Sunday, 22 January 2012
Corn and Soybean Albedo Variations with Zenith Angle
Hall E (New Orleans Convention Center )
As technology has advanced, meteorological and climatological models have increased their spatial resolution considerably, from a scale of 100-500km to a scale of 10-40km. The smaller scale has the potential to improve the accuracy of these models, but models are only as good as the data input into the model and the parameters used by the model to represent the true physics of the Earth system. With the advancement in technology, however, some model input variables fail to produce detailed results on the new model's scale. Updated albedo values over various crop fields could provide more precise results from the models. A more accurate estimate of albedo and how certain variables affect it, such as the zenith angle or type of vegetation, will lead to a better representation of long wave radiation, sensible heat flux, and latent heat flux values. In addition, albedo can change significantly over time, especially in agribulutal regions. Data were collected from an agricultural field near the Iowa State University campus in Ames, Iowa, in cooperation with the USDA ARS National Laboratory for Agriculture and the Environment. Each year the crop planted rotates between corn and soybeans.
The goal of this project is to determine a correlation between the zenith angle of the sun and albedo over corn and soybean fields during the growing season of May to October. If a correlations is found, we will develop a simple empirical model and propose some possible physical models for the change in albedo with zenith angle. The albedo will be compared between the different stages of plant growth, from bare soil to full plant growth to maturity. We hypothesize that as the sun zenith angle decreases as the sun nears solar noon, albedo values will increase over both corn and soybean. In addition, the albedo values for corn and soybean fields will vary moderately from general values used in current weather and climate models, so the albedo values will be more precise and useful for model use.