Showing papers on "Moving target indication published in 1999"

Space-time processing for multichannel synthetic aperture radar

Abstract: Synthetic aperture radar (SAR) provides high-resolution images of a non-moving ground scene, but fails to indicate the presence and position of moving objects. As in airborne MTI (moving-target indication) systems the solution to this problem is to use an array of antennas or subapertures and several receiving channels ('MSAR', or multichannel SAR), and to apply multichannel clutter suppression. One of the most efficient methods is adaptive space-time processing (STAP), which can be simplified to frequency-dependent spatial processing in the Doppler domain. Some of these techniques applied to SAR are reviewed and illustrated with data gathered by the German experimental multichannel SAR system 'AER-II'.

JointSTARS and GMTI: past, present and future

Abstract: The concept of airborne surveillance of enemy ground forces with a Ground Moving Target Indicator [now called GMTI] radar capable of detecting moving ground vehicles and helicopters was proposed in 1968 and resulted in a DoD program to realize its potential. This article traces the program history starting with the Army's Stand Off Target Acquisition System [SOTAS] as it evolved through the Small Aerostat Surveillance System [SASS] and the Assault Breaker/Pave Mover programs into the currently fielded Joint Surveillance and Target Attack System [JointSTARS], which, in prototype form, more than proved its worth in the 1991 Gulf War. New developments and trends in GMTI radars are also discussed together with other potential platforms.

Topography-based VS-IMM estimator for large-scale ground target tracking

Abstract: The Interacting Multiple Model (IMM) estimator has been shown to be very effective in various target tracking problems. It is possible to vary the set of models in the IMM estimator based on some criteria to yield better estimates. This results in a Variable Structure IMM (VS-IMM) estimator where the mode set not only differs across targets, but also varies with time for a given target. This paper addresses the problem of tracking convoys of ground targets using Moving Target Indicator (MTI) reports to illustrate the development, operation and the benefits of an adaptive VS-IMM estimator. The targets under track are moving along a constrained path, for example, a highway, with varying obscuration due to changing terrain conditions. Here we present a VS-IMM estimator, where filter modules are adaptively modified, added or removed depending on the terrain topography, for tracking on-road and off-road targets within the same framework. At each scan, the structure of the estimator for every target is individually modified based on the known topography of the surveillance region and the predicted location of the target. This enables the estimator to handle the variation in the possible motion modes across targets as well as with time for each target. Because of the nonlinear nature of the MTI reports, which consist of two-dimensional positions and range rate, extended Kalman filters are used as IMM estimator modules. (4 pages)

Airborne array aperture UWB UHF radar-motivation and system considerations

Abstract: The paper discusses the necessity, feasibility and technology of FOPEN GMTI. It argues that this functionality may be one mode in a multi-function UWB UHF system, which jointly possesses the capabilities for air target MTI and high resolution FOPEN SAR. The radar platform may be a UAV or an aircraft, whereas it is proposed to use the push boom type of antenna mounting previously adopted with advantage for the CARABAS II UWB VHF SAR. Presently the push booms will hold a set of UWB UHF antenna elements. The paper relates GMTI to SAR, extended from imaging stationary ground to the 4-parameter set of targets in linear and uniform motion relative to ground. It is recognised that this extended imaging problem only depends on one new parameter viz. the SAR focusing velocity. The required signal processing may be tackled in an efficient manner by a hierarchical scheme based on iteratively merging subapertures and increasing the resolution. Rejection of stationary clutter and detection occurs on all the levels of increasing the resolution. The paper also provides a brief presentation of the Swedish FOA efforts to produce an experimental demonstrator of this multi-function radar system.

A signal processing architecture for space-based GMTI radar

Abstract: Ground moving target indicator (GMTI) radars detect and classify targets with low velocities. Placing such radars in the Earth's orbit can provide wide area coverage with high revisit rates. However, because of the radar's large footprint (on the ground) and high velocity, target signals must compete with extremely intense nearby clutter. Requirements on antenna aperture, bandwidth, coverage rate, and computational complexity all play significant roles in shaping the radar's signal processing chain. This paper describes a signal processing architecture that rejects interference. By addressing issues such as aperture configuration, bandwidth-induced decorrelation, adaptive training, and degree-of-freedom requirements, a multistage space-time adaptive processing (STAP) architecture is constructed.

