Colorado Agricultural Experiment Station
Active Projects 2013

Note: A NEW project—initiated within last year—might not have an annual report, publications, or outcomes/impact.
Project: COL00707 Department: Civil & Environmental Engineering  
PIs: Elhaddad, A
Title: Use of Remote Sensing of Evapotranspiration model (ReSET) in the South Platte River Basin
Begin Date: 07/01/2011 Term Date: 06/30/2014 Most recent project status: Terminated
Objectives: Goals/Objectives: The previous AES project provided funding for the South Platte Mapping and Analysis Program (SPMAP), which has been extremely successful. As part of the SPMAP effort a number of computer tools have been developed and are widely used by water users and consultants (see attached letter of support from Northern Colorado Water Conservancy District). There are additional needs to continue to enhance the tools and incorporate new technology. This funding would allow us to enhance a new model for calculating CU/ET (consumptive use/evapotranspiration) using remote sensing called ReSET (Remote Sensing of ET). Expected Outputs: a) The development of a practical procedure for ReSET implementation that can be applied efficiently to large areas to determine the actual ET near real-time after a satellite image is taken. b) The potential for a CU monitoring system using remote sensing over an entire field(s) to account for spatial variability (i.e., versus soil moisture monitoring at just a specific location in the field) that can be the basis for an ADI (Augmented Deficit Irrigation) Program to determine saved water from deficit irrigation, rotational fallowing or non-irrigation cropping. Actual accumulated ET can then be compared to the historic ET to determine the amount of water saved. Subtracting actual ET from measured inflows to fields/farms will be a quantification of return flows that must be maintained/augmented in a successful ADI Program. c) The development of a ReSET website where processed images (raster/vector) are placed soon after processing for all to use in the South Platte. The raster/vector image will have values of ET (inches/day) by pixel and website tools will allow a user to determine ET for fields. d) Use ReSET to evaluate the accuracy of determining crop type (i.e., alfalfa versus corn) and determine water adequacy in a ditch system both currently and historically with past satellite images.
Approach: The ReSET land surface energy balance model (Elhaddad and Garcia 2008) will be used to process available satellite images of the South Platte River Basin in Colorado. Summing up values of actual ET (ETa) over a time period Delta_t, and multiplying by the area of an irrigated field will provide an estimate of QET for use in the field water balance. The model can be applied to historical data since satellite images are available at no cost in most instances for the past 20 years or so. The model can also be applied to large areas (180 km x 180 km) yet retaining a resolution of 30m x 30, which allows the model to determine the ET for small parcels. The ReSET model is built on the same theoretical basis of its two predecessors METRIC (Allen et al. 2007 a,b) and SEBAL (Bastiaanssen et al 1998 a,b) with the additional ability to handle data from multiple weather stations. This enhances regional ETa estimates by taking into consideration the spatial variability of weather conditions through data acquired from different weather stations (across the area covered by the remote sensing system/imagery). ReSET can be used in both the calibrated and the un-calibrated modes. The calibrated mode is similar to METRIC in which the reference ETr from weather stations is used to set the maximum ETa value in the processed area, while in the un-calibrated mode the model follows a similar procedure as SEBAL where no maximum ETr value is imposed. Estimating Seasonal ET: Cumulative ET calculations are needed to estimate seasonal water savings from specific fields that either had deficit irrigation, rotational fallowing or non-irrigation cropping. Seasonal ET is calculated using actual individual ET grids developed at each image date and filling interpolated ET grids between them. The ET grids on days when images are not available are calculated using the ReSET seasonal tool, which is a GIS application that uses the actual ReSET ET daily grids as well as nearby weather stations to estimate the ET taking into consideration the spatial and temporal variability of ET. Next all calculated ET grids can be added to total water volume per unit area for the season for each field being monitored.
Keywords: Remote Sensing RESER Energy Balance Crop Coefficients Consumptive Use Evapotranspiration