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Title: A comparison between evapotranspiration estimates based on remotely sensed surface energy balance and ground-based soil water balance analyses

Author
item TAGHVAEIAN, SALEH - Oklahoma State University
item PAUL, GEORGE - Texas Agrilife Research
item OCHSNER, TYSON - Oklahoma State University
item Gowda, Prasanna
item MAREK, THOMAS - Texas Agrilife Research

Submitted to: Proceedings of the World Environmental and Water Resources Congress Conference
Publication Type: Proceedings
Publication Acceptance Date: 4/15/2015
Publication Date: 5/17/2015
Citation: Taghvaeian, S., Paul, G., Ochsner, T., Gowda, P., Marek, T. 2015. A comparison between evapotranspiration estimates based on remotely sensed surface energy balance and ground-based soil water balance analyses. In: Proceedings of the World Environmental and Water Resources Congress 2015:Floods, Droughts, and Ecosystems, May 17-21, 2015, Austin, Texas.2015 CDROM.

Interpretive Summary: Evapotranspiration (ET) is a critical component of the water balance. Traditional methods of estimating crop ET rely on meteorological data, soil water content, or lysimeter techniques which have smaller foot prints. Mapping of ET as the residual of the remotely sensed surface energy balance has proved to be an effective method for estimating ET over fairly large areas at relatively low cost. In this study, we compared actual ET derived by closing soil water balance method against remote sensing based ET at four weather stations maintained by the Oklahoma Mesonet. Results indicated that remote sensing can provide accurate estimates of ET over longer periods. However, differences between the ET estimates at weekly interval was significant. This may be partly due to errors in the extrapolation of daily ET values between the image acquisition dates.

Technical Abstract: Remotely sensed and in-situ data were used to investigate dynamics of root zone soil moisture and evapotranspiration (ET) at four Mesonet stations in north-central Oklahoma over an 11-year period (2000-2010). Two moisture deficit indicators based on soil matric potential had spatial and temporal patterns that were consistent with collected precipitation and reference ET data, as well as the state-wide historical trends. Actual ET was estimated by closing the soil water balance using in-situ soil moisture data, as well as by applying a surface energy balance approach to Landsat Thematic Mapper 5 imagery. When averaged over all years, weekly ET estimates with both approaches had a small mean signed difference (0.5 mm·week-1), but a large root mean square deviation (11.6 mm·week-1). This difference may be partly due to errors caused by interpolation of ET estimates between less-frequent satellite overpasses. Averaging over longer periods or modifying the interpolation methods may improve the accuracies for short-term remotely sensed ET estimates.