Towards Operational Repeat-Pass SAR Interferometry at Active Volcanoes

Measurement of volcanic surface movement is an operational technique at many volcano observatories to help understand internal processes and to aid in eruption forecasting. The potential of differential radar interferometry (DInSAR) to map patterns of surface deformation on volcanoes is well-proven. However, the technique has not yet become operational, partly because current spaceborne radars were not designed for the task. We discuss the limitations of the European Space Agency's ERS SARs for this purpose in terms of: radar system constraints, volcano surface characteristics, interpretational uncertainties and the operational context. We illustrate the drawbacks at typical stratovolcanoes in South America, chosen to represent a range of conditions. For non expert users of DInSAR, knowing how well DInSAR will work on a particular volcano is important. Freely-available global datasets of vegetation cover and atmospheric water vapour content can be used as proxy measures of coherence and path delay effects, which are the two main determinants of data quality. Operational volcano DInSAR is still years away, but many of the characteristics of such a system can be specified based on the experience learned from earlier radars.