MODELING L-BAND RADAR BACKSCATTER OF ALASKAN BOREAL FOREST

Synthetic aperture radar (SAR) data were acquired over Bonanza Creek E xperimental Forest (Alaska) in March 1988 under thawed and frozen cond itions. For five stands analyzed, L-band backscatter at 42-degrees-45- degrees incidence angle was 2.7-6.9 dB smaller under frozen than under thawed conditions for white spruce and balsam poplar, with the larges t difference at HV and the smallest at HH polarization. The difference s were smaller for a stand of small black spruce. The VV-HH phase diff erences observed by SAR were almost-equal-to 0-degrees for all the sta nds. Ground data were used to parameterize the Santa Barbara canopy ba ckscatter model. For the white spruce and balsam poplar stands under t hawed conditions, simulations agreed with the SAR data within the cali bration uncertainty. The model underestimated the HH, HV, and VV backs catter for all five stands under frozen conditions, and for the black spruce stand under thawed conditions. The modeled VV-HH phase differen ces were close to 0-degrees for all the stands except the black spruce stand. The discrepancies in model predictions of backscatter and phas e difference were attributed to inadequate surface backscatter modelin g. Model results supported the hypothesis that the weaker backscatter from frozen, as compared with thawed stands, was because of the smalle r dielectric constant of the frozen trees.