REQUIREMENTS FOR SATELLITE LAND-SURFACE TEMPERATURE VALIDATION USING A SILT PLAYA

We investigate the validation of satellite land surface temperature (L ST) products. In particular, the planned EOS/MODUS global LST accuracy of 1 degrees C must be confirmed by independent measurements for a ra nge of cover types. Simple flat surfaces are the most easily instrumen ted and characterized and so provide a logical starting point. Such su rfaces include inland water, sand, snow, ice, and playa. Validation wi th water is straight-forward, but other land surfaces are more difficu lt to measure accurately. The analysis we present is based on a sequen ce of MODIS Airborne Simulator (MAS) images collected over a playa (si lt dry lake bed). Atmospheric effects in the MAS images are corrected by an in-scene method and are then converted to a time sequence of tem perature maps. These form the basis for estimating the spatial and tem poral sampling requirements to achieve a surface measurement accuracy of better than 0.5 degrees C for 1 km(2) MODIS pixels. We conclude tha t a grid of thermistors appears to be the most practical instrumentati on method for such a large area. Depending on the environmental condit ions, between 4 and 16 points are required per km(2), and we recommend that these be sampled at intervals ranging from 1 min to 2.5 min. A M AS underflight validation is possible if it is synchronized to within several minutes of the MODIS overpass. Finally, radiometers should be used at several of the thermistor locations to verify the skin tempera ture corrections and to characterize the temperature transients and an gular effects. (C) Elsevier Science Inc., 1997.