| Abstract | In order to determine the forest-related information which can be obtained from multi-temporal and multipolarization SAR observations, we have acquired a series of multipolarization C-Band images with
the CCRS airborne C-SAR system over a representative area of the boreal forest biome near Whitecourt, Alberta. Data were acquired in early and late spring, summer, fall and winter, to emphasize the pronounced seasonal variability experienced in the
boreal forest. Comprehensive field measurements were obtained for 93 mature test stands, which were subsequently stratified into three classes (spruce, pine, and aspen-dominated hardwood) based on the dominant stand species. Meteorological
observations were obtained from two automated stations deployed in the test area throughout the data acquisition phase. As a result of the analysis of this data set, we have determined that the backscatter dynamic range in the boreal forest shows a
pronounced seasonal cycle. For the species studied, and for all dates, the dynamic range is usually less than four dB in like polarization and six dB in cross polarization. The dynamic range is largest during the spring and fall, and smallest during
summer and winter. The backscatter from spruce is greater than from pine, but the difference becomes very small in summer and winter. The backscatter from hardwoods is greater than that from the conifers except in the summer, when it is essentially
the same. These seasonal changes make it feasible to use multi-date C-band backscatter observations to discriminate these important boreal forest cover types. Discrimination with single-date, multiple polarization data was comparable to
discrimination with multi-date, single-polarization data. Discrimination was poor (generally less than 80%) with all single-date, single-polarization images. Using single and multiple regression techniques, this large data set was exhaustively tested
for relationships between C-band backscatter and stand structure measures, including crown closure, mean diameter-at-breast-height, mean tree height, mean crown closure, mean age, stems/hectare, timber volume/hectare, and biomass per hectare. Several
weak relationships were found but none were strong enough to suggest that C-band backscatter might be capable of providing reliable estimates of stand structural parameters. Species composition is identified as the most important influence driving
backscatter differences in C-band SAR images of the mature boreal forest. |