• 16:30 On the capability of compact polarimetry SAR architectures to observe oil slicks at sea

  Buono, Andrea; Nunziata, Ferdinando; Migliaccio, Maurizio Università degli Studi di Napoli Parthenope, Italy

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  Sea oil pollution, involving both accidental disasters and illicit vessel discharges is a matter of great concern, since it strongly affects the marine ecosystem and, indirectly, the human health. Hence, a non-cooperative monitoring system, with almost all-weather day and night capability, is fundamental to support law enforcement and an early warning system to apply proper countermeasures. It is worldwide recognized that Synthetic Aperture Radar (SAR) is a key tool to observe oil at sea, providing a continuous and updated monitoring. In particular, there is a general consensus that the unique capabilities of Full-Polarimetric (FP) SARs are useful for observe oil slicks. In fact, a FP SAR architecture, measuring the whole scattering matrix for each resolution cell, provides an unprecedented level of information to classify the scattering mechanisms of the observed scene. Several polarimetric features, e. g. the target entropy, the degree of polarization, the normalized pedestal height and the standard deviation of the co-polarized phase difference, have been show to allow both oil slicks detection and discriminating strong-damping oil spills from weak-damping lookalikes (i.e. algae, plankton, thin biogenic films). Hence, FP features allow generating value-added products that are more physically reliable and robust than the single-polarization ones. However, the scattering information of the observed scene provided by a FP SAR architecture comes at a cost in terms of high transmitted power, limited swath width and limited range of admissible incidence angles. To mitigate those drawbacks Compact Polarimetry (CP) SAR architectures have been proposed, representing a good compromise between single-polarization SAR mode and full-polarization ones. In fact, they provide polarimetric performance that are expected to be close to the one related to FP SARs, while avoiding their principal drawbacks. The idea that lies at the basis of CP SAR architectures is transmitting only one polarization while receiving coherently, i.e. both amplitude and the relative phase, according to an orthogonal polarization basis. In this study, the capability of CP SAR architectures to observe oil slicks at sea is investigated. Among them, three different architectures have been analyzed: Hybrid Polarity (HP) SAR architecture, which consists of transmitting a circularly-polarized field while receiving coherently according to a linear h-v basis, the Linear SAR one, in which a linearly-polarized field, oriented at π/4 in the h-v plane, is transmitted, and the Circular-Circular (CC) architecture, which consists of receiving coherently, according to an orthogonal right hand-left hand circular basis, a circularly-polarized transmitted field. The degree of polarization and the wave entropy of the received field scattered off the observe scene have been considered, and interpreted in terms of sea surface scattering with or without oil slicks under low to moderate wind conditions and for intermediate angles of incidence. The capability of CP architectures to classify oil slicks according to their information content have been analyzed, providing a ranking among the different CP architectures considered. They are expected to obtain performance very close to FP SAR architectures, showing a different sensitivity with respect to slick-free, weak-damping slick-covered and oil-covered sea surface. This sensitivity is verified against emulated CP data obtained transforming actual L- and C-band quad-polarimetric SAR measurements where well-known oil slicks and weak-damping look-alikes, together with different marine features, are present.

  
   

• 17:10 A SHIP DETECTION EXPERIMENT: THE CASE OF SOUTH AFRICA

  Paes, Rafael L (1); Buono, Andrea (2); Nunziata, Ferdinando (2); Migliaccio, Maurizio (2); Velotto, Domenico (3); Lehner, Susanne (3); Misra, Tapan (4); Ravoori, Nagaraja (4); Kleynhans, Waldo (5); Otto, Karl (6) 1: National Institute for Space Research (INPE), Brazil; 2: Università degli Studi di Napoli "Parthenope", Italy; 3: Deutschen Zentrums für Luft- und Raumfahrt (DLR), Germany; 4: Indian Space Research Organisation (ISRO), India; 5: Council for Scientific and Industrial Research (CSIR), South Africa; 6: South African Maritime Safety Authority (SAMSA), South Africa

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  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.

