Ground Moving Target Indication System Research Articles

Efficient knowledge‐aided target relocation algorithm for airborne radar

This letter addresses the problem of target relocation in wide-area ground moving target indication system. The antenna pattern information is exploited as prior knowledge to enhance the performance of airborne radar. Firstly, the ideal target relocation model for moving targets based on the dual-channel radar system is analysed and the mismatch model of the receiving channel is constructed. Then the reason for poor relocation performance is analysed and the channel error model is constructed. Based on this fact, the problem of target relocation is converted into a problem of channel phase estimation. Moreover, a least-squares method is utilised to estimate the phase error by exploiting the real antenna pattern information and a modified mono-pulse curve (MPC) is derived. Finally, the real geometry location of the moving target can be achieved with the modified MPC. Airborne radar experiments are given to verify the effectiveness of the proposed algorithm.

GLRT Detection of Micromotion Targets for the Multichannel SAR-GMTI System

This letter investigates the micromotion target detection problem for the multichannel synthetic aperture radar (SAR)- ground moving target indication system. The multichannel SAR signal models of the micromotion target and the ground clutter in the raw data domain are established firstly. Then the generalized likelihood ratio test (GLRT) of the micromotion target is derived. Based on the analysis of the probability density functions of the test statistics, theoretical detection performance dependent on the micromotion parameters is provided. Simulated heterogeneous SAR data validate the effectiveness of the GLRT detector.

Distributed Compressed Sensing Based Ground Moving Target Indication for Dual-Channel SAR System.

The dual-channel synthetic aperture radar (SAR) system is widely applied in the field of ground moving-target indication (GMTI). With the increase of the imaging resolution, the resulting substantial raw data samples increase the transmission and storage burden. We tackle the problem by adopting the joint sparsity model 1 (JSM-1) in distributed compressed sensing (DCS) to exploit the correlation between the two channels of the dual-channel SAR system. We propose a novel algorithm, namely the hierarchical variational Bayesian based distributed compressed sensing (HVB-DCS) algorithm for the JSM-1 model, which decouples the common component from the innovation components by applying variational Bayesian approximation. Using the proposed HVB-DCS algorithm in the dual-channel SAR based GMTI (SAR-GMTI) system, we can jointly reconstruct the dual-channel signals, and simultaneously detect the moving targets and stationary clutter, which enables sampling at a further lower rate in azimuth as well as improves the reconstruction accuracy. The simulation and experimental results show that the proposed HVB-DCS algorithm is capable of detecting multiple moving targets while suppressing the clutter at a much lower data rate in azimuth compared with the compressed sensing (CS) and range-Doppler (RD) algorithms.

An enhanced approach based on energy loss for multichannel SAR-GMTI systems in heterogeneous environment

For ground moving target indication (GMTI) in heterogeneous terrains, most detectors could not effectively solve the problem of a high probability of false alarms (PFA) due to the presence of isolated interference with large radar cross section (RCS). To address this issue, we construct a new criterion called as energy loss, which is the energy difference between input and output in the adaptive processing, and develop an enhanced approach based on energy loss for multichannel synthetic aperture radar (SAR)-GMTI systems in heterogeneous environment. In this method, the magnitude-based detection after clutter suppression is first applied to detect potential targets with a relatively low threshold. Then, a complementary detection based on energy loss test is performed to reduce false alarms. To compute the detection thresholds, the statistics of the energy loss test and the overall PFA of the detection approach are analyzed theoretically. Finally, the experimental results on simulations and real data, collected in China's urban area, demonstrate the superiority of the proposed approach compared with state-of-art methods.

An Extended Moving Target Detection Approach for High-Resolution Multichannel SAR-GMTI Systems Based on Enhanced Shadow-Aided Decision

This paper develops a framework based on enhanced shadow-aided decision for multichannel synthetic aperture radar-based ground moving target indication system according to the relationships between the moving target and its shadow information in position, dimensions, and intensity. As a sort of feature information available, the moving target shadow may improve the ground target detection performance. A critical precondition for shadow utilization is to obtain the good detection performance for the moving target shadow. However, shadow detection performance will deteriorate inevitably as a result of target motion that blurs its shadow. To address this issue, a knowledge-aided shadow detection algorithm with adaptive thresholds is proposed to improve the shadow detection performance in the developed framework. Furthermore, the theoretical performance analysis is performed, which indicates that the proposed knowledge-aided shadow detection algorithm has a better performance than that of the conventional shadow detection algorithm with a fixed threshold. Finally, numerical simulation experiments are presented to demonstrate that the developed framework can obtain good results for extended ground moving target detection.

Improved MIMO radar GMTI via cyclic-shift transmission of orthogonal frequency division signals

ABSTRACTMinimum detectable velocity (MDV) and maximum detectable velocity are both important in ground moving target indication (GMTI) systems. Smaller MDV can be achieved by longer baseline via multiple-input multiple-output (MIMO) radar. Maximum detectable velocity is decided by blind velocities associated with carrier frequencies, and blind velocities can be mitigated by orthogonal frequency division signals. However, the scattering echoes from different carrier frequencies are independent, which is not good for improving MDV performance. An improved cyclic-shift transmission is applied in MIMO GMTI system in this paper. MDV performance is improved due to the longer baseline, and maximum detectable velocity performance is improved due to the mitigation of blind velocities via multiple carrier frequencies. The signal model for this mode is established, the principle of mitigating blind velocities with orthogonal frequency division signals is presented; the performance of different MIMO GMTI waveforms is analysed; and the performance of different array configurations is analysed. Simulation results by space–time–frequency adaptive processing proves that our proposed method is a valid way to improve GMTI performance.

