Mitigation of Tropospheric Delay on InSAR Interseismic Displacements

One of the major challenges of Interferometric Synthetic Aperture Radar (InSAR) technique is the existence of tropospheric effect on the results. The tropospheric effect is due to the changes of atmospheric parameters including temperature, pressure, and humidity between the master and slave images. In this research, two different methods based on spatial-temporal filters and calculation of phase delay using MERIS data were evaluated. The main objective is to monitor the interseismic deformation across the Tasouj fault located in West and East Azarbaijan provinces. To this end, Stanford Method for Persistent Scatterer (StaMPS) is applied on 12 ascending ENVISAT ASAR images spanning between 2004 and 2008. The deformation time series obtained from StaMPS are two rough due to the atmospheric effect. In the first method employed for the atmospheric effect reduction,  considering that the atmospheric effect is a temporally-decorrelated and spatially-correlated signal, two different high pass and low pass filters are applied in the temporal and spatial space in order to extract the atmospheric signal which is then subtracted from the time series analysis results. In the second method, the phase delay due to the troposphere is estimated using the MERIS water vapor product. GPS measurements are finally used in order to evaluate the performance of different atmospheric reduction methods. Two quantitative criteria, i.e. Root Mean Square Error (RMSE) calculated from GPS and corrected time series and standard deviation of atmospherically-corrected time series are considered as two relevant methods for evaluating the fluctuations reduction. The method based on spatial-temporal filters shows more superiority over the other one with RMSE and standard deviation of 13 mm and 40 mm, respectively, at its best case.