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Current Issue
2025
Vol. 14,
No. 2
Previous Issue
2025,
14(2):
249-268.
Abstract
5729KB
Passive radar plays an important role in early warning detection and Low Slow Small (LSS) target detection. Due to the uncontrollable source of passive radar signal radiations, target characteristics are more complex, which makes target detection and identification extremely difficult. In this paper, a passive radar LSS detection dataset (LSS-PR-1.0) is constructed, which contains the radar echo signals of four typical sea and air targets, namely helicopters, unmanned aerial vehicles, speedboats, and passenger ships, as well as sea clutter data at low and high sea states. It provides data support for radar research. In terms of target feature extraction and analysis, the singular-value-decomposition sea-clutter-suppression method is first adopted to remove the influence of the strong Bragg peak of sea clutter on target echo. On this basis, four categories of ten multi-domain feature extraction and analysis methods are proposed, including time-domain features (relative average amplitude), frequency-domain features (spectral features, Doppler waterfall plot, and range Doppler features), time-frequency-domain features, and motion features (heading difference, trajectory parameters, speed variation interval, speed variation coefficient, and acceleration). Based on the actual measurement data, a comparative analysis is conducted on the characteristics of four types of sea and air targets, summarizing the patterns of various target characteristics and laying the foundation for subsequent target recognition.
2025,
14(2):
269-279.
The meter-wave radar, known for its wide beamwidth, often faces challenges in detecting low-elevation targets due to interference from multipath signals. These reflected signals diminish the strength of the direct signal, leading to poor accuracy in low-elevation angle measurements. To solve this problem, this paper proposes a multipath suppression and high-precision angle measurement method. This method, based on a signal-level feature game approach, incorporates two interconnected components working together. The direct signal extractor mines the direct signal submerged within the multipath signal. The direct signal feature discriminator ensures the integrity and validity of the extracted direct signal. By continuously interacting and optimizing one another, these components suppress the multipath interference effectively and enhance the quality of the direct signal. The refined signal is then processed using advanced super-resolution algorithms to estimate the Direction of Arrival (DoA). Computer simulations have shown that the proposed algorithm achieves high performance without relying on strict target angle information, effectively suppressing multipath signals. This approach noticeably enhances the estimation accuracy of classic super-resolution algorithms. Compared to existing supervised learning models, the proposed algorithm offers better generalization to unknown signal parameters and multipath distribution models.
2025,
14(2):
280-292.
Aiming to address the problem of increased radar jamming in complex electromagnetic environments and the difficulty of accurately estimating the target signal close to a strong jamming signal, this paper proposes a sparse Direction of Arrival (DOA) estimation method based on Riemann averaging under strong intermittent jamming. First, under the extended coprime array data model, the Riemann averaging is introduced to suppress the jamming signal by leveraging the property that the target signal is continuously active while the strong jamming signal is intermittently active. Then, the covariance matrix of the processed data is vectorized to obtain virtual array reception data. Finally, the sparse iterative covariance-based estimation method, which is used for estimating the DOA under strong intermittent interference, is employed in the virtual domain to reconstruct the sparse signal and estimate the DOA of the target signal. The simulation results show that the method can provide highly accurate DOA estimation for weak target signals whose angles are closely adjacent to strong interference signals when the number of signal sources is unknown. Compared with existing subspace algorithms and sparse reconstruction class algorithms, the proposed algorithm has higher estimation accuracy and angular resolution at a smaller number of snapshots, as well as a lower signal-to-noise ratio.
2025,
14(2):
293-308.
The resolving power of traditional radar is mainly analyzed using the ambiguity function, and its limit is generally characterized by the Rayleigh limit. Bats have a rather sensitive auditory system. Researchers have proposed the Spectrogram Correlation And Transformation (SCAT) model to represent the auditory system of bats, explored their super-resolution principle, and provided a possible means to break through the conventional (Rayleigh) resolving power limit of radar targets. To further enhance the discriminative performance of the SCAT model, two bat-auditory-system-based super-resolution models, namely the base vector deconvolution method and Baseband SCAT (BSCT), are improved by suppressing redundant wave flaps at the negative semiaxis of the range profile and at the origin. Meanwhile, the concept and computation method of reliable discriminative power are proposed to unify the measurements of SCAT and Rayleigh discriminative powers. Further, a comparison is made to validate the rationality of the concept of reliable discriminative power, and the effectiveness of the improved models is verified. Simulation and real experiments show that the improved super-resolution models achieve a sizable increase in the resolving power. Notably, the improved base vector deconvolution method performs the best, improving the resolving power of the original method by ～2 dB while enhancing the matched filtering resolving power by ～5 dB.
