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MODIS Aqua SDSM

Gerhard Meister, presentation to CalVal, 2006. MODIS Aqua SDSM. MODIS SDSM . SDSM (Solar Diffuser Stability Monitor) views SD, sun, and background SDSM sun screen installed at wrong angle. 9 detectors from 412nm to 936nm. 9 Detectors, from 412nm to 936 nm. h. VIIRS SDSM .

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MODIS Aqua SDSM

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  1. Gerhard Meister, presentation to CalVal, 2006 MODIS Aqua SDSM

  2. MODIS SDSM • SDSM (Solar Diffuser Stability Monitor) views SD, sun, and background • SDSM sun screen installed at wrong angle • 9 detectors from 412nm to 936nm 9 Detectors, from 412nm to 936 nm h

  3. VIIRS SDSM

  4. SDSM sun screen: theory • MODIS screen misalignment confirmed by MCST modeling for yaw maneuvers, but not for regular calibrations Scan Directions

  5. MODIS SDSM: measured SD/sun ratios for detector 9 (936nm) Slope: -0.2%

  6. Effect of reducing number of data points on linear fit to detector 9 data:

  7. MCST method: divide detectors by detector 9

  8. Divide detector 7 (857nm) by detector 9 No

  9. Divide detector 1 (412nm) by detector 9

  10. Epsilon trend: divide detector 6 (747nm) by detector 7 (857nm) MCST modeled slope of the ratio: -0.45% My estimate: -0.3 to -0.5%

  11. Conclusions • No evidence that assumption ‘SD is stable at 936nm’ is wrong, data is too noisy • Independent of the above assumption, the SD reflectance ratio of 748nm to 870nm is modeled well by MCST (to within 0.1%) • SD degradation may be slower than model prediction (0.2% at 412nm) (expected from modified calibration schedule, but this explanation not well supported by data)

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