 		Lsd(t) = Lsd + δLsd(t) = Lsun + Learth + δLearth(t)
- 		Learth = -1.5% Lsun   (for B8)
- 		δLearth(t) = +/- 0.2% Lsun   (for B8 – one day)

- R. Wolfe, Feb. 11, 2004

## Simulation of Sun-glint at High Solar Zenith

- Measured

- Simulated (6S)

- R. Wolfe, Feb. 11, 2004

## Next Steps

- Better understand spectral dependence by simulation of various surface components (snow, vegetation, water) and atmospheric components (aerosols, clouds, water vapor)
- Better understand individual detector’s view of SD
- Better understand Earth-shine contribution to SDSM measurements
- what is the Earth-shine contribution (if any)?
- what is the SDSM response to non-uniform SD – which part of the SD does the SDSM see?
- Better understand the variability of the SD measurements since SD door fixed open
- Understand impact on NPP/VIIRS – very similar solar diffuser geometry

- R. Wolfe, Feb. 11, 2004

## Backup Slides

## SD Spectral Response Asymmetry – Preliminary Analysis

- Caveats – data not corrected for:
- Individual detector gains
- Band-to-band offsets
- Sampling time
- These results do not agree with individual detector m1’s (computed in the sweet spot)

- R. Wolfe, Feb. 11, 2004

## Top vs. Bot (T/B) ratio (3 detectors)

- SD Response during from partial (~50%) to full illumination

- T/B ratio w.r.t. Band 19 (3 detectors)

- T/B ratio w.r.t. Band 19 (5 detectors)

- ~50% illumination (24o inst. elevation)

- “Sweet Spot” (14.2o to 10.2o inst. elevation)

- R. Wolfe, Feb. 11, 2004

## T/B ratio w.r.t. all bands (3 detectors) – day 183

- T/B ratio w.r.t. all bands (3 detectors) – day 184

- T/B ratio w.r.t. all bands (5 detectors) – day 183

- T/B ratio w.r.t. all bands (5 detectors) – day 184

- R. Wolfe, Feb. 11, 2004