Evaluation of Terra MODIS PC bands optical leak correction algorithm

Abstract

MODIS is one of the key instruments for the NASA's EOS mission, currently operated on both Terra and Aqua spacecraft making continuous and complementary observations in 36 spectral bands from 0.4 to 14.2 micrometers. Among them are long-wave infrared (LWIR) bands (11-14.2 micrometers) with Photoconductive (PC) HgCdTe detectors. The Terra MODIS pre-launch thermal vacuum calibration and characterization have shown clear evidence of an optical leak presented by the 11 micron band (band 31) into other PC bands (bands 32-36). A correction algorithm has been designed and implemented in the MODIS Level 1B (L1B) code using coefficients determined from the lunar observations made in year 2000. In this work we evaluate the optical leak correction coefficients derived from Terra MODIS lunar observations from January 2001 to December 2004. Our method assumes that in the absence of an optical leak the detector's signal would decay away from its peak response to the moon as an inverse power series function of the frame offset number. The least Chi-squared minimization method is used to calculate the parameters in the fitting function. Analysis results from the lunar and Earth view observations show that the Terra MODIS PC optical leak has been effectively removed. The Level 1B algorithm has been shown to be stable.