Terra and Aqua MODIS on-orbit spectral characterization for reflective solar bands

Abstract

The MODerate resolution Imaging Spectroradiometers (MODIS) onboard the NASA EOS Terra and Aqua spacecraft were launched on December 18, 1999 and May 4, 2002 respectively. They have both successfully operated on-orbit for more than a decade. The spectral characteristics of the MODIS instruments were calibrated pre-launch using a ground calibration device called the Spectral Measurement Assembly (SpMA). The ground spectral characterization was transferred to an on-board device called the Spectro-Radiometric Calibration Assembly (SRCA) for the Reflective Solar Bands (RSB) by measuring the sensor spectral responses near simultaneously with both SRCA and SpMA. After transferring the calibration reference from the SpMA, the SRCA was able to track the on-orbit spectral changes by performing periodic spectral mode operations. This paper provides brief descriptions of MODIS on-orbit spectral characterization via its on-board SRCA. In the algorithm description section, functional steps and spectral calibration methodologies are presented. This study will focus on MODIS SWIR bands (bands 5, 6, 7 and 26) as their center wavelengths are longer than 1μm, which is beyond the specified SRCA spectral calibration range. In addition to the SWIR bands, band 2 results are also included. Because of the pre-launch and on-orbit configuration differences, band 2 spectral characterization is referenced to the first onorbit results. A summary of Terra and Aqua MODIS on-orbit relative spectral response changes, such as center wavelength and bandwidth changes, is provided in this paper for all the RSB bands.