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MODIS Terra Time-dependent NIR RVS

MODIS Terra Time-dependent NIR RVS. Gerhard Meister, Presentation to CalVal, 11/31/06. RVS Basics. RVS: Response versus scan, normalized to 1 at SD view angle (~pixel 900) L1B code: dn are multiplied by m1, divided by RVS RVS is a 2 nd order polynomial, initially measured prelaunch

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MODIS Terra Time-dependent NIR RVS

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  1. MODIS Terra Time-dependent NIR RVS Gerhard Meister, Presentation to CalVal, 11/31/06

  2. RVS Basics • RVS: Response versus scan, normalized to 1 at SD view angle (~pixel 900) • L1B code: dn are multiplied by m1, divided by RVS • RVS is a 2nd order polynomial, initially measured prelaunch • On-orbit change is tracked by lunar measurements, but bands 13-16 saturate

  3. Which bands for bands 15 and 16 ?

  4. Terra time series • Time series is one method to evaluate impact of temporal RVS trend, TV tests probably better • TT02 is the run with LUT where NIR RVS is constant over time, TT05 is run with LUT where NIR RVS is time dependent • AT10 and AT11 are corresponding Aqua runs

  5. Terra AOT ratio to Aqua Average ratio: Increased from ~0.95 to ~0.98 Trend difference: April-April almost unchanged 10% variation similar as Aqua/ SeaWiFS variation TT02: AOT MS2<MS1 by 1%

  6. Terra Epsilon ratio to Aqua Average ratio: Decreased from ~1.02 to ~1.01 Trend difference: Maybe 0.5% decrease Of TT05/TT02 1% variation same as Aqua/ SeaWiFS variation TT02: Eps. MS2>MS1 by 0.5%

  7. nLw comparison

  8. Terra nLw ratio to Aqua Average ratio: 412nm and 551nm higher (good) 443nm and 488nm lower (bad) Trend difference: Downward trend reduced for all Bands, 551nm almost flat now

  9. Summary: The NIR RVS time dependency… • improved Terra AOT ratio to Aqua from 0.95 to 0.98 • improved epsilon ratio to Aqua from 1.02 to 1.01 • introduced downward trend in epsilons, which increased the nLw, especially at 531nm and 551nm (551nm up 4%, almost flat now; still large downward trends at 443nm and 488nm) Adjusting mirror side 2 to mirror side 1 is likely to bring AOT and Epsilon ratios even closer to 1

  10. How about Aqua ? • If NIR RVS is time dependent for Terra, there is no reason to assume it is constant for Aqua (like we currently do) • Would most likely require a reprocessing (new vic. Cal.) • Change would probably be on the same order of magnitude as for Terra

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