2025,
14(2):
309-321.
Obtaining internal layout information before entering unfamiliar buildings is crucial for various applications, such as counter-terrorism operations, disaster relief, and surveillance, highlighting its great practical significance and research value. To enable the acquisition of the building layout information, this paper presents a building layout tomography method based on joint multidomain direct wave estimation. First, a linear approximation model is established to map the relationship between the propagation delay of direct wave signals and the layout of the unknown building. Using this model, the distribution characteristics of direct wave and multipath signals in the fast-time, slow-time, and Doppler domains are analyzed in the tomographic imaging mode. A joint multidomain direct wave estimation algorithm is then proposed to achieve the suppression of multipath interference and precise estimation of direct wave signals. Additionally, a projection matrix adaptive correction algebraic reconstruction algorithm with total variation constraints is proposed, which enhances building layout inversion quality under limited data scenarios. Finally, electromagnetic simulation and experimental results demonstrate the effectiveness of the proposed building layout tomography method, with structural similarity indices of 91.2% and 81.7% for the reconstructed results, significantly outperforming existing building layout tomography methods.
2025,
14(2):
322-337.
Land-sea clutter classification is essential for boosting the target positioning accuracy of skywave over-the-horizon radar. This classification process involves discriminating whether each azimuth-range cell in the Range-Doppler (RD) map is overland or sea. Traditional deep learning methods for this task require extensive, high-quality, and class-balanced labeled samples, leading to long training periods and high costs. In addition, these methods typically use a single azimuth-range cell clutter without considering intra-class and inter-class relationships, resulting in poor model performance. To address these challenges, this study analyzes the correlation between adjacent azimuth-range cells, and converts land-sea clutter data from Euclidean space into graph data in non-Euclidean space, thereby incorporating sample relationships. We propose a Multi-Channel Graph Convolutional Networks (MC-GCN) for land-sea clutter classification. MC-GCN decomposes graph data from a single channel into multiple channels, each containing a single type of edge and a weight matrix. This approach restricts node information aggregation, effectively reducing node attribute misjudgment caused by data heterogeneity. For validation, RD maps from various seasons, times, and detection areas were selected. Based on radar parameters, data characteristics, and sample proportions, we construct a land-sea clutter original dataset containing 12 different scenes and a land-sea clutter scarce dataset containing 36 different configurations. The effectiveness of MC-GCN is confirmed, with the approach outperforming state-of-the-art classification methods with a classification accuracy of at least 92%.
2025,
14(2):
338-352.
Most existing specific emitter identification technologies rely on supervised learning, making them unsuitable for scenarios with label loss due to factors such as the acquisition environment (e.g., weather conditions, terrain, obstacles, and interference sources), device performance (e.g., radar resolution, signal processing capabilities, and hardware failures), and tagger level. In this study, a weakly labeled specific emitter identification algorithm based on the Weakly Supervised Wav-KAN (WSW-KAN) network is proposed. First, a WSW-KAN baseline network is constructed by integrating the unique learnable edge function of the KAN network with the multiresolution analysis of the wavelet function. The weakly labeled dataset is then divided into a small labeled dataset and a large unlabeled dataset, with the small labeled dataset used for initial model training. Finally, based on the pretrained model, Adaptive Pseudo-Label Weighted Selection (APLWS) is used to extract features from the unlabeled data using a contrast learning method, followed by iterative training, thereby effectively improving the generalization capability of the model. Experimental validation using a real acquisition radar dataset demonstrates that the proposed algorithm achieves a recognition accuracy of approximately 95% for specific emitters while maintaining high efficiency, a small parameter scale, and strong adaptability, making it suitable for practical applications.
2025,
14(2):
353-365.
The ground terrain classification using Polarimetric Synthetic Aperture Radar (PolSAR) is one of the research hotspots in the field of intelligent interpretation of SAR images. To further promote the development of research in this field, this paper organizes and releases a polarimetric SAR ground terrain classification dataset named AIR-PolSAR-Seg-2.0 for large-scale complex scenes. This dataset is composed of three L1A-level complex SAR images of the Gaofen-3 satellite from different regions, with a spatial resolution of 8 meters. It includes four polarization modes: HH, HV, VH, VV, and covers six typical ground terrain categories such as water bodies, vegetation, bare land, buildings, roads, and mountains. It has the characteristics of large-scale complex scenes, diverse strong and weak scattering, irregular boundary distribution, diverse category scales, and unbalanced sample distribution. To facilitate experimental verification, this paper cuts the three complete SAR images into 24,672 slices of 512×512 pixels, and conducts experimental verification using a series of common deep learning methods. The experimental results show that the DANet based on the dual-channel self-attention method performs the best, with the average intersection over union ratio reaching 85.96% for amplitude data and 87.03% for amplitude-phase fusion data. This dataset and the experimental index benchmark are helpful for other scholars to further carry out research related to polarimetric SAR ground terrain classification.
