Showing papers on "Moving target indication published in 2000"

Ground target tracking with variable structure IMM estimator

Abstract: In this paper we present the design of a Variable Structure Interacting Multiple Model (VS-IMM) estimator for tracking groups of ground targets on constrained paths using Moving Target Indicator (MTI) reports obtained from an airborne sensor. The targets are moving along a highway, with varying obscuration due to changing terrain conditions. In addition, the roads can branch, merge or cross-the scenario represents target convoys along a realistic road network with junctions, changing terrains, etc. Some of the targets may also move in an open field. This constrained motion estimation problem is handled using an IMM estimator with varying mode sets depending on the topography, The number of models in the IMM estimator, their types and their parameters are modified adaptively, in real-time, based on the estimated position of the target and the corresponding road/visibility conditions. This topography-based variable structure mechanism eliminates the need for carrying all the possible models throughout the entire tracking period as in the standard IMM estimator, significantly improving performance and reducing computational load. Data association is handled using an assignment algorithm. The estimator is designed to handle a very large number of ground targets simultaneously. A simulated scenario consisting of over one hundred targets is used to illustrate the selection of design parameters and the operation of the tracker. Performance measures are presented to contrast the benefits of the VS-IMM estimator over the Kalman filter and the standard IMM estimator, The VS-IMM estimator is then combined with multidimensional assignment to gain "time-depth." The additional benefit of using higher dimensional assignment algorithms for data association is also evaluated.

Analysis of radar micro-Doppler with time-frequency transform

Abstract: Micro-Doppler induced by mechanical vibration or rotation of structures in a radar target is potentially useful for target detection, classification and recognition. While the Doppler frequency induced by the target body is constant, the micro-Doppler due to vibrating or rotating structures of the target is a function of dwell time. Analysis of the time-varying Doppler signature in the joint time-frequency domain can provide useful information for target detection, classification and recognition.

Update with out-of-sequence measurements in tracking: exact solution

Abstract: In target tracking systems measurements are typically collected in scans or frames and then they are transmitted to a processing center. In multisensor tracking systems that operate in a centralized manner there are usually different time delays in transmitting the scans or frames from the various sensors to the center. This can lead to situations where measurements from the same target arrive out of sequence. Such out-of-sequence measurement (OOSM) arrivals can occur even in the absence of scan/frame communication time delays. The resulting negative- time measurement update problem, which is quite common in real multisensor systems, was solved approximately in [2] by neglecting the process nosie in the backward prediction or retrodiction. In the standard case, the (forward) state prediction can be easily carried out, since the process noise, because of its whiteness, is independent of the current state. However, in retrodiction this independence does not hold anymore. The standard smoothing algorithms cannot be used because the time stamp of the measurement is, in general, arbitrary. The results of [4,3] accounted only partially for the process noise. In view of this, the exact state update equation for such a problem is presented. The three algorithms are compared on a number of realistic examples, including a GMTI (ground moving target indicator) radar case.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Multi-channel moving target radar detection and imaging apparatus and method

Abstract: A radar detection and imaging system provides for the simultaneous imaging of the stationary objects on the earth's surface and the detection and imaging of moving targets. The radar system includes at least one transmitting aperture and a plurality of receiving apertures that are simultaneously operated in a synthetic aperture radar (SAR) mode caused by the motion of the satellite or airborne platform on which they are mounted. Each receiving aperture is connected to its own coherent receiver and the digitized signals from all receivers are processed to image both stationary clutter and moving targets. The system employs space- time adaptive processing (STAP) algorithms to better compensate for channel mismatches, better suppress stationary clutter, and to suppress mainbeam jamming. Moving target detection and estimation modules are also included and are their performance is improved as a result of the STAP algorithms. The system also employs SAR processing algorithms to create high- resolution images of stationary objects, and to image moving targets. The SAR and STAP algorithms are uniquely integrated in the radar signal processor (RSP) to provide improved performance while reducing the computational requirements, facilitating real-time implementation.

