PS Interferometry overcomes the temporal and geometrical decorrelation limitations through selection of so-called Persistent Scatterers (PS) with coherent scattering behavior over time using a large stack of interferometric SAR image. In Stanford Method for Persistent Scatterers, StaMPS, the deformation can be extracted even in areas lacking the corner reflectors, but the high subsidence rates lead to significant phase unwrapping errors. Therefore, in this paper we present an improved algorithm based on StaMPS in order to estimate deformation rate in rural area undergoing high and nearly constant deformation rate. In this approach, the linear deformation is approximated using Periodogram method and is subtracted in order to eliminate the unwrapping error. The approach is applied to the ENVISAT ASAR images of Tehran Southwestern basin and the results is compared with leveling measurements demonstrating the high performance of the proposed algorithm.