SURFACE-TEMPERATURE OBSERVATIONS FROM AVHRR IN FIFE

Observations of the surface radiometric temperature by the AVHRR senso r on board the NOAA-9 satellite during the First ISLSCP (International Satellite Land Surface Climatalogy Project) Field Experiment conducte d in central Kansas during 1987 are presented. The satellite observati ons were corrected for atmospheric effects using a path radiance model (MODTRAN3) and radiosonde measurements. Problems with this approach i nclude the nonsimultaneity of the soundings with the overpass and erro rs involved in profile measurements. For the former, soundings before and after the overpass were interpolated to the time of the overpass. For the latter, some of the errors arise from the +/-0.5 degrees C unc ertainty in the dry-and wet-bulb temperatures, which can produce up to a +/-14% relative uncertainty in the water vapor. To overcome this un certainty, the water vapor profiles were adjusted until the channel 4 and 5 temperature differences over a large reservoir were reduced to z ero. This adjusted profile was then used over the entire site. The res ults are compared to ground broadband temperature readings at 10 sites and to aircraft results from the thermal channel of the NS001 sensor on the C-130 aircraft. The AVHRR values were found to be 5 degrees to 6 degrees C warmer than the average of the ground measurements. This d ifference is attributed to the fact that the ground measurements were made preferentially on well-vegetated surfaces while the AVHRR integra tes over the entire site, which includes many warm surfaces.