Post-emplacement lava subsidence and the accuracy of ERS InSAR digital elevation models of volcanoes

Repeat-pass synthetic aperture radar interferometry (InSAR) using data acquired by the ERS platforms is an attractive method for acquiring topographic data of volcanoes. Caution is advised, however, when using this technique in regions covered by young, thick lava flows. In this study, the magnitude of post-emplacement subsidence associated with the 1991-93 lava flow at Mount Etna, Sicily, was measured using differential radar interferometric techniques, and it was found that the rates of subsidence are large enough to contribute a significant component to the measured phase shift, even in ERS data acquired on consecutive orbits. It demonstrates the detrimental effect that such phase shifts have on the accuracy of digital elevation models derived by repeat-pass radar interferometry.