Clutter and jammer multipath cancellation in airborne adaptive radar

Abstract: Airborne surveillance radars must detect and localize targets in diverse interference environments consisting of ground clutter, conventional jamming, and terrain scattered jammer multipath. Multidimensional adaptive filtering techniques have been proposed to adaptively cancel this interference. However, a detailed analysis that includes the effects of multipath nonstationarity has been elusive. This work addresses the nonstationary nature of the jammer multipath and its impact on clutter cancellation and target localization. It is shown that the weight updating needed to track this interference will also modulate sidelobe signals. At the very least, this complicates the localization of targets. At the worst, it also greatly complicates the rejection of clutter. Several techniques for improving cancellation of jammer multipath and clutter are proposed, including 1) weight vector interpolation, extrapolation, and updating; 2) filter architecture, constraint, and beamspace selection; 3) prefilters; 4) 3-D STAP architectures; and 5) multidimensional sidelobe target editing.

Stochastic-constraints method in nonstationary hot-clutter cancellation. II. Unsupervised training applications

Abstract: For pt. I see ibid., vol. 34, pp. 1271-1292 (1998). This paper considers the use of "stochastically constrained" spatial and spatio-temporal adaptive processing in multimode nonstationary interference ("hot clutter") mitigation for scenarios that do not allow access to a group of range cells that are free from the backscattered sea/terrain signal ("cold clutter"). Since supervised training methods for interference covariance matrix estimation using the cold-clutter-free ranges are inappropriate in this case, we introduce and analyze adaptive routines which can operate on range cells containing a mixture of hot and cold clutter and possible targets (unsupervised training samples). Theoretical and simulation results are complemented by surface-wave over-the-horizon data processing, recently collected during experimental trials in northern Australia.

Bias modeling and estimation for GMTI applications

Abstract: This paper describes an approach to sensor bias modeling and estimation for ground target tracking applications using multiple airborne Ground Moving Target Indicator (GMTI) radar sensors. This approach was developed as part of the Precision Firecontrol Tracking (PFCT) segment of the DARPA Affordable Moving Surface Target Engagement (AMSTE) program. For airborne sensors, slowly varying platform location, heading and velocity errors lead to time-dependent measurement biases. Track accuracy can be improved by using a Kalman filter to estimate and correct the biases in real time, based on fixed reference points. The reference point location can be known a priori or estimated online as part of the bias correction algorithm. When the reference locations are known a prior, bias effects can be nearly completely eliminated. When the reference point is estimated online, significant performance improvement is obtained relative to uncorrected measurements.

Airborne array aperture UWB UHF radar-motivation and system considerations

Abstract: This 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, we propose to use the push boom type of antenna mounting previously adopted with the advantage for the CARABAS II UWB VHF SAR. Presently, the push booms will hold a set of UWB UHF antenna elements. This 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 depends on one new parameter, i.e., 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 levels of increasing resolution. This paper also provides a brief presentation of the Swedish FOA efforts to produce an experimental demonstrator of this multi-function radar system.

SAR-GMTI processing with Canada's Radarsat 2 satellite

Abstract: Space-based radar (SBR) has been proposed for various military and civilian applications, including wide area surveillance and theatre defence. Reliable, slow, ground moving target indication (GMTI) of tanks and jeeps, for example, poses a significant challenge, due to strong clutter returns that occupy most, if not all of the available spectrum. Space-time adaptive processing (STAP) techniques can be used to implement radar signal processors capable of providing the required sub-clutter visibility. Despite extensive research studies, at present no space-based GMTI systems are in operation. Canada and the United States are presently conducting experimental programs that will include the launching of space-based radar systems capable of synthetic aperture radar (SAR) and GMTI modes. This paper reports on Canada's Radarsat 2 GMTI mode and provides a preliminary analysis of SAR-GMTI performance based on computer simulations.

