SINGLE-SOURCE AND DUAL-SOURCE MODELING OF SURFACE-ENERGY FLUXES WITH RADIOMETRIC SURFACE-TEMPERATURE

Single- and dual-source models of the surface energy transfer across t he soil-vegetation-atmosphere interface were used in conjunction with remotely sensed surface temperature for computing the surface energy b alance over heterogeneous surfaces. Both models are relatively simple so that only a few parameters are specified, making them potentially u seful for computing surface fluxes with operational satellite observat ions. The models were tested with datasets collected from a semiarid r angeland environment with canopy cover generally less than 50% and a s ubhumid tallgrass prairie environment having canopy cover typically gr eater than 50%. For the semiarid site, differences between the single- source and dual-source model estimates of the sensible heat flux (H) a nd the observations averaged about 25%. For the tallgrass prairie, the disagreement between observations and single-source model estimates o f H was significantly larger, averaging nearly 55%. The average differ ence between observations and the dual-source model predictions for th e tallgrass prairie site increased slightly from the semiarid site to 30%. The latent heat flux (LE) was determined by residual from measure ments of net radiation and model estimates of the soil heat flux. For the semiarid site, the single-source model estimates of LE differed on average with the observations by about 15%, whereas the LE values com puted by the dual-source model differed by about 20%. For the tallgras s prairie site, the LE values from the single-source model differed fr om the observations by almost 35%, on avenge, whereas the dual-source model estimates produced an average difference of about 20%. Given the fact that energy nux observations by various techniques have been fou nd to differ by at least 20%, the single-source model performed satisf actorily for the semiarid site but had difficulty reproducing the flux es at the tallgrass prairie site. The dual-source model, however, perf ormed reasonably well at both sites. To obtain results comparable to t he dual-source model for the tallgrass prairie site, the single-source model required significant modifications to a parameter used in estim ating the roughness length for heat.