2025,
14(2):
366-388.
Synthetic Aperture Radar (SAR) image target recognition technology based on deep learning has matured. However, challenges remain due to scattering phenomenon and noise interference that cause significant intraclass variability in imaging results. Invariant features, which represent the essential attributes of a specific target class with consistent expressions, are crucial for high-precision recognition. We define these invariant features from the entity, its surrounding environment, and their combined context as the target’s essential features. Guided by multilevel essential feature modeling theory, we propose a SAR image target recognition method based on graph networks and invariant feature perception. This method employs a dual-branch network to process multiview SAR images simultaneously using a rotation-learnable unit to adaptively align dual-branch features and reinforce invariant features with rotational immunity by minimizing intraclass feature differences. Specifically, to support essential feature extraction in each branch, we design a feature-guided graph feature perception module based on multilevel essential feature modeling. This module uses salient points for target feature analysis and comprises a target ontology feature enhancement unit, an environment feature sampling unit, and a context-based adaptive fusion update unit. Outputs are analyzed with a graph neural network and constructed into a topological representation of essential features, resulting in a target category vector. The t-Distributed Stochastic Neighbor Embedding (t-SNE) method is used to qualitatively evaluate the algorithm’s classification ability, while metrics like accuracy, recall, and F1 score are used to quantitatively analyze key units and overall network performance. Additionally, class activation map visualization methods are employed to validate the extraction and analysis of invariant features at different stages and branches. The proposed method achieves recognition accuracies of 98.56% on the MSTAR dataset, 94.11% on SAR-ACD dataset, and 86.20% on OpenSARShip dataset, demonstrating its effectiveness in extracting essential target features.
2025,
14(2):
389-404.
Due to the side-looking and coherent imaging mechanisms, feature differences between high-resolution Synthetic Aperture Radar (SAR) images increase when the imaging viewpoint changes considerably, making image registration highly challenging. Traditional registration techniques for high-resolution multi-view SAR images mainly face issues, such as insufficient keypoint localization accuracy and low matching precision. This work designs an end-to-end high-resolution multi-view SAR image registration network to address the above challenges. The main contributions of this study include the following: A high-resolution SAR image feature extraction method based on a local pixel offset model is proposed. This method introduces a diversity peak loss to guide response weight allocation in the keypoint extraction network and optimizes keypoint coordinates by detecting pixel offsets. A descriptor extraction method is developed based on adaptive adjustment of convolution kernel sampling positions that utilizes sparse cross-entropy loss to supervise descriptor matching in the network. Experimental results show that compared with other registration methods, the proposed algorithm achieves substantial improvements in the high-resolution adjustment of convolution kernel sampling positions, which utilize sparse cross-entropy loss to supervise descriptor matching in the network. Experimental results illustrate that compared with other registration methods, the proposed algorithm achieves remarkable improvements in high-resolution multi-view SAR image registration, with an average error reduction of over 65%, 3～5-fold increases in the number of correctly matched point pairs, and an average reduction of over 50% in runtime.
2025,
14(2):
405-423.
