Natural terrain infrared radiance statistics: daily variation.

The statistical distribution of the radiance in a thermal image of natural terrain is analyzed. The radiance of each spatial element is related through the heat balance equation to the thermal properties of this element and to the heat input from an external source. As the heat exchange factors of each spatial element over a large area are distributed, the radiance will be distributed as well. Due to nonlinear coupling of the temperature to the thermal properties and heat source, the radiance distribution varies in a complex manner while the heat source changes, the most noticeable result being the asymmetry of the distribution density of the radiance and the change in the sign of that asymmetry with changing heat source.