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MODIS Terra Time-dependent NIR RVS

Explore the impact of NIR RVS trend over time on Terra data, compare with Aqua, evaluate AOT and epsilon ratios, and assess nLw trends. Adjustments and potential reprocessing may lead to closer conformity.

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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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