Seasonal evapotranspiration mapping using Landsat visible and thermal data with an energy balance approach in central Nebraska

摘要

Accurate estimation of evapotranspiration (ET) plays an important role in quantification of the water balance at the watershed, basin and regional scales for better planning and managing water resources. Knowledge of spatio-temporal distribution of ET on large scales, as quantified by satellite remote sensing techniques, can provide important information on a variety of water resources issues such as evaluating water distributions, water use by different land surfaces, water allocations, water rights, consumptive water use and planning, and better management of groundwater and surface water resources. While field measurements of evapotranspiration can provide vital data for a variety of purposes, point measurements need to be scaled up to larger areas to make water resources assessments on a watershed, district, or regional scale. Furthermore, ET is highly variable in space and time due to variability in land use, climatic conditions, soil properties, and management practices. Spatial variation in soil properties affects soil evaporation and surface energy balances, causing within-field and across field variability in ET. Satellite/ remote sensing technology provides an opportunity for representing spatial and temporal variation of ET. Thus, this advanced technique provides the spatial distribution of actual ET and consumptive water use over different land surfaces. This has enabled the estimation of ET from individual fields and this can enable policy makers to better understand and address the issue of water allocation and identifying and quantifying beneficial and unbeneficial water use that will result in better understanding and management of limited water resources. We applied the Mapping Evapotranspiration at High Resolution with Internal Calibration (METRIC™) to obtain ET maps for Central Platte Natural Resources District (CPNRD) in Nebraska, USA. A total of 45 images from Landsat 5 and Landsat 7 for paths 29-0 and rows 31-32 were processed for the 2007 growing season to obtain instantaneous and daily ET. In order to produce monthly and seasonal ET maps, individual daily ET maps generated from METRIC™ were interpolated between dates on a daily basis using a cubic-spline model. Cloud artefacts were removed and filled back in using interpolated ET data, and a background evaporation adjustment based on the FAO-56 Ke evaporation model was used.