Editorial

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3 pages, 159 KiB

Open AccessEditorial

Special Issue on “Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement”

by Hirokazu Kobayashi and Toshifumi Moriyama

Electronics 2020, 9(4), 653; https://doi.org/10.3390/electronics9040653 - 16 Apr 2020

Viewed by 1992

Abstract

A radar system is made of many elemental and hard/software technologies [...] Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

Research

Jump to: Editorial, Review

12 pages, 369 KiB

Open AccessArticle

Atomic Norm-Based DOA Estimation with Dual-Polarized Radar

by Min Han and Wenbin Dou

Electronics 2019, 8(9), 1056; https://doi.org/10.3390/electronics8091056 - 19 Sep 2019

Cited by 4 | Viewed by 3067

Abstract

In the dual-polarized radar system, the horizontally and vertically polarized signals can be exploited to improve the direction of arrival (DOA) estimation performance. In this paper, the DOA estimation problem is considered in the dual-polarized radar. By exploiting the target sparsity in the [...] Read more.

In the dual-polarized radar system, the horizontally and vertically polarized signals can be exploited to improve the direction of arrival (DOA) estimation performance. In this paper, the DOA estimation problem is considered in the dual-polarized radar. By exploiting the target sparsity in the spatial domain, the sparse-based method is proposed after formulating the DOA estimation problem as a sparse reconstruction problem. In the traditionally sparse methods using the compressed sensing (CS) theory, the spatial domain is discretized into grids to establish a dictionary matrix and solve the sparse reconstruction problem, but the off-grid error is introduced in the discretized grids. Therefore, we formulate a novel definition of atomic norm for the dual-polarized signals and give an atomic norm-based method to denoise the received signals. Then, an efficient semidefinite program (SDP) is derived, and the DOA is estimated by searching the peak values of the denoised signals. Simulation results show that the proposed method can significantly improve the DOA estimation performance in the dual-polarized radar. Additionally, compared with the state-of-art methods, the proposed method has better estimation performance with relatively low computational complexity. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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10 pages, 2943 KiB

Open AccessArticle

Micro-Motion Feature Extraction of a Rotating Target Based on Interrupted Transmitting and Receiving Pulse Signal in an Anechoic Chamber

by Feng Zhao, Xiaobin Liu, Zhiming Xu, Yuan Liu and Xiaofeng Ai

Electronics 2019, 8(9), 1028; https://doi.org/10.3390/electronics8091028 - 13 Sep 2019

Cited by 5 | Viewed by 2044

Abstract

The pulse signal is widely used in micro-motion feature extraction of rapidly rotating targets as its pulse repetition frequency (PRF) can be high. However, when the pulse signal is implemented in a range-limited anechoic chamber for micro-motion feature extraction, the transmitted and reflected [...] Read more.

The pulse signal is widely used in micro-motion feature extraction of rapidly rotating targets as its pulse repetition frequency (PRF) can be high. However, when the pulse signal is implemented in a range-limited anechoic chamber for micro-motion feature extraction, the transmitted and reflected pulse signals may be coupled at the receiver. To solve this problem, the interrupted transmitting and receiving (ITR) method is applied to transmit the pulse signal with hundreds of sub-pulses. The target echo can be received when the sub-pulse is not transmitted. Hence, it avoids the coupling effect of transmitted signals and echoes. Then, the whole process of micro-motion feature extraction for rotating target is proposed based on the ITR method. At last, the simulations and experiments verify that the rotating target micro-Doppler can be extracted by the ITR pulse signal. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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21 pages, 6353 KiB

Open AccessArticle

Wideband Noise Interference Suppression for Sparsity-Based SAR Imaging Based on Dechirping and Double Subspace Extraction

by Guojing Li, Qinglin Lu, Guochao Lao and Wei Ye

Electronics 2019, 8(9), 1019; https://doi.org/10.3390/electronics8091019 - 11 Sep 2019

Cited by 3 | Viewed by 2700

Abstract

Sparsity-based synthetic aperture radar (SAR) imaging has attracted much attention since it has potential advantages in improving the image quality and reducing the sampling rate. However, it is vulnerable to deliberate blanket disturbance, especially wideband noise interference (WBNI), which severely damages the imaging [...] Read more.

Sparsity-based synthetic aperture radar (SAR) imaging has attracted much attention since it has potential advantages in improving the image quality and reducing the sampling rate. However, it is vulnerable to deliberate blanket disturbance, especially wideband noise interference (WBNI), which severely damages the imaging quality. This paper mainly focuses on WBNI suppression for SAR imaging from a new perspective—sparse recovery. We first analyze the impact of WBNI on signal reconstruction by deducing the interference energy projected on the real support set of the signal under different observation parameters. Based on the derived results, we propose a novel WBNI suppression algorithm based on dechirping and double subspace extraction (DDSE), where the signal of interest (SOI) is reconstructed by exploiting the known geometric prior and waveform prior, respectively. The experimental results illustrate that the DDSE-based WBNI suppression algorithm for sparsity-based SAR imaging is effective and outperforms the other algorithms. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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12 pages, 2573 KiB

Open AccessArticle

Low Altitude Measurement Accuracy Improvement of the Airborne FMCW Radio Altimeters

by Ján Labun, Pavol Kurdel, Marek Češkovič, Alexey Nekrasov and Ján Gamec

Electronics 2019, 8(8), 888; https://doi.org/10.3390/electronics8080888 - 12 Aug 2019

Cited by 15 | Viewed by 3908

Abstract

This manuscript focuses on the analysis of a critical height of radio altimeters that can help for the development of new types