Mapping surface energy flux partitioning at large scales with optical and microwave remote sensing data from Washita '92

A model evaluating the energy balance of the soil/substrate and vegetation (i.e., two-source) was applied to remotely sensed near-surface soil moistur e maps generated from passive microwave data collected during the Washita ' 92 experiment. Model parameters were derived from a soil texture and a land -use/land cover database along with a normalized difference vegetation inde x map created from a SPOT satellite image, The Bowen ratio (B-O, ratio of s ensible to latent heat flux) was used for investigating the temporal and sp atial variability in model output. Comparisons between predicted and observ ed heat fluxes were made with values summed over the daytime period. Daily maps of midday B-O indicated areas with low vegetation cover or bare soil a nd senescent vegetation were drying out significantly (i.e., dramatic incre ases in B-O), while other areas with higher vegetation cover showed smaller increases in B-O in response to a drying soil surface. This result agrees with the profile soil moisture and surface flux observations indicating ade quate moisture was available to the vegetation for meeting atmospheric dema nd. The predicted daytime fluxes agreed to within 1 mm of the observations with approximate to 25% difference between modeled and observed daytime eva potranspiration. Differences between modeled and measured surface temperatu res averaged approximate to 2 K. The discrepancies between model output and observations are similar to the uncertainty in these measurements, indicat ing that the model provided reliable daytime energy flux maps for the Washi ta '92 study area using remotely sensed nearsurface soil moisture.