Buono, Andrea

In this study, the scattering mechanisms associated to internal waves (IWs) are investigated at L-band. IWs represent key geophysical factors for sea-air heat exchange and play a paramount role in the biological primary production and in the understanding of the evolution of climate ecosystem. In addition, a better understanding of IWs microwave scattering mechanisms can improve the modeling capability and, therefore, can boost the development on advanced synthetic aperture radar (SAR)-based added-value products to mitigate the risk for offshore drilling operations and aquaculture activities associated to IWs. The analysis of L-band multi-polarization SAR scattering of IWs under the influence of surface current straining is performed using a meaningful full-polarimetric Advanced Land Observing Satellite Phased Array type L-band 1 SAR data set collected over IWs observed under different imaging and wind conditions. Time and space co-located ancillary information is also available. Experimental results demonstrate that the non-polarized scattering mechanisms constitute a significant contribution to the total IW backscattering, especially in the case of surface current gradients owing to IWs (about 48–57%). It is also found that the non-polarized scattering contribution associated to IW concentrates along the wave crests, i.e. it is at least 60% larger than the one observed along the wave troughs. In addition, considering the IW traveling directions relative to that of the wind, the non-polarized scattering contribution associated to IWs is more remarkable at upwind direction while it is less significant at down/crosswind directions. The non-polarized scattering mechanisms also calls for a modulation induced by IWs which is much more significant,i.e. at least three times, that the one that characterizes the polarized scattering mechanism.

This study focuses on a very complex environment, namely the Ionian coast of the Basilicata region, Southern Italy, which includes different kinds of beaches, river mouths and built-up areas. This complex environment is used as a test case to analyze the time variability of the coastline using measurements that were remotely sensed by the satellite European Copernicus Synthetic Aperture Radar (SAR) mission. First, the accuracy of the coastline, extracted by the SAR, is discussed with respect to finer-spatial-resolution drone-based light detection and ranging (LIDAR) measurements. Then, a time series of SAR dual-polarimetric measurements acquired by the European Copernicus mission is used to discuss the time variability of the coastline of the area of interest in a time period spanning from 2015 to 2021. The experimental results show that the accuracy of the SAR-based coastline is better than 15 m, which is reasonably good precision for monitoring the erosion/accretion processes that characterize the area of interest at a moderate scale. The estimated time variability of the extracted coastline suggests a dominant erosion process, which is always within 60 m.

To monitor polar regions is of paramount importance for climatological studies. Climate change due to anthropogenic activities is inducing global warming that, for example, has resulted in glacier melting. This has had a significant impact on sea levels and ocean circulation. In this study, the temporal trend of the marine-terminated d’Iberville glacier (Ellesmere Island, Canada) is analysed using C-band synthetic aperture radar satellite imagery collected by the Radarsat-2 and Sentinel-1 missions. The data set consists of a time series of 10 synthetic aperture radar data collected from 2010 to 2022 in dual-polarimetric imaging mode, where a horizontally polarised electromagnetic wave was transmitted. An automatic approach based on a global threshold constant false alarm rate method is applied to the single- and dual-polarisation features, namely the HH-polarised normalised radar cross-section and a combination of the HH- and HV-polarised scattering amplitudes, with the aim of extracting the ice front of the glacier and, therefore, estimating its behaviour over time. Independent collocated satellite optical imagery from the Sentinel-2 multi-spectral instrument is also considered, where available, to support the experimental outcomes. The experimental results show that (1) the HH-polarised normalised radar cross-section achieved better performance with respect to the dual-polarised feature, especially under the most challenging case of a sea-ice infested sea surface; (2) when the HH-polarised normalised radar cross-section was considered, the ice front extraction methodology provided a satisfactory accuracy, i.e., a root mean square error spanning from about 1.1 pixels to 3.4 pixels, depending on the sea-surface conditions; and (3) the d’Iberville glacier exhibited, during the study period, a significant retreat whose average surface velocity was 160 m per year, resulting in a net ice area loss of 2.2 km2 (0.18 km2 per year). These outcomes demonstrate that the d’Iberville glacier is behaving as most of the marine-terminated glaciers in the study area while experiencing a larger ice loss.

