Location: Soil and Water Management Research
Title: Radiometric surface temperature calibration effects on satellite based evapotranspiration estimation Authors
Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 2008
Publication Date: May 1, 2009
Citation: Chavez Eguez, J.L., Gowda, P., Howell, T.A., Copeland, K.S. 2009. Radiometric surface temperature calibration effects on satellite based evapotranspiration estimation. International Journal of Remote Sensing. 30(9):2337-2354. Interpretive Summary: Crop water use needs to be quantified in order to manage irrigation systems more efficiently. In this study, a remote sensing based method was evaluated for its ability to estimate spatial daily crop water use or evapotranspiration. Data from five large weighing lysimeters located at a USDA-ARS research facility in Bushland, Texas were used for this purpose. Results show that the remote sensing method requires correction of thermal images for atmospheric effects. Further, a region-specific leaf area index model would enhance the ET estimation accuracy. Overall, the remote sensing method seems to be an appropriate tool for mapping ET in the Texas High Plains. More evaluation is needed for all major crops under different climatic conditions.
Technical Abstract: Agriculture on the Texas High Plains (THP) uses approximately 89% of groundwater withdrawals from the Ogallala Aquifer, leading to steady decline in water table levels. Therefore, efficient water management is essential for sustaining agricultural production in the THP. Accurate evapotranspiration (ET) maps provide critical information on actual spatio-temporal crop water use. METRIC (Mapping Evapotranspiration at High Resolution using Internalized Calibration) is a remote sensing based energy balance method that uses radiometric surface temperature (Ts) for mapping ET. However, Ts calibration effects on satellite based ET estimation is less known. Further, METRIC has never been tested for the advective conditions of the semi-arid THP. In this study, METRIC was evaluated by comparing predicted ET with measured values from five monolithic weighing lysimeters at the USDA-ARS Conservation and Production Research Laboratory in Bushland, Texas, USA. Three different levels of calibration were applied on a Landsat 5 Thematic Mapper’s thermal image acquired on 23 July 2006 to derive Ts. Application of METRIC on a MODTRAN calibrated image improved the accuracy of distributed ET prediction. In addition, ET estimates were further improved when a THP-specific model was used for estimating leaf area index. Results indicated that METRIC performed well with ET mean bias error ± root mean square error of 0.4 ± 0.7 mm d-1. The use of METRIC for the advective conditions of the THP is promising; however, a thorough evaluation of METRIC’s submodels is needed for major crops under different agroclimatological conditions.