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Tomographic synthetic aperture radar (TomoSAR) technology has demonstrated significant practical value in forest parameter extraction, accumulating a wealth of airborne data and research results over the years. This paper addresses the problem of TomoSAR underlying topography inversion in forested areas, where the complex vertical structure of forests contributes to diverse scattering mechanisms, making it difficult to determine the exact number of scatterers within each unit. To tackle this issue, we propose a TomoSAR underlying topography inversion method that combines density clustering with the multiple signal classification (MUSIC) technique. The proposed algorithm achieves superior estimation for the positions of unknown scatterers by utilizing eigenvalue density clustering to distinguish the signal and noise subspaces. A series of simulated experiments were conducted to showcase the robustness of the proposed algorithm in estimating scatterer phase centres under challenging conditions such as low signal-to-noise ratio and limited snapshots. Moreover, the practicality of the proposed algorithm in accurately reconstructing the underlying topography is validated by experimental results of real data obtained from the BioSAR 2008 campaign dataset. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate and compare the clinical and radiological outcomes of three different patellar fixation techniques on medial patellofemoral ligament reconstruction (MPFLR) in the treatment of patellar dislocation (PD). Methods: Between 2015 and 2020, 130 patients with recurrent PD who underwent surgical reconstruction were eligible for this retrospective study: 48 patients were treated with the semi‐tunnel bone bridge fixation technique (Group A), 42 patients were treated with the suture anchor fixation technique (Group B) and 40 patients were treated with the transpatellar tunnel fixation technique (Group C). Clinical outcomes included functional outcomes (Kujala, Lysholm and International Knee Documentation Committee scores), activity levels (Tegner activity score and return to sports), physical examinations, patellar re‐dislocation rate and complications. Radiological outcomes included patellar congruence angle, patellar tilt angle, lateral patellar translation and lateral patellar angle. Results: All clinical and radiological outcomes improved significantly in all groups, without any significant difference among these three groups. At the final follow‐up, no re‐dislocation occurred, and all groups achieved a successful return to sports. However, the semi‐tunnel bone bridge and suture anchor fixation techniques showed statistically higher Tegner activity scores (p = 0.004) and shorter time from surgery to return to sports (p = 0.007) than the transpatellar tunnel fixation technique. Conclusion: The three MPFLR patellar fixation techniques achieved favourable and comparable clinical and radiological outcomes in the treatment of PD. Compared with the transpatellar tunnel fixation technique, the semi‐tunnel bone bridge and suture anchor fixation techniques may be more effective with higher activity levels. Level of Evidence: Level III. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the clinical effect of derotational femoral osteotomy combined with medial patellofemoral ligament reconstruction for patellar dislocation and the effect of the distribution of femoral torsion at different segments on postoperative function. Methods: Forty‐two patients with patellar dislocation who underwent derotational femoral osteotomy from 2017 to 2021 were retrospectively analysed. All patients received computed tomography scans from the hip to the knee to evaluate correction of the femoral anteversion (FA) angle, patellar tilt angle (PTA) and congruence angle (CA) after derotational femoral osteotomy. Subjective scores, such as the Kujala, Lysholm, International Knee Documentation Committee (IKDC), Tegner and visual analog scale (VAS) scores, were used to evaluate knee function before and after the operation. Patients with supracondylar torsion > distal torsion were categorized into the supracondylar torsion group and patients with distal torsion > supracondylar torsion were categorized into the distal torsion group. Subgroup analyses were performed. Results: No presentation of redislocation occurred in these patients at the minimum 2‐year follow‐up visit. The mean preoperative FA angle in the supracondylar torsion group was 30.2° ± 4.2°, and the mean postoperative FA angle was 14.5° ± 2.5° (p < 0.001). The mean preoperative FA angle was 26.7° ± 1.4° and the mean postoperative FA angle was 14.1° ± 1.4° in the distal torsion group. In addition, postoperative PTA and CA were significantly corrected in both groups (p < 0.001). The postoperative Kujala, Lysholm, IKDC, Tegner and VAS scores were significantly improved in both groups (p < 0.001). Subgroup analyses showed a higher preoperative FA in the supracondylar torsion group and a higher occurrence of high‐grade trochlear dysplasia in the distal torsion group. However, there was no significant difference in their postoperative clinical outcomes. Conclusion: Through a minimum of 2‐year follow‐up visits of patients with patellar dislocation and increased FA, it was found that derotational femoral osteotomy could significantly reduce FA and improve subjective knee function. The pattern of torsion distribution did not significantly affect the clinical outcomes of derotational femoral osteotomy. These findings readvised orthopaedic surgeons that derotational femoral osteotomy remains the preferred procedure for correcting rotational malalignment, but that they should be more cautious about its indications. Level of Evidence: Level IV. [ABSTRACT FROM AUTHOR]

