Solar and lunar observation planning for Earth-observing sensor

Abstract

MODIS on-orbit calibration activities include the use of the on-board solar diffuser (SD), SD stability monitor (SDSM) and regularly scheduled lunar observations for the Reflective Solar Bands (RSB) radiometric calibration. Normally, the SD door is closed when there is no SD/SDSM observation to avoid the unnecessary illumination of the sunlight on the SD, which causes the SD degradation. The SD is illuminated over a very short period of time when the spacecraft crosses from the night side to the day side. To implement a SD/SDSM calibration, the SD door needs to be open and the SDSM needs to be turned on during the short period of time when the SD is illuminated. A planning tool is needed to predict the exact times for the opening and closing of SD door and SDSM on/off operations of SDSM for each SD/SDSM calibration. The tool is also needed for MODIS yaw maneuvers implemented for SD bi-direction reflectance factor (BRF) validation and SD screen vignetting function (VF) derivation. MODIS observes the Moon through its space view (SV) port. To increase the opportunity for more lunar observations and to keep the lunar phase angle in a selected narrow range that minimizes the view geometric effect on the observed lunar irradiance, a spacecraft roll maneuver is allowed and implemented for MODIS lunar observations. A lunar observation planning tool is required to predict the time and roll angle needed for each lunar observation in the selected phase angle range. The tool is also needed to determine the phase angle range such that the MODIS can view the Moon in as many months as possible each year with the phase angle in the range. The MODIS Characterization Support Team (MCST) is responsible for MODIS instrument operation and calibration. We have developed a set of tools to address these needs and have successfully applied them to both Terra and Aqua MODIS. In this paper, we describe the design methodologies and the implementation of the tools. The tools have also been applied to VIIRS and can be applied to other remote sensors.