Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2002
Publication Date: N/A
Interpretive Summary: Reliable estimates of spatially distributed surface energy balance components are essential for accurate modeling of the hydrologic cycle and assessing vegetative conditions over a landscape. The Two-Source Energy Balance (TSEB) model designed to use remotely-sensed surface temperature (TSEBtr) and remotely-sensed surface soil moisture ( TSEBsm) have been applied to data collected during the Southern Great Plains 1997 (SGP97) experiment. Computed heat fluxes from both modeling schemes have been validated using tower and aircraft-based flux observations from SGP97 study sites. However, these observations represent a very small fraction of the land surface and thus it is nearly impossible to validate the spatial patterns in heat flux produced by such models over a landscape. In order to gain more insight into the uncertainty in spatially distributed fluxes from such models, output from both TSEBtr and TSEBsm output are compared on a pixel-by-pixel basis with remotely-sensed surface temperature and soil moisture collected concurrently during SGP97. Results of the comparisons suggested revisions to TSEBsm parameterizations are needed to better constrain flux predictions from the soil and vegetation allowing TSEBsm to accommodate a wider range of environmental conditions. It was also found that under high fractional vegetative cover conditions, estimates of energy partitioning between heat and evaporation flux at the soil surface by TSEBtr gave inconsistent results and indicated the TSEBtr scheme needs modifying when applied to dense vegetation cover conditions.
Technical Abstract: A Two-Source (soil + vegetation) Energy Balance (TSEB) modeling scheme has been developed to use either microwave-derived near-surface soil moisture (TSEBsm) or radiometric surface temperature (TSEBtr) as the key remotely sensed surface boundary condition for computing spatially distributed heat fluxes. Output of the surface heat fluxes from both two-source schemes have ebeen validated using tower and aircraft-based flux observations. However, these observations rarely provide the necessary spatial information for evaluating heat flux patterns produced by spatially-based models. By having microwave and radiometric surface temperature observations collected concurrently during the Southern Great Plains 1997 (SGP97) experiment conducted in Oklahoma, USA, heat flux estimates by the two modeling schemes were compared on a pixel-by-pixel basis. This provided a unique opportunity for evaluating the consistency in spatial patterns of the heat fluxes. Since the TSEBsm modeling scheme computes an effective surface temperature comparisons with radiometric surface temperature observations helped to elucidate factors contributing to discrepancies between TSEBsm and TSEBtr output. Results from the heat flux comparisons and simulated versus observed surface temperatures suggested revisions to TSEBsm parameterizations are needed to better constrain flux predictions from the soil and vegetation. When the revisions are made, TSEBsm accommodates a wider range of environmental conditions. The revisions involve an adjustment to the soil evaporation algorithm for differential drying of the near-surface soil layer and assimilation of the Priestley-Taylor coefficient estimated from the TSEBtr model. It was also found that under high fractional vegetative cover conditions, estimates of energy