Sensitivity of modeled C-band backscatter from loblolly pine forests to surface soil roughness and moisture

The authors investigated effects of surface-related scattering on C-band radar backscatter in loblolly pine forests at Duke Forest, North Carolina. Five loblolly pine stands, aged from 8 to over 60 years old, were used. Stand density ranged from 589 trees/ha to 5505 trees/ha, and mean tree trunk diameter at breast height (dbh) was between 0.10 m and 0.27 m. The authors used the ratio of the modeled total backscatter to modeled canopy scattering (T/C) to evaluate the importance of ground surface-related scattering. C-band backscatter at 20°, 30°, and 40° incidence angles (θo) was simulated for the stands. C-HH and C-VV backscatter showed modest sensitivity to the surface-related scattering in the young stand (8 years old) at θ₀ of 20° and 30°, and in a mid-aged stand (25 years old) at θ ₀ of 20°. C-HV backscatter was somewhat sensitive to surface scattering in the young stand at θ₀=20°. In the other cases, C-band backscatter was not sensitive. The changes in C-band T/C ratios due to surface scattering occurred only in the young and mid-aged stands. As incidence angle increased, the maxima of T/C ratios decreased for all stands, a consequence of the larger relative contribution of canopy scattering to total backscatter at large θ ₀ than at small θ₀