Clouds and the Earth's Radiant Energy System (CERES) instruments are currently flying on two satellite platforms, Terra, launched 18 December 1999 and Aqua, launched 04 May 2002. Both satellites are at a 705-km altitude, in high inclination, polar orbits. Terra crosses the equator at local morning, while Aqua crosses at local afternoon. Each platform carries two CERES instruments. Each CERES instrument contains three scanning radiation-detecting bolometers. The three detectors measure reflected solar and Earth emitted radiation in three bandwidths: shortwave (0.3-5 μm), window (8-12 μm), and total (0.3 to >100 μm). Earth views of each instrument are geolocated to the Earth fixed coordinate system using satellite attitude, ephemeris, and instrument pointing data. An analysis has been developed which uses radiation gradients at ocean-land boundaries measured by the CERES instrument as an aid to validate the computed geolocation. The detected coastlines are compared to known map coordinates and an error analysis is performed after a best fit is made in the coastline comparison. Spatial differences are mapped from latitude, longitude to absolute distance in along-track (ground path) and cross-track (perpendicular to ground path) of the satellite. Results of the Terra CERES instruments have shown maximum errors to be within 10% of the nadir footprint size. A
description of the coastline detection and error analysis will be presented along with results for the Terra CERES instruments. Initial results from the coastline detection and error analysis for the Aqua instruments will be presented also.