Clutter mitigation techniques for space-based radar

Abstract: The mission of a ground moving target indication (GMTI) radar, as its name implies, is to detect and classify ground-based vehicles, even ones with very low velocities. This type of radar can provide a wide area of coverage and frequent updates of a specific area of interest if the radar is placed on a satellite with a low Earth orbit. However because of the large footprint of the radar on the ground and the high satellite velocity target signals must compete with very strong, nearby clutter. This paper describes how space-time adaptive processing (STAP) can be used for the purposes of clutter rejection in order to perform the GMTI function. In addition, we confront several important issues for a space-based radar such as pulse repetition frequency (PRF) selection, the choice of a STAP algorithm, and the number of spatial channels. These results are quantified in terms of clutter cancellation and angle accuracy.

Performance of distributed CFAR test under various clutter amplitudes

Abstract: We evaluate the performances of several distributed constant false-alarm rate (CFAR) tests operating in different background clutter conditions. The analysis considers the detection of Rayleigh target in various clutters with the possibility of differing clutter power levels in the test cells of distributed radars. Numerical results studied for a two-radar system show how the false-alarm rate of the maximum order statistic (MOS) test changes with differences in the clutter power levels of the test cells. The analysis for the detection of Rayleigh target in Rayleigh clutter indicates that, with the power levels of differing test cells, the OR fusion rule can be quite competitive with the new normalized test statistic (NTS). However, for the detection of Rayleigh target in Weibull or K-distributed clutter, the results show that NTS outperforms both the OR and the AND rules under the condition of large signal-to-clutter power ratio and moderate shape parameter values.

Advanced Jindalee Tracker: Probabilistic Data Association Multiple Model Initiation Filter

Abstract: : This paper presents the theory and examples of performance for a new algorithm that initiates tracks using a multiple model Probabilistic Data Association (PDA) filter. The analysis is generalized for the case of multiple non-uniform clutter regions within the measurement data that updates the filter. The algorithm starts multiple parallel PDA filters from a single sensor measurement. Each filter is assigned one of a range of possible target model parameters. To reduce the possibility of clutter measurements forming established tracks, the solution includes a model for a visible target. That is, a target that gives sensor measurements that satisfy one of the target models. Other features included in the algorithm are the selection of a fixed number of nearest measurements and the addition of signal amplitude to the target state vector. The inclusion of signal amplitude is one coordinate that is applicable to the non-uniform clutter model developed in this a paper.

Analysis of a 1D HRR moving target ATR

Abstract: This paper presents the performance of a multi-class, template-based, system-oriented High Range Resolution (HRR) Automatic Target Recognition (ATR) algorithm for ground moving targets. The HRR classifier assumes a target aspect estimate derived from the exploitation of moving target indication (MTI) mode target tracking to reduce the template search space. The impact of the MTI tracker target aspect estimate accuracy on the performance and robustness of the HRR ATR is investigated. Next, both individual and hybrid MTI/HRR and Synthetic Aperture Radar (SAR) model-based ATR algorithm results are presented. The hybrid ATR under consideration assumes the coordination of a multimode sensor to provide classification or continuous tracking of targets in a move- stop-move scenario. That is, a high-value moving target is tracked using the GMTI mode and its heading estimated. As the indicated target stops, the last GMTI tracker update is used to aid the SAR mode ATR target acquisition and classification. As the target begins to move again, the MTI-assisted HRR ATR target identification estimates are fused with the previous SAR ATR classification. The hybrid MTI/SAR/HRR ATR decision- level fusion provides a method for robust classification and/or continuous tracking of targets in move-stop-move cycles. Lastly, the baseline HRR ATR performance is compared to a QuickSAR (short dwell or non-square pixel SAR) ATR algorithm for varying cross-range resolutions.

Simulated DPCA performance for dual-channel SAR processing

Abstract: Interests in slow target imaging lead us to the synthetic aperture radar (SAR) simulation and performance evaluation of the dual-channel displaced phase center antenna (DPCA) clutter suppression technique for SAR processing. The Doppler chirp signature of a moving target signal is altered by the DPCA and has to be restored by a correction factor. Suppressed clutter powers in signal-to-clutter ratios (SCR) the improvement factors (IF) are measured in this numerical experiment and presented. This investigation offers a guide to the SCR requirement on the next-in-line processors such as parameter estimation.

