Assessment and analysis of microwave emissivity and transmissivity of a deciduous forest towards the estimate of vegetation biomass

Forests play an important role in the global carbon cycle and have a potential impact on global climatic change. Monitoring forest biomass is of considerable importance in understanding the hydrological cycle. Because of the problem of dense forest cover, no reliable method with which to retrieve soil moisture in forest areas from the microwave emission signature has been established. All of these issues relate to the microwave emissivity and transmissivity characteristics of a forest. The microwave emission contribution received by a sensor above a forest canopy comes from both the soil surface and the vegetation layer. To analyze the relationship of forest biomass and forest emission and transmissivity, a high-order emission model, the matrix-doubling model, which consists of both soil and vegetation models, was developed and then validated for a young deciduous forest stand in a field experiment. To simulate the emissivity and transmissivity of a deciduous forest in the L and X bands using the matrix-doubling model, the parameters of components of deciduous trees when the leaf area index varies from 1 to 10 were generated by an L-system and a forest growth model. The emissivity and transmissivity of a forest and the relationships of these parameters to forest biomass are presented and analyzed in this paper. Emissivity in the L band when the leaf area index is less than 6 and at viewing angles less than 40°, and transmissivity in the L band are the most sensitive parameters in deciduous forest biomass estimation.