Moving Target Indication Research Articles

Vital signs detection of moving targets using FMCW radar

Abstract Respiratory and heartbeat rates are crucial indicators for human health assessment. Compared to contact-based measurements, millimeter-wave radar detection of these vital signs avoids the discomfort caused by physical contact and better protects personal privacy, making it highly valuable for home health monitoring. The use of millimeter-wave radar for vital sign detection of the human body is mostly focused on targets in a stationary state at present. However, the human body may sway or even move during actual detection. This article proposes a non-contact vital sign detection method for moving targets. Compared with methods for detecting vital signs of stationary targets, detecting vital signs of moving targets requires determining the range bin where the targets are located continuously and extracting target phase information. The noise components such as movement and sway contained in the phase signal need to be removed. In this paper, moving target indication is used to remove static components, an adaptive range bin selection method is proposed to determine the range bin where the targets are located, and range bin selection fluctuation is smoothed using a moving average filter. The wavelet transform is used to decompose the phase signal, remove swaying noise based on autocorrelation function, and reconstruct the life signal for different scale factors. A bandpass filter is used to separate the respiratory and heartbeat signals, and a notch filter is designed to suppress respiratory harmonic signals. The experimental results show that the proposed method can separate vital signs signals from the phase signals of moving targets, achieving detection of respiration and heartbeat rate. The average accuracy of respiration and heartbeat rate detection is 94.7% and 95.5%, respectively.

Along-track deployment control of space tether system for SAR-GMTI mission

Global, 24/7, and all-weather Synthetic Aperture Radars (SARs) are optimal platforms for Ground Moving Target Indication (GMTI) missions, and the tether constraint provides a stable mechanic connection for such configurations. To fulfill the requirements of such missions, the Space Tether System (STS) must be deployed to horizontal positions to form the necessary along-track interference baseline, which is unstable relative to traditional vertical positions and has not received adequate focus. To deal with this problem, this study focuses on the deployment control of the STS to the unstable horizontal positions. Firstly, the properties of the STS at the horizontal position are analyzed, and a synthetic criterion of measurement error is defined based on the observation principle of the GMTI mission. Secondly, two deployment control strategies are proposed, and corresponding desired trajectories are generated by considering two occasions respectively. In the end, considering the instability of horizontal positions, an adaptive closed-loop controller is designed utilizing the backstepping method to address gravitational moment and other disturbances. Simulations demonstrate that the system can successfully attain the desired horizontal positions under both deployment strategies, and the designed controller can quickly track trajectories under initial state errors and external disturbances.

IMM Filtering Algorithms for a Highly Maneuvering Fighter Aircraft: An Overview

The trajectory estimation of a highly maneuvering target is a challenging problem and has practical applications. The interacting multiple model (IMM) filter is a well-established filtering algorithm for the trajectory estimation of maneuvering targets. In this study, we present an overview of IMM filtering algorithms for tracking a highly-maneuverable fighter aircraft using an air moving target indicator (AMTI) radar on another aircraft. This problem is a nonlinear filtering problem due to nonlinearities in the dynamic and measurement models. We first describe single-model nonlinear filtering algorithms: the extended Kalman filter (EKF), unscented Kalman filter (UKF), and cubature Kalman filter (CKF). Then, we summarize the IMM-based EKF (IMM-EKF), IMM-based UKF (IMM-UKF), and IMM-based CKF (CKF). In order to compare the state estimation accuracies of the IMM-based filters, we present a derivation of the posterior Cramér-Rao lower bound (PCRLB). We consider fighter aircraft traveling with accelerations 3g, 4g, 5g, and 6g and present numerical results for state estimation accuracy and computational cost under various operating conditions. Our results show that under normal operating conditions, the three IMM-based filters have nearly the same accuracy. This is due to the accuracy of the measurements of the AMTI radar and the high data rate.

