Aqua MODIS Thermal Emissive Bands Calibration Algorithm and Preliminary Results

摘要

The MODerate Resolution Imaging Spectroradiometer (MODIS) Flight Model (FM1) was launched on-board the NASA Earth Observing System (EOS) Aqua spacecraft on May 4, 2002. Following initial instrument outgas, focal plane cooling, and functional testing, Aqua MODIS opened its nadir aperture door (NAD) on June 24, 2002 and acquired the first on-orbit image. MODIS has 36 spectral bands with wavelengths ranging from 0.412μ to 14.5μ. The 16 thermal emissive bands (B20-25 and 27-36) with wavelengths above 3.5μare calibrated on-orbit by an on-board calibrator blackbody (OBC BB) on a scan by scan basis. In this paper, we provide a brief review of MODIS thermal emissive bands (TEB) calibration algorithm and present early results from Aqua MODIS on-orbit calibration and characterization, including sensor's response stability, noise assessment, and the response versus scan angle (RVS) difference between the two sides of the scan mirror. In general, the on-orbit performance of Aqua MODIS TEB has been consistent with the instrument pre-launch calibration and characterization. Compared to its Protoflight Model (PFM), or the Terra MODIS, launched on December 18, 1999, a number of improvements have been achieved. During instrument on-orbit operation, the BB can be operated from 270-315K (during scheduled warm-up/cool-down cycle). When the BB temperature is above certain limits, three thermal emissive bands (33, 35, and 36) saturate when directly viewing the calibration source. We have developed an algorithm of using the Look-Up Table (LUT) gain coefficients for these three bands to keep the Earth view data calibrated under this situation. An illustration of on-orbit performance of this approach is provided.