An enhanced Doppler resolution and sidelobe suppression have long been practical issues for moving target detection using Golay complementary waveforms. In this paper, Golay complementary waveform radar returns are combined with a proposed processor, the pointwise thresholding processor (PTP). Compared to the pointwise minimization processor (PMP) illustrated in a previous work, which could only achieve a Doppler resolution comparable to existing methods, this approach essentially increases the Doppler resolution to a very high level in theory. This study also introduced a further filtering process for the delay-Doppler map of the PTP, and simulations verified that the method results in a delay-Doppler map virtually free of range sidelobes. [ABSTRACT FROM AUTHOR]

In the urban environment, the radar is easily affected by multipath (MP) returns. The problem of detecting point‐like targets in the urban environment with the existence of resolvable MP returns under the background of heterogeneous clutter is addressed. Two adaptive detectors have been devised with a combination of prior information on the environment and echoes of target. The detectors can use the MP echoes in all MP prediction range cells for detection or in some available paths for signal detection by the available path selection algorithm that eliminates the weak signal propagation paths. Remarkably, the proposed decision schemes exhibit the desirable constant false alarm rate property with respect to the unknown parameters of the heterogeneous interference. The performance assessment, conducted on simulated data in terms of detection probability also in comparison with conventional solutions, highlights the effectiveness of the MP exploitation, while the MP signal is strong and shows the detection performance enhancement potential. [ABSTRACT FROM AUTHOR]

Assuming uncertain multipath return, this paper considers the robust joint transmit waveform and the receiving filter bank design of a multiple-input–multiple-output (MIMO) radar for multipath exploitation. The actual multipath return is considered to belong to an uncertain set, and we focus on the worst-case optimization of the signal-to-interference-plus-noise ratio (SINR) in the output of the filter bank. The design is cast as a non-convex max–min problem, which is very hard to solve. To tackle it, an equivalent reformulation is utilized and a cyclic optimization paradigm is devised. At each iteration, the filter's optimization problem is equal to a set of separate solvable problems, the closed-form solution to which can be given directly. Moreover, we have shown that the max–min problem for the waveform optimization belongs to the area of generalized fractional programming, and it can be globally solved by resorting to Dinkelbach's algorithm. Through simulations, the superiority of the proposed algorithm is demonstrated via a number of examples. [ABSTRACT FROM AUTHOR]

Existing one-bit direction of arrival (DOA) estimate methods based on sparse recovery or subspace have issues when used for massive uniform linear arrays (MULAs), such as high computing cost, estimation accuracy depending on grid size, or high snapshot-number requirements. This paper considers the low-complexity one-bit DOA estimation problems for MULA with a single snapshot. Theoretical study and simulation results demonstrate that discrete Fourier transform (DFT) can be applied to MULA for reliable initial DOA estimation even when the received data are quantized by one-bit methods. A precise estimate is then obtained by searching within a tiny area. The resulting method is called one-bit DFT. This method is straightforward and simple to implement. High-precision DOA estimates of MULA can be obtained with a single snapshot, and the computational complexity is significantly less than that of existing one-bit DOA estimation methods. Moreover, the suggested method is easily extensible to multiple snapshot scenarios, and increasing the number of snapshots can further improve estimation precision. Simulation results show the effectiveness of the one-bit DFT method. [ABSTRACT FROM AUTHOR]

