PSInSAR as a new tool to monitor pre‐eruptive volcano ground deformation: Validation using GPS measurements on Piton de la Fournaise

The Permanent Scatterers Synthetic Aperture Radar Interferometry (PSInSAR™) is a technique, which aims at ground deformation mapping with millimetric precision. In the framework of the Globvolcano ESA project, we evaluated a PSInSAR derived approach to monitor ground deformation in highly active volcanic areas, based on the example of Piton de La Fournaise. The Permanent Scatterer (PS) velocities show two main areas of deformation: (1) the eastern flank displaying old lava flow subsidence (0.05–0.13 m.y −1 ); and (2) the summit cone highly disturbed by eruptions. The PS time series for the summit area agree with the cGPS trends with small long‐term (weeks/months) ground displacements preceding eruptions (0.05–0.35 m.y −1 ) and large rapid ground displacements linked to eruptions. Despite some limitations, such as the loss of coherence during the most rapid ground displacements and lava flow emplacement, PSInSAR and its derived approach provide a reliable inference of the volcano ground deformation over large areas.