A ship detection experiment: the case of South Africa

Kurzfassung

South Africa has a coastline of approximately 3900 km in length and is the 39th longest coastline in the world. The coastal area over which South Africa has jurisdictional rights (Exclusive Economic Zone, EEZ) cover approximately 1.5 million square km. This area represents a key zone for South Africa economical activities (fishing, shipping, etc.), international maritime trading: one may think that about 30% of European- and Americans-bound oil from the Middle East comes through the Cape Sea Route, one of the most important routes between East and West. Furthermore, South Africa is located at a maritime choke point surrounded by three oceans, the Indian, the South Atlantic and the Southern one. The South Africa large number of well-developed ports and related maritime infrastructures accounts for a value excess of 90% of its imports and exports carried by sea. Moreover, the commercial fishing industries emply approximatively 25000 people producing a gross income of more than 300 million euros annually. This information witnesses that a continous and updated surveillance of the maritime environment with its activities is of fundamental importance for South Africa trading and security. Traditionally, ships have been monitored using transponder cooperative systems such as the Automatic Identification System (AIS). Damages and sabotages of transponder-based systems, together with delays in communication, make this monitoring unsatisfactory. Hence, by combining the advantages of Synthetic Apeture Radar (SAR) observations with the information gathered by AIS, such drawbacks can be overcome. In such a context, a controlled experiment has been set up off the South Africa coasts from December 10 to December 16, 2013 to analyze the performance of different multi-polarization/multi-frequency algorithms. SAR acquisitions have been planned together with the Italian Space Agency ASI, the German Aerospace Center DLR and the Indian Space Research Organization ISRO, while available ground reference and ancillary data have been provided by the South African Maritime Safety Authority (SAMSA) and the Council for Scientific and Industrial Research (CSIR). The processed data set consists of multi-polarization and multi-frequency SAR data collected by several satellite missions: the Italian X-band Cosmo-SkyMed (CSK), the German TerraSAR-X, and the Indian C-band RISAT-1. All the scenes have been collected from December 10 to December 16, 2013. Eight CSK Stripmap scenes have been collected (7 by the single-polarization Himage mode and 1 by the incoherent dual-polarimetric PingPong mode). Six coherent dual-polarimetric TerraSAR-X scenes have been collected by the Stripmap dual-polarimetric mode, while four Fine Resolution Stripmap scenes have been collected by RISAT-1 according to the new hybrid-polarity mode. The data set is processed using different algorithms. Single-pol co-polarized SAR data are processed using the approach proposed in [1][2]. Single-pol cross-polarized SAR data are processed using the approach proposed in [2]. Dual-polarimetric coherent SAR data are processed using the approach proposed in [3][4]. Hybrid-polarity SAR data are processed using new tailored methodologies developed starting from wave-polarimetry concepts.