3-D InSAR Phase Unwrapping with Extended Kalman Filter: Applications to interseismic deformation detection across the North Anatolian and San Andreas Fault zones
Abstract:Interferometric Synthetic Aperture Radar (InSAR) is a method that allows researchers to map elevations, analyze surface deformation and even detect ground water level changes. The InSAR phase measurements are wrapped between 0 and 2π and therefore have to be unwrapped to reveal the full scale of the observations. Even though there are algorithms for finding discrete irrotational fields among neighboring pixels in two-dimensions, a three dimensional unwrapping approach is important as it can constrain the solution of our data to a more robust and accurate state. We developed a 3-D unwrapping algorithm based on an Extended Kalman Filter (EKF) that is capable of simultaneously filtering, unwrapping and inverting multiple interferograms to obtain a DEM or deformation map. The method is based on a path-following algorithm that unwraps the dataset starting from a reference point and moves to the next-highest quality neighboring point. The EKF algorithm allows us to better resolve unwrapping problems, especially in vegetated areas, which tend to be decorrelated, and hence obtain more accurate results.
In this study we apply our 3-D EKF unwrapping algorithm to North Anatolian and San Andreas fault zones in order to detect interseismic crustal movement across these two major fault systems. For the North Anatolian Fault we processed 37 Envisat scenes that covers the Ismetpasa segment of the fault, and generated 237 interferograms. The generated interferograms are used with both EKF and SBAS algorithms to estimate the deformation in the area. Our previous study of this segment based on the SBAS technique revealed that the Ismetpasa segment creeps at a rate of 8 mm/yr. For the San Andreas Fault (SAF) we processed 37 descending Envisat ASAR scenes acquired between November 2005 and October 2010. Our area of interest includes the central SAF near its intersection with the Garlock Fault. Initial results show deformation across the fault but the results have low fit to the data and further work is needed. In this presentation, we will also present the results from the SAF using SBAS and EKF.