Evaluation of an empirical radar backscatter model for predicting backscatter characteristics of geologic units at Pisgah Volcanic Field, California

Abstract

Comparison of radar backscatter coefficients (σ°, in dB), calculated by using the empirical model of Oh et al. [1992], to σ° extracted from AIRSAR data of four geologic units at Pisgah shows that the model predicts measured σ°vv and σ°hv to within ±3 dB. The model predicts higher σ°hh than those observed. For smooth surfaces (rms height=s, s<8 cm), model results depend strongly on the accuracy of the surface measurements ( s and dielectric constant, ϵr). For rougher surfaces, the model is less dependent on the accuracy of surface characterizations. The model may be inverted to estimate s from measured σ° for surfaces with ks<3 (k = wavenumber, or 2π/λ, where λ = radar wavelength). Model inversion for a pahoehoe unit at 30° to 50° incidence angles (θ) resulted in an estimate of s to within <1 cm of the measured 3 cm. The inability of the model to estimate accurately σ°hh and the anomalously high nadir Fresnel reflection coefficients (Γo) and ϵr required in the model inversion may both be due to ∼equal co‐polarized ratios (σ°hh/σ°vv=p∼1) of the soils used to derive the model. For effective application to many geologic surfaces, for which p<1 is often observed at θ>30°, the model will require modification to include surfaces with non‐unity σ°hh/σ°vv.