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

Abstract

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.

Maritime Moving Target Long Time Integration for GNSS-Based Passive Bistatic Radar

“…This provides a set of Nf range Doppler compensated maps ( , ) where targets moving according to the condition under test have been correctly aligned to their range-Doppler position occupied at the reference time instant. This scheme properly generalizes the one presented in [26]- [27] since:…”

“…To analyze the degradation in integration gain of the basic plane-based technique, we evaluate the maximum dwell time for which such technique loses a maximum of 3 dB with respect to the optimum integration, reached by the local plane-based technique, for different target distances and velocities. Moreover, in order to quantify the improvement due to the compensation of both intra-frame and inter-frame migration with respect to interframe migration only, results obtained by neglecting intraframe migration (as done in [26]- [27]) are also analyzed. It is worth to note that for the purpose all the calculations do not take into account the length of time a target may be in the field of view of the surveillance antenna.…”

“…Particularly, it should be noted that a full coherent integration as in [29]- [31] is not feasible over such long dwells and therefore we need to resort to hybrid coherent/non-coherent integration of the received signal. A preliminary long integration time technique for the GNSS-based passive radar was proposed in [26] [27] while, referring to a generic space based passive radar, a Fractional Fourier transform based approach was considered in [32].…”

“…Some very preliminary results along this line were reported in [33]. As a suboptimum solution in terms of achievable integration gain, but more efficient from a computational point of view, also a second technique is proposed that works in the basic plane and properly generalizes results in [26] [27]. Particularly, the generalization consists in: (i) the consideration and compensation of the target migration at both intra-frame and inter-frames level (in contrast to [26] [27] where only inter-frames migration was considered) to possibly increase frame length; (ii) in changing the order of the different processing steps required for migration compensation to reduce the computational load.…”

“…As a suboptimum solution in terms of achievable integration gain, but more efficient from a computational point of view, also a second technique is proposed that works in the basic plane and properly generalizes results in [26] [27]. Particularly, the generalization consists in: (i) the consideration and compensation of the target migration at both intra-frame and inter-frames level (in contrast to [26] [27] where only inter-frames migration was considered) to possibly increase frame length; (ii) in changing the order of the different processing steps required for migration compensation to reduce the computational load. For both local and basic plane approaches the adaptation to the unknown target motion conditions is obtained by resorting to proper banks, being each branch in bank matched to a specific motion: to allow the design of the bank, specific criteria are analytically derived and provided for both cases.…”