Comparison of radar backscatter coefficients (&sgr;¿, in dB), calculated by using the empirical model of Oh et al. [1992>, to &sgr;¿ extracted from AIRSAR data of four geologic units at Pisgah shows that the model predicts measured &sgr;¿vv and &sgr;¿hv to within ¿3 dB. The model predicts higher &sgr;¿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, &egr;r). For rougher surfaces, the model is less dependent on the accuracy of surface characterizations.

The model may be inverted to estimate s from measured &sgr;¿ for surfaces with ks<3 (k=wavenumber, or 2&pgr;/&lgr;, where &lgr;=radar wavelength).

Model inversion for a pahoehoe unit at 30¿ to 50¿ incidence angles (&thgr;) resulted in an estimate of s to within <1 cm of the measured 3 cm. The inability of the model to estimate accurately &sgr;¿hh and the anomalously high nadir Fresnel reflection coefficients (&Ggr;0) and &egr;r required in the model inversion may both be due to ~equal co-polarized ratios (&sgr;¿hh/&sgr;¿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 &thgr;<30¿, the model will require modification to include surfaces with non-unity &sgr;¿hh/&sgr;¿vv. ¿ American Geophysical Union 1994