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MODIS LWIR CO2 Band Radiometric Performance

MODIS LWIR CO2 Band Radiometric Performance. Terra MODIS L1B validation Aqua MODIS L1B validation L1B radiometric bias application in MOD06 What are we learning?. Moeller 1 , Frey 1 , Tobin 1 , MCST 2 1.Univ. Wisconsin 2. MODIS Characterization Support Team January 4, 2006.

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MODIS LWIR CO2 Band Radiometric Performance

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  1. MODIS LWIR CO2 Band Radiometric Performance • Terra MODIS L1B validation • Aqua MODIS L1B validation • L1B radiometric bias application in MOD06 • What are we learning? Moeller1, Frey1, Tobin1, MCST2 1.Univ. Wisconsin 2. MODIS Characterization Support Team January 4, 2006 Presented at MCST Calibration breakout meeting, January 04, 2006

  2. 2000 2001 2002 Terra MODIS Aqua MODIS SAFARI-2000 WISC-T2000 TX-2002 CLAMS TX-2001 2004 2005 2003 THORpex-2003 Tahoe-2004

  3. Terra MODIS CO2 wv 11 12 4 CO2 MODIS - MAS_SHIS (K) Detector averaged Vertical bars represent radiometric accuracy spec. MODIS Band Number Along Track Profile MAS and SHIS data sets collected on the NASA ER-2 aircraft have been key for directly assessing Terra and Aqua MODIS L1B accuracy. Terra MODIS 11 um 04/01/01

  4. April 9, 2004 0544 UTC Terra MODIS SHIS SHIS Predicted – Measured Brightness Temperature (K) MODIS - MAS_SHIS (K) MODIS Observed BT (K) Vertical bars represent radiometric accuracy spec. Wavelength (um) MAS_SHIS Simulated MODIS BT (K) MODIS Band Number Buoy Sites The Lake Tahoe 2004 field activity evaluated Terra MODIS radiometric performance. 3.7um 3.9um CO2 4 wv 11 12 CO2 11um 12um Detector averaged

  5. Sept. 11, 2000 MODIS orbital tracks Terra MODIS 11um CO2 CO2 4 wv 11 12 MODIS - MAS_SHIS (K) Detector averaged Vertical bars represent radiometric accuracy spec. MODIS Band Number SAFARI-2000 field experiment objectives included Terra MODIS radiometric performance.

  6. Possible Sources of Radiometric Bias(Cold Scenes) • PC band optical leak 0.5 - 1 K • Spectral characterization up to 1 K • Terra MODIS RSR in ambient • Aqua MODIS RSR in T/V • Calibration coefficients 0.5 K • Set A0=0 for Terra LWIR CO2 bands • Scan Mirror Reflectance < 0.3 K • DSM characterization • External Cal/Val standard < 0.3 K

  7. Optical leak region Normalized Response Position on Focal Plane Courtesy of MCST

  8. PC Band Optical Leak Crosstalk Impact Simulation Simulated B35 Simulated Radiometric Impact on B35

  9. Courtesy of MCST

  10. B36 transmittance from sfc to TOA is effectively 0.

  11. Baja 11um 14.3um Pre launch correction A known optical leak at 11um caused the image of the Baja peninsula to be present in MODIS 14.3um data. Through testing, the pre-launch correction coefficients were revised, removing the contamination. 14.3um Post launch correction

  12. MODIS RSR PFM: solid lines; FM-1: dashed Response or Transmittance Wavelength (um)

  13. PFM – FM-1 (K) Wavelength (um)

  14. Aqua Aqua MODIS CO2 Nov. 21, 2002 1941 UTC wv 11 12 4 CO2 MODIS - MAS_SHIS (K) Detector averaged MODIS Band Number Nov 21, 2002 MAS B45 (11 um) TX-2002 Experiment Assess Aqua MODIS Cal/Val Detector dependent (atmospheric bands) Detector dependent (window bands)

  15. AIRS – MODIS (K) MODIS Band Number Mean brightness temperature differences and uncertainties for 6 September 2002 (blue) and 18 February 2004 (red).

  16. Radiometric Bias and L2 • Level 2 MOD06 product relies on LWIR CO2 bands • Test Radiometric Bias Correction on Cloud Top Pressure (CTP) product of MOD06

  17. Aqua MODIS B36 Aqua MODIS B31

  18. Aqua MODIS Collect 5 CTP Before subtracting Radiometric Bias After subtracting Radiometric Bias

  19. Aqua MODIS B31 Aqua MODIS B36

  20. MODIS Band Pair Representing the Best CTP Retrieval Pink, cyan, and green are 36/35, 35/34, 34/33, respectively Chosen band pair for retrieval is more physically consistent Before subtracting Radiometric Bias After subtracting Radiometric Bias

  21. Terra MODIS B31 Terra MODIS B36

  22. Terra MODIS Collect 5 CTP Before subtracting Radiometic Bias After subtracting Radiometric Bias

  23. What Are We Learning • MODIS LWIR CO2 bands have shown out-of-spec radiometric behavior. • Aqua MOD06 Cloud Top Pressure results are qualitatively improved by applying a radiometric bias based on AIRS and ER-2 based comparisons to MODIS L1B radiances. • Early testing of Terra MOD06 CTP suggests that it also benefits from applying a radiometric bias. • We are left with a question of why the radiometric bias apparently exists in MODIS. There are suspects, but no conviction.

  24. Backup

  25. CO2-slicing equation: Rcld(1) - Rclr(1) N1∫pcld (1)dB(1) dp LHS = ----------------------- = ------------------------------- = RHS + Error Rcld(2) - Rclr(2) N2 ∫pcld (2)dB(2) dp where 1and 2 are MODIS bands 34/33, 35/34, or 36/35 Traditionally, HIRS, GOES products use observations on LHS; RHS is calculated from NCEP 1-degree T(p), q(p), and forward radiance model. For MODIS, Rclr(1), Rclr(2) are calculated, adding an error term on the LHS. To mitigate this, we apply clear-sky radiance biases, as functions of geographic region and band (Collection 5). Work on the CHAPS (Collocated HIRS and AVHRR Products) algorithm in the mid-1990s indicated close agreement between CTP results when calculated clear-sky radiances were used with bias corrections.

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