The unique radar properties of silicic lava domes

Abstract

Silicic lava domes exhibit distinct morphologic characteristics at scales of centimeters to kilometers. Multiparameter radar observations capture the unique geometric signatures of silicic domes in a set of radar scattering properties that are unlike any other natural geologic surfaces. Backscatter cross‐section values are among the highest observed on terrestrial lava flows and show only a weak decrease with incidence angle. Cross‐polarization backscatter (HV) shows a unique behavior, increasing with increasing wavelength. Circular polarization ratios are relatively high, in the 0.3–0.95 range, and increase with increasing wavelength. Field measurements of boulder size frequency distributions and microtopography indicate that silicic dome surfaces are among the roughest ever measured. Rms heights at a 1 m lateral scale range from 13 cm to 50 cm. Rms slopes at 1 m spacing range from 12 to 43 degrees. Modeling of the scattering behavior suggests it results from a combination of rough surface (facet) scattering and scattering from block edges that act as a random collection of dipoles. The unusual wavelength dependence of the radar parameters appears to result from a higher component of edge scattering at large wavelengths, producing, for example, higher cross‐polarized backscatter at P band (68 cm). Steep‐sided volcanic domes on Venus superficially resemble terrestrial silicic domes in plan view gross morphology, but few similarities remain when the radar scattering and three‐dimensional shapes of the features are compared. The unique radar scattering properties suggest that such volcanic surfaces can be identified with multiparameter radar observations in future planetary radar missions and in active terrestrial volcanoes, where dome development can represent serious hazards.