This paper is a first introduction to the concept of using Global Navigation Satellite Systems (GNSS) as illuminators of opportunity in a passive bistatic real-time radar system for maritime target indication applications. An overview of the system concept and the signal processing algorithms for Moving Target Indication (MTI) is provided. To verify the feasibility of the system implementation as well as test the developed signal processing algorithms, an experimental test bed was developed and the appropriate experimental campaign with the new Galileo satellites and a ferry as the target was carried out. The results confirm the system concept and its potential for multi-static operation, with the ferry being detected simultaneously by two satellites.

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This paper addresses the exploitation of GNSS as opportunistic sources for the joint detection and localization of vessels at sea in a passive multistatic radar system. A single receiver mounted on a proper platform (e.g., a moored buoy) can collect the signals emitted by multiple navigation satellites and reflected from ship targets of interest. This paper puts forward 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. A proper strategy is defined to form a long-time and multistatic range&Doppler (RD) map, where the total target power can be reinforced with respect to, in turn, the case in which the RD map is obtained over as a short dwell and the case in which a single transmitter is employed. The exploitation of both the long integration time and the multiple transmitters can greatly enhance the performance of the system, allowing counteracting the low power budget provided by the considered sources representing the main bottleneck of this technology. Moreover, the proposed singlestage approach can reach superior detection performance than a conventional two-stage process where peripheral decisions are taken at each bistatic link and subsequently the localization is achieved by multilateration methods. Theoretical and simulated performance analysis is proposed and also validated by means of experimental results considering Galileo transmitters and different types of targets of opportunity in different scenarios. Obtained results prove the effectiveness of the proposed method to provide detection and localization of ship targets of interest.

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.