Temperature and emissivity are defined for homogeneous and isothermal surfaces. However

natural land surfaces are neither homogeneous nor isothermal. The directional effects of thermal emission can not be neglected. We developed a model to describe the directional emission of vegetation canopies in thermal infrared band based on a conceptual model. The complex nonisothermal land surfaces are separated as homogeneous and isothermal components with distinct temperature in this model. A nonisothermal leaf canopy is modeled and inverted in this paper as an illustration. By statistical analysis of the inversion results

it is shown that this model is robust to noises. When a priori guesses for the component temperatures have errors of 2K and the noise equivalent temperature difference （ NE Δ T ） in the observations is about 0.29K

the mean inverted temperatures have biases of 0.08K and 0.24K for the top and bottom layer respectively. The standard deviations of the inversion results are 0.15K and 0.48K respectively.