Variable structure interacting multiple-model filter (VS-IMM) for tracking targets with transportation network constraints

Abstract: A Ground Moving Target Indicator (GMTI) is developed using a Variable Structure Interacting Multiple Model Filter (VS-IMM). Current trackers use road network database information to either condition GMTI measurements, thereby altering the detection report, or constrain tracks formed on measurements near roads to the road network, thus making a hard decision about the location of the target. The VS-IMM allows for soft decisions about which road a target is possibly located on. The VS- IMM filter developed adaptively adds and deletes road models based upon history of measurement data or extrapolated tracks. As measurements are associated with existing tracks, a search of possible road segment models is performed to either add or delete road segment models as required. As targets on roads approach junctions, additional potential road segment models are added, as the targets pass the intersection only the most likely model is retained. When a target beginst o move into a road segment that is obscured, a model is added that modified the filter estimate and likelihood according to a hidden target model. The VS-IMM Filter includes two models for characterizing temporal vehicle movement. A model with low process noise is used to model targets that are traveling straight and a model with high process noise is used to model highly maneuvering targets. The state estimates from the possible road models are combined with the state estimate of the on-road and off-road multiple temporal models to produce the composite state estimate for the VS-IMM Filter.

Ground moving target indication using knowledge based space time adaptive processing

Abstract: Space-time adaptive processing (STAP) techniques promise to offer the best means to detect weak targets in severe dynamic interference scenarios. Traditionally, STAP techniques were developed for the detection of low RCS, high velocity airborne targets, well removed from main-beam clutter in Doppler. STAP algorithms are only now being used for ground moving target indication (GMTI) from an airborne reconnaissance platform. We present a practical approach to STAP incorporating three components: nonhomogeneity detection, statistical processing of measured data, and hybrid processing. This combined approach ties together previous research in different aspects of STAP into one algorithm. The algorithm is tested using measured data from the Multi-Channel Airborne Radar Measurements program with particular interest in ground moving target detection.

Subband STAP in wideband radar systems

Abstract: The detection of moving targets, both airborne and ground-based, is enabled by ground clutter mitigation using space-time adaptive processing (STAP). As technological advances make it possible to perform wide bandwidth processing and future systems require high resolution for target identification, the need has arisen for the effective implementation of wideband STAP. In order to prevent the deleterious effects of dispersion for wideband systems, STAP is performed in subbands, which is also computationally more efficient than full bandwidth STAP. The separate, independent adaptive processing in the individual subbands, however, introduces complications that must be addressed in order to maintain desired performance. These issues are unique to subband STAP, namely, target Doppler dispersion across subbands and range sidelobe levels following subband recombination. In each case, we identify the cause of the problem and propose an effective solution. Throughout this paper, we focus on practical solutions that are tractable and do not require an inordinate amount of computation.

Space-time adaptive processing for over-the-horizon spread-Doppler clutter mitigation

Abstract: We address the problem of mitigating spread-Doppler distortion in over-the-horizon (OTH) HF radar returns, caused by motion of electron density irregularities in the ionosphere. For targets with significant radial velocity, discrimination from surface clutter is possible in Doppler space. However, this scheme breaks down in the presence of moving perturbations in the refracting ionosphere, which can cause Doppler spreading of the surface clutter ridge, limiting detection performance, These ionospheric irregularities should be highly correlated in the direction of geomagnetic field lines. We exploit this correlation across range by using neighboring range cells to estimate the spread-Doppler clutter (SDC) in the range cell of interest, and to selectively suppress this clutter, thereby increasing target visibility. For targets directly obscured in Doppler by clutter we enhance target visibility by employing a single additional spatial channel to act as a sidelobe canceler on the main beam.

Tracking evasive move-stop-move targets with a MTI radar using a VS-IMM estimator

Abstract: In this paper we present the design of a Variable Structure Interacting Multiple Model (VS-IMM) estimator for tracking evasive ground targets using Moving Target Indicator reports obtained from an airborne sensor. In order to avoid detection by the MTI sensor, the targets use a move- stop-move strategy, where a target deliberately stops or moves at a very low speed for some time before accelerating again. In this case, when the target's radial velocity (along the line of sight from the sensor) falls below a certain Minimum Detectable Velocity, the target is not detected by the sensor. Under these conditions, the use of an estimator, which does not take care of this move-stop-move motion explicitly, can result in broken tracks. The tracker proposed in this paper handles the evasive move-stop-move motion via the VS-IMM estimator, where the tracker mode set is augmented with a stopped-target model when the estimated speed of the target falls below a certain threshold. Using this additional stopped-target model, the target state is kept alive even in the absence of a measurement. A simulated scenario is used to illustrate the selection of design parameters and the operation of the tracker. Performance measures are presented to contrast the benefits of the VS-IMM estimator, which uses the stopped-target model, over a standard IMM estimator.

