A strategy to assess the pointing accuracy of the CERES FM1-FM5 scanners

The Clouds and the Earth's Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the Earth and thermal radiation emitted by the Earth. Five CERES instruments are currently in service; two aboard the Terra spacecraft, launched in 1999; two aboard the Aqua spacecraft, launched in 2002; and one instrument about the NPP spacecraft, launched in 2011. Verifying the pointing accuracy of the CERES instruments is required to assure that all earth viewing data is correctly geolocated. The CERES team has developed an on-orbit technique for assessing the pointing accuracy of the CERES sensors that relies on a rapid gradient change of measurements taken over a well-defined and known Earth target, such as a coastline, where a strong contrast in brightness and temperature exists. The computed coastline is then compared with World Bank II map to verify the accuracy of the measurement location. This paper briefly restates the algorithm used in the study, describes collection of coastline data, and summarizes the results of the study the CERES FM1, FM2, FM3, and FM5 instruments.