1,720,997 research outputs found
Target localization and velocity estimation in near Forward Scatter Radar Systems: Preliminary results
No full textIn this paper we investigate the two-dimensional target localization and motion parameters estimation capabilities of a near Forward Scatter (NFS) Radar system with a dual receiving antenna. Taking advantage of the low-cost Crystal Video Detector (CVD) commonly adopted in Forward Scatter Radar (FSR) configurations, in this work we propose a short-time CVD to test for target detection. Once the target has been detected, the Doppler frequency and the Direction of Arrival measurements extracted at two separate time instants are jointly exploited to localize the target in the (x,y) plane and to estimate its velocity components. As expected the achievable estimation accuracy depends on the time delay between the measurements. The experimental results achieved by means of a passive NFS system where FM transmissions are exploited as waveforms of opportunity support the practical applicability and confirm the effectiveness of the proposed approach
Maritime targets velocity estimation in space-based passive multistatic radar using long integration times
Full text linkTarget detection by means of space-based passive radar sensors generally requires the adoption of long integration time strategies to reinforce sufficiently the signal strength. These are usually based on the recovery of the target Doppler-rate to cope with the range and Doppler migration experienced over the long dwell considered. In this work, we put forward a Taylor-series approach that capitalizes on the set of bistatic Doppler-rates estimated in Global Navigation Satellite Systems (GNSS)-based multistatic radar configurations to estimate the velocity of ship targets with increased accuracy with respect to conventional Doppler-based procedures. Both the cases of single-element and array receiver configurations have been considered. Theoretical and numerical results under different use cases show as leveraging on the long integration times adopted at the detection stage could significantly increase the accuracy of the estimated ship velocity components. Few experimental results are also provided, verifying the potentialities of the proposed approach in operative scenarios of practical interest for this technology. The proposed approach is not limited at the GNSS case, but it could be potentially applied to any multistatic passive radar system
DVB-S based passive radar imaging of ship targets
No full textThis work investigates the potentialities of DVB-S based passive ISAR for maritime surveillance applications. Specifically, in order to characterize the bound on the achievable performance, a knowledge based approach is adopted: Assuming known the target motion, the image is focused in both the range/Doppler domain and the x-y plane via backprojection. The approach is applied to experimental data acquired during a field trial by exploiting an experimental system developed at Fraunhofer FHR. Obtained results clearly demonstrate the potentialities of DVB-S based passive ISAR at providing output products suitable for the extraction of the length/width of the ship and of its shape
Maritime target imaging via simultaneous DVB-T and DVB-S passive ISAR
No full textThis work presents an analysis of passive inverse synthetic aperture radar images obtained exploiting simultaneously digital video broadcasting-Terrestrial (DVB-T) and digital video broadcasting-satellite (DVB-S) as illuminators of opportunity (IOs) over a cooperative maritime target with known motion. The combined exploitation of these two IOs is extremely appealing for passive imaging purposes, given their complementary characteristics. The analysis is first conducted in a simulated environment, to show the different expected outcomes from the two considered bistatic geometries and operating bandwidths. Subsequently, the same analysis is repeated over real data acquired during a field trial, by exploiting experimental setups developed at Fraunhofer FHR. In particular, DVB-T and DVB-S data are focused by means of back projection, which enables an easier comparison of the different ISAR products. Real data results show good match with simulated ones. Target size can be estimated with good accuracy in both DVB-T and DVB-S cases, and dominant scatterers can also be identified. DVB-S also enables target-shape recognition, given its higher signal bandwidth
Experimental demonstration of ship target detection in GNSS-based passive radar combining target motion compensation and track-before-detect strategies
Full text linkThis work discusses methods and experimental results on passive radar detection of moving ships using navigation satellites as transmitters of opportunity. The reported study highlights as the adoption of proper strategies combining target motion compensation and track-before-detect methods to achieve long time integration can be fruitfully exploited in GNSS-based passive radar for the detection of maritime targets. The proposed detection strategy reduces the sensitivity of long-time integration methods to the adopted motion models and can save the computational complexity, making it appealing for real-time implementations. Experimental results obtained in three different scenarios (port operations, navigation in open area, and river shipping) comprising maritime targets belonging to different classes show as this combined approach can be employed with success in several operative scenarios of practical interest for this technology
Application of track-before-detect techniques in GNSS-based passive radar for maritime surveillance
Full text linkGNSS-based passive radar has been recently proved able to enable moving target detection in maritime surveillance applications. The main restriction lies in the low Equivalent Isotropic Radiated Power (EIRP) level of navigation satellites. Extending the integration times with proper target motion compensation has been shown to be a viable solution to improve ship detectability, but this involves computational complexity and increasing sensitivity to motion model mismatches. In this work, we consider the application of a Track-Before-Detect (TBD) method to considerably increase the integration time (and therefore the detection capability) at the same time keeping the computational complexity affordable by practical systems. Dynamic programming TBD algorithms have been specialized for the considered framework and tested against experimental dataset. The obtained results show the effectiveness of this approach to improve the detection capability of the system despite the restricted power budget
Optimal receivers positioning for target motion parameters estimation in dual-baseline FSR systems: preliminary results
No full textAn important field of application of Forward Scatter Radar systems (both single-node and multi-node) consists in the estimation of the target kinematic parameters. In the past different studies have shown the possibility to extract these parameters by estimating the main target signal parameters (i.e. Doppler rate, derivative of the Doppler rate) and the time instant at which the target crosses the baseline. The estimation accuracy of the motion parameters depends on the estimation accuracy of the target signal parameters and on the FSR geometry. In this frame, the main goal of this paper is to provide a simple tool which can be used to (i) optimize the receivers position in a dual baseline FSR configuration and (ii) evaluate the minimum angular separation between the two baselines that guarantees the estimation of all the kinematic parameters with a desired accuracy. To this aim, for a target following a linear trajectory, the motion parameters are estimated by jointly exploiting the time delay between the signals acquired at the two different receivers and the estimates of their Doppler rates
Joint detection and localization of vessels at sea with a GNSS-Based multistatic radar
Full text linkThis paper addresses the exploitation of global navigation satellite systems 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 and 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 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 single-stage 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
A closed-form model for long- and short-range forward scatter radar signals from rectangular conductive targets
No full textA closed-form model for the forward scatter radar (FSR) signal is presented with the goal to overcome the far-field (FF) limitation of the commonly used models. The proposed Fresnel closed-form (FCF) model, based on an approximation of the Helmholtz-Kirchhoff electromagnetic theory, correctly represents the received field of rectangular metallic targets crossing the baseline either in the short range or long range of the FSR transmitter and receiver. The FCF model outputs are validated by comparison with numerical results of a full-wave simulation tool in terms of received field amplitude and phase. The FCF model is exploited to assess the FSR detection performance loss, caused by the use of the FF models for some case studies of practical interest. Based on the proposed FCF model, we provide an analysis of the FSR ideal optimum performance achievable in these scenarios
GNSS-based multistatic passive radar imaging of ship targets
No full textThis work brings forward a framework for passive radar imaging of ship targets by exploiting the reflections of navigation satellite signals. The specific objective is taking advantage of the inherent multistatic nature of the system for the ship passive imagery. To this aim, a bistatic image formation stage is first defined. Then, the bistatic images obtained over multiple baselines are mapped in a domain independent on the particular satellite viewing angle. Finally, different combination rules of the multiple images are defined in order to enable multistatic imagery with enhanced quality, potentially enabling finer feature extraction procedures for ship classification. The proposed approaches are validated and compared via an experimental campaign comprising multiple Galileo satellites and a commercial ferry undergoing different types of motion
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