One trillion operations per second on-board VLSI signal processor for Discoverer II space based radar

Abstract: A high-performance low-power radar signal processor is being developed for the Discoverer II space-based radar application. The signal processor will perform real-time ground moving target indication (GMTI) and synthetic aperture radar (SAR) front-end signal processing functions, which significantly reduces the downlink communication bandwidth. In order to minimize the signal dispersion, the wideband receive signal is first channelized into multiple digital subbands and all the subsequent processing tasks including beamforming, pulse compression, and space-time adaptive processing (STAP) are done in the subband domain. In order to meet over one trillion operations per second (Teraops) computational throughput requirement with low power consumption and small form factor, a highly optimized scalable VLSI bit-level systolic array technology is used. The 1 Teraops on-board processor is currently projected to consume less than 50 watts and to be less than 1/8 cubic foot and 12 kg.

AMSTE precision fire control tracking overview

Abstract: The DARPA Affordable Moving Surface Target Engagement (AMSTE) program is a research effort to develop a system concept to track and engage a moving surface target with a single unitary warhead. Engaging a moving surface target requires precision tracking to a degree that has not been demonstrated in previous work. Tracking moving surface targets is especially difficult because of the targets ability to maneuver in unpredictable ways, such as coming to a stop, and the potential for a large number of nearby confusing targets. Because of the importance of tracking to the overall AMSTE system, a significant portion of the program is dedicated to developing advanced tracking algorithms. This paper will briefly describe the current state of the art of surface target trackers developed under the DARPA Moving Target Exploitation (MTE) program. It then identifies the inadequacies in association and bias removal that must be overcome to obtain the high fidelity tracks required for weapon targeting. The improved tracking techniques discussed include the use of data from multiple Ground Moving Target Indicator (GMTI) sensors to improve location accuracy, bias removal techniques, advanced multiple hypothesis trackers, variable state interacting multiple models using higher order motion models, feature aided tracking and terrain analysis.

On parametric detection of small targets in sea clutter

Abstract: A new algorithm is presented that instantaneously estimates the clutter characteristics in the environment of the radar cell that is processed. No a priori information is used, since the algorithm operates directly on the data of the incoming burst. It is a technique that adapts continuously and instantaneously to the environment. The algorithm, after having identified the sea clutter rejects this sea clutter from the data; thus enhancing the probability of detecting small objects in a clutter environment. The final step is the actual detection that makes use of the advantages of the parametric representation. This results in a lower rate of false detections and as a consequence the later stages, like clustering and tracking, receive a more accurate input. The technique behind this algorithm uses recent developments in parametric time series analysis and performs well in suppressing sea as well as land clutter.

Global space-based ground surveillance: mission utility and performance of Discoverer II

Abstract: The Discoverer II (DII) program will demonstrate an affordable space-based radar (SBR) with High Range Resolution Ground Moving Target Indication (HRR-GMTI), Synthetic Aperture Radar (SAR) imaging, and Digital Terrain Elevation Data (DTED) collection that is expected to revolutionize reconnaissance, surveillance and precision targeting support to the tactical warfighter. This paper presents a utility analysis of DII, including mobile missile launcher surveillance, strategic facilities monitoring, maritime surveillance, and detection of underground facility construction. A subbanding approach to the signal processing that allows parallel implementation is presented. A 30 Gflop chip set capable of wideband channelization and delivering 128 point FFTs every 200 nsec, with 25 to 50 GOPS per Watt power efficiency is described. Performance analyses of space time adaptive processing (STAP), GMTI tracker operation, STAP clutter suppression and GMTI tracking results from airborne collections are presented. Approaches for collecting precision DTED, and airborne testbed results near the DTED 5 level are presented.

