Seasonal effects on C- and X-band backscattering properties of Finnish boreal forests

The seasonal changes of the backscattering properties of boreal forests are investigated by applying (1) a semi-empirical C- and X-band forest backscattering model and (2) multi-temporal ERS-1 SAR data from several test sites in Finland. The results are presented as a function of forest stem volume (which is closely related to forest biomass). The empirical modeling of forest canopy backscattering and extinction properties is based on the high-resolution ranging scatterometer (HUTSCAT) data. The response of ERS-1 SAR data to forest stem volume is investigated by employing the National Forest Inventory test sites that cover the ERS-1 test areas in a regular pattern. The model results and ERS-1 data show that the correlation of radar response to forest biomass may be positive, negative or about zero. This variation is primarily caused by the changes in soil and vegetation moisture, and by the seasonal snow-cover