Insolation Model
We're proud to offer the "take" from the UW Space Science insolation model, which estimates insolation at the surface by comparing each pixel of a satellite image with one taken when no clouds are present. This model, which has undergone over a decade of rigorous quality control and continual improvement, offers a remarkably good fit to data obtained from ground instruments.
Daily solar energy amounts are estimated using data in the visible portion of the spectrum which come from the Geostationary Operational Environmental Satellites (GOES). Simple physical models of radiative transfer for the clear and cloudy atmosphere are used with these data to evaluate whether a particular location is cloudy or clear and, if cloudy, to what extent clouds have depleted the solar beam. Usually, about eight to twelve individual GOES images are used during the course of a day to make estimates of the solar energy at the satellite image times. These instantaneous estimates are later summed to produce the daily solar energy totals.
Yesterday's insolation map: Eastern US Western US
Evapotranspiration Model
Maps of potential evapotranspiration (ET) are calculated from satellite-derived measurements of solar radiation and air temperatures at regional airports. The ET values on the maps are a reasonable estimate of daily crop water use for most crops that have reached at least 80% coverage of the ground. Prior to 80% or greater coverage, ET will be a fraction of the map value in proportion to the amount of coverage. The map values may vary slightly from ET estimates from AWON and other more site-specific models, but these differences are believed to be within the uncertainty of even measurements of actual water use made directly in a given field.
Yesterday's ET map: Wisconsin and Minnesota Florida
Irrigation Scheduling (NEW SOFTWARE!)
A newly-revised irrigation scheduling spreadsheet is available which uses these models to implement an allowable-depletion balance. This replaces the old ADCosmET.xls spreadsheet, and was developed by Dr. John Panuska of UW Extension/UW-Madison Biological Systems Engineering and Dr. John Norman, UW-Madison Soil Science. The documentation for the spreadsheet is available here. Watch this space for a new online irrigation scheduling tool, due for testing in Summer 2011!
Theory Behind the Models
For more details on the science behind these products, see Diak et al, "Agricultural Management Decision Aids Driven by Real-Time Satellite Data", Bulletin of the American Meteorological Society 79 (1998): 1345-1355.