  
   

• 16:50 ANALYSIS AND OPTIMIZATION OF TARGET SCATTERED WAVE POLARIZATION SIGNATURE FOR ENHANCED SHIP DETECTION USING RADARSAT-2

  Touzi, Ridha (1); Hurley, J. (2); Vachon, P.W. (3) 1: Canada Centre for Remote Sensing; 2: MDA; 3: DRDC

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  Ship detection has many potential applications within the commercial, fishery, vessel traffic service, and military sectors. The importance of transmit-receive antenna polarizations on ship detectability is now well understood. Better ship-sea contrast is obtained with HH polarization, whereas VV polarization provides more information on the sea surface conditions. The use of ASAR and RADARSAT-2 single polarization HV imagery in ScanSAR mode or dual polarization (HH-HV or VV-VH) in standard mode has provided promising results for ship detection [1, 2]. While HV provides the best ship detection at steep incidence angles, the co- polarization (HH or VV) may perform better at larger incidence angle [1, 2]. However, it is now admitted that the performance of single and dual-polarization SAR over wide swaths can be ineffective for small vessels, and there is an urgent requirement for earth observation sensors that permit an improved detection of small vessels In this study, the added value of polarimetric SAR information for ship detection is investigated using wide swath (50km) fine quad-pol RADARSAT-2 (RS2) data collected off Strait of Georgia, near Vancouver (Canada). Shore-based radar tracks of ship traffic obtained from the Canadian Coast Guard (CCG) are used as a source of ground truth for the identification of ships imaged with RS2 at 29º and 38º incidence angle. The “scattered wave” polarization signature is introduced as a convenient graphical representation of variations of the scattered wave rotation invariant parameters as a function of the transmitting antenna polarization. It is shown that the signature of the degree of polarization (DoP) and the total scattered intensity (R0) provide important information on ocean and ship scattering, which is complementary to the one provided by conventional Van Zyl “received intensity" polarization signatures [3]. The DoP optimization method introduced in [4] is reconsidered and adopted as a convenient tool for optimum exploitation of scattered wave information for enhanced ship detection. It is shown that the excursion of DoP, Δp, and the minimum DoP, pmin, permits a significant increase in ship-sea contrast in comparison with (i.e., scalar) single channel polarizations (i.e., HH, VV, or HV) and dual-polarization (conventional and Compact) SAR. Furthermore, the additional information provided by the maximum DoP, pmax, resolves for ship ambiguities with land targets. Quantification of ship-sea contrast is discussed in terms of ship signal non stationarity. It is shown that the contrast obtained with the local peak of the ship signal provides an accurate assessment of ship detector performance. The local pmin performs better than the local peak of Δp for small and large vessels. References: [1] P.W. Vachon and J. Wolfe. Validation of ship signatures in Envisat ASAR AP mode data using AISLive: Data acquistion, processing, and analysis results. Technical report, DRDC Ottawa TM 2008-005, Defence R&D Canada – Ottawa, 2008. [2] G.C. Staples and J. Hurley. Marine surveillance with Radarsat2: ship and oil slick detection. In Proc. of IGARSS 2011, Vancouver, Canada, 2011. [3] J.J. Van Zyl, H.A. Zebker, and C. Elachi. Imaging radar polarization signatures: theory and observation. Radio Science, 22:529–543, 1987. [4] Touzi R., S. Goze, T. Le Toan , A. Lopes, and E. Mougin , “Polarimetric discriminators for SAR images” , IEEE Trans. Geoscience Rem. Sens., Vol.30, No. 5, pp 973 980, Sep. 1992.

