Conference Agenda

In our era of global climate change and rapid urban expansion, escalating natural and human activities contribute to a wide range of geohazard phenomena worldwide. These hazards include earthquakes, volcanic eruptions, landslides, urban subsidence, floods, tsunamis, droughts, and forest fires. Effectively addressing such threats from global to local scales necessitates advanced, efficient, and precise monitoring tools and techniques. Satellite-based Synthetic Aperture Radar (SAR) remote sensing has fundamentally transformed the monitoring of Earth’s environments and geohazards, providing high-resolution data on inundation, land movement, and risk exposure essential for disaster response and planning. Several multi-temporal Interferometric synthetic aperture radar (MT-InSAR) techniques [1]-[3] have been developed and successfully applied in such context. Several noise-filtering methods have been proposed to mitigate the noise effects in the differential SAR interferograms, most working independently on single interferograms. Subsequently, new efforts have been made to extend these methods to include space-time information [4], [5], [6].

This work shows the results of some recent technological and applicative advancements of the Mt-InSAR technologies through dedicated experiments with Sentinel-1 SAR data. The experiments concern the test-site areas of the active “Campi Flegrei” Caldera (Italy), the zone in Turkey-Syria hit by the Mw 7.9 earthquake on February 6, 2023, and the city of Hanoi. These experiments give the Dragon 6 audience a clue about the state-of-the-art and recent development trends of the used radar technologies. The efforts realised to retrieve the three-dimensional field of deformation in areas subjected to severe earthquakes and/or volcanic activities are evidenced by the problems of phase unwrapping, co-registration, burst-overlapped interferometry and large-swath datasets processing. Concerning the applications in urban zones, the focus is on the region of the Red River Delta, which represents one of the most crucial economic zones of Vietnam, and its capital, the city of Hanoi. In this work, a comprehensive analysis relying on the exploitation of the interferometric SAR technologies and the use of multi-track SAR datasets acquired from the European Copernicus Sentinel-1 and TerraSAR-X was carried out to generate and interpret the 2017-2024 dynamics of the RRD terrain deformations, by generating 2-D maps, along the vertical and horizontal directions, and ground deformation time series. As a result, the megacities Hanoi, Hai Duong, and Nam Dinh of the delta are found to be affected by significant subsidence. Overall, our study analyses the state-of-the-art of Mt-InSAR technologies and provides some insights into the relationships between population, land-cover changes, the distribution of built-up areas, the role of over-pumping groundwater, geological setting, and ground subsidence.

References

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2. A. K. Gabriel, R. M. Goldstein, e H. A. Zebker, «Mapping small elevation changes over large areas: Differential radar interferometry», J. Geophys. Res., vol. 94, n. B7, pp. 9183–9191, lug. 1989, doi: 10.1029/JB094iB07p09183.
3. Hansen, M.C.; Loveland, T.R. A Review of Large Area Monitoring of Land Cover Change Using Landsat Data. Remote Sens. Environ. 2012, 122, 66-74.
4. P. Berardino, G. Fornaro, R. Lanari, and E. Sansosti, «A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms», IEEE Transactions on Geoscience and Remote Sensing, vol. 40, n. 11, pp. 2375–2383, nov. 2002, doi: 10.1109/TGRS.2002.803792.
5. A. Ferretti, C. Prati, e F. Rocca, «Permanent scatterers in SAR interferometry», IEEE Transactions on Geoscience and Remote Sensing, vol. 39, fasc. 1, pp. 8–20, gen. 2001, doi: 10.1109/36.898661.
6. C. Colesanti, A. Ferretti, C. Prati, e F. Rocca, «Monitoring landslides and tectonic motions with the Permanent Scatterers Technique», Engineering Geology, vol. 68, n. 1, pp. 3–14, feb. 2003, doi: 10.1016/S0013-7952(02)00195-3.

Driven by multiple factors, including tides, wind fields, ocean currents, and seafloor topography, the marginal seas exhibit abundant dynamic processes. Among these, sub-mesoscale oceanic eddies are the key driver in the mixing of the upper ocean layer and the transport of heat, salt, and nutrients. Spaceborne synthetic aperture radar (SAR), with its high spatial resolution and wide coverage, is the superior sensor for studying ocean sub-mesoscale eddies.

During the first year of DRAGON 6, we have been focusing on the detection and identification of multi-scale eddies on SAR imagery and on their spatio-temporal variation and coverage. Ten years of Sentinel-1 SAR-C data of the Western Mediterranean Sea have been used for an automated detection of oceanic eddies by the EOLO system, an AI technique developed during DRAGON 5. A comparison with results of visual inspections of SAR-C data of the same region reveals that the results achieved by EOLO show the same seasonalities and spatial distributions.

Given the robustness of the EOLO on the large volume of SAR data acquired in the Mediterranean Sea, the EOLO is further applied to multiple sources of SAR-C data acquired in the global ocean, including Sentinel-1 and Envisat SAR imagery, with a total of 3,192,002 scenes. The detected 82,750 eddies, 97% of which have a diameter less than 40 km, are compared with the concurrent mesoscale eddies detected by radar altimeter. The spatial comparison results show a high consistency of sub-mesoscale and mesoscale eddies. Quantitative analysis indicates about 50% of sub-mesoscale eddies are located within twice the radius of mesoscale eddies, where sub-mesoscale eddies in the core area of mesoscale eddies only account for approx. 9%.

Using the spatial variation of the mesoscale strain rate (MSR) in the normalized mesoscale eddy-center coordinate system, we found that the high MSR band is located within a ring-shaped area, i.e., 0.5 to 1.5 times the normalized radius of mesoscale eddies around the eddy center. The radial distribution further shows that the MSR is positive in the ring-shaped area, while it is negative in the core area. This quantitative analysis shows that about 50% of the global sub-mesoscale eddies are generated by shear instabilities along mesoscale eddies.