Target Detection in Heterogeneous Clutter with Low Resolution Radar

This thesis develops a framework for SAR target detection and super-resolution in low-resolution environments. The primary focus in this research is the background clutter heterogeneity that often accompanies low range and cross-range resolutions. A corrective model which accounts for clutter replacement is developed to define the detection and false alarm rates of the detector more accurately than a traditional model in which the radar return from the target supplements the existing clutter. In a heterogeneous clutter cell, the clutter replacement model leverages the different scattering distributions among the individual clutter types to generate a probability distribution function for the areas of each clutter type which are obstructed by a target. The location of the target can be extrapolated from the clutter replacement areas, and a multiple hypothesis detection test is conducted to determine which location estimate yields the lowest average error

On Detection and Ranking Methods for a Distributed Radio-Frequency Sensor Network: Theory and Algorithmic Implementation

A theoretical foundation for pre-detection fusion of sensors is needed if the United States Air Force is to ever field a system of distributed and layered sensors that can detect and perform parameter estimation of complex, extended targets in difficult interference environments, without human intervention, in near real-time. This research is relevant to the United States Air Force within its layered sensing and cognitive radar/sensor initiatives. The asymmetric threat of the twenty-first century introduces stressing sensing conditions that may exceed the ability of traditional monostatic sensing systems to perform their required intelligence, surveillance and reconnaissance missions. In particular, there is growing interest within the United States Air Force to move beyond single sensor sensing systems, and instead begin fielding and leveraging distributed sensing systems to overcome the inherent challenges imposed by the modern threat space. This thesis seeks to analyze the impact of integrating target echoes in the angular domain, to determine if better detection and ranking performance is achieved through the use of a distributed sensor network. Bespoke algorithms are introduced for detection and ranking ISR missions leveraging a distributed network of radio-frequency sensors: the first set of bespoke algorithms area based upon a depth-based nonparametric detection algorithm, which is to shown to enhance the recovery of targets under lower signal-to-noise ratios than an equivalent monostatic radar system; the second set of bespoke algorithms are based upon random matrix theoretic and concentration of measure mathematics, and demonstrated to outperform the depth-based nonparametric approach. This latter approach shall be shown to be effective across a broad range of signal-to-noise ratios, both positive and negative

Maritime forward scatter radar

This thesis is dedicated to the study of forward scatter radar (FSR) in the marine environment. FSR is a class of bistatic radar where target detection occurs at very large bistatic angle, close to the radar baseline. It is a rarely studied radar topology and the maritime application is a completely novel area of research. The aim is to develop an easily deployed buoy mounted FSR network, which will provide perimeter protection for maritime assets—this thesis presents the initial stages of investigation. It introduces FSR and compares it to the more common monostatic/bistatic radar topologies, highlighting both benefits and limitations. Phenomenological principles are developed to allow formation of forward scatter signal models and provide deeper understanding of the parameters effecting the operation of an FSR system. Novel FSR hardware has been designed and manufactured and an extensive measurement campaign undertaken. The outcome of this was the creation of the first comprehensive maritime FSR target and clutter signal database—results from which have been shown with preliminary analysis. Alongside experimental work, a sea surface model has been produced in order to estimate the effects of wave blocking in high sea states and assess FSR performance in these conditions

Detection and motion parameters estimation techniques in Forward Scatter Radar

Forward scatter Radar systems designed to take advantage of the greater radar cross section, that is robust to Radar Absorbing Material and other stealth technology, and of the long integration times, due to the little phase and amplitude fluctuations, are attractive for a variety of applications. Many of which fit well with the needs of augmentation of the surveillance capabilities of low-observable targets that may have a small backscatter RCS when observed with the conventional radar systems. This thesis reports on research into this field of radar systems with additional contributions to target detection and motion parameters estimation. Particularly, the first part of the thesis deals with the detection of moving targets that follow a linear trajectory in a single node FSR configuration. The detection scheme based on a square-law detector followed by an appropriate matched filter, here addressed as Crystal Video Detector (CVD) following the traditional terminology (Crystal Video Receiver), has already been put forward in the literature. Performance prediction and FSR system design were key motivator to analytically characterize the detection performance of CVD in terms of both, probability of false alarm and probability of detection. The derived closed-form expressions were validate from Monte Carlo simulations under different geometrical conditions and from experimental data acquired by a passive FSR based on FM signals. Furthermore, new detection schemes based on the CVD ensuring the constant false alarm rate (CFAR) condition were devised and analytically characterized. The performance analysis showed quite small losses of the CFAR-CVD detectors compared to the fixed threshold CVD. The second part of the thesis still handles the problem of target detection through the derivation of innovative detection schemes based on the Generalized Likelihood Ratio Test (GLRT). A comparison with the detection performance of the CVD has proven the better performance of the GLRT-based detectors. In most cases the improvement has an upper bound of 3 dB. However, there are specific circumstances where the standard FSR detector shows significant losses while the GLRT schemes suffer a much smaller degradation. Moreover the possibility to have a set of secondary data assumed target free, drove to the devising of new GLRT schemes. The results demonstrated a non-negligible further improvement over the previous GLRT schemes when the operation conditions get close to the near field transition point. The detection performance of the derived detectors without and with secondary data were analytically characterized. This analytical performance allowed to derive simplified equivalent SNR expressions that relate the GLRT detection performance to the main system and target parameters. These expressions showed to be useful for the design of effective FSR geometries that guarantee desired detection performance for specific targets. In the third part of the thesis the focus is moved to the motion parameters estimation through both, a single baseline and a dual baseline FSR configuration. Accordingly, the Doppler signature extracted from the Crystal Video based scheme is exploited. Following motion parameters estimation approaches already introduced in the literature, a two dimensional filter bank technique was proposed. The main target parameters encoding Doppler rate, main lobe width and crossing time instant were estimated from such technique. The accuracy of the proposed technique was investigated from a theoretical point of view through the derivation of simplified closed-form expression of the Cramer Rao Lower Bound (CRLB). The analysis proved that unbiased estimates of the desired target parameters can be obtained that approach the derived CRLB in the high SNR region. After the dependence of the kinematic parameters on the parameters estimated from the bank was exploited. The cross baseline velocity in a single baseline configuration was estimated under the assumption that the baseline crossing point is known. Meanwhile the dual baseline configuration ensures the possibility to estimate also the baseline crossing point without a priori knowledge on the other target kinematic parameters. Once more, the CRLB of the target motion parameters for both reference scenarios was derived. The analysis proved that unbiased estimates of the target motion parameters can be obtained with high accuracy even for low SNR conditions. The effectiveness of the proposed approach was also shown from experimental data acquired by a passive FSR based on FM signals

