1US Dept of Agriculture, Beltsville, MD, USA
2Dept. of Soil Science, University of Wisconsin-Madison, Madison, WI, USA
3I.M. Systems Group at NOAA/NESDIS, Camp Springs, MD, USA
4Dept. Atmospheric Sciences, University of Alabama-Huntsville, Huntsville, AL, USA
5IFAPA Andalusian Agriculture and Fisheries Dept, Córdoba, Spain
6Dept. Civil, Environ. and Aerosp. Eng., Università degli Studi di Palermo, Palermo, Italy
7Dept. Agricultural Engineering and Agronomy, University of Naples Federico II, Naples, Italy
8Dept. of Fruit Production and Enology, Pontificia Universidad Católica de Chile, Santiago, Chile
9NASA Goddard Space Flight Center and Earth Resources Technology Inc., MD, USA
Received: 16 Jul 2010 – Discussion started: 23 Aug 2010
Abstract. Thermal infrared (TIR) remote sensing of land-surface temperature (LST) provides valuable information about the sub-surface moisture status required for estimating evapotranspiration (ET) and detecting the onset and severity of drought. While empirical indices measuring anomalies in LST and vegetation amount (e.g., as quantified by the Normalized Difference Vegetation Index; NDVI) have demonstrated utility in monitoring ET and drought conditions over large areas, they may provide ambiguous results when other factors (e.g., air temperature, advection) are affecting plant functioning. A more physically based interpretation of LST and NDVI and their relationship to sub-surface moisture conditions can be obtained with a surface energy balance model driven by TIR remote sensing. The Atmosphere-Land Exchange Inverse (ALEXI) model is a multi-sensor TIR approach to ET mapping, coupling a two-source (soil + canopy) land-surface model with an atmospheric boundary layer model in time-differencing mode to routinely and robustly map daily fluxes at continental scales and 5 to 10-km resolution using thermal band imagery and insolation estimates from geostationary satellites. A related algorithm (DisALEXI) spatially disaggregates ALEXI fluxes down to finer spatial scales using moderate resolution TIR imagery from polar orbiting satellites. An overview of this modeling approach is presented, along with strategies for fusing information from multiple satellite platforms and wavebands to map daily ET down to resolutions on the order of 10 m. The ALEXI/DisALEXI model has potential for global applications by integrating data from multiple geostationary meteorological satellite systems, such as the US Geostationary Operational Environmental Satellites, the European Meteosat satellites, the Chinese Fen-yung 2B series, and the Japanese Geostationary Meteorological Satellites. Work is underway to further evaluate multi-scale ALEXI implementations over the US, Europe, Africa and other continents with geostationary satellite coverage.
Revised: 04 Jan 2011 – Accepted: 06 Jan 2011 – Published: 21 Jan 2011
Anderson, M. C., Kustas, W. P., Norman, J. M., Hain, C. R., Mecikalski, J. R., Schultz, L., González-Dugo, M. P., Cammalleri, C., d'Urso, G., Pimstein, A., and Gao, F.: Mapping daily evapotranspiration at field to continental scales using geostationary and polar orbiting satellite imagery, Hydrol. Earth Syst. Sci., 15, 223-239, doi:10.5194/hess-15-223-2011, 2011.