As a representative of China’s new generation of space-borne long-wavelength Synthetic Aperture Radar (SAR), the LuTan-1A (LT-1A) satellite was launched into a solar synchronous orbit in January 2022. The SAR onboard the LT-1A satellite operates in the L band and exhibits various earth observation capabilities, including single-polarization, linear dual-polarization, compressed dual-polarization, and quad-polarization observation capabilities. Existing research has mainly focused on LT-1A interferometric data acquisition capabilities and the accuracy evaluation of digital elevation models and displacement measurements. Research on the radiometric and polarimetric accuracy of the LT-1A satellite is limited. This article uses tropical rainforest vegetation as a reference to evaluate and analyze the radiometric error and polarimetricstability of the LT-1A satellite in the full polarization observation mode through a self-calibration method that does not rely on artificial calibrators. The experiment demonstrates that the LT-1A satellite has good radiometric stability and polarimetric accuracy, exceeding the recommended specifications of the International Organization for Earth Observations (Committee on Earth Observation Satellites, CEOS). Fluctuations in the Normalized Radar Cross-Section (NRCS) error within 1,000 km of continuous observation are less than 1 dB (3σ), and there are no significant changes in system radiometric errors of less than 0.5 dB (3σ) when observation is resumed within five days. In the full polarization observation mode, the system crosstalk is less than −35 dB, reaching as low as −45 dB. Further, the cross-polarization channel imbalance is better than 0.2 dB and 2°, whilethe co-polarization channel imbalance is better than 0.5 dB and 10°. The equivalent thermal noise ranges from −42～−22 dB, and the average equivalent thermal noise of the system is better than −25 dB. The level of thermal noise may increase to some extent with increasing continuous observation duration. Additionally, this study found that the ionosphere significantly affects the quality of the LT-1A satellite polarization data, with a Faraday rotation angle of approximately 5°, causing a crosstalk of nearly −20 dB. In middle- and low-latitude regions, the Faraday rotation angle commonly ranges from 3° to 20°. The Faraday rotation angle can cause polarimetric distortion errors between channels ranging from −21.16～−8.78 dB. The interference from the atmospheric observation environment is considerably greater than the influence of about −40 dB system crosstalk errors. This research carefully assesses the radiomatric and polarimetric quality of the LT-1A satellite data considering dense vegetation in the Amazon rainforest and provides valuable information to industrial users. Thus, this research holds significant scientific importanceand reference value.
2025,
14(2):
424-438.
Inverse Synthetic Aperture Radar (ISAR) is an important tool for imaging and monitoring space targets. The large rotation angle of space targets can exacerbate the phenomenon of Migration Through Resolution Cells (MTRC), seriously affecting the ISAR imaging performance. For the fast estimation and compensation of echo phase errors caused by the motion of space targets, this paper proposes an ISAR space-target imaging method based on the rapid estimation of joint motion parameters. This method combines the advantages of the high efficiency of the Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimization algorithm and the high compensation accuracy of the Polar Format Algorithm (PFA) algorithm. The proposed method formulates an image entropy minimization model considering the joint estimation of the translation and rotation parameters of the target. To reduce the possibility of optimization falling into local optima, the proposed method solves sub-steps, which comprise rough and fine estimations of the target motion parameters, using the BFGS optimization algorithm. The proposed method rapidly estimates target rotation parameters and performs quick MTRC compensation under large rotation angles. The simulation of point targets and imaging results of actual civil aircraft data show that compared with the Particle Swarm Optimization-Polar Format Algorithm (PSO-PFA) algorithm, the proposed method estimates motion parameters with a higher accuracy under low signal-to-noise ratio conditions. Further, the computational efficiency is improved by more than five times, which is significantly advantageous.
2025,
14(2):
439-455.
With the rapid development of electronic technology, the electromagnetic environment is becoming increasingly complex. For instance, adaptive beamforming cannot suppress main-lobe jammers for traditional phased array radars; therefore, developing measures to tackle this common problem is an urgent need in radar technology. This study addresses the problem of main-lobe deceptive jammer suppression using space-time multidimensional coding. The first step is to design a three-dimensional phase coding scheme applicable across transmit channels, pulses, and subpulses. A Doppler division multiple access technique is employed at the receiver to separate the transmit signals. To solve the problem of waveform misalignment caused by high-speed moving targets, a novel approach is proposed to estimate the compensation index according to differences in beamforming energy. Subsequently, a dual-phase compensation method that leverages the phase differences between the main-lobe deceptive jammers and the target is proposed; this method can distinguish the true target, pulse-delayed jammers, and rapidly generated jammers in the transmit spatial frequency domain. Moreover, spatial filtering is applied to suppress all the main-lobe deceptive jammers by designing an appropriate transmit-receive weight vector. Additionally, an optimization problem aiming to maximize the output Signal-to-Interference-plus-Noise Ratio (SINR) is formulated to address the problem of performance degradation due to the Direction of Arrival (DOA) Errors. Further, to solve this problem, an alternating optimization method is utilized to obtain the optimized weight vector and transmit and receive coding coefficients iteratively to improve the SINR. Simulation results demonstrate that the proposed method suppresses the main-lobe deceptive jammers more effectively than other radar frameworks. Specifically, compared to the conventional multiple-input multiple-output radar, the proposed method achieves an SINR improvement of 34 dB in the presence of four main-lobe deceptive jammers.
2025,
14(2):
456-469.