High-fidelity MTI modeling and analysis of a distributed aperture spaceborne concept

Abstract: This paper investigates the performance of a spaceborne, distributed aperture system operating in a moving target indication (MTI) mode. A cluster of microsatellites, orbiting in proximity, house the antenna subapertures of the distributed array; the subapertures electronically share the transmit function and receive data. We discuss the modeling and simulation of the distributed aperture MTI sensor operation, examine system performance for several scenarios of interest, and discuss specialized signal processing techniques. Our results indicate that among its various attributes, a distributed aperture, spaceborne MTI system provides excellent detection performance potential; sparse aperture signal processing, coupled with space-time adaptive processing, represents a critical, enabling component. Using a spiral spoke cluster and optimal space-time processing, the average SINR loss with respect to the noise-limited case averages about -2 dB for a radial velocity greater than 3 m/s for the analyzed orientation of the cluster.

Bistatic GMTI experiment for airborne platforms

Abstract: The concept of bistatic ground moving target indicator BGMTI is presented here. Monostatic GMTI radars use separate modes for ground movers whose Doppler does and does not allow separation of the target return from ground clutter using frequency processing. Bistatic flight scenarios that minimize Doppler spreading in the vicinity of a designated target area are presented as candidate flight test plans. Flight scenarios supporting a sustained broadside spot mode and an oblique spot mode are presented.

Performance analysis for an interferometric space-based GMTI radar system

Abstract: This paper presents an algorithm which may be applied to multiple aperture space-based radar systems, and the major aspects of its performance may be summarized as follows: (1) 2D irregularly spaced aperture distributions can be used, allowing for forward and backward looking operation in the presence of orbital motion; (2) clutter statistics are not necessary for evaluating the probability of target detection; (3) clutter is completely separated from target information, thus SNR is the limiting factor to performance; (4) there are multiple ways to deal with ambiguities, but Doppler ambiguities are less cumbersome. Work continues to evaluate the true computational burden, as well as try to minimize it and distribute the operation over multiple processors. In addition, the algorithm is being tested, first against simulated target/clutter data, and eventually against real target return data from the Air Force Research Laboratory's TechSat 21 Distributed Satellite System experiment.

SAR wavefront reconstruction using motion-compensated phase history (polar format) data and DPCA-based GMTI

Abstract: This paper address the problem of processing an X-band SAR database that was originally intended for processing via a polar format imaging algorithm. In our approach, we use the approximation-free SAR wavefront reconstruction. For this, the measured and motion compensated phase history (polar format) data are processed in a multi-dimensional digital signal processing algorithm that yields alias-free slow-time samples. The resultant database is used for wavefront image formation. The X-band SAR system also provides a two channel along-track monopulse database. The alias-free monopulse SAR data are used in a coherent signal subspace algorithm for Ground Moving Target Indication (GMTI). Results are provided.

An Analysis of RADARSAT2 SAR-GMTI Performance for Standard Beam Mode

Abstract: : Canada's RADARSAT2 (R2) commercial SAR satellite will have an experimental operating mode that will allow ground moving target indication (GMTI) measurements to he made with received data. This mode is also called MODEX (Moving Object Detection Experiment). In the GMTI or MODEX mode of operation, the spacecraft's radar antenna is partitioned into two apertures that sequentially observe the scene of interest from the same points in space. Data is simultaneously and coherently received from both apertures and is down-linked in parallel channels for processing to extract moving target radial speeds in their SAR image context. This paper provides an analysis of SAR-GMTI performance at the R2 Standard Beam Mode based on computer modeling and simulations. Two SAR-MTI processing approaches are being explored. One utilizes the classical DPCA clutter cancellation technique to provide sub clutter visibility for dim slowly moving targets. The other is based on the along-track (temporal) SAR interferometer technique, where amplitude and phase information of the slow-moving targets are exploited to allow their extraction from the dominant clutter background. Performances of the two approaches are compared. Effects of target signal contamination by background clutter is also examined. The results indicate that the two processing approaches are similar in their GMTI performance.

