The effect of varying acquisition parameters on the interpretation of SIR-C radar data: The Virunga volcanic chain

In 1994, the Spaceborne Imaging Radar experiment C (SIR-C) acquired five data takes with different acquisition parameters over the Virunga volcanic chain, Zaire. Changes in incidence angle (20.0–48.1°), look direction (west- and east-looking), and pulse bandwidth (10 MHz, 20 MHz, and 40 MHz) affect the geologic interpretations drawn from these data. We examine differences in spatial distortion of features near the summit of Nyiragongo volcano, finding that opposite look direction data are helpful in interpreting volcanic features, such as the shape of small craters, in areas of high relief. The relative brightness of lava flows and vegetation change (and actually reverse) for different wavelengths and polarizations. Although L-band data are best for mapping the outline of the flows, C- and X-band cross-polarization data show differences in backscatter intensity between and within flows. In addition, our ability to discriminate lava flows and vents from surrounding vegetation is strongly influenced by pulse bandwidth (resolution) and angle of incidence. Pulse bandwidth is the most important parameter in mapping small topographic features such as volcanic cones and a set of particularly thick flows on the flanks of Karisimbi volcano. These examples illustrate important considerations of the tradeoffs and priorities in acquisition parameters for future missions such as ENVISAT, as well as potential pitfalls for interpretation of existing data.