SATELLITE-VIEW BIASES IN RETRIEVED SURFACE TEMPERATURES IN MOUNTAIN AREAS

Ground surface temperatures retrieved from satellite data taken in mou ntain areas may have biases that depend strongly on the satellite view ing angle and the time of day. Biases occur whenever there is a correl ation between the viewing angle and the temperatures of subpixel mount ainsides, such as when the satellite's view directly faces the most br ightly sunlit slopes. This paper reports simulations of this satellite -view bias effect for mountain terrain in central and southwestern Col orado and the southern Sierra Nevada in California. Surface temperatur es for the simulations were computed by using a mesoscale numerical we ather prediction model with a parameterization for terrain features th at are at a scale finer than the model grid resolution. The representa tion of terrain in the simulations was based on elevation data with hi gh resolution (30 m) from U.S. Geological Survey Digital Elevation Map data sets. Biases as large as 9 C degrees were found while assuming a satellite sensor resolution of 14 km. Even larger biases were found w ith finer sensor resolutions. These biases are substantially larger th an those that had previously been found from modeling with terrain dat a at about 90 m resolution (3'' latitude/longitude) from the Defense M apping Agency. The simulations suggest that satellite-view biases coul d cause substantial local errors when surface temperature retrievals a re used for climate diagnosis, weather analysis, soil moisture estimat ion, or geologic mapping. (C) Elsevier Science Inc., 1997.