Synthetic aperture radar and moving target indication

Abstract: The problems about the detection of moving objects and observation by the synthetic aperture radars(SAR) are described in this paper.It also explains the moving target indication(MTI) SAR approach using the reflectivity displacement method,the MTI SAR aproach using the multilook image displacement method,and the MTI SAR approach using more than one antenna along the flight direction and an adaptive space time filtering to maximize signal to disturbance ratio.The position and the velocity estimation of moving objects on the ground are also discussed.

Optimization of single transmit pulse shape to maximize detection and identification of ground mobile targets

Abstract: This paper investigates the optimization of a single transmit pulse shape and the receiver response to maximize either target detection or identity discrimination between two structurally similar ground mobile targets: the T-72 and M1 main battle tanks. This theory incorporates effects due to the uncertainty in the prior knowledge of the target aspect relative to the sensor. The improvement in the signal-to-interference-plus-noise (SINR) resulting from the optimized transmit pulse shape over that of a standard chirped waveform typically lies between 4 dB and 9 dB. Similar improvements in target identification performance are also obtained.

Performance of RADARSAT2 SAR-GMTI Processors at High SAR Resolutions

Abstract: : Canada' 5 RADARSAT2 commercial Synthetic Aperture Radar (SAR) satellite, scheduled to be launched in Spring 2003, will have an experimental operating mode that will permit Ground Moving Target Indication (GMTI) measurements to be made with received data. In this mode of operation, the radar antenna is partitioned into two sub-apertures that sequentially observe the scene of interest from the same points in space. Two GMTI processing approaches are currently being explored. One utilizes the classical SAR/DPCA (Displaced Phase Center Antenna) clutter cancellation technique to provide sub-clutter visibility for dim slowly moving objects. The other is based on the Along-Track Interferometric SAR (SARIATI) technique, where amplitude and phase information of the targets are exploited to extract them from the background clutter. In this paper the performance of each processor is examined for RADARSAT2's ultrafine beam mode. The study focuses on the influence of SAR resolution cell size on the GMTI processor performance. Results indicate that at high SAR resolutions the SAR/ATI is a better technique compared to the SAR/DPCA in its ability to detect slow-moving targets.

Moving target feature extraction with polarisation diversity in the presence of arbitrary range migration and phase errors

Abstract: High range resolution (HRR) moving target indication (MTI) is increasingly important in many military and civilian applications such as the detection and classification of moving targets in strong clutter backgrounds. Meanwhile using polarisation diversity in radar systems has been shown to result in improved performance as compared with using only a single polarisation channel. The authors extract HRR moving target features with polarisation diversity in the presence of strong stationary clutter. The problem considered takes into account arbitrary range migration and phase errors, which may be induced by unknown target and platform motions as well as atmosphere turbulence and/or system instability. A relaxation-based algorithm is presented for the joint clutter suppression and super resolution target feature extraction and its performance is compared to the Cramer-Rao bound, the best performance bound an unbiased estimator can achieve. Numerical results are also provided to demonstrate the performance of the proposed algorithm.

Joint super-resolution moving target feature extraction and stationary clutter suppression

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

Dynamic airborne sensor resource management for ground moving target tracking and classification

Abstract: In this paper we describe an algorithm for dynamic sensor resource management (SRM) of a multimode sensor for tracking and classification of ground moving targets. The sensor is an airborne mechanically steered radar that operates in ground moving target indicator (GMTI) and high range resolution (HRR) modes. The SRM problem is cast into an optimization framework with a multiobjective criteria, namely, minimize tracking kinematic and target classification uncertainties where Markov models and decision trees are utilized, respectively, to dynamically capture (at the frame revisit rate) the tracking and classification information state. The SRM algorithm derives a sensor collection schedule on a frame by frame basis utilizing tracking updates from a GMTI multiple hypothesis tracker (MHT) and classification updates from an HRR 1D automatic target recognition (ATR) algorithm. Preliminary results based on a simulated ground target scenario are presented demonstrating the inherent trade-offs between the two radar modes and the multiobjective SRM criteria.