Geodaysit 2023

Multi-temporal SAR Interferometry (MTInSAR) techniques allow detecting and monitoring millimetric displacements occurring on selected point targets that exhibit coherent radar backscattering properties over time. Successful applications to different geophysical phenomena have been already demonstrated in literature. New application opportunities have emerged in the last years thanks to the greater data availability offered by recent launches of radar satellites, and the improved capabilities of the new space radar sensors in terms of both resolution and revisit time. Currently, different space-borne Synthetic Aperture Radar (SAR) missions are operational, e.g. the Italian COSMO-SkyMed (CSK) constellation and the Copernicus Sentinel-1 (S1) mission.

Each CSK satellite is equipped with an X-band SAR sensor that acquires data with high spatial resolution (3x3 m2), thus leading to a very high spatial density of the measurable targets and allowing the monitoring of very local scale events. Thanks to the nationwide acquisition plan “MapItaly”, CSK constellation covers the Italian territory with a best effort revisit time of 16 days since 2010.

S1 mission is instead operational since 2014 and acquires in C-band at medium resolution (5x20 m2) with a minimum revisit time of 12 days (only 6 days between 2016 and 2021, when the full S1 constellation was operational), thus allowing to monitor ground instabilities back in time almost all over the Earth. Moreover, all data acquired by the S1 mission are provided on an open and free basis by the European Space Agency (ESA) and the European Commission (EC), for promoting full utilization of S1 data, with the aim of increasing the scientific research, growing the EO markets and fostering the development of continuous monitoring services, such as the European Ground Motion Service (EGMS) and the Rheticus® Displacement Geo-information Service.

The EGMS is based on the MTInSAR analysis of S1 radar images at full resolution, updated annually, and provides consistent and reliable information regarding natural and anthropogenic ground motion over the Copernicus Participating States and across national borders.

Rheticus® offers monthly updates of the millimetric displacements of the ground surface, through the MTInSAR processing chain based on the SPINUA© algorithm (“Stable Point Interferometry even in Un-urbanized Areas”). Rheticus® is capable to process SAR images acquired by different SAR missions, including CSK and S1. Thanks to the technological maturity as well as to the wide availability of SAR data, these ground motion services can be used to support systems devoted to environmental monitoring and risk management. This work shows the results obtained in the framework of the SeVaRA project (“Environmental Risk Assessment Service”), coordinated by Omnitech srl. The goal of SeVaRA is to implement an innovative system for calculating an aggregate environmental risk index, derived from several parameters related to hydrogeological instability phenomena and/or Weather-related extreme events. In particular, the present work is focused on the analysis of the “Deformation Sub-System”, that has been designed for the computation of risk indices related to structural and ground instabilities (landslides). The first step consists in the Hazard Map computation, which requires the following input data:

• Susceptibility Map (i.e., the European Landslide Susceptibility Map, provided by the Joint Research Centre European Soil Data Centre)
• National mosaic of landslide hazard zones, provided by ISPRA (River Basin Plans PAI)
• Cumulated precipitations (derived by cumulating ground measurement data collected by weather stations, if available, or by interpolating hourly rainfall data provided by the Global Satellite Mapping of Precipitation service, GSMaP, offered by the JAXA Global Rainfall Watch)
• Land Cover Change (i.e., the CORINE Land Cover inventory)
• Seismic events inventory, provided by INGV, to account for earthquake-induced landslides
• MTInSAR ground displacement time series.

The last input is essential for detecting instable areas, whose MTInSAR displacement trend exhibits a significant velocity in the whole observation period and/or an acceleration in the acquisition dates of the last year. The SeVaRA “Deformation Sub-System” has been primarily designed to be interfaced with the Rheticus® Displacement Service, but it supports also products offered by the EGMS service as well as by other MTInSAR services available on the EO market. The final step consists in the computation of the landslide risk index, obtained by combining the previous hazard index with the vulnerability and the exposure of the area of interest. The results of this study over specific areas of interest will be presented and commented.

Acknowledgments

Study carried out in the framework of the SeVaRA project, funded by Apulia Region (PO FESR 2014/2020).