Multiple model estimator for a tightly coupled HRR automatic target recognition and MTI tracking system

Abstract: The goal of this research is to exploit couplings between tracking and ATR systems employing high range resolution radar (HRRR) and moving target indicator (MTI) measurements. As will be shown, these systems are coupled via pose, kinematic, and association constraints. Exploiting these couplings results in a tightly coupled system with significantly improved performance. This problem deals with two different types of spaces, namely the continuous space kinematics (e.g. position and velocity) and the discrete space target type. A multiple model estimator (MME) was chosen for this problem. The MME consist of a bank of extended Kalman filters (one for each target type). The continuous space kinematics are dealt with via these extended Kalman filter. Further, the probability of each Kalman filter is computed and used to determine the corresponding discrete space target probability. Presented in this paper are empirical results that show improvement over conventional techniques.

Adaptive dwell timing for radar tracking

Abstract: In an air traffic control radar system, a processor is described for correlating primary target data received from a target with a target report and a target track, wherein the processor has a search acquisition time that is adapted to the distance of the target from the radar site. The search acquisition time is shorter for more distant targets. The processor can employ a shorter cycle time (time quantum) to establish a correlation between target data and target reports than would otherwise be possible with conventional fixed search acquisition times. The average total dwell time may be reduced while complying with the mandated maximum processing time for more difficult radar reports.

Wigner-Ville analysis of HF radar measurement of an accelerating target

Abstract: The paper describes results obtained by applying the Wigner-Ville distribution to high frequency line-of-sight radar measurements of a theatre ballistic missile during powered flight. The Wigner-Ville distribution is able to discriminate between target and interfering transient events and to accurately determine the instantaneous Doppler law of the target. It is a useful pre-processing step for determining the instantaneous received signal level and the coherent processing loss due to target acceleration.

Coverage area analysis for decentralized detection in Weibull clutter

Abstract: The performance of a decentralized constant false-alarm rate (CFAR) detection system with data fusion in homogeneous non-Gaussian background is analyzed in terms of ground area covered. The advantages of using a distributed radar system and the differences between the system behavior in Rayleigh clutter and in Weibull clutter are stressed. Notably, the increasing benefit of cooperative decision making when clutter becomes spikier is pointed out.

Subspace transformation techniques applied to multi-channel SAR/MTI

Abstract: Using SAR-systems with several along-track sub-apertures has proven to be a highly sensitive technique for detection and positioning of moving targets. The core of multi-channel SAR/MTI processing is an adaptive filter for clutter suppression. In the SAR environment the processing in the Doppler domain is favourable, since an infinite train of pulses is used. But some problems arise from the large number of degrees of freedom: at the edges of the clutter spectrum the clutter power may be too weak to perform a sufficient adaptation, so that moving target signals are suppressed as well. The objective of this paper is to propose a problem-matched architecture of the clutter adaptation using the technique of "coherent subspace transformation". This offers stabilisation against rapid flight manoeuvres, coverage of uncertain frequency regions and avoiding the suppression of moving target signals. The proposed processing is illustrated by data gathered with the German "Airborne Experimental Radar" (AER) using four along-track subapertures.

Efficient detection and ground mapping of selected moving targets using SAR raw-data

Abstract: This work addresses moving targets detection and imaging using airborne SAR data. Targets are selected according to user-defined radial velocity and direction. The computational burden is drastically reduced because azimuth compression is done only for ranges with a positive moving target indication. Furthermore, the knowledge of the velocity sign allows to tune the detection and focusing of moving targets with higher SNR than the usual methods. Range migration is easily tackled because radial velocity is known, enabling the correct compression filter design.

Airborne adaptive MTI scheme with preventing the whitening of the target

Abstract: A new airborne MTI scheme that applies to non-homogeneous clutter environment is presented. Results of simulation have proved that the scheme has a superior ground clutter suppression performance and can effectively prevent the whitening of a target.

Mitigation of range folded clutter by a nonrecurrent waveform

Abstract: This paper describes the application of a new nonrecurrent waveform (NRWF) to a relocatable over-the-horizon radar (ROTHR) located in southern Virginia. The waveform is designed to improve the detection of aircraft targets through the mitigation of long-range spread Doppler clutter (SDC) encountered during nighttime operations. A discussion of the NRWF and its principle of operation are included, along with a description of ROTHR modifications. The focus of the paper is the presentation of test results from engineering, clutter mitigation, and target detection tests conducted during January through April of 1997.