Application of Digital Twin Technology in Synthetic Aperture Radar Ground Moving Target Intelligent Detection System

In recent years, the detection performance of SAR-GMTI (synthetic aperture radar-ground moving target indication) algorithm based on deep learning has always been limited by insufficient measured data due to the heavy operation complexity and high cost of real SAR systems. To solve this problem, this paper proposes an overall DT-based implementation framework for SAR ground moving target intelligent detection tasks. In particular, by virtue of a SAR imaging algorithm, a high-fidelity twin replica of SAR moving targets is established in digital space through parameter traversal based on the prior target characteristics of the obtained measured datasets. Then, the constructed SAR twin datasets is fed into the neural network model to train an intelligent detector by fully learning features of the moving targets and preset the SAR scene in the twin space, which can realize the robust detection of ground moving targets in related practical scenarios with no need for multiple and complex field experiments. Moreover, the effectiveness of the proposed framework is verified on the MiniSAR measured system, and a comparison with traditional CFAR detection method is given simultaneously.

Spaceborne HRWS-SAR-GMTI System Design Method with Optimal Configuration

The spaceborne high-resolution and wide-swath synthetic aperture radar (HRWS-SAR) system combined with the ground moving target indication (GMTI) mode provides a promising prospect in the realization of wide-area target surveying and high-resolution target imaging. In this paper, a system design method is proposed for an HRWS-SAR-GMTI system with ideal reconstruction configuration. In the proposed method, the whole azimuth receiving channels are uniformly divided into multiple groups, where HRWS-SAR imaging is implemented in each sub-group and then GMTI processing is performed based on the reconstructed SAR images. Then, an optimal candidate PRF is properly selected with respect to the optimal reconstruction configuration. After that, the digital beam forming scanning on receive (DBF-SCORE) technique is applied to further enlarge the range swath and improve the noise equivalent scattering coefficient (NESZ). Based on the predesigned system, HRWS-SAR image-based GMTI processing can finally be accomplished. The effectiveness of the proposed method is validated by simulated experiments.

A high precision estimation algorithm for multi‐channel wide‐area surveillance ground moving target indication mode based on maximum likelihood method

A high precision estimation algorithm for multi‐channel wide‐area surveillance ground moving target indication mode based on maximum likelihood method

Angle-Dependent Matched Filtering for Moving Target Indication With Coherent FDA Radar

Angle-Dependent Matched Filtering for Moving Target Indication With Coherent FDA Radar

U.S. strategy of damage limitation vis-à-vis China: long-term programs and effects

A number of U.S. military programs, if successfully developed and deployed, could undermine China's nuclear retaliatory capabilities, thereby enhancing U.S. damage limitation capabilities vis-à-vis China. Meanwhile, China seeks to maintain the credibility of its nuclear retaliatory capabilities and increase the survivability and penetration of its nuclear weapons. These interactions are part of the nuclear competition between the United States and China. This article discusses three cases: the U.S. homeland missile defense system, anti-submarine warfare (ASW) preparations, and the space-based Ground Moving Target Indicator. These programs may serve declaratory purposes in one way or another, but their development has had a negative impact on China’s strategic nuclear retaliatory capabilities. Using non-nuclear means that differ technologically from the measures taken by China, these programs have created an asymmetric competition between the two sides. These U.S. programs have endured for several decades, and have continued to introduce new technologies despite occasional interruptions. The main element of development in these programs has been qualitative improvement, while quantitative increases have not always been evident. The development of these U.S. damage limitation capabilities put pressure on China’s nuclear retaliatory capabilities. The arms race theories developed during the Cold War are inadequate for fully understanding nuclear competition between the United States and China. We need new theories and wisdom to explore cooperative solutions.

Parameter estimation of ground moving targets in synthetic aperture radar systems based on vortex echo data

Ground Moving Target Indication is a critical field within synthetic aperture radar (SAR) research, as traditional SAR images are defocused and displaced due to the target’s trajectory-direction velocity and radial velocity, respectively. Therefore, an accurate estimation of the target’s motion parameters is required. This study introduces a two-dimensional method for estimating target motion parameters using vortex SAR. It utilises the Bessel magnitude and spatial phase term from vortex echo data to calculate the pitch and azimuth angle, from which the motion parameters of ground slow-motion targets are derived. The proposed algorithm operates faster and has a lower computational cost than the traditional parameter estimation algorithm. Its efficacy was confirmed through simulation experiments and mean square error analysis of the estimated parameters.

