LAVA FLOW TOPOGRAPHIC MEASUREMENTS FOR RADAR DATA INTERPRETATION

Surface topography is of great importance in radar backscattering, but the quantitative interpretation of data collected in the field is sti ll a difficult problem. We present topographic profiles at 25-cm and 5 -cm horizontal resolution for three sites along a lava flow on Kilauea Volcano, and use these data to illustrate techniques for surface roug hness analysis. Height and slope distributions and the height autocorr elation function are evaluated as a function of varying lowpass filter wavelength for the 25-cm data. Rms slopes are found to increase rapid ly with decreasing topographic scale and are typically much higher tha n those found by modeling of Magellan altimeter data for Venus. A more robust description of the surface roughness appears to be the ratio o f 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.