Spatially distributed sensible heat flux over a semiarid watershed .1. Use of radiometric surface temperatures and a spatially uniform resistance

Spatially distributed radiometric surface temperatures over a semiarid watershed were computed using remotely sensed data acquired with an aircraft-based multispectral scanner during the Monsoon '90 Large Scale Field Experiment. The multispectral scanner data provide watershed coverage of surface temperature at a resolution of 6.3 m and nearly daily temporal resolution. At high spatial resolution, the surface temperature values appear to be correlated strongly with surface aspect; at more coarse spatial resolution, the surface temperatures variations across the watershed appear to be correlated with background soil moisture variations caused by highly localized precipitation events. The surface temperature data were aggregated to 400-m spatial resolution for the purpose of computing spatially distributed sensible heat fluxes over the watershed. The practicality of using a spatially uniform transfer coefficient was evaluated by examining the variability of surface and meteorological factors across the watershed at the times of the aircraft overpasses. Maps of sensible heat flux over the area were computed for three aircraft overpass dates and compared to localized patterns of recent precipitation in the basin. Maps of instantaneous sensible heat flux tracked well with the spatial patterns of variable surface soil moisture that arose from the localized precipitation events.