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.
The MODerate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands with wavelengths from 0.41 to 14.5 micrometers. The 36 spectral bands, with a total of 490 detectors, are distributed on four focal plane assemblies (FPAs): visible (VIS), near infrared (NIR), short- mid-wave infrared (SMIR), and long wave infrared (LWIR). Nearly identical copies of the MODIS are currently operating onboard the NASA EOS Terra (launched on December 18,1999) and Aqua spacecraft (launched on May 4, 2002). Prelaunch and on-orbit characterizations of both Terra and Aqua MODIS have shown small but non-negligible out-of-band (OOB) response in the sensor's short-wave infrared bands (SWIR): bands 5-7, and band 26. To minimize the impact due to OOB response on the MODIS SWIR bands calibration and the Earth scene product retrieval, an algorithm has been developed and implemented in the Level 1B (L1B) software for both Terra and Aqua MODIS. In this paper, we describe the algorithm and its applications to the MODIS L1B calibration algorithms. We illustrate how the correction coefficients are derived from on-orbit observations and discuss the test procedures involved before the final implementation in the L1B code. Performance is evaluated for both Terra and Aqua MODIS and the two results are compared.