Multitemporal behavior of L- and C-band SAR observations of boreal forests

An analysis of L- and C-band boreal forest backscattering properties with r espect to various temporally changing parameters is presented. The seasonal and weather dependent parameters considered include the depth of soil fros t, topsoil moisture, snow water equivalent, air temperature and precipitati on. The effect of these parameters on sigma(o) are studied for various stei n volume (biomass) classes by comparing the results against a cloud model-b ased semi-empirical modeling approach. Semi-empirical modeling is also used for a for est biomass retrieval experiment. The SAR data set includes 4 JE RS-1 (L-band, HIT-polarization) and 19 ERS-1 (C-band, VV-polarization) imag es for a test area in southern Finland, Additionally, a set of 2 JERS-1 and 3 ERS-1 images for another. test al ea in northern Finland is employed. Th e results show that radar response to forest biomass is more sensitive to c hanges in temporally varying parameters at C-band than at L-band. The semi- empirical modeling approach describes well the behavior of sigma(o) at both frequency bands when large forest areas are considered. Moreover, the mode ling approach appeals to be applicable for different conifer-dominated bore al for est types. Since the modeling approach explains satisfactorily the a verage backscattering behavior, the results in biomass retrieval show high accuracies (25-30% relative RMSE) when areas under investigation are large enough, i.e, about 20 ha.