Probing the ultimate capabilities of radar interferometry for deformation with low gradient: a new mission?

The use of radar interferometry for measuring geophysical ground deformation was demonstrated using the large displacement field generated by a major earthquake. This study has been quickly followed by others where the amplitude of the phenomena was lower, whether caused by smaller earthquakes or by volcanic activity. At the same time two quests were initiated in parallel: the first aimed at interpreting properly this new signal, the second, more technology oriented, aimed at pushing the limit of the method down to the artifact level while trying to observe phenomena characterized by low gradients of deformation such as post-seismic evolution. The authors discuss the prospects of extending the use of radar interferometry to a whole class of phenomena it did not explore so far. Such phenomena include post-glacial rebound, interseismic deformation, tidal loading over large areas as well as large and deep earthquakes. Some of these have their amplitudes maximized with time, which raises the question of long term coherence and the parallel issue of the proper satellite mission required to seize this opportunity. Tidal loading, a cyclic phenomenon, may be maximized by stacking adequate image pairs. The deformation field of deep earthquakes can be discriminated against noise by the consistency in the signal of adjacent radar tracks. Eliminating the artifactual phenomena-orbit adjustment, radar clock drift, meteorological phenomena-is demanding as the authors show in several examples, but outlines the requirements of a dedicated, cost-effective radar satellite which could grasp the heritage of ERS, perfect some technical aspects and drop the unnecessary design margins. The simulation of the new specifications using existing ERS data on well known sites allows a very safe and reliable prediction of the performances