Golay complementary waveforms are, by definition, able to generate narrow pulses with low sidelobes via coherent signal processing. However, while an ideal impulse can be obtained for target returns at zero-Doppler, significant sidelobes are observed at nonzero Doppler shifts. In this paper, a Generalized Binominal Design (GBD) procedure is proposed for the waveforms consisting of complementary sets in an attempt to reduce the Doppler-induced sidelobes. Our theoretical analysis as well as simulation results show that the proposed approach performs as good as existing Binominal Design method used for sidelobe suppression with Golay complementary waveforms and can also achieve around 28 % enhancement on the Doppler resolution, with an acceptable loss in peak to peak-sidelobe ratio (PPSR). [ABSTRACT FROM AUTHOR]

Here, a novel off‐grid direction‐of‐arrival (DOA) estimation algorithm for nested arrays in the context of sparse recovery is proposed. The framework of existing off‐grid approaches is to correct the on‐grid parameter with a grid mismatch variable. From another perspective, we treat the direction‐of‐arrival deviation as the steering vector deviation equivalently, and the concept of steering vector uncertainty set is introduced to approximate the desired steering vector. Based on this idea, an optimization problem with respect to the uncertainty set for the purpose of steering vector reconstruction is formulated. After that, phase‐ambiguity resolving and phase‐difference approximation are orderly performed on the optimized uncertainty set to extract the off‐grid direction of arrival. Even though a coarse grid is given, simulation results are presented to demonstrate the performance advantage of the proposed direction‐of‐arrival estimation algorithm compared with several existing approaches. [ABSTRACT FROM AUTHOR]

Objective To explore morphological characteristics of patellofemoral joint surface of patients with patellar instability by adopting the MRI‐based method. Methods: A retrospective analysis was performed from March 2016 to January 2020 to assess morphological characteristics of the patellofemoral joint surface by Magnetic Resonance Imaging (MRI) scanning knees of 30 patients (24 females, six males) with patellar instability and trochlear dysplasia and knees of 30 subjects from a randomly selected control group (25 females, five males). The control group was matched as per age and sex. All participants had undergone MRI scans in the supine position and keep knees in or near full extension. Six parts were measured in total, including thickness of trochlear cartilage, thickness of patella cartilage, cartilaginous sulcus angle, cartilaginous Wiberg angle, contact range and frequency and distributions of the mean difference measurement of the femoral trochlea, to evaluate the difference of trochlear and patellar morphology between the patient group and the control group. The threshold for statistical significance was set at P < 0.05. Results: There were significant differences in four values between the two groups (P < 0.05). The cartilage thickness two‐third along the lateral condyle in the patient group was significantly lower than that in the control group (LCT2,1.80 ± 0.37 vs 2.06 ± 0.52, 1.92 ± 0.36 vs 2.17 ± 0.50), but there was no significant difference in other sites. There was no significant difference in patella thickness between the patient group and the control group. The cartilaginous sulcus angle in the patient group was larger than that in the control group (157.90 ± 6.64 vs 142.23 ± 3.95, P < 0.001), but there was no significant difference in cartilaginous Wiberg angle. The patient group had a larger initial contact ratio (59.47 ± 6.13 vs 46.50 ± 3.67, P < 0.001), and a smaller contact range (16.55 ± 4.14 vs 27.55 ± 4.09, P < 0.001). The deepest part of the intercondylar suclus appears more often in the lateral of the deepest part of the osseous concavity of the femoral trochlea. Among the patient group, 18 cases (60%) were found with the deepest part of the intercondylar suclus lateral to the deepest point of the osseous concavity of the femoral trochlea while among the control group only 4 cases (13.33%) were found. The distribution of trochlear dysplasia of Dejour grades was type B (n = 22), type C (n = 5), and type D (n = 3). Conclusion: Thickness of partial lateral trochlear cartilage decreases in patients with patellar instability and the trochlear cartilage develops abnormal morphological characteristics. Moreover, it also suggests that MRI can be used to further present the morphology of cartilage for the convenience of surgical planning. [ABSTRACT FROM AUTHOR]

