Radiometric Surface Temperature Components for Row Crops.

Land surface temperature is a boundary condition often used in assessing soil moisture status and energy exchange from the soil-vegetation-atmosphere interface. For row crops having incomplete canopy cover, the radiometric surface temperature is a composite of sunlit and shaded vegetation and substrate. Relative contributions of each temperature component are dependent on sun-target-sensor geometry. We developed a model that partitions the composite radiometric surface temperature into its respective temperature components for arbitrary orientations of the sun, row crop, and infrared thermometer viewing angle. The model assumes an elliptical sensor field-of-view overlaid on a continuous elliptical canopy. The model was tested using field measurements of vegetation, sunlit soil, shaded soil, and the soil-vegetation composite of row crops. For clear-sky conditions, dry soil, and a non-water-stressed cotton canopy, shaded soil was up to 10°C greater than vegetation; however, sunlit soil was up to 40°C greater than vegetation.