GNSS-based passive radar techniques for maritime surveillance

The improvement of maritime traffic safety and security is a subject of growing interest, since the traffic is constantly increasing. In fact, a large number of human activities take place in maritime domain, varying from cruise and trading ships up to vessels involved in nefarious activities such as piracy, human smuggling or terrorist actions. The systems based on Automatic Identification System (AIS) transponder cannot cope with non-cooperative or non-equipped vessels that instead can be detected, tracked and identified by means of radar system. In particular, passive bistatic radar (PBR) systems can perform these tasks without a dedicated transmitter, since they exploit illuminators of opportunity as transmitters. The lack of a dedicated transmitter makes such systems low cost and suitable to be employed in areas where active sensors cannot be placed such as, for example, marine protected areas. Innovative solutions based on terrestrial transmitters have been considered in order to increase maritime safety and security, but these kinds of sources cannot guarantee a global coverage, such as in open sea. To overcome this problem, the exploitation of global navigation satellites system (GNSS) as transmitters of opportunity is a prospective solution. The global, reliable and persistent nature of these sources makes them potentially able to guarantee the permanent monitoring of both coastal and open sea areas. To this aim, this thesis addresses the exploitation of Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in passive bistatic radar (PBR) systems for maritime surveillance. The main limitation of this technology is the restricted power budget provided by navigation satellites, which makes it necessary to define innovative moving target detection techniques specifically tailored for the system under consideration. For this reason, this thesis puts forward long integration time techniques able to collect the signal energy over long time intervals (tens of seconds), allowing the retrieval of suitable levels of signal-to-disturbance ratios for detection purposes. The feasibility of this novel application is firstly investigated in a bistatic system configuration. A long integration time moving target detection technique working in bistatic range&Doppler plane is proposed and its effectiveness is proved against synthetic and experimental datasets. Subsequently the exploitation of multiple transmitters for the joint detection and localization of vessels at sea is also investigated. A single-stage approach to jointly detect and localize the ship targets by making use of long integration times (tens of seconds) and properly exploiting the spatial diversity offered by such a configuration is proposed. Furthermore, the potential of the system to extract information concerning the detected target characteristics for further target classification is assessed

Ship targets feature extraction with GNSS-based passive radar via ISAR approaches. Preliminary experimental study

This paper focuses on a passive radar system based on Global Navigation Satellite Systems for maritime surveillance. While in the past the capability of this technology to detect ship targets at sea was proved, despite the low EIRP level of the GNSS, the objective of this paper is investigating the potential of the system to extract information concerning the detected target characteristics. An experimental study is here provided, showing that the Doppler gradient observed for ship targets of interest can be exploited making use of ISAR approaches for extracting ship features to be exploited in target recognition procedures

Multistatic GNSS-based passive radar for maritime surveillance with long integration times. Experimental results

The focus of this paper is on multi-transmitter GNSS passive radar for maritime surveillance. Particularly, working in the range-Doppler domain, the possibility to integrate over long time intervals (required to counteract restricted power budget provided by navigation satellites) the returns from a moving target illuminated by multiple GNSS transmitters is experimentally demonstrated. The obtained results show that the exploitation of multiple satellites can provide an improvement in the detection performance potentially enabling the detection of targets not detectable with the single satellites at the same time allowing target localization

Passive radar imaging of ship targets with GNSS signals of opportunity

This article explores the possibility to exploit global navigation satellite systems (GNSS) signals to obtain radar imagery of ships. This is a new application area for the GNSS remote sensing, which adds to a rich line of research about the alternative utilization of navigation satellites for remote sensing purposes, which currently includes reflectometry, passive radar, and synthetic aperture radar (SAR) systems. In the field of short-range maritime surveillance, GNSS-based passive radar has already proven to detect and localize ship targets of interest. The possibility to obtain meaningful radar images of observed vessels would represent an additional benefit, opening the doors to noncooperative ship classification capability with this technology. To this purpose, a proper processing chain is here conceived and developed, able to achieve well-focused images of ships while maximizing their signal-to-background ratio. Moreover, the scaling factors needed to map the backscatter energy in the range and cross-range domain are also analytically derived, enabling the estimation of the length of the target. The effectiveness of the proposed approach at obtaining radar images of ship targets and extracting relevant features is confirmed via an experimental campaign, comprising multiple Galileo satellites and a commercial ferry undergoing different kinds of motion

Ship targets feature extraction with GNSS-based passive radar via ISAR approaches:preliminary experimental study

This paper focuses on a passive radar system based on Global Navigation Satellite Systems for maritime surveillance. While in the past the capability of this technology to detect ship targets at sea was proved, despite the low EIRP level of the GNSS, the objective of this paper is investigating the potential of the system to extract information concerning the detected target characteristics. An experimental study is here provided, showing that the Doppler gradient observed for ship targets of interest can be exploited making use of ISAR approaches for extracting ship features to be exploited in target recognition procedures

Comparing Non-coherent and Coherent techniques for the Detection of Scene changes from multi-Temporal SAR imagery

In this work several techniques, both coherent and non-coherent, for detecting scene changes from multitempora SAR images are discussed and their performance evaluated and compared. Assuming given scenari conditions this paper aims at discussing and comparing the performance of the different approaches for both th non-Adaptive (a priori knowledge of the scene correlation characteristics) and adaptive (estimated characteristics cases. Moreover, considering the complementary information given by the non-coherent and coherent approaches also a decentralized combination is studied. Reported results show that the adaptive change detection technique show performance close to the corresponding non adaptive ones and that the joint use of non-coheren and coherent approaches can sensibly improve the performance with respect to those achievable by the singl technique. © VDE VERLAG GMBH · Berlin · Offenbach

Maritime target detection using GNSS-based radar: Experimental proof of concept

This paper investigates the feasibility of using the Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in a passive bistatic radar system for maritime target detection applications. To this purpose, the experimental test bed was developed, and the practical campaign was conducted for maritime data acquisition with the new Galileo satellites and a ferry as the target. By developing and applying the appropriate signal processing algorithm, the obtained experimental results have not only verified the system performance, but also showed the potentialities of a multi-static configuration utilising multiple satellites simultaneously

GNSS-based passive radar for maritime surveillance: Long integration time MTI technique

The exploitation of the Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in passive radar systems for maritime surveillance is particularly attractive because of the main advantages consisting in a global coverage (even in open sea) and in the availability of multiple sources (different satellites and constellations). The main drawback stays in the restricted power budget provided by navigation satellites. This makes necessary to conceive, define and develop innovative moving target detection techniques specifically tailored for the system under consideration, in order to make this technology a powerful tool for persistent surveillance of sea areas of interest. To this aim, a long integration time Maritime Moving Target Indication technique is proposed in this work, and its effectiveness is proved against experimental data involving a small maritime target, not detectable by conventional MTI techniques. Obtained results prove the feasibility of a maritime MTI mode for GNSS based passive systems