Estimation of tangential speed of ground moving targets in SAR

In parallel with the development of systems of highly detailed mapping of the underlying surface, methods of ground moving targets indication (GMTI) were also improved. A dramatic improvement in the resolution characteristics of onboard radars occurred after the introduction of mapping modes with synthetic artificial antenna aperture. The advent of synthetic aperture radars (SAR) made it possible to detect ground moving targets (GMT) against the background of reflections from the underlying surface, which made it possible to further implement GMTI algorithms for detecting low-speed moving ground objects. The simple way to carry out GMTI is if the observed target has a radial component of the velocity vector, which generates a Doppler frequency shift in the reflected signal. A more complex situation arises when it is necessary to detect targets moving at a tangential speed relative to the onboard radar. The difficulty of detecting targets moving at tangential speed is due to the fact that target movement in the direction perpendicular to the line of sight leads to deformation of the phase structure of the signal. This particular deformation manifests itself in the appearance of quadratic phase modulation of the reflected trajectory signal. With consistent signal processing in mapping mode, due to the appearance of quadratic phase modulation, the response of the observed moving target will be defocused. To detect the presence of a moving target with tangential speed, it is proposed to use an algorithm similar to the well-known phase difference algorithm for autofocusing radar images. It consists in dividing the implementation of the trajectory signal into two parts, after which the bottom of them is subjected to a complex conjugation procedure. Next, the two implementations are multiplied with each other and the amplitude spectrum of the result of the multiplication is calculated. The shift of the maximum spectral density relative to the origin is proportional to the tangential velocity of the observed target. The sign of the shift (to the right or to the left) depends on the direction of movement of the GMT relative to the velocity vector of the carrier. This algorithm was justified by an analytical method, then its mathematical modeling was carried out. In the case of observation of spruce trees by on-board radar with a high tangential velocity, the error in its estimation increases, which is due to the spreading of the spectrum of the signal reflected from the GMT to reduce the influence of this effect.

Low-cost solutions for mobile passive radar based on multichannel DPCA and NULA configurations

Abstract In this paper, we investigate low-cost solutions for enabling ground moving target indication applications with multichannel mobile passive radar systems. As known, in order to be competitive with their active counterparts, passive radars are typically characterized by severe constraints in terms of cost, complexity, and compactness, especially when installed on moving platforms. On the one hand, carrying out the computations onboard requires processing techniques as simple as possible. On the other hand, the need for lightweight and compact systems that can be installed on a moving platform requires using a limited number of receiving channels. To meet these requirements, we propose a series of nonadaptive detectors based on multichannel displaced phase center antennas, which allow suppressing the Doppler-spread clutter component without requiring computationally intensive space–time adaptive processing techniques. Moreover, we explore the use of nonuniformly spaced array configurations on receive, which represent a good alternative to conventional uniform linear arrays when a limited number of receiving channels can be implemented. The effectiveness of the proposed processing techniques and antenna design solutions is demonstrated via numerical analysis for the case of a DVB-T-based mobile passive radar system.

Accurate multi-target vital signs detection method for FMCW radar

The frequency modulated continuous wave (FMCW) radar has gained increasing attention in the field of noncontact vital signs detection. However, the detection of the target chest’s range bin is easily influenced by various clutters and interferences, posing numerous challenges to vital signs detection, particularly in scenarios involving multiple targets This paper proposes an anti-clutter and interference method that combinates moving target indication (MTI), constant false alarm rate (CFAR) detection, K-means clustering, and local search with moving average filtering to accurately detect multi-target vital signs. Moreover, it employs the extended differentiate and cross multiply algorithm for phase demodulation to overcome phase discontinuity. The proposed method is evaluated using a 77 GHz FMCW radar in an office environment. Experimental results demonstrate that the proposed method can effectively detect multiple targets amidst various clutters and small random body movement, yielding mean accuracies of 94.2 % and 95.1 % for breathing rate and heartbeat rate, respectively.

