Lava Flow Topographic Measurements for Radar Data Interpretation

Surface topography is of great importance in radar back scattering, but the quantitative interpretation of data collected in the field is still a difficult problem. We present topographic profiles at 25-cm and 5-cm horizontal resolution for three sites along a lava flow on KUauea Volcano, and use these data to illustrate techniques for surface roughness analysis. Height and slope distributions and the height autocorrelation function are evaluated as a function of varying lowpass filter wavelength for the 25-cm data, Rms slopes are found to increase rapidly with decreasing topographic scale and are typically much higher than those found by modeling of Magellan altimeter data for Venus. A more robust description of the surface roughness appears to be the ratio of rms height to surface height correlation length. For all three sites this parameter falls within the range of values typically found from model fits to Magellan altimeter waveforms. The 5-cm profile data are used to estimate the effect of small-scale roughness on quasi-specular scattering.