Investigating Vertical Land Movements along the Northern Caspian Sea Coastal Area by SAR Based Methodologies

Solonchaks, more commonly known as saline soils, are a soil variety widespread along the northern coastal area of the Caspian Sea. Salts dissolved in the soil moisture remain behind after evaporation/transpiration of the water and accumulate at the soil surface. Detecting ground displacement by SAR-based methodologies is challenging in these regions. Interferometric Point Target Analysis (IPTA) and Small BAseline Subset (SBAS) methods have been optimized to obtain ground displacement rates on salted soils with a nominal accuracy of millimetres per year. The SBAS approach is developed to maximize the spatial and temporal coherence by construction of small baseline interferograms. The IPTA approach extracts deformation signals on point targets by modelling and analyzing their phase value that remains stable in time for all interferograms performed with a common master image. In this paper, we evaluate the performance of both approaches, their limitations and their complementarities through an inter-comparison, on salted soils. We apply SBAS and IPTA on 33 ENVISAT images acquired between 2003 and 2009. Results allow mapping the subsidence within a frame in the northern coast of the Caspian Sea, Kazakhstan. Hence, we demonstrated that this environment is suitable to the application of SAR methodologies.