A fast disturbance cancellation scheme for orthogonal frequency division multiplexing‐based passive radar exploiting reciprocal filter

AbstractThis paper proposes a simple non‐adaptive approach for the suppression of direct signal and clutter contributions in a passive radar system based on orthogonal frequency division multiplexing transmissions, exploiting the properties of a reciprocal filter (RF). The use of a RF allows to circumvent the limits posed by the waveform ambiguity function, producing a data‐independent time‐invariant response to a stationary point‐like target echo at the output of the range compression stage. This feature enables simple clutter cancellation strategies, based on the subtraction of delayed portions of the surveillance signal, according to the conventional moving target indication methodologies. The proposed processing scheme consists of a range compression stage based on a RF, followed by a Single Canceller. Its performance is investigated against a simulated and an experimental data set, for the case of a digital video broadcasting‐terrestial‐based passive radar scenario, and it is compared to an alternative scheme based on a conventional matched filter and adaptive cancellation techniques. The proposed approach is shown to yield a perfect cancellation of the clutter returns from a stationary scene under ideal conditions. Moreover, it proves to be robust to real‐world conditions, despite its considerably limited computational load compared to adaptive clutter cancellation techniques.

A method for extracting micro-motion features of rotor targets based on GS-IRadon algorithm

Aiming the extract micro-motion features of rotor targets when the flashes are in the echo, this paper proposes a method based on the GS-IRadon algorithm. At first, we analyze the time-frequency characteristics of rotor targets through a scattering point signal model. Then, we analyze and study the usage conditions of the algorithm and use the Moving Target Indication (MTI) algorithm to remove the direct-current (DC) frequency component in signal's time-frequency results. Finally, we utilize the Inverse Radon transform algorithm based on the golden section method (GS-IRadon) to extract the target micro-motion features. The estimation of speed, length, and number of blades in the presence of flashes phenomenon in rotor targets was achieved. Simulation results showed that the algorithm can significantly reduce computational complexity while maintaining high estimation accuracy and has a more stable performance than regular algorithms.

Infrared Dim Star Background Suppression Method Based on Recursive Moving Target Indication

Space-based infrared target detection can provide full-time and full-weather observation of targets, thus it is of significance in space security. However, the presence of stars in the background can severely affect the accuracy and real-time performance of infrared dim and small target detection, making star suppression a key technology and hot spot in the field of space target detection. The existing star suppression algorithms are all oriented towards the detection before track method and rely on the single image properties of the stars. They can only effectively suppress bright stars with a high signal-to-noise ratio (SNR). To address this problem, we propose a new method for infrared dim star background suppression based on recursive moving target indication (RMTI). Our proposed method is based on a more direct analysis of the image sequence itself, which will lead to more robust and accurate background suppression. The method first obtains the motion information of stars through satellite motion or key star registration. Then, the advanced RMTI algorithm is used to enhance the stars in the image. Finally, the mask of suppressing stars is generated by an accumulation frame adaptive threshold. The experimental results show that the algorithm has a less than 8.73% leakage suppression rate for stars with an SNR ≤ 2 and a false suppression rate of less than 2.3%. The validity of the proposed method is verified in real data. Compared with the existing methods, the method proposed in this paper can stably suppress stars with a lower SNR.

Efficient Clutter Cancellation Algorithm Based on a Suppressed Clutter Map for FMCW Radar Systems

This paper proposes an efficient clutter cancellation algorithm based on suppressed clutter map for frequency-modulated continuous wave radar systems. In conventional clutter cancellation algorithms based on clutter maps, range-Doppler maps are employed. However, if the radar cross section (RCS) of the targets is significantly lower than the RCS of the clutter, a problem may occur in that the targets may also be removed in the clutter-removal process. To solve this problem, the proposed algorithm creates a range-Doppler map to which the moving target indicator (MTI) algorithm is applied instead of the general range-Doppler map that does not include the MTI algorithm. The range-Doppler map, used after applying the clutter suppression filter, significantly reduces the clutter removal effect on targets in which RCS is relatively weak by suppressing the effect of relatively dominant clutter signals. The experimental results showed that the proposed algorithm detects weak targets that remain undetected by the existing map-based clutter-removal algorithm.

