Time Series Analysis of SAR Images Using Small Baseline Subset (SBAS) and Persistent Scatterer (PS) Approaches to Determining Subsidence Rate of Qazvin Plain

Monitor and detection of displacement field due to changes in land surface are one of the practical and important studies in different topics of the Geodesy, Geological and geophysical which have a significant role in trends and preventing natural disasters such as earthquake, subsidence and landslide. In the meantime, there are different methods for detection this displacement and geodetic measurement, that among them, Interferometric Synthetic Aperture Radar (InSAR) with a feature wide spatial coverage, fine spatial and time resolution and high accuracy has become one of the important and significant techniques. Land subsidence due to groundwater extraction has been a common geohazards in many arid countries and districts of the world. In Iran, this is a serious challenge for many regions, particularly in the plains with arid and semi-arid climate, for example, Mashhad valley, Hashtgerd, Yazd and Golpayegan plains. Gazvin plain is one of these regions where the land subsidence has seriously developed. This region is located in the north-central Iran, with an area size of about 4430 km2. Gazvin plain in terms of industrial, agriculture and population point is one of the important plain in Iran. In recent years, high rate of extracting water from underground source due to agricultural activity, industrial and population development caused decreasing the groundwater level, so because of the groundwater level downfall, subsidence occurs and it’s trace is seen as cracks and fractures in the ground surface. Studies show that a large area in Qazvin plain is subject to the land subsidence induced by overexploitation of groundwater for the purposes of agricultural, industrial and population development. Therefore, this research study on the pattern and rate of subsidence occurred in Qazvin plain between 2003 and 2010, using radar is Interferometric synthetic aperture radar (InSAR) techniques. The data set consists of 20 and 18 images of descending tracks D192 and D421 during 2003 to 2010. We processed radar data with the open source software StaMPS/MTI (Stanford Method of PS/Multi-Temporal InSAR). The interferograms are corrected for the phase signature due to orbital separation using precise doris orbital data for ENVISAT satellite which is provided by DEOS are stored in a binary format (ODR) that believed to have a radial precision of 5-6 cm. then the 90 m SRTM DEM has been used to estimate the topographic phase contribution. The atmospheric phase delay in each individual interferograms corrected using the retrieved water vapors from MERIS data. We also improve signal to noise ratio of each differential interferogram using a Goldstein filter. The time series analysis of permanent scatterer (PS) and small baseline subset (SBAS) algorithms are used for deformation time series analysis. The time series results show that a considerable and continuously land subsidence in the study area. Results show a good agreement between the PS and SBAS time series, both of two approaches identify peak amplitude of ~ 30-35 mm/year for the 2003-2010 times period. With comparison width and extent of subsidence of InSAR results and plain wells density map of Qazvin plain determines the subsidence occurred in the area with the density of deep wells to extract groundwater and subsequent subsidence occurred in this area.