Submitted to: Agronomie Agriculture Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2001
Publication Date: N/A
Interpretive Summary: This is a short communication of the first results on the use of the multi-spectral thermal infrared data acquired with the new ASTER instrument on NASA-s Terra satellite. Estimates of the surface heat fluxes are made and compared favorably with ground measures of the fluxes.
Technical Abstract: The recent availability of 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 at 90 meter resolution. One critical variable in evapotranspiration models is surface temperature. With ASTER the temperature can be reliably determined over a wide range of vegetative conditions. The requirements for accurate temperature measurement include minimization of atmospheric effects, correction for surface emissivity variations and sufficient resolution for the type of vegetative cover. When ASTER imagery are combined with meteorological observations, these requirements are usually met and result in surface temperatures accurate within 1-2 C. ASTER-based evapotranspiration estimates for September 4, 2000 were made over grazing and wheat lands in central Oklahoma. Daily evapotranspiration 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 energy balance Bowen ratio measurements and illustrate how ASTER measurements can be applied to heterogeneous terrain.