Thursday, 17 January 2002: 9:00 AM
Utility of remote sensing in modeling spatial patterns of evapotranspiration
Validation of the spatial patterns of evapotranspiration (ET) produced by spatially-based energy balance models using remotely sensed data is problematic. This is because tower-based observations provide a relatively small sample of the entire modeling domain, while the aircraft-based measurements reflect area-average values over the landscape. A logical first step in addressing this issue and in assessing the utility of remotely-sensed based approaches is to compare the consistency in the spatial patterns of ET from different models. A Two-Source (soil + vegetation) Energy Balance (TSEB) modeling scheme developed to use either microwave-derived near-surface soil moisture or radiometric surface temperature as the key remotely sensed surface boundary condition for computing spatially distributed heat fluxes is used for this purpose. With microwave and radiometric surface temperature observations collected concurrently during the 1997 Southern Great Plains experiment (SGP97) conducted in Oklahoma, USA, model heat flux estimates by the two schemes are compared on a pixel-by-pixel basis providing a means for assessing uncertainty in spatial patterns of ET. In addition, since the TSEB scheme using microwave remote sensing computes an effective surface temperature, the remotely sensed surface temperatures are used to evaluate model parameters. Results from the heat flux comparisons and simulated versus observed surface temperatures provide insights into the reliability of the remotely-sensed based schemes. In addition, the comparisons suggest revisions are needed in model algorithms, and indicate when surface conditions contribute to inconsistencies in ET patterns during a dry down period.