Lava-flow textural trends using SAR: the Virunga Volcanic Chain, East Africa

Multi-frequency polarimetric Shuttle Imaging Radar-C (SIR-C) data acquired in October 1994 were analyzed for the Virunga Volcanic Chain, East Africa. The synthetic aperture radar (SAR) data can be used to define the roughness, texture, orientation, and dielectric properties of scattering elements of volcanic surfaces. SIR-C acquired C- and L-band SAR in two polarizations, horizontal transmit and receive (HH), and horizontal transmit and vertical receive (HV). The SAR backscatter from the volcanoes is mainly controlled by roughness and vegetation cover, as there is a correlation between radar intensity parameters and age of lava-flow. This is best illustrated by the ratio of C-HV/C-HH, and to some extent, L-HV/L-HH, which show positive linear relationships with age of flow until a threshold age of ~30 years (~12000 days) is reached. The H-polarized incident energy is converted to significant amounts of V-polarized backscatter, so that the cross-polarized backscatter intensity increases with flow age. For flows older than ~30 years, the backscatter signature is from volume scattering due to vegetation cover. The vegetation signature threshold with time can serve as an age proxy to determine recent flank eruption frequency