Applications / Terrain Displacement Monitoring

SAR interferometry and the PSP approach

Repeat-pass satellite synthetic aperture radar (SAR) interferometry (IFSAR) is a very effective technology for terrain displacement mapping with applications in subsidence, landslides, earthquakes and monitoring of volcanic phenomena. This technology allows measurement of terrain displacement with millimetric accuracy by processing data acquired from satellites orbiting 600 kilometres above the Earth.

The technique is based on the fact that the phase difference between two SAR images acquired at different times and with slightly different view angles is related to the topography and to changes, at the different observation dates, of the observed scene and the transmission medium. Usually the measurements are possible over sparse points (to be identified) corresponding to objects on the ground exhibiting radar backscattering properties stable over time. These points, called persistent scatterers (PS), are usually found in non-cultivated and lightly vegetated areas and, in particular, corresponding to man-made or natural structures like buildings, rocks, etc.

The extraction of terrain movements from SAR data is a complex task requiring the identification of the measurement points and the separation of the displacement information from the other components of the phase signal. e-GEOS has developed an advanced persistent scatterer interferometry approach, named Persistent Scatterer Pairs (PSP) - IFSAR, characterized by original solutions to the main limitations of classical techniques and able to efficiently extract accurate terrain displacement measurements.

The e-GEOS PSP-IFSAR processing chain runs on a high performance computing (HPC) system to provide PS measurements over large areas. Key elements of the system are:

• High quality terrain displacement measurements, both in terms of accuracy and density of the measurements, even in areas where radiometrically stable structures are very scarce or displacements that evolve non-linearly over time are present.
• Robustness: the algorithm is designed to exploit redundant information in order to obtain very reliable results.
• Automation: the robustness of the algorithm and the processing chain based on a workflow system minimize the need for human intervention.
• Parallelism: the implemented SW is parallel and runs on a HPC system to reduce the processing time.

PSP-IFSAR Products

The PSP-IFSAR technology provides measurements of displacements - typically due to subsidence, landslides, earthquakes and volcanic phenomena - of objects on the ground exhibiting radar backscattering properties stable over time, called persistent scatterers (PS). The PSP-IFSAR products are:

• PS positions: the measured positions (cartographic or geographic coordinates and, optionally, heights) of the PS points.
• PS mean velocities: the measured PS points mean velocities during the period between the first and the last SAR acquisition dates.
• PS displacement temporal evolutions: the measured PS displacement at each acquisition date in the analysed period.

Land deformation of volcanic origin around Campi Flegrei (Naples, Italy). An example of mean velocity product obtained by PSP-IFSAR processing of ERS-1 and ERS-2 SAR data acquired from 1995 to 2000

Land deformation of volcanic origin around Campi Flegrei. An example of mean velocity product obtained by PSP-IFSAR processing of ENVISAT SAR data acquired from 2003 to 2008.

Validation of PSP-IFSAR measurements. Precise levelling measurements (green) of a point in the area of Campi Flegrei, characterized by volcanic phenomena are compared with PS displacement temporal evolution measurements obtained by PSP-IFSAR processing of ERS (blue) and ENVISAT (red) SAR data.