SENSITIVITY OF MODELED C-BAND AND L-BAND RADAR BACKSCATTER TO GROUND SURFACE PARAMETERS IN LOBLOLLY-PINE FOREST

Variations and fluctuations of forest floor scattering properties can lead to variability in. radar backscatter from forest, thereby interfe ring with SAR backscatter-based estimation of forest biophysical chara cteristics. Understanding how forest backscatter varies over the range of probable surface conditions is important in the selection of appro priate radar bands and incidence angles for forest sensing application s and for quantifying uncertainty of the derived forest characteristic s. Using a canopy backscatter model, we examined the sensitivity of mo deled C- and L-band backscatter to five surface para meters in three l oblolly pine stands representing different stages of development in Du ke Forest (NC). The parameters were litter depth and moisture content, soil ms height and correlation length, and soil moisture content. Of the bands considered L-HN backscatter had the highest sensitivity to t he surface parameters, followed by L-VV. In the incidence angle range of 20 degrees-40 degrees, L-HH varied by 5.3-9.6 dB as the surface par ameters changed over their range. whereas L-W varied by 3.7-4.5 dB. At shallower incidence angles, the sensitivities were lower but probably not negligible. C-HH and C-VV were sensitive only at steep incidence (theta(0)=20 degrees-30 degrees) for the lowest biomass stand studied. C-HH and C-VV sensitivity fell off with increasing incidence angle an d stand maturity. L-HV showed slight sensitivity for the low-biomass s tand and at theta(0)=20 degrees-30 degrees but was otherwise insensiti ve. C-HV was insensitive to the surface for all stands and angles. At L-band, the most influential of the five parameters was soil mts heigh t, whereas, at C-band all parameters were about equal in influence. Th e modeled sensitivities suggested that the surface-related uncertainty in forest backscatter at L-HH and L-VV and at C-HH and C-W at steep i ncidence angles, may be unacceptably large for many applications. (C) Elsevier Science Inc., 1998.