METRICTM (Mapping Evapotranspiration at high Resolution and with Internalized Calibration) is an image-processing tool for calculating ET as a residual of the energy balance at the earth’s surface. METRICTM is a variant of the important model SEBAL, an energy balance model developed in the Netherlands and applied worldwide by Bastiaanssen. METRICTM has been extended to provide tighter integration with ground-based reference ET and has been applied with Landsat images in southern Idaho to predict monthly and seasonal ET for water rights accounting and for operation of ground water models. METRICTM has also had limited application in the Imperial Valley of Southern California. ET “maps” (i.e., images) provide the means to quantify, in terms of both the amount and spatial distribution, the ET on a field by field basis. Results from METRICTM have been compared and validated using precision-weighing lysimeter measurements from the U.S. Department of Agriculture – Agricultural Research Service (USDA-ARS) at Kimberly, Idaho, and from Utah State University for the Bear River. ET for periods between satellite overpasses was computed using ratios of ET from METRICTM to reference ET computed for ground-based weather stations. ET maps via METRICTM provide the means to quantify, in terms of both the amount and spatial distribution, ET from individual fields. The ET images generated by METRICTM show a progression of ET during the year as well as distribution in space. Initial application and testing of METRICTM indicates substantial promise as an efficient, accurate, and relatively inexpensive procedure to predict the actual evaporation fluxes from irrigated lands throughout a growing season. ET from satellite images may replace current procedures used by Idaho Department of Water Resources and other management entities that rely on ground-based ET equations and generalized crop coefficients that have substantial uncertainty. 1 This paper was originally presented at the 2002 meeting of the United States Committee on Irrigation, Drainage, and Flood Control at San Luis Obispo, CA. It has been edited and updated for republication by California Dept. Water Resources in 2004. 2 Professor of Water Resources Engineering, University of Idaho, 3793 N. 3600 E., Kimberly, Idaho 83341 3 Manager, Remote Sensing Section, Idaho Dept. Water Resources (IDWR), Boise, ID 4 Grad. Assist. and now Post-Doctoral Researcher, Univ. Idaho, Kimberly 5 Ph.D. student, Utah State Univ., Logan, Utah and now Professor, Univ. Andes, Maleda, Venezuela. 6 President, WaterWatch, Wageningen, The Netherlands 7 Scientist, (now retired) USDA-Agricultural Research Service, Kimberly, Idaho 8 Remote Sensing Analyst, IDWR
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