Determination of noise characterization of MODIS thermal emissive bands for cold scene observations

MODIS is a key instrument on-board both EOS Terra and Aqua satellites launched in December 1999 and May 2002, respectively. It has 16 thermal emissive bands (TEB) with a wavelength range from 3.5 to 14.4 mu m and 10 detectors in each band. The TEB detectors are located on cold focal plane assembles nominally controlled at 83K. TEB on-orbit calibration is performed for each band, detector and mirror side on a scan-by-scan basis with the dominant gain response determined through observations of a temperature controlled on-board blackbody (1313). The noise equivalent temperature difference (NEdT) is a key parameter to characterize the calibration uncertainty. Values of the NEdT are normally monitored at a fixed 1313 temperature of 285K for Aqua and 290K for Terra. Variations of NEdT with 1313 temperature are determined using the 1313 warmup/cooldown cycle scheduled every three months for a BB temperature range between 270 and 315K. In this study, we extend TEB detector NEdT characterization to temperatures below the 1313 temperature range. This approach uses detector responses to the interior of the instrument cavity, which varies in temperature between 210 and 270K depending on the viewing portion of the cavity inner surface. This study examines the stability of the cavity inner surface responses. Comparison of the NEdT obtained from cavity and 1313 measurements shows good agreement at the same temperature of 270K. Finally, the results of both Terra and Aqua NEdT determined from cavity measurements are presented.