Accurate measurements of tropospheric effects in volcanic areas from SAR interferometry data: application to Sakurajima volcano (Japan)

The accuracy of surface deformation maps derived from DinSAR (differential interferomery synthetic aperture radar) in volcanic areas is limited by temporal variations of the vertical refractivity profile in the troposphere between the radar data acquisitions. Due to their dependence on altitude, such variations may produce topography-related fringes in the computed interferograms. The variations should be carefully estimated in a given area so that they can be discriminated with real ground deformation signals. In this paper, we present a clear example of tropospheric induced fringes (reaching up to 2.9 fringes over 1200 m), evidenced on Sakurajima volcano (Japan) from ERS-1 and ERS-2 data. The analysis of phase–altitude correlations based on network adjustments of the interferometric dataset leads to a simple linear model of the tropospheric excess path delay (with an rms accuracy of 0.4 cm) that might be used for further corrections. A more detailed investigation of these phase variations providing accurate measurements of linear and non-linear contributions of tropospheric effects is also presented and shows that tropospheric phase delays can be better modeled on Sakurajima with a non-linear model.