Abstract
The physics of the imaging mechanism underlying the emergence of ship wakes in Synthetic Aperture Radar (SAR) images has been studied in the past by many researchers providing a well-understood theory. Therefore, many publications describe how well ship wakes are detectable on SAR under the influence of different environmental conditions like sea state or local wind, ship properties like ship speed or ship heading, and image acquisition parameters like incidence angle or satellite heading. The increased imaging capabilities of current satellite SAR missions facilitate the collection of large datasets of moving vessels. Such a large dataset of high resolution TerraSAR-X acquisitions now enables the quantitative analysis of the previously formulated theory about the detectability of ship wakes using real data. In this paper we propose an extension of our wake detectability model by using a non-linear basis which allows consideration of all the influencing parameters simultaneously. Such an approach provides new insights and a better understanding of the non-linear influence of parameters on the wake detectability and their interdependencies can now be represented. The results show that the non-linear, interdependent influence of the different influencing parameters on the detectability of wakes matches well to the oceanographic expectations published in the past. Also possible applications of the model for the extraction of missing parameters and automatic for wake detection systems are demonstrated.
Highlights
The detection of ships on space-borne Synthetic Aperture Radar (SAR) imagery is hardly possible, when the ship’s construction material is non-conductive and in turn the ship’s SAR-signatures are not or badly represented in the SAR images [1]
The physics of the imaging mechanism underlying the emergence of ship wakes in Synthetic Aperture Radar (SAR) images has been studied in the past by many researchers providing a well-understood theory
In this paper we propose an extension of our wake detectability model by using a non-linear basis which allows consideration of all the influencing parameters simultaneously
Summary
The detection of ships on space-borne Synthetic Aperture Radar (SAR) imagery is hardly possible, when the ship’s construction material is non-conductive and in turn the ship’s SAR-signatures are not or badly represented in the SAR images [1]. A similar context can be observed in the existence of approaches for modeling the detectability of ship or wake signatures in dependency to parameters influencing their detectability in SAR imagery. In the following these parameters will be called influencing parameters. Bragg waves can be modulated by ship-generated internal waves on the ocean surface making them visible on X-Band [27], but their emergence depends among other things on the water depth and the presence of either surface films or interactions with surface currents [19,28] These kinds of influences can neither be derived from SAR automatically nor be provided by oceanographic models in adequate resolution. Possible applications of the extended wake detectability model are demonstrated
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