The goal of this project is to calculate spatially distributed daily reference evapotranspiration (ETo) and produce daily ETo maps for the State of California at high spatial resolution (1 km2-16km2). Methodology for creating Statewide ETo maps will use National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environmental Satellite (GOES) imager and/or sounder data, combined with the California Irrigation Management Information System (CIMIS) and/or NOAA weather station data, and ancillary datasets. Methods exist to convert raw radiance data into physical units and these calibrations can be implemented using standard methods without requiring extensive research to implement existing protocols.

CalSpace will host a web site for the daily ETo images and other data (mirrored to CIMIS), offering a map query interface to daily datasets, with simple boundary, roads, and hydrographic overlays. Data will be provided daily to CIMIS (or at time intervals requested) for long term storage. CalSpace will produce a monthly archive of Statewide Daily ETo, and yearly archive of 10 day averages of ETo. Geotiff images of daily ETo will be produced for downloading by client users. Datasets will be projected using Alber's equal area projection following the Teale Data Center model, at a resolution of 1 km2 to 16 km2. A daily archive of intermediate data products and calibration programs and parameters will be available to CIMIS. All data, programs, and documentation produced by the project will use GPL licensed (open source).

ETo estimation will follow the Penman-Monteith procedures while using the GOES and weather station data for estimating net radiation as the first product incorporated into the ETo model, to be followed by surface temperature, relative humidity, and wind speed using satellite data. Surface temperature is to be correlated with air temperature at the CIMIS and/or NOAA weather station sites. We propose to use interpolated CIMIS weather station data as an alternative to the secondary products if the GOES products are deemed unsatisfactory. Interpolation schemes are known to have problems from topography, undersampling, and poorly distributed weather stations. Improved interpolation schemes (e.g., cokriging with topography) may help to overcome these problems but will require additional research and time to implement. If topography creates large errors in the ETo estimates for mountainous regions of the State, a short-term solution would involve masking the non-agricultural regions of the state as a first step in producing a statewide map.