  
   

• 17:30 Ships and Maritime targets observation campaigns using available C- and X-band SAR satellite

  Velotto, Domenico (1); Bentes, Carlos (2); Lehner, Susanne (3) 1: German Aerospace Center – IMF-SAR, Bremen, Germany; 2: German Aerospace Center – IMF-SAR, Bremen, Germany; 3: German Aerospace Center – IMF-SAR, Bremen, Germany

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  Maritime metallic targets are usually responsible of a mixture of basic scattering mechanisms: single-bounce returns from surfaces perpendicular to the radar illumination; double-bounce returns due to the dihedral formed by vertical structure over the sea surface; multiple-bounce returns. Detection of these targets using Synthetic Aperture Radar (SAR) data relies on the fact that the signal return of such objects is usually stronger than the one from the surrounding sea surface where only the single bounce of the Bragg waves is in place. This means that the large values of Normalized Radar Cross Section (NRCS) in a SAR ocean image can be associated with the presence of a maritime target. Nevertheless this correspondence is not unique in the sense that other oceanic (internal waves, rain cells etc.) and non-oceanic effects (azimuth ambiguities) show large value of NRCS and hence produce false alarms. The information content provided by the NRCS collected by a single-polarization SAR is in general quite poor to efficiently observe metallic targets at the sea. A vast amount of scientific publications have shown that polarimetric SAR (PolSAR) data are able to fulfil this gap. Several PolSAR ship detectors have been developed in the last decades [1-5]. In spite of these optimum scientific results, the use of PolSAR data for maritime applications has been limited because of the small coverage reachable when a SAR system is operating in polarimetric mode. In fact from the SAR system design point of view, the acquisition of the full scattering matrix implies the use of a higher Pulse Repetition Frequency (PRF) that in turns affects range and azimuth ambiguities performance. To keep range and azimuth ambiguities under the system design parameterization, the swath width needs to be reduced. In general, PolSAR acquisitions are at expenses of coverage and resolution. Obviously resolution and coverage are two very important factors when it comes to maritime targets detections. The dilemma of using a single polarimetric SAR system with higher resolution and coverage or a quad- (or dual-polarimetric) system with its richness of information, is still unsolved when it comes to maritime targets applications. In the framework of ESA project MARISS and EU project DOLPHIN, in situ campaigns aimed at solving this dilemma have been carried out. Single and multi-polarimetric SAR data acquired by TerraSAR-X, RADARSAT-2 and COSMO-SkyMed have been acquired with close time gaps and partial coverage overlap. In this way several moving and non-moving maritime targets have been imaged with different polarization, geometry and working frequency. Available ground truth reports provided by Automatic Identification System (AIS) data, nautical chart and wind farm location are used to validate the different types of maritime targets. REFERENCES [1] S. Brusch, S. Lehner, T. Fritz and M. Soccorsi “Ship Surveillance With TerraSAR-X”, IEEE Transactions on Geoscience and Remote Sensing, Vol.49, No.3, p1092-1103, 2011. [2] D. Velotto, F. Nunziata , M. Migliaccio and S. Lehner, “Dual‐polarimetric TerraSAR‐X SAR data for target at sea observation,” IEEE Geoscience and Remote Sensing Letters, vol. 10, no. 5, 2013. [3] C. Liu and C. H. Gierull, “A New Application for PolSAR Imagery in the Field of Moving Target Indication/Ship Detection,” IEEE Trans. Geosci. Remote Sens.,vol. 45, no. 11, pp. 3426-3436, 2007. [4] A. Marino, S.R. Cloude, and I.H., Woodhouse, “Detecting depolarizing targets using a new geometrical pertubation filter”, IEEE Trans. Geosci. Remote Sens., vol. 50, no. 10, pp. 3787-3799, 2012. [5] D. Velotto, M. Soccorsi, and S. Lehner, “Azimuth Ambiguities Removal for Ship Detection using Full Polarimetric X-band SAR data,” IEEE Trans. Geosci. Remote Sens., vol. 52, no. 1, pp. 76-88, 2014.

  
   

• 17:50 Round Table Discussion

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  Round Table Discussion

  
   

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