Operational activities and on-orbit performance of Terra MODIS on-board calibrators

The Moderate Resolution Imaging Spectroradiometer (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). The SD and SDSM, used for calibration of the reflective solar bands (RSB), are normally operated on a bi-weekly basis (weekly during the first year of the mission). The BB is primarily used for calibration of the thermal emissive bands (TEB) on a scan-by-scan basis. The sensor's spatial and spectral stability is monitored bi-monthly and quarterly respectively by the SRCA. The MODIS characterization support team (MCST) at NASA/GSFC is responsible for scheduling and implementing the calibration and characterization activities, performing calibration data analyses, and monitoring instrument on-orbit performance (short-term and long-term). This paper provides a description on how each of the OBCs is operated and a summary of the activities that support instrument calibration and characterization and data product quality. Using the EOS Terra MODIS (launched in December 1999) as an example, this paper illustrates and evaluates the OBCs' design capabilities and summarizes their overall on-orbit performance. Several papers included in these proceedings focus on individual on-board calibrators.