Clutter suppression for multichannel synthetic aperture radar ground moving target indication system with the capability of high-resolution wide-swath imaging

Clutter suppression is a key step for efficient detection of moving targets and accurate estimation of their parameters. Current clutter suppression approaches are available for the case in which clutter signals of each channel are free from Doppler ambiguity. However, for a multichannel high-resolution wide-swath (HRWS) synthetic aperture radar (SAR) system, the received echoes of each channel suffer Doppler ambiguity, thus current clutter suppression approaches may not perform well. To address this issue, the signal models of stationary and moving targets with Doppler ambiguity should be derived. This paper presents their analytical models in the complex image domain by two-dimensional azimuth compression, from which the linear coupling of a moving target induced by radial velocity can be eliminated, and thus signal-to-noise ratio loss caused by this linear coupling can be avoided. Considering that there is a difference between stationary and moving targets in the complex image domain, a clutter suppression approach for a multichannel HRWS SAR system is proposed. The simulated results and real data processing results both validate the proposed approach.

Geometry-Information-Aided Efficient Radial Velocity Estimation for Moving Target Imaging and Location Based on Radon Transform

Real-time radial velocity estimation is a key challenge for moving target imaging and location in current single-antenna synthetic aperture radar (SAR)-ground moving target indication systems. Since the conventional methods suffer from ambiguity, complexity realization, or heavy computation load for fast moving target motion estimation, this paper emphasizes the estimation efficiency by simple realization. An efficient Radon transform (RT) estimation is proposed to estimate the radial velocity of fast moving target by utilizing the geometry information, and much more geometry information is exploited to realize clutter cancellation, noise cancellation, and estimation error minimizing in the RT domain, which is not proposed by the others. With only two to four angles used to calculate rather than search for the radial velocity of moving targets, the proposed methods simplify the conventional range and angle (2-D) searching procedure into several time range (1-D) searching procedure efficiently. The theoretical and experimental analysis provides qualitative and quantitative evaluations into the effectiveness of the proposed methods. In the single-antenna SAR system, the proposed methods can estimate the radial velocity of fast moving target efficiently and accurately in high signal to clutter plus noise ratio scenarios.

Channel balancing algorithm in multichannel wide‐area surveillance systems

Channel balancing is one of the crucial steps to obtain a satisfactory result in multichannel moving target detection. Therefore many algorithms have been proposed to realise channel balancing in multichannel synthetic aperture radar (SAR)-ground moving target indication (GMTI) systems, such as an adaptive two-dimensional calibration algorithm, linear fitting algorithm and eigen-decomposition algorithm. However, all of these aforementioned algorithms have some small defects in certain conditions, when used in the real data of multichannel wide area surveillance (WAS)–GMTI systems. The small defects can increase the false alarm probability, which is undesirable in moving target detection. In this study, after the detailed analysis about the interference phase in the wide-area surveillance mode, a novel channel balancing algorithm is proposed to perform channel balancing in multichannel WAS–GMTI systems. The new algorithm mainly concentrates on the balancing of systematic azimuthal phase errors. The effectiveness of the proposed algorithm is demonstrated when compared with other typical channel balancing algorithms in Monte Carlo simulations and real data processing.

NOVEL PRE-PROCESSING TECHNIQUES FOR COHERENCE IMPROVING IN ALONG-TRACK DUAL-CHANNEL LOW FREQUENCY SAR

The coherence between the complex image pair from two channels is important for improving the capability of along- track interferometry (ATI) processing in synthetic aperture radar (SAR) ground moving target indication (GMTI). The along-track dual-channel low frequency SAR can be easily in∞uenced by not only mismatch errors of the image pair but also the radio frequency interference (RFI). RFI has great impacts on the joint probability density function (PDF) of magnitude and phase in the interferometric image. However, little work has been done to investigate the coherence improvement under RFI. This study develops an algorithm to improve the coherence of the image pair for along-track dual-channel low frequency SAR, which can be used by ATI. After analyzing RFI imaging in detail, it is proposed that the along-track interferometric image in the range frequency and cross-range slow time domain can be used to detect RFI. Median fllters are proposed to further suppress RFI. This suppression has the same implementations to the image pair without heavy computation load. Considering RFI suppression and mismatch errors compensation, a pre-processing ∞ow is proposed to achieve high coherence of the interferometric image in low frequency SAR. It is shown that the coherence of the complex image pair can be improved greatly by using this pre-processing ∞ow. The efiectiveness of this algorithm is demonstrated with real data acquired by an airborne along-track dual-channel P-band SAR GMTI system.

Analysis of the Multimode Feedhorn Concept for Multichannel SAR-GMTI

This paper presents the theoretical and experimental performance evaluation of a novel and innovative concept to add a multichannel ground moving target indication (GMTI) capability to a synthetic aperture radar (SAR) reflector antenna with a standard single feed. This approach exploits the capability to achieve a phase center displacement by combining signals obtained from different electromagnetic excitation modes of the feedhorn. While, in the past, this so-called multimode concept has been mainly analyzed in simulation and by various antenna laboratory measurements, several flight experiments have been recently conducted to verify and demonstrate its GMTI performance. The theoretical and experimental analysis provides qualitative and quantitative insights into the effectiveness of multimode SAR-GMTI applications, such as the SAR image-based along-track interferometry (ATI) or post-Doppler GMTI approaches based on space-time adaptive processing. In addition, it introduces practical lessons learned, along with an example of the detection and parameter estimation for a large vessel using ATI. This paper finishes with an examination of the expected performance improvement when the transmitted modes are alternated between subsequent pulses. This toggling results in a time-multiplexed three-channel GMTI system with significantly enhanced estimation performance.