Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: January 11, 2008
Publication Date: February 6, 2008
Citation: Anderson, M.C., Kustas, W.P. 2008. Mapping evapotranspiration and drought at local to continental scales with a thermal-based surface energy balance model. In: National Integrated Drought Information System (NIDIS) Knowledge Assessment Workshop, February 6-7, 2008, Boulder, Colorado. 2008 CDROM. Technical Abstract: Water lost to the atmosphere through evapotranspiration (ET) has the effect of cooling the Earth’s surface. Land-surface temperature (LST), as mapped using thermal-infrared (TIR) band data, is therefore a valuable remote indicator of both ET and the surface moisture status (Moran, 2003). In partially vegetated landscapes, depletion of water from the soil surface layer (0-5 cm) causes the soil component of the scene to heat rapidly. Moisture deficiencies deeper in the soil profile, in the plant root zone (down to 1-2 m depth), lead to stomatal closure, reduced transpiration, and therefore elevated canopy temperatures, which can be effectively detected from space (Anderson et al., 2007c). Given current trends in population growth and climate change, it will become increasingly critical to be able to accurately remotely monitor the earth’s freshwater resources at local to global scales. The suite of thermal imaging sensors available over the U.S. currently provides this broad coverage. With the Geostationary Operational Environmental Satellites (GOES) we can obtain thermal images every 15min, but at fairly coarse spatial resolution (~5-10 km). At the other end of the spectrum, the aging Landsat-5 and -7 platforms provide thermal data at 60-120 m resolution, but only periodically (~monthly), and now with degraded coverage due to system failures. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra and Aqua satellites provides moderate resolution (1 km) TIR snapshots of land-surface conditions a couple of times each day, depending on cloud cover. These various data sources have good potential to be used synergistically in a variety of applications, at field to watershed to national scales. Proper interpretation of the TIR land-surface signal in terms of the underlying moisture status requires ancillary information about vegetation amount, which can be related to vegetation indices (VIs) derived from shortwave satellite reflectance data, and information about the local energy constraints (radiative and meteorological forcings) on the combined soil-plant-atmosphere system. These factors can be accounted for in a physical way within the context of a surface energy balance model. The Atmosphere-Land Exchange Inverse (ALEXI) modeling scheme described below is an example of one possible framework for synthesizing multi-scale, multi-platform thermal imagery into useful end-products for operational monitoring of drought and evaporative water loss.