SAR monitoring of progressive ground deformation using the permanent scatterers and SBAS techniques in Aitoliko

Περίληψη

The Messolonghi-Etoliko lagoons complex is located in the north part of the Gulf of Patras in the central west coast of Greece. It is one of the most important Mediterranean lagoons for both environmental and financial reasons. It is a shallow area of 150 km2, extended between the Acheloos and Evinos rivers, it is protected by the Ramsar Convention and it is also included in the Natura 2000 network. The town of Etoliko, known as the Little Venice of Greece, is a municipal section of Messolonghi municipality with a population of 5,349 inhabitants, ten kilometers northwest of Messolonghi. Etoliko is developed on a small island rooted in water in the middle of the lagoon. It is connected east and west to the mainland by two stone arched bridges with original length of about 300 meters each. This paper studies the ground deformation of the town of Etoliko using Multitemporal SAR Interferometry techniques and more precisely, the Persistent Scatterers Interferometry Technique (PSInSAR) and Small Baseline Subset (SBAS), which have proven a remarkable potential for mapping ground deformation phenomena. This approach allows to make accurate measurements very close to its theoretical limit (in the order of 1 mm), and to obtain from the numerous radar targets very precise displacement information. We applied the PS approach (Gamma-IPTA chain) and an ad-hoc SBAS approach on 105 SAR images from the European Remote Sensing satellites ERS-1, ERS-2 and 55 ENVISAT images that cover the two time periods, 1992-2000 and 2002-2009, to map the Etoliko subsidence. In contrast to discrete point in-situ deformation measurement techniques, multi-temporal InSAR processing can be used to obtain a broader view of deformation processes at a site and to detect localized deformation features. Results highlight the deformation phenomena occurring the last 2 decades, showing low rate of subsidence. Subsidence is an important hazard related with the development of urban areas. In order to have a thorough study of the ground surface deformation demands a continuous and wide spatialtemporal monitoring. By studying the deformation rates obtained by the PS technique, the lithology of the area, the sea level rise and any kind of human interventions, we can make a reliable prediction for the forthcoming years concerning the risk of flooding, the stability of the area and therefore to reduce the negative effects of these risks to humans.