Evapotranspiration Estimation Using Multispectral Thermal Infrared Data from ASTER and MODIS

Estimating evapotranspiration (ET) from space is important for monitoring water use at local and regional scales. Terra platform sensors ASTER and MODIS have been valuable for this goal because of their multispectral capabilities and high (90 m with ASTER) to moderate ( 1 km with MODIS) spatial resolutions. These capabilities have allowed discrimination of land cover conditions unobtainable from more conventional satellite imagery. In particular the multiple thermal channels provided by ASTER and MODIS have helped collect accurate observations of land surface temperature and emissivity which can be used to detect water stress and to distinguish between living and senescent vegetation. Each of these characteristics is important for modeling water fluxes. The frequent coverage by MODIS is also very important for this endeavor. To demonstrate how this can be accomplished, ASTER and Terra/MODIS data were modeled using images collected over the Jornada Experimental Range, a semi-arid research site in southern New Mexico. By combining 27 ASTER clear sky scenes with several hundred 1-km scale MODIS scenes between 2001 and 2003, it was feasible to estimate ET at weekly time steps and to also assess longer-term changes in vegetation distributions.