Terra MODIS Instrument Status and Calibration Performance

The Moderate Resolution Imaging Spectro-radiometer (MODIS) has been flying aboard the NASA's Terra satellite for 20 years. MODIS observations are made in 36 spectral bands at three spatial resolutions (250 m, 500 m, and 1 km), covering wavelengths from 0.4 to 14.2 μm, and have enabled the generation of numerous long-term data records. MODIS was designed with a set of on-board calibrators (OBCs) that include a solar diffuser (SD), a solar diffuser stability monitor (SDSM), a blackbody (BB), and a spectro-radiometric calibration assembly (SRCA). In addition, a space view (SV) port provides measurements of the instrument background and dark offsets. The MODIS reflective solar bands (RSB) with wavelengths from 0.4 to 2.1 μm employ a reflectance-based calibration using the SD and SDSM. The SDSM, designed to track on-orbit changes in SD reflectance, is currently operated tri-weekly. For the thermal emissive bands with wavelengths above 3.7 μm, the calibration is performed using the on-board BB on a scan-by-scan basis. The sensor's spatial and spectral characterization is monitored via routine calibrations performed using the SRCA. In addition, regularly scheduled lunar observations are performed to support sensor on-orbit calibration and characterization. This presentation provides an overview of instrument status, describes how each of the OBCs has been operated over the entire mission, and reviews strategies developed to extend its capabilities. It provides a summary of various calibration activities and data collected to help maintain sensor data quality, including examples to illustrate sensor on-orbit radiometric, spatial, and spectral performance. Also discussed in this paper are lessons from Terra MODIS that could benefit and have already benefitted other Earth observing missions and instruments.