MODerate resolution Imaging Spectro-radiometer (MODIS) has been operated on-board the Terra spacecraft since December 18, 1999 and Aqua MODIS since May 4, 2002. Both MODIS Relative Solar Bands (RSBs) and Thermal Emissive Bands (TEBs) are calibrated on-orbit by a set of on-board calibrations (OBCs) in radiometric, spatial and spectral modes, providing accurate measurements for scientific researches. The Spectro-Radiometric Calibration Assembly (SRCA) is one of the key OBCs which can be operated at all three calibration modes. When operating in spectral mode, the SRCA is utilized for MODIS On-Orbit Spectral Characterization (MOOSC), monitoring and measuring the center wavelength (CW) shift of each RSB throughout the entire mission. However, some uncertainties in the SRCA measurement may affect the precision of the results due to possible system degradation, mechanical/optical backlash, deformation, and optical performance change.
In this study, the instrument background and the algorithm for calculating the CW shift of RSBs using the SRCA measurements are briefly introduced. We analyze or estimate the impact on the final CW value caused by the uncertainties on the Terra MODIS on-orbit spectral characterizations, including cavity temperature variation, limited number of sample points, noise of background, and the variation of β and θoff. The results show that the influence is small and the maximum uncertainty is less than 1nm.
The lessons we learned in this study provide helpful information and experiences for the sensors which have no on-orbit spectral characterization capability and the useful guidance for the next generation satellite remote sensors.