The monitoring of ships is of paramount importance for ocean and coastal area surveillance. The synthetic aperture radar is shown to be a key sensor to provide effective and continuous observation of ships due to its unique imaging capabilities. When advanced synthetic aperture radar imaging systems are considered, the full scattering information is available that was demonstrated to be beneficial in developing improved ship detection and classification algorithms. Nonetheless, the capability of polarimetric synthetic aperture radar to observe marine vessels is significantly affected by several imaging and environmental parameters, including the incidence angle. Nonetheless, how changes in the incidence angle affect the scattering of ships still needs to be further investigated since only a sparse analysis, i.e., on different kinds of ships of different sizes observed at multiple incidence angles, has been performed. Hence, in this study, for the first time, the polarimetric scattering of the same ship, i.e., a small fishing trawler, which is imaged multiple times under the same sea state conditions but in a wide range of incidence angles, is analysed. This unique opportunity is provided by a premium L-band UAVSAR airborne dataset that consists of five full-polarimetric synthetic aperture radar scenes collected in the Gulf of Mexico. Experimental results highlight the key role played by the incidence angle on both coherent, i.e., co-polarisation signature and pedestal height, and incoherent, i.e., multi-polarisation and total backscattering power, polarimetric scattering descriptors. Experimental results show that: (1) the polarised scattering component is more sensitive to the incidence angle with respect to the unpolarised one; (2) the co-polarised channel under horizontal polarisation dominated the polarimetric backscattering from the fishing trawler at lower angles of incidence, while both co-polarised channels contribute to the polarimetric backscattering at higher incidence angles; (3) the HV polarisation provides the largest target-to-clutter ratio at lower incidence angles, while the HH polarisation should be preferred at higher angles of incidence.

This study focused on the analysis of the time variability of the morphology of the Drygalski ice tongue (DIT), Antarctica, using – for the first time – satellite synthetic aperture radar (SAR) images. A time series of Sentinel-1 interferometric wide swath SAR imagery collected from 2016 to 2021 is considered and an unsupervised methodology, based on a global threshold constant false alarm rate approach, is used to extract the boundary between the DIT and the surrounding ice-free/ice-infested sea water. The most prominent rifts/fractures identified on the extracted profiles and the ice front are selected to analyse the DIT time variability. The feature tracking allows deriving information on the morphological evolution of the DIT, including the annual displacement and average surface velocity. Experimental results show that the DIT ice front calls for a relatively stable motion trend towards the sea with an average surface velocity of about 670 m per year. Our outcomes show a fairly good agreement with similar studies appeared in the scientific literature, which are mostly based on optical imagery.

he oceans cover roughly 2/3 of the Earth’s surface and are a fundamental ecosystem regulating climate, weather and representing a huge reservoir of biodiversity and natural resources . The preservation of the oceans is therefore not only relevant on an environmental perspective but also on an economical one. A sustainable approach is requested that cannot be simply achieved by improving technologies but calls for a shared new vision of common goods.Within such a complex and holistic problem, the role of satellite microwave remote sensing to observe marine ecosystem and to assist a sustainable development of human activities must be considered. In such a view the paper is meant. Accordingly, the key microwave sensor technologies are reviewed paying particular emphasis on those applications that can provide effective support to pursue some of the UN Sustainable Development Goals. Three meaningful sectors are showcased:oil and gas, where microwave sensors can provide continuous fine-resolution monitoring of critical infrastructures; renewable energy, where microwave satellite remote sensing allows supporting the management of offshore wind farms during both feasibility and operational stages; plastic pollution, where microwave technologies that exploit signals of opportunity offer large-scale monitoring capability to provide marine litter maps of the oceans.