Determination of CERES flight models 1 and 2 sensors zero-radiance response variability with elevation and azimuth scan angles on-orbit aboard TERRA Spacecraft

摘要

The Clouds and the Earth's Radiant Energy System (CERES) instrument has scanning thermistor bolometers that measure broadband radiances in the shortwave (0.3 - 5.0 micrometer), total (0.3 - >100 micrometer) and 8 - 12 micrometer water vapor window regions. The CERES Flight models I and II (FM1 and FM2) instruments were launched aboard the Earth Observing System-Terra platform on December 1999. The CERES instrument can operate in fixed as well as rotating azimuth positions with the elevation head moving in full scan or short scan modes. The sensor measurements have shown a dependency on observation geometry during each of these scan modes of operation. The zero radiance offsets of the sensors were measured using end caps (low emittance aluminum targets) on the ground at each elevation observation angle in fixed azimuth scan mode. The Terra spacecraft have conducted two sets of calibration maneuvers viewing the deep space on-orbit in March and April 2003. During these tests where the spacecraft is constantly pitched to view the cold space (3 degree K blackbody), zero radiance offsets were measured for the CERES sensors in all scan modes of operation. This paper describes the procedures used to determine the zero radiance scan offsets for CERES sensors. The measured offset values calculated from ground and in-flight tests for the FM1 and FM2 sensors are also presented.