Forest Structure Dependency of the Relation Between L-Band and Biophysical Parameters

Biophysical parameters and L-band polarimetry synthetic aperture radar observation data were taken for 59 test sites in Tomakomai national forest, which is located in the northern part of Japan. Correlations between the derived sigma_HH ⁰, sigma_HV ⁰, and sigma_VV ⁰ and the biophysical parameters are investigated and yield the following results. 1) The above-ground biomass-sigma⁰ curves saturate above 50 tons/ha for sigma_VV ⁰, 100 tons/ha for sigma_HH ⁰, and over 100 tons/ha for sigma_HV ⁰ when all forest species are included in the curves. 2) The sigma_HH ⁰-above-ground biomass curve for one forest species indicates a higher saturation level than that for the other forest species. Dependence on the forest species was absent for VV polarization and low for HV polarization. 3) A simple three-component scattering model indicates that volume scattering accounts for 80%-90% when the above-ground biomass exceeds 50 tons/ha. The surface-scattering components are up to ~20% for young stands, and the volume-scattering components are down to 70%. The origin of the dependency among the forest species was examined for the sigma_HH ⁰-above-ground biomass. It is concluded that a possible cause of the dependency is the different characteristics of the stands rather than forest species