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United States Department of Agriculture

Agricultural Research Service

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Location: Hydrology and Remote Sensing Laboratory

2011 Annual Report

1a. Objectives (from AD-416)
Produce near-real-time maps of hourly insolation maps at 20km resolution over the continental U.S. for the year 2009-2010 using GOES imagery. This product will be used in realtime execution of the Atmosphere-Land Exchange Inverse (ALEXI) model, developed at the USDA-ARS, to estimate evapotranspiration (ET) and other land surface fluxes.

1b. Approach (from AD-416)
Work with UW scientists to coordinate production and daily transfer of insolation dataset to HRSL. In addition, the UW cooperators will work on improvements to the existing algorithms, including a) incorporation of more reliable estimates of precipitable water from the NCEP GFS model; b) development of a validation/calibration procedure using pyranometer data from the U.S. Climatological Radiation Network; and c) transitioning of this new insolation algorithm to operations (including documentation).

3. Progress Report
This product is being used in real time execution of the Atmosphere-Land Exchange (ALEXI) model, developed at the USDA-ARS, to estimate evapotranspiration and other land-surface fluxes. Legacy code was updated and optimized for execution speed. A calibration technique was developed using ground-based pyranometer data, which is used to adjust model cloud albedo using an objective analysis technique. The resulting calibration coefficient has dramatically improved the estimation of insolation from GOES measurements at high-reflectance (high cloud albedo, low insolation) situations. Atmospheric total precipitable water (TPW) is another important variable in the estimation of insolation from GOES data. Code has been written that accesses the NOAA Global Forecast System (GFS) TPW, a reliable and general source obtainable from the NOAA Web site. A new model framework including these improvements has been constructed and is easily portable to any McIDAS location. USCRN (U.S. Climate Reference Network) pyranometer data access has been automated in order to validate satellite daily and hourly insolation estimates from the new insolation model and calibrate the visible channel on GOES satellites via newly-developed techniques. Model resolution has been improved to 10-km spatial (down from 20 km), and half-hour temporal (up from hourly) to facilitate higher resolution mapping applications. Finally, it is apparent that errors in hourly satellite estimates of insolation can often be related to the bidirectional components of radiation that the insolation model does not take into account. We are researching simple bidirectional models that might be used to improve the accuracy of the hourly satellite estimates. Methods researched to date either require pre-classification of the scene type (clear, partly cloudy, ocean, land, etc.), which would make the estimation of insolation from GOES an iterative and computationally-expensive effort, or simply too much computer time due to the complexity of the radiative transfer model. The search for an appropriate model will continue. The new insolation model has been transferred to SSEC Data Center, where it is undergoing debugging and testing. Once this has concluded, the model will be transferred to operations, where it will replace the currently running production model. The ADODR has monitored the progress of this project through email correspondences and conference calls with University of Wisconsin scientists.

4. Accomplishments

Last Modified: 2/23/2016
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