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Comparison of Two Remote Sensing Approaches for ET Estimation in the San Joaquin Valley

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  5th National Decennial Irrigation Conference Proceedings, 5-8 December 2010, Phoenix Convention Center, Phoenix, Arizona USA  IRR10-9653.(doi:10.13031/2013.35875)
Authors:   Thomas J Trout, Lee F Johnson, Dong Wang, Byron Clark
Keywords:   Irrigation management, Irrigation scheduling, Remote Sensing, Surface Energy Balance, SEBAL

Two approaches that use satellite or aerial imagery to estimate evapotranspiration (ET) from land surfaces are surface energy balance techniques (eg: Surface Energy Balance Algorithm for Land (SEBAL)) and indirect methods based on vegetation indices. Field data collected in the San Joaquin Valley in 2008 was used to compare these approaches with ground-based measurements. Ground-based measurements of fractional ground cover and surface soil moisture were compared with satellite-based vegetation indices and combined with ground-based reference ET measurements to calculate ET estimates. This method was compared to SEBAL estimates on a field-by-field basis. Although the results from the two methods were correlated fairly well (r2=0.76), the SEBAL estimates of ET tended to be about 25% lower than those estimated from ground cover. The data indicated that perennial crops in the study area (pistachio and grape) may have been under water stress. The two approaches are based on differing data and analysis, and each has relative advantages and disadvantages.

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