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

1. D. Massonnet e K. L. Feigl, «Radar interferometry and its application to changes in the Earth’s surface», Reviews of Geophysics, vol. 36, n. 4, pp. 441–500, 1998, doi: 10.1029/97RG03139.
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.

The emergence of wide swath radar altimeter provides a new observation method for ocean dynamic environment monitoring, which can achieve two-dimensional synchronous observation of sea surface height, wave height and sea surface wind speed. The SWOT satellite launched in December 2022 is equipped with Ka-band Radar Interferometer (KaRIn), which can achieve two-dimensional observation of marine dynamic environment. Based on SWOT ocean observation data, the spectral analysis method is used to evaluate the observation ability of ocean sub-mesoscale processes in sea surface height data, and buoy data is used to evaluate the accuracy of significant wave height and sea surface wind speed.

The spatial and temporal distribution of satellite altimeter along track observation data is sparse, making it difficult to comprehensively capture the spatial and temporal structure of ocean circulation. The fusion of multi-source altimetry data can compensate for the shortcomings of single satellite altimetry observation data and obtain more comprehensive sea surface height information. Based on ocean reanalysis data, the spatiotemporal correlation scale of global ocean dynamic processes is calculated and the variable spatiotemporal scale optimal interpolation method is developed for multi-source satellite altimetry data fusion. Research on multi-source satellite altimetry data fusion based on two-dimensional variational method, efficiently fusing multi-source satellite altimetry data by fully utilizing the error characteristics and covariance information of background field and observation data, optimizing the accuracy of fusion results and improving their spatial resolution. Temporal dynamic interpolation of sea surface height anomalies based on quasi geostrophic models is developed by introducing SST data as physical constraints to more accurately describe SLA temporal evolution and improve the temporal resolution of fusion results. The Northwest Pacific Ocean is taken as study area to conduct data fusion experiments and evaluate the developed data fusion method.

The Lofoten Basin (LB) is located along the advective path of Atlantic Water (AW) is the most eddy active part of the Nordic Seas. A main feature of the LB circulation is the spinning up off eddies from the Norwegian Atlantic Current, which in turn transports warm AW into the basin. The AW transported into the basin interior is found to penetrate deep down to 1000 m, and not surprisingly, the LB is the largest heat reservoir in the Nordic Seas. The eddy shedding from the slope current to the deeper areas of the basin, transports heat to the basin interior and thus mediates the gradual cooling of the slope current on its way toward the Arctic. This is of great importance since AW transported to the Arctic Ocean through the Nordic Seas plays a major role in the global climate system. Furthermore, this also links to the “Atlantification”, a commonly used term for the increasing influence of AW in the Arctic Ocean, having a large impact on the Arctic marine ecosystem.

The overall objective of LoWa is to quantify the impact of ocean eddies on the heat transport across the LB affecting Atlantification. To address the overall objective LoWa uses a holistic approach, thanks to the outstanding opportunities offered by the: available satellite constellations with multi-sensor covariability/synergies; in-situ observational networks, gliders and ARGO drifters; co-location of in-situ and remote-sensed data and data driven Artificial Intelligence (AI) methods. Such an approach also extends the possibility to not only investigate ocean mesoscale eddies but also the sub-mesoscale eddies that are even less studied in comparison to mesoscale eddies.

We will report ongoing activities associated with mesoscale eddies in the Lofoten Basin. In addition, we will also present results of a recent study (Dong et al., 2025, manuscript in revision, Nature Communication), focusing on the Warm Rings in Mesoscale Eddies in a Cold Straining Ocean. In here we show the role of submesoscale heat transport as the primary mechanism for substantial heat loss from AW in the Lofoten Basin.

The objectives of project 95549 are that we take advantage of the multiple satellites such as CFOSAT, FY series, Sentinel series, to provide the combined satellite monitoring of marine environment disasters and a better understanding of the associate marine environment dynamics. So far, we have carried out the following work：

1.Validation of CFOSAT and multiple satellite data

CFOSAT and HY-2 series satellites can measure the sea surface wind speed (WS) and significant wave height (SWH) at nadir points. By comparing and verifying with the calibrated sea surface WS and SWH such as Jason-3 and sentinel-3, we have carried out unified benchmark calibration of the observation data of multiple satellites. Besides, previously result shows that the non-fully-developed-sea (NFDS) wind-wave relation is robust for different satellite observations. For example, such relation derived from the Jason series satellite is comparable with the buoy observation and is also valid for the CFOSAT data. It is thus useful for wind-wave mutual correction since they might be underestimated by the satellite for the high wind condition with wave breakings. So we carried out a reconstruction study of the SWH based on the 10 WS measurements.

2. Multiscale description of the W²CI

To understand better the W²CI in typical regions and events, the multiscale scale-to-scale flux analysis is being performed. The scale-to-scale flux is the cornerstone of the W²CI. However, due to the lack of observation data, the understanding is incomplete. It is thus one of the major uncertainties of climate models. With high temporal and spatial observation, this issue will be overcome. More precisely, we would like to explore the multiscale description and analysis of the W²CI. Such analysis will be applied to two typical regions. They are the western Pacific with one of the strongest ocean currents, namely Kuroshio current, mesoscale eddies and typhoon; and ACC with strong ocean circulation. The analysis result will enrich our understanding of the underlying dynamics.

3. Machine-Learning-Based Optical Flow

For the high temporal resolution observation, such as the geostationary satellite, the optical flow is a potential technique to estimate the ocean surface velocity. With aid of the machine learning, the Machine-Learning-Based Optical Flow (MLBOF) is being developed for geostationary satellite, such as FengYun-4, to retrieve the ocean surface velocity. Jointly combined with other satellite measurements, we expect to carry out a comparison. Moreover, MLBOF will be applied to the archived data provided by other geostationary satellites (e.g., FY-2, Sentinel-4, Himawari-8, etc) to construct a historical ocean surface velocity field. The historical data will be useful for climate change study.