The point response functions of CERES instruments aboard the Terra and Aqua spacecrafts over the mission-to-date

Abstract

The point response function (PRF) describes the response of an instrument to radiance from a point within its field of view. The Clouds and Earth Radiant Energy System (CERES) PRF is used together with measurements from the Moderate Resolution Imaging Spectro-radiometer (MODIS) to compute cloud information for each CERES pixel. Knowledge of the point response function (PRF) of CERES is essential to accurately align these data sets. The PRF has been measured for each CERES instrument during ground calibrations. Using in-orbit lunar calibrations, over ten years of data have been compiled for the Flight Models-1 and -2 aboard the Terra satellite and over eight years have been recorded for Flight Models-3 and -4 aboard the Aqua satellite. These data are used to examine the stability of the PRF of these instruments over the duration of their operations-to-date. In-orbit calibrations are taken at a lower scanning rate when compared to ground testing. As a result, these lunar scans provide more precise detector mapping capability due to a higher data sampling rate. Additional instrument performance measurements which can be gleaned are detector sensitivity stability and pointing accuracy.