Statistical Analysis of Coherent Monostatic and Bistatic Radar Sea Clutter

Radar sea clutter analysis has been an important area of radar research for many years. Very limited research has been carried out on coherent monostatic sea clutter analysis and even less on bistatic sea clutter. This has left a significant gap in the global scientific knowledge within this area. This thesis describes research carried out to analyse, quantify and model coherent sea clutter statistics from multiple radar sources. The ultimate goal of the research is to improve maritime radars' ability to compensate for clutter and achieve effective detection of targets on or over the sea surface. The first analyses used monostatic data gathered during the fight trials of the Thales Searchwater 2000 AEW radar. A further sea clutter trials database from CSIR was then used to investigate the variation of clutter statistics with look angle and grazing angle. Finally simultaneous monostatic and bistatic sea clutter data recorded in South Africa using the S-band UCL radar system NetRAD were analysed. No simultaneous monostatic and bistatic coherent analysis has ever been reported before in the open literature. The datasets recorded included multiple bistatic angles at both horizontal and vertical polarisations. Throughout the analysis real data have been compared to accepted theoretic models of sea clutter. An additional metric of comparison was investigated relating to the area of information theoretic techniques. Information theory is a significant subject area, and some concepts from it have been applied in this research. In summary this research has produced quantifiable and novel results on the characteristics of sea clutter statistics as a function of Doppler. Analysis has been carried out on a wide range of monostatic and bistatic data. The results of this research will be extremely valuable in developing sea clutter suppression algorithms and thus improving detection performance in future maritime radar designs

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

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Remote sensing and electromagnetic modeling applied to weather and forward scatter radar

This dissertation deals with electromagnetic modelling and data analysis, related to radar remote sensing and applied to forward scatter and meteorological polarimetric systems. After an overview of radar fundamentals to introduce the general terminology and concepts, results are presented at the end of each chapter. In this respect, a generalized electromagnetic model is first presented in order to predict the response of forward scatter radars (FSRs) for airtarget surveillance applications in both near-field and far-field regions. The model is discussed for increasing levels of complexity: a simplified near-field model, a near-field receiver model and a near-field receiver and transmitter model. FSR results have been evaluated in terms of the effects of different target electrical sizes and detection distances on the received signal, as well as the impact of the trajectory of the moving objects and compared with a customized implementation of a full-wave numerical tool. Secondly, a new data processing methodology, based on the statistical analysis of ground-clutter echoes and aimed at investigating the monitoring of the weather radar relative calibration, is presented. A preliminary study for an improvement of the ground-clutter calibration technique is formulated using as a permanent scatter analysis (PSA) and applied to real radar scenarios. The weather radar relative calibration has been applied to a dataset collected by a C-band weather radar in southern Italy and an evaluation with statistical score indexes has drawn through the comparison with a deterministic clutter map. The PSA technique has been proposed using a big metallic roof with a periodic mesh grid structure and having a hemispherical shape in the near-field of a polarimetric C-band radar and evaluated also with an ad-hoc numerical implementation of a full-wave solution. Finally, a radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths (i.e., at X, Ka and W band) using a high-quality database of collocated ground-based precipitation measurements and radar multi-frequency observations. Coefficients for the multifrequency radar snowfall intensity retrieval are empirically derived using multivariate regression techniques and their interpretation is carried out by particle scattering simulations with soft-ice spheroids. For each topic, conclusions are proposed to highlight the goals of the whole work and pave the way for future studies

The probability of detecting and tracking RADAR targets in clutter at low grazing angles

Modern military acquisition and tracking RADARs are required to operate against aircraft and missiles specifically designed to have minimal radar cross section (RCS) and which fly at very low level to take maximum advantage of terrain screening. A model for predicting system performance is necessary for a range of terrain types in varying precipitation and seasonal cultural conditions. While the main degradation is from surface clutter and denial of sightline due to terrain and other local obstructions, several other factors such as multipath propagation, deliberate jamming and even operator performance contribute to the total model. The possibility that some radars may track obscured targets, however briefly, by using the diffraction path, is of particular interest. Although this report critically examines each of the contributory factors in order to select optimum values for inclusion in an overall computer prediction model; a new surface clutter model is specifically developed for sloped terrain using actual clutter measurements. The model is validated by comparison with an extensive survey of worldwide clutter results from both published and unpublished sources. Certain constraints have been necessary to restrict the study to a manageable size, while meeting the requirements of the sponsors. Attention is therefore focussed upon performance prediction for typical mobile tracking radar systems designed for operation against small RCS low level targets flying overland