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.
The MODerate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments for the NASA’s Earth Observing System (EOS). The MODIS ProtoFlight Model (PFM) was launched on-board the EOS Terra spacecraft on December 18, 1999. The science data acquisition started on February 24, 2000. Since then it has been providing the science community and public users unprecedented amount of data sets for the global monitoring of the Earth’s land, oceans, and atmosphere. MODIS has 36 spectral bands with wavelengths ranging from 0.41 micrometer to 14.5 micrometers. Its 16 thermal emissive bands (TEB) range from 3.7 to 14.2 micrometers and have a total of 160 individual detectors (10 detectors per band). The thermal emissive bands are calibrated on-orbit by an on-board calibrator blackbody (OBC BB) on a scan by scan basis. The detectors responses to the BB source track their operational stability and therefore their noise characteristics as well. In this paper, we provide a brief review of the MODIS TEB on-orbit calibration algorithm with a focus on detector stability using over three years of on-orbit calibration data sets. The on-orbit changes in detectors responses from one operational configuration to another, the changes within the same operational condition, and the impact of these changes on the calibration and on the Earth scene observations are carefully examined. Except for a few detectors that were identified from pre-launch or became noisy on-orbit, the overall performance of MODIS TEB detectors is very satisfactory according to the design specifications.
MODerate Resolution Imaging Spectroradiometer (MODIS) Proto-Flight Model (PFM) on-orbit spatial characterization includes Band to Band registration (BBR) and the Modulation Transfer Function (MTF) of 36 bands located on four focal plane assemblies (VIS, NIR, SMWIR, and LWIR). These parameters were also measured prelaunch using ground calibration equipment. The on-board Spectro-Radiometric Calibration Assembly (SRCA) was used both prelaunch and on-orbit to monitor the BBR and MTF changes. In this paper, we report the MODIS on-orbit spatial characterization results derived from the SRCA and their comparisons with pre-launch values. Results from SRCA measurements show that the BBR stabilized on-orbit after about 100 days. Currently, the averaged FPA positions in the along-scan direction, relative to band 1 (NIR), have changed from prelaunch values by -2m for VIS, 17m for SMWIR, and -20m for LWIR; along-track changes are 43m for VIS, -36m for SMWIR, and -22m for LWIR. The MTF in the along-scan direction shows a small improvement over prelaunch. Also in this paper, we discuss a methodology that uses the sensor's on-orbit views of the Moon for the BBR characterization. Comparison of the results from the Moon and those from the SRCA provides an evaluation of the methodology and its applicability for other remote sensing instruments without an on-board spatial characterization calibrator.