Traditional multifunctional radar systems optimize transmission resources solely based on target characteristics. However, this approach poses challenges in dynamic electromagnetic environments owing to the intelligent time-varying nature of jamming and the mismatch between traditional optimization models and real-world scenarios. To address these limitations, this paper proposes a data-driven integrated transmission resource management scheme designed to enhance the Multiple Target Tracking (MTT) performance of multifunctional radars in complex and dynamic electromagnetic environments. The proposed scheme achieves this by enabling online perception and utilization of dynamic jamming information. The scheme initially establishes a Markov Decision Process (MDP) to mathematically model the risks associated with radar interception and adversarial jamming. This MDP provides a structured approach to perceive jamming information, which is then integrated into the calculation of MTT. The integrated resource management challenge is formulated as an optimization problem with constraints on the action space. To solve this problem effectively, a greedy sorting backtracking algorithm is introduced. Simulation results demonstrate the efficacy of the proposed method, demonstrating its ability to significantly reduce the probability of radar interception in dynamic jamming environments. Furthermore, the method mitigates the impact of jamming on radar performance during adversarial interference, thereby improving MTT performance.
2025,
14(2):
470-485.
Modern radar systems face increasingly complex challenges in tasks such as detection, tracking, and identification. The diversity of task types, limited data resources, and strict execution time requirements make radar task scheduling a strongly NP-hard problem. However, existing scheduling algorithms struggle to efficiently handle multiradar collaborative tasks involving complex logical constraints. Therefore, Artificial Intelligence (AI)-based scheduling algorithms have gained significant attention. However, their efficiency is heavily dependent on effectively extracting the key features of the problem. The ability to quickly and comprehensively extract common features of multiradar scheduling problems is essential for improving the efficiency of such AI scheduling algorithms. Therefore, this paper proposes a Model Knowledge Embedded Graph Neural Network (MKEGNN) scheduling algorithm. This method frames the radar task collaborative scheduling problem as a heterogeneous network graph, leveraging model knowledge to optimize the training process of the Graph Neural Network (GNN) algorithm. A key innovation of this algorithm is its capability to capture critical model knowledge using low-complexity calculations, which helps to further optimize the GNN model. During the feature extraction stage, the algorithm employs a random unitary matrix transformation. This approach utilizes the spectral features of the random Laplacian matrix from the task’s heterogeneous graph as global features, enhancing the GNN’s ability to extract shared problem features while downplaying individual characteristics. In the parameterized decision-making stage, the algorithm leverages the upper and lower bound knowledge derived from guiding and empirical solutions of the problem model. This strategy significantly reduces the decision space, enabling the network to optimize quickly and accelerating the learning process. Extensive simulation experiments confirm the effectiveness of the MKEGNN algorithm. Compared to existing approaches, it demonstrates improved stability and accuracy across all task sets, boosting the scheduling success rate by 3%～10% and the weighted success rate by 5%～15%. For particularly challenging task sets involving complex multiradar collaborations, the success rate improves by over 4%. The results highlight the algorithm’s stability and robustness.
2025,
14(2):
486-500.
Imaging of passive jamming objects has been a hot topic in radar imaging and countermeasures research, which directly affects the detection and recognition capabilities of radar targets. In the microwave band, the long dwell time required to generate a single image with desired azimuthal resolution makes it difficult to directly distinguish passive jamming objects based on imaging results. In addition, there is a lack of time-dimensional resolution. In comparison, terahertz imaging systems require a shorter synthetic aperture to achieve the same azimuthal resolution, making it easier to obtain low-latency, high-resolution, and high-frame-rate imaging results. Hence, terahertz radar has considerable potential in Video Synthetic Aperture Radar (ViSAR) technology. First, the aperture division and imaging resolutions of airborne terahertz ViSAR are briefly analyzed. Subsequently, imaging results and characteristics of stationary passive jamming objects, such as corner reflector arrays and camouflage mats, are explored before and after motion compensation. Further, the phenomenon that camouflage mats with fluctuating grids exhibit roughness in the terahertz band is demonstrated, exhibiting the special scattering characteristics of the terahertz band. Next, considering rotating corner reflectors as an example of moving passive jamming objects, their characteristics regarding suppressive interference are analyzed. Considering that stationary scenes feature similarity under adjacent apertures, rotating corner reflectors can be directly detected by incoherent image subtraction after inter-frame image and amplitude registrations, followed by the extraction of signals of interest and non-parametrical compensation. Currently, few field experiments regarding the imaging of passive jamming objects using terahertz ViSAR are being reported. Airborne field experiments have been performed to effectively demonstrate the high-resolution and high-frame-rate imaging capabilities of terahertz ViSAR
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