Maintaining and Refining the Calibration of Infrared Radiances…… with MODIS Chris Moeller, Paul Menzel (PI), Dan LaPort

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MAS data collected at same viewing geometry as MODIS Baja MODIS on Terra Cirrus 11um 14.3um Pre launch correction MAS, SHIS on ER-2 705 km 20 km q 14.3um MODIS IR Spectral Bands, MAS FWHM Post launch correction Band 36 (14.2 um) B36 B36 destriped B27 B27 destriped Mirror side “1” Mirror side “1” Calibrated Temperature change BOS EOS Cross Track Frame Number Brightness Temperature (K) B34 B34 destriped Mirror side “2” Calibrated Temperature change Mirror side “2” BOS EOS Cross Track Frame Number Cross Track Frame Number MODIS Scan Mirror Reflectance Measurement Scan mirror reflectance depends on angle of incidence (AOI) on the mirror Aqua MODIS TX-2002 MODIS Residual (K) 10 detector average for each band 3.7 4.5 7 11 14 11 7 3.7 4.5 14 wavelength MODIS Band Number Maintaining and Refining the Calibration of Infrared Radiances…… with MODIS Chris Moeller, Paul Menzel (PI), Dan LaPorte, Liam Gumley • Accomplishments • PC band Xtalk mitigation • 1.38um filter replacement • 5um thermal leak mitigation • Response vs Scan (RVS) assessment • Band 26 destriping and OOB influence reduction • MODIS TIR band radiometric assessment • TIR band destriping U N I V E R S I T Y O F W I S C O N S I N - M A D I S O N Objective: Assess Terra and Aqua emissive band L1B radiometric accuracy as a validation of MODIS L1B performance. Issue: MODIS 1% radiometric accuracy (0.5% for 11 m and 12 m; 0.75% for 3.7 m) requires validation on-orbit. L1B accuracy directly affects L2 science product accuracy. Solution: Underfly the Terra and Aqua satellites with the NASA ER-2 carrying the SHIS and MAS instruments. Simulate MODIS spectral, spatial, and geometric characteristics using the MAS and SHIS observations and directly compare to the MODIS co-incident observations. Example of ER-2 flight and data collection on April 1, 2001 over the Gulf of Mexico. MAS, SHIS and MODIS data profile along the ER-2 flight line is shown at far right. The MODIS detector averaged residuals for Terra (left) and Aqua (right). Positive residuals indicate MODIS L1B calibrated temperature is warmer than expected. The residuals for most spectral bands fall within or very near to the radiometric accuracy specification envelope (open bars), indicating that MODIS is performing within radiometric accuracy specification for these Collect 4 data sets. Band 20 is affected by sunglint in the Aqua comparisons. OBJECTIVE: Participate in Terra and Aqua MODIS L1B refinement. Ongoing Efforts 1) MODIS L1B data vigilance to uncover performance anomalies and ongoing issues. 2) Data analysis to model performance issues and document behavior. 3) Generate or contribute to generation of correction algorithms to mitigate performance issues. 4) Work closely with MCST to exchange information and insight on MODIS calibration. 5) Plan and conduct field operations to underfly Terra and Aqua with the NASA ER-2 aircraft 6) Evaluate MODIS L1B radiometric accuracy through comparisons with MAS and SHIS data sets including re-analysis of existing data sets when MODIS L1B is updated. Objective: Develop a correction algorithm to remove the majority of striping and out-of-band influence present in global MODIS band 26 (1.38 m) radiances. Issue: MODIS band 26 is used to detect thin cirrus in the atmosphere. The inherent low signal level of thin cirrus is very near that of the contaminated signal in band 26 land scenes from the combined effects of filter leaks, electronic crosstalk, and unexplained detector striping. Solution: MODIS band 5 (1.24 m) is a useful surrogate for the signal level of the contamination. Band 5 and band 26 radiances were used to develop a simple relationship to remove the bulk of the contamination. The correction coefficients were fine-tuned empirically for each detector to reduce detector striping. Objective: Eliminate scan mirror reflectance influence on emissive band L1B radiances. Issue: The MODIS scan mirror reflectance is dependent upon the angle of incidence (AOI) of the upwelling radiance. Pre-launch characterization was good but not entirely effective at characterizing the response vs scan (RVS) of the scan mirror. Error in the RVS causes scan angle dependent biases in the MODIS L1B radiances and L2 science products. Solution: Terra Deep Space Maneuvers (DSM) were completed in the spring of 2003. MCST analyzed the DSM data sets and generated a new RVS for Terra MODIS. The new RVS has undergone testing by the science team and has been implemented in operational processing. Terra MODIS scan mirror reflectance changes with view angle. This was characterized in prelaunch using witness samples, however on-orbit data showed scan angle effects. The DSM characterized the scan mirror reflectance on orbit. The DSM RVS characterization has directly influenced the MODIS LWIR Atmospheric bands, esp. Band 36 (14.2 um), shown above. The impact, different for each mirror side, does not totally remove mirror side striping; however across track effects are largely removed. Detector and mirror side destriping (see next panel) can be applied to remove residual mirror side differences. Objective: Reduce detector and mirror side striping in MODIS emissivie bands. Issue: MODIS, with ten detectors per 1 km band and two mirror sides, exhibits striping despite calibration characterization for each detector/mirror side combination. The striping flows into L2 science products. Some striping is due to noisy detectors. Solution: An empirical distribution function (EDF) approach has been used to destripe the MODIS imagery. A reference detector is chosen for each band, and the EDF of other detectors/mirror sides is matched to that EDF. Radiometry impact is small (<0.5°C) when median restore is applied. In Terra MODIS Collect 5 processing, destriping will be used to create a destriped intermediate MODIS L1B product before making selected L2 cloud products. Note: Also see the poster “Destriping MODIS L1B by Matching Empirical Distribution Functions” by Gumley et al. Destriping is effective in along track direction (Band 27 and 36 Examples above) but not effective for across track influences such as low frequency noise in Band 34. The continuity at granule interfaces has been reviewed for a few chosen MODIS granules. Destriping does not appear to degrade continuity across granule interfaces. However, this has not been investigated on a global data set. A median restore technique is used to bring the median of the destriped histogram back to the median of the original image. Red histograms are before median restore; blue historgrams are after median restore. Procedure 1) Underfly Terra satellite with a NASA ER-2 to obtain co-located MODIS and MAS, SHIS clear sky observations. 2) Filter the co-located scenes, keeping those with same viewing geometry from MODIS and MAS, SHIS. 3) From the MAS and SHIS data, produce simulated MODIS radiances at ER-2 level (20km) for the filtered co-locations. 4) Adjust the simulated MODIS radiances from 20 km (ER-2 level) to 705 km (Terra level) using forward model. 5) Difference the simulated and observed MODIS radiances to arrive at residuals. MODIS 11um imagery MAS 11um imagery MODIS Footprint ER-2 Flight Lines 38 km Objective: Develop a correction algorithm to remove OOB influence present in MODIS LWIR CO2 band radiances (Bands 32-36). Issue: MODIS LWIR CO2 bands are used to determine cloud height and emissivity and atmospheric temperature and moisture. A known optical leak at 11 m caused contamination of these atmospheric bands with window band radiance (causing, for example, the image of Baja peninsula to appear in the middle image below). Though laboratory based pre-launch correction coefficients were generated, upon going to orbit the contamination was still present in the earth scenes. Solution: A simple linear correction algorithm and correction coefficients were jointly developed with MCST to remove the contamination. Moon and earth view scenes were used to develop and test the post-launch correction coefficients. Terra MODIS TX-2001