Performance Analysis of the SBAS Algorithm for Surface Deformation Retrieval
Riccardo Lanari(1) , Francesco Casu(1)
, and Mariarosaria Manzo(1)
IREA - CNR,
via Diocleziano, 328,
Differential Synthetic Aperture Radar Interferometry (DInSAR) is a remote sensing technique that allows us to analyze deformation phenomena by exploiting the phase difference of SAR image pairs relevant to an area under study . In this context, several approaches aimed at following the temporal evolution of the detected displacements have been presented. In particular, we consider the technique referred to as Small BAseline Subset (SBAS) algorithm  that has been originally developed to investigate large spatial scale displacements with relatively low resolution (typically of the order of 100 x 100 m). The capability of this approach to generate deformation maps and time-series from ERS data have been already shown in different applications [3, 4], but no extensive analysis on the quality of the DInSAR measurements have been carried out.
Accordingly, we present in this work a quantitative assessment of the SBAS algorithm performance by processing SAR data acquired by the ERS sensors. The key idea is to concentrate on two test areas where different deformation phenomena are present and, at the same time, a large amount of SAR data are available as well as ground measurements to be used for an extensive SAR/geodetic measurements comparison. We stress that the presented study is not aimed to the investigation of the ongoing deformation processes relevant to the selected zones. On the contrary, we benefit of the knowledge of these phenomena and of the availability of large SAR and geodetic measurements data set, the latter assumed as reference, for carrying out the assessment of the procedure performance.
In particular, the first test site is located in the Napoli bay (Italy) area which includes three active volcanoes (the Campi Flegrei caldera, the Somma-Vesuvio volcanic complex and the Ischia island) and the highly urbanized area of the city of Napoli. In this area a very large spirit leveling network is present, including several hundreds of benchmarks with repeat measurements that are systematically carried out. Moreover, a huge SAR data set relevant to ascending and descending tracks of the ERS-1 and ERS-2 sensors, spanning the time interval from 1992 until 2003, is available to us. The availability of these SAR data allows us to analyze the temporal behavior of the detected deformations and, at the same time, to discriminate vertical and East-West displacement components. The former will be compared with the measurements available from the leveling campaigns in areas where both SAR and geodetic data are available.
The second test area is the Los Angeles (California) metropolitan zone which is a tectonically active region with surface deformations that are a combination of natural and anthropogenic signals. Also in this case a large number of ERS acquisitions is available from descending orbits. Moreover, a very large amount of geodetic measurements has been recorded through the Southern California Integrated GPS Network (SCIGN). Accordingly, a detailed comparison between the DInSAR and the GPS measurements will be carried out.
As a result of the overall DInSAR/geodetic measurements comparison, a quantitative assessment of the SBAS procedure performance for surface deformations retrieval will be finally provided.
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