Recent and current Air Force space based radar efforts

Abstract: Efforts at fielding satellite based radar systems for performing tactical and strategic moving target indication (MTI), and synthetic aperture radar (SAR) imaging, have been underway since the 1960's. While some success has been achieved in SAR imagery, very little success has occurred for MTI. In 1995, an Air Force General Officer conference was held at which briefings were given on the feasibility of transitioning the MTI sensor functions of the Airborne Warning and Control System (AWACS) and the Joint Surveillance Target Attack Radar System (JSTARS) to space. These briefings concluded that although it would be too expensive to transition these functions in 1995, there was a real potential that by 2000 the problem might become affordable. Accordingly, the AF Chief of Staff directed that space based radar studies continue. This paper provides an overview of major studies and development efforts which have occurred since 1995.

High range resolution ground moving target atr using advanced space-based sar/mti concepts

Abstract: This paper smmnarizes a preliminary investigation into a space-based multi-class system-oriented High Range Resolution (HRR) Automatic Target Recognition (ATR) algorithm. Recent conflicts have highlighted the need to detect, track and recognize time critical moving ground targets in all-weather standoff (airborne and space-based) sensor platforms. Current sensor technologies based on Moving Target Indication (MTI) and/or Synthetic Aperture Radar (SAR) imaging are inadequate. While MT1 provides the ability to detect and track ground moving targets, it lacks target discrimination capability due to limited bandwidth. SAR has target discrimination capability for stationary targets, but target motion will blur the image. As a result, ATR of ground moving targets using HRR radar has recently received increased interest within the Air Force. The baseline algorithms presented in this paper are template-based mean squared error classifiers. The paper includes a brief introduction into recent HRR ATR efforts at the Air Force Research Laboratory Sensors Directorate's ATR Assessment Branch (AFRL/SNAA). Motivations and limitations for space- based sensors are discussed along with potential sensor fusion algorithms. The paper concludes by discussing the advantages of HRR ATR for feature aided

Apparatus and methods for moving target indicator simulation

Abstract: A moving target simulator system for pulse Doppler radar includes a processor for processing received radar signal and transforming the signal into patterned pulses before subjecting the patterned pulses to an 180 degree phase-shift by a phase-shifter. The system also includes a reference signal provided by a corner reflector located in proximity of the simulator. The reference signal and a phase-shifted signal from the simulator are processed by the radar equipped with a phase corrector circuitry to correct a phase drift problem associated with the use of a small antenna with the simulator.

Automated video and infrared tracking technology

Abstract: PAR Government Systems Corporation (PGSC) has recently developed a complete activity detection and tracking system using standard NTSC Video or Infrared (IR) camera inputs. The inputs are processed using state-of-the-art signal processing hardware and software developed specifically for real-time applications. The system automatically detects and tracks moving objects in video or infrared imagery. Algorithms to automatically detect and track moving objects were implemented and ported to a C80 based DSP board for real-time operation. The real-time embedded software performs: (1) Video/IR frame registration to compensate for sensor motion, jitter, and panning; (2) Moving target detection and track formation; (3) Symbology overlays. The hardware components are PC based COGS which include a high speed DSP board for real-time video/IR data collection and processing. The system can be used for a variety of detection and tracking purposes including border surveillance, perimeter surveillance including building, airport, correctional facilities, and other areas requiring detection and tracking of intruders. The system was designed, built and tested in 1998 by PAR Government Systems Corporation, La Jolla, CA. This paper addresses the algorithms (Registration, Tracking, Outputs) as well as hardware used to port the algorithms (C80 DSP board) for real-time processing.

An analysis of the shadow feature technique in radar detection

Abstract: Good target detection can be achieved by using shadow feature algorithms, particularly in heavy clutter environments. The performance enhancement of a shadow feature algorithm applied to a maximum likelihood constant false-alarm rate (ML-CFAR) detector is analyzed. Results show that detection performance is significantly improved.

