Modeling directional brightness temperature over a maize canopy in row structure

A modeling study on the variations of directional brightness temperature (DBT) for row-structure crops was carried out with the help of the images captured by a large aperture thermal infrared camera over a maize canopy. The model assumes that the DBT is a function of component brightness temperatures and their directional fractions. The canopy has three brightness temperature components: sunlit soil, shaded soil and vegetation, each component has a unique temperature value. Component fractions in the scene of view depend on sun-view geometry and the distributions of gaps within and between plant rows. To describe canopy geometrical features, a system of porous hedgerows with rectangle cross-section has been used; the directional variations of gap fraction are described by Nilson function. The model demonstrates directional variations of DBT as a function of sun-viewing geometry and canopy geometrical structure as well as component brightness temperatures. In the simulation of DBT over a middle dense canopy near the noontime, the results reveal an evident row-direction-oriented hot stripe in the DBT polar map, where appeared the hot spot along the sun direction. The sensitivities of the model to the input parameters have been tested. Further validation analysis has also been conducted which demonstrates modeled DBT agreeing closely with field observations.