Scalable and effective artificial intelligence for multivariate radar environment

Ground based radar is a key system for aerial defence of any country. Current generations of radar use Moving Target Indicator (MTI) filter, Constant False Alarm Rate (CFAR) and Peak Detection (PD) algorithms for detection of target and rejection of non-target (static clutter, dynamic clutter, interference and noise) objects. These conventional Radar Signal Processing (RSP) techniques find their limitation when either targets are not detected or false alarms are generated due to lack of built-in intelligence. In order to eliminate both the issues, a realistic radar environment has been analyzed using Artificial Intelligence (AI). Special emphasis has been made on invalid detections caused by weather clutter, which was never worked upon previously using AI. A novel deep learning based object detection approach has been devised keeping radar environment, high accuracy requirement and real-time constraint of radar in view. The proposed approach has been validated for its efficacy through standalone testing as well as Poof of Concept (PoC) implementation on a real radar. Integration of AI model in radar platform also involves a novel implementation scheme, whereby results of AI model are augmented by conventional RSP. Inference time of AI models is a bottleneck for their use in radar systems, in this context, new strategies have also been analyzed to achieve a real-time performance for radar application. As the objective of this research is to devise scalable and effective solutions for upcoming generations of radar; therefore, the work is of practical value for realistic deployments.

Road-Map Aided Gaussian Mixture Labeled Multi-Bernoulli Filter for Ground Multi- Target Tracking

Ground multi-target tracking (MTT) is one of the core tasks of airborne ground moving target indicator (GMTI) radar and automotive radar. However, ground MTT still remains a challenging issue especially in complex traffic scenarios, since it often suffers from high clutter, dense targets, low visibility, etc. To enhance the tracking performance for ground multiple targets, in this paper, we present a comprehensive solution named road-map aided Gaussian mixture labeled multi-Bernoulli filter (RA-GMLMB) filter, which incorporates road-map information into the labeled multi-Bernoulli (LMB) filter. Specifically, we first propose a hybrid circular arc and line segments approximation approach to extract road-map information, which alleviates approximation errors in the procedure of road-map approximation. Then, we deduce the RA-GMLMB filter by integrating the extracted road-map information into the LMB filter with Gaussian mixture implementation. Simulation experiments are conducted and experimental results show that the proposed RA-GMLMB filter outperforms the state-of-the-art methods.

A Priori Knowledge Based Ground Moving Target Indication Technique Applied to Distributed Spaceborne SAR System

Through formation flying, the distributed spaceborne SAR(synthetic aperture radar) system can increase the number of spatial degree of freedoms (DOFs) and provide flexible multi-baselines for SAR-GMTI (ground moving target indication), which improves the system performance. This paper proposes an a priori knowledge-based adaptive clutter cancellation and moving target detection technique applied to the distributed spaceborne SAR-GMTI systems. Firstly, the adaptive clutter cancellation technique is exploited to suppress the ground clutter. A priori knowledge, such as road network information, is integrated to the adaptive clutter cancellation processor to reduce any moving target steering vector mismatch. Secondly, adaptive matched filter (AMF) and adaptive beamformer orthogonal rejection test (ABORT) are exploited as adaptive detection techniques for moving target detection. Due to the dense road network, the moving target steering vector estimation may be ambiguous for the different position and orientation of the roads. The multiple hypothesis testing (MHT) technique is proposed to detect the moving targets and resolve the potential ambiguities. A scheme is exploited to detect, classify, and relocate the moving targets. Finally, simulation experiments and performance analysis have demonstrated the effectiveness and robustness of the proposed technique.

Harmonics and intermodulation products-based fuzzy logic (HIPBFL) algorithm for vital sign frequency estimation using a UWB radar

The ultra-wide band (UWB) radar can achieve non-contact measurement of human vital sign including respiration and heartbeat. This can be applied in the fields of healthcare, security and search-rescue mission. At present, most studies adopt the relationship between harmonics and fundamental frequency to estimate the frequency of vital sign. In this work, the harmonics and intermodulation products-based fuzzy logic (HIPBFL) algorithm for vital sign frequency estimation is proposed. For the first time, to the best of our knowledge, intermodulation products information is considered to locate possible heart rates. Then a fuzzy logic system is designed to select the optimal heart rate from them. 120 s measurement experiment on human beings was carried out at the hospital. Compared with the commonly used chirp Z-transform and moving target indicator (CZT-MTI), the harmonic multiple loop detection (HMLD) and the variational mode decomposition (VMD), the proposed HIPBFL algorithm obviously improves the estimation accuracy of heart rate. This work paves a way for the investigation of non-contact vital signs monitoring via UWB radars.