Submitted to: International Symposium on Remote Sensing for Agriculture Ecosystems Hydrol
Publication Type: Proceedings
Publication Acceptance Date: August 30, 2001
Publication Date: N/A
Technical Abstract: Multi-band thermal infrared imagery from the Advanced Spaceborne Thermal Emission & Reflection radiometer (ASTER) on NASA's Terra satellite has made feasible the estimation of evapotranspiration (ET) at 90 meter resolution. One critical variable in ET models is surface temperature. With ASTER the temperature can be reliably determined over a wide range of vegetative conditions. When ASTER imagery are combined with meteorological observations, the resulting surface temperatures are accurate within 1-2 C. ASTER-based ET estimates were made during September 2000 over the sub-humid grazing and wheat lands at the USDA/ARS Grazinglands research laboratory near El Reno in central Oklahoma. Daily ET was estimated by applying instantaneous ASTER surface temperatures, as well as ASTER-based vegetation indices from visible-near infrared bands, to a two-source energy flux model and combining the result with separately acquired hourly solar radiation data. The estimates of surface fluxes show reasonable agreement (50-100 W/m^2) with ground-based Bowen Ratio Energy Balance measurements and illustrate how ASTER measurements can be applied to heterogeneous terrain. There are some discrepancies which may in part be due to difficulty quantifying fractional cover of senescent vegetation.