Displaced phase center array (DPCA) and along-track interferometry (ATI) have been widely used for ground moving target indication (GMTI) in multi-channel circular synthetic aperture radar (CSAR) system. In ideal conditions, these methods can suppress background clutter effectively. However, the nonideal movement of platform may create a nonzero crab angle, which will induce a cross-track baseline offset and affect GMTI processing seriously. This letter analyzes the influence of crab angle on interferometric phase theoretically. Here, we propose a two-step phase calibration method to greatly improve the performance of CSAR-GMTI by eliminating the range-varying phase error. This method is independent of imaging and GMTI processing. Simulated and measured data results verify the correctness of the theoretical analysis and the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Coprime arrays can highly increase degree-of-freedom by operating the second-order virtual signal. However, the corresponding virtual array is discontiguous, and thus most existing direction-of-arrival estimation approaches fail to utilise all received information. To avoid performance loss, the authors intend to convert the discontiguous array into a contiguous one in this Letter and propose two virtual array interpolation algorithms for the coprime array from the perspective of signal reconstruction. By promoting the sparsity of the signal via simplified atomic norm minimisation and enhanced matrix completion, respectively, the two algorithms can effectively reconstruct the signal of the interpolated virtual array in a gridless manner. Simulation results are presented to demonstrate the performance advantage of the two proposed approaches. [ABSTRACT FROM AUTHOR]

Space-time adaptive processing based on clutter sparse recovery (SR-STAP) methods outperform traditional statistical-STAP algorithms in scenarios with limited training numbers. However, the computational burden of current SR-STAP methods is extremely heavy, particularly when the number of discretized angle and Doppler grid points is large, which hinders these methods from coming into practical use. This letter proposes a spectrum-aided reduced-dimension SR-STAP method to overcome this issue. The proposed method employs the clutter spectrum estimated by training samples to design the reduced-dimension dictionary. By solving a reduced-dimension sparse recovery problem, the computational load of the proposed method can be reduced significantly while only slightly degrading the performance of clutter suppression and target detection compared with current SR-STAP methods. Numerical experiments using both simulated and measured data validate the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

A medical image registration method is proposed. An enhanced mutual information is employed as the similarity measure. A hybrid optimisation technique based on Powell's method and cuckoo search is developed as the optimiser. Experimental results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Dynamic cable-tension is an important bridge-health indicator. However, it is difficult to be measured precisely and efficiently. A remote bridge dynamic cable-tension measurement method is proposed. It uses an interferometric radar sensor, a time-frequency analysis technique, and a tension estimation approach based on a string-vibration-equation. One radar can measure the displacements of multiple cables aligned on one side of a bridge, at the same time. By solving the string vibration equation, each cable-tension is calculated from its fundamental frequency, which is obtained by time-frequency analyzing a short section of the cable's whole displacement vector in an overlapped-piecewise manner. An adaptive amplitude and phase estimation (APES) algorithm is used to solve the frequency resolution deterioration problem due to the short duration. Simulations and field experiments with a K band interferometric radar validate that the proposed method is superior to traditional cable-tension measurements in terms of precision, robustness, and efficiency. The proposed method is of great application value in measuring and monitoring large cable-stayed bridges and cable-suspended bridges. [ABSTRACT FROM AUTHOR]

Particle Swarm Optimization (PSO) is a well-known meta-heuristic. It has been widely used in both research and engineering fields. However, the original PSO generally suffers from premature convergence, especially in multimodal problems. In this paper, we propose a double-group PSO (DG-PSO) algorithm to improve the performance. DG-PSO uses a double-group based evolution framework. The individuals are divided into two groups: an advantaged group and a disadvantaged group. The advantaged group works according to the original PSO, while two new strategies are developed for the disadvantaged group. The proposed algorithm is firstly evaluated by comparing it with the other five popular PSO variants and two state-of-the-art meta-heuristics on various benchmark functions. The results demonstrate that DG-PSO shows a remarkable performance in terms of accuracy and stability. Then, we apply DG-PSO to multilevel thresholding for remote sensing image segmentation. The results show that the proposed algorithm outperforms five other popular algorithms in meta-heuristic-based multilevel thresholding, which verifies the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]