Remote sensing using satellite-mounted SAR sensors


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  • Remote sensing using satellite-mounted SAR sensors

    GAP Srl has successfully developed and applied its proprietary SPINUA© (Stable Point Interferometry over Unurbanised Areas) algorithm in numerous projects. This algorithm belongs to the family of PSI (Persistent Scatterers Interferometry) processing tools.

    The SPINUA© algorithm has been applied and tested in both large urban areas and sparsely urbanised regions for the monitoring of unstable areas (affected by subsidence, landslides and post-seismic deformations) and unstable infrastructure (dams, bridges, railways, pipelines, etc.).

    Innovative features and specific solutions have been developed and tested, making the tool flexible and suitable even for applications in areas characterised by a low density of natural radar reflectors. In particular, original algorithms for PSI techniques have been developed; these have been successfully applied at numerous test sites affected by ground instability within or near urban areas, but have also been optimised for sparsely urbanised territories.

    The SPINUA© algorithm implements a DInSAR (Differential Interferometric Synthetic Aperture Radar) technique for topography measurement, utilising the phase difference between the backscattered microwave signals from two images acquired from slightly different satellite orbits. When the two SAR acquisitions are also separated in time and preliminary information on the ground topography is available, it is possible to detect displacements that have occurred between the two acquisitions relative to the known topography, with an accuracy of the order of a millimetre.

    When a time series of SAR acquisitions is available for a given site, these can be combined to generate several differential interferograms, making it possible to track the evolution of displacements over time (multi-temporal DInSAR).

    SPINUA© overcomes the limitations of conventional InSAR and extends the applicability of radar interferometry from regional-scale geological analyses to local investigations of ground instability. The system provides highly accurate measurements of ground displacement even over long observation periods.

    Atmospheric effects and the influence of topography can be eliminated by using at least 25 SAR images. The high level of error compensation enables the generation of time series that represent the evolution of displacements at each fixed point. Ground deformation is measured with an accuracy of approximately 1.5 mm/year along the satellite’s line of sight (which, for the ERS and ENVISAT satellites, is close to vertical). The horizontal positioning accuracy of the measurement points is approximately 10 metres.

    SPINUA© is also capable of detecting ground movements of the order of a millimetre in areas designated for oil and gas extraction and storage, along oil and gas pipelines, as well as monitoring:

    • surface uplift associated with production processes using Steam Assisted Gravity Drainage (SAGD);
    • ground movements caused by pressure variations at underground CO₂ storage sites, used for emissions control;
    • the stability of moored offshore platforms.

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