![]() This effect, together with the availability of more advanced Earth observation satellite missions equipped with polarimetric SAR (polSAR) imaging sensors, triggered the development of scattering-based marine vessel observation approaches. However, the difference in sea–ship backscattering is severely affected by SAR imaging parameters, e.g., incident wavelength and incidence angle, meteo-marine conditions and by the properties of the marine vessel, e.g., the material it consists of, the heading, and the geometric structure. Generally speaking, SAR observation of ships relies on the fact that the metallic structures of marine vessels are characterised by a backscattered signal stronger than the one from the surrounding sea. When dealing with the latter, several methods, which are either based on single- or multi-polarisation measurements, have been proposed. SAR monitoring of marine vessels is an important application that triggered the development of many approaches that can be roughly classified in image processing- and scattering-based methods. The synthetic aperture radar (SAR) is a microwave remote sensing tool that, due to its all-day and almost all-weather imaging capabilities together with its fine spatial resolution and wide area coverage, is a key instrument for open ocean and coastal area surveillance, including the observation of metallic targets at sea. ![]() 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. 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. ![]() 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. 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. 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. 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. 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. 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. The monitoring of ships is of paramount importance for ocean and coastal area surveillance.
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