P-band radar mapping of forest biomass in boreal forests of interior Alaska

AIRSAR data gathered in winter, spring, and summer over the Bonanza Creek Experimental Forest, near Fairbanks, Alaska are compared to estimates of whole-tree aboveground dry biomass from 21 forest stands and 2 clear-cuts. Using empirical relationships, biomass values are predicted from the radar at various frequencies and polarizations and compared to actual biomass values. Predicted biomass levels are most accurate at P-band. At that frequency, the radar discriminates 7 biomass levels, up to the maximum observable biomass level for these forests, with 18% error. Within these 7 biomass levels data dispersion is large because of significant inner-stand spatial variations in biomass, interactions of the radar signals with a spatially varying three-dimensional structure of the canopy, as well as uncertainties associated with the estimation of stand biomass from empirical equations. Multiple incidence angle data also reveal that the incidence angle θ_i of the radar illumination affects the retrieval of biomass from the radar data even at HV-polarization when θ_i>50° or θ_i<25°. One consequence is that topographic information is required for mapping biomass in areas of moderate topography. Finally, the inversion curve for biomass retrieval varies with season and environmental conditions