Theoretical analysis of a continuous tracking system

Abstract: Today's radar exploitation system utilize information from both Ground Moving Target Indication (GMTI) and Synthetic Aperture Radar (SAR) obtained from various airborne platforms. GMTI detects and supports the classification of moving targets, whereas SAR detects and supports the classification of stationary targets. However, there is currently no ability to integrate the information from these two classes of radars in tracking targets that execute sequences of move-stop-move maneuvers. The solutions of this dilemma is the development of a Continuous Tracking (CT) architecture that uses distinctive GMTI and SAR features to associate stationary and moving target detections through move-stop-move maneuvers. This paper develops a theoretical model and present corresponding numeric computations of the performance of the CT syste. This theory utilizes a two- state Markov process to model the successive SAR and MTI detections are derived from typical traffic and sensor behaviors. This analysis of the sensor characteristics and the underlying traffic model provides a foundation in designing a CT systems with the maximum possible performance.

Simulations of ground moving target indication in an ultrawideband and wide-beam SAR system

Abstract: This paper discusses the methods for ground moving target identification (GMTI) in a bistatic ultra-wideband and wide- beam (UWB-WB) SAR system. Simulations of GMTI in UWB-WB SAR system are shown. Bistatic compensation in a time domain SAR processing system is given, and clutter leakage caused by bistatic radar and time domain fast backprojection SAR algorithms is studied. The clutter leakage is investigated both for the scatter and for the sidelobes of the scatter. In the paper we also discuss clutter leakage caused by bistatic scattering. As the scatter size increases the bistatic wave will scatter differently then the monostatic wave. Also the effect of bistatic nadir and antenna configuration is studied.

New methods of radar detection performances analysis

Abstract: Original methods of radar detection performance analysis are derived for a fluctuating or non-fluctuating target embedded in additive and a priori unknown noise. This kind of noise can be, for example, the sea or ground clutter encountered in surface-sited radar for the detection of a target illuminated at low grazing angles or in high resolution radar. For these cases, the spiky clutter tends to have a statistic which strongly differs from the gaussian assumption. Therefore, the detection theory becomes difficult to perform since the nature of the statistics has to be known. The new methods proposed here are based on the parametric modelisation of the moment generating function of the noise envelope by Pade approximation and lead to a powerful estimation of its probability density function. They allow to evaluate the radar detection performance of a target embedded in any noise without knowledge of the closed form of its statistic and allow in the same way to take into account any possible fluctuation of the target. These methods have been tested successfully on synthetic signals and have been performed on experimental signals such as ground clutter.

Simultaneous HRR feature extraction and Doppler shift estimation of moving target with rigid bodies

Abstract: High Range Resolution (HRR) Moving Target Indicator (MTI) is becoming increasingly important for many military and civilian applications involving the detection and classification of moving targets in the clutter background. For ground-based HRR radar, when targets are moving slowly or near-broadside and the coherent processing interval (CPI) (or dwell time) is not too long, the effects of range migration and range feature distortion can be ignored. Based on the above assumptions, relaxation-based algorithms, which are robust and computationally simple, are proposed in this paper for the HRR feature extraction of moving targets consisting of scatterers very closely spaced in range and common Doppler shift in the presence of stationary clutter. Numerical examples show that the proposed algorithms exhibit super resolution and excellent estimation performance.

Minefield overwatch using moving target indicator radar

Abstract: Traditional antipersonnel land mines are an effective military tool, but they are unable to distinguish friend from foe, or civilian from military personnel. The concept described here uses an advanced moving target indicator (MTI) radar to scan the minefield in order to detect movement towards or within the minefield, coupled with visual identification by a human operator and a communication link for command and control. Selected mines in the minefield can then be activated by means of the command link. In order to demonstrate this concept, a 3D, interactive simulation has been developed. This simulation builds on previous work by integrating a detailed analytical model of an MTI radar. This model has been tailored to the specific application of detection of slowly moving dismounted entities immersed in ground clutter. The model incorporates the effects of internal scatterer motion and antenna scanning modulation in order to provide a realistic representation of the detection problem in this environment. The angle information on the MTI target detection is then passed to a virtual 3D sight which cues a human operator to the target location. In addition, radar propagation effects and an experimental design in which the radar itself is used as a command link are explored.

Noncooperative radar target identification using fourth-order correlations

Abstract: In this communication, a new method for radar target identification using only radar returns or scattered responses of conducting targets is proposed. Our scheme includes, before filtering with a constructed discriminant filter and named extinction filter (EF), a new stage in which the fourth-order correlation (FOC) sequence of the unknown-target impulse-response is estimated. The subsequent stage uses these natural resonances to identify the target. Simulation results clearly show that significant improvements are achieved by using the fourth-order moments sequence of x(n) as the unknown-target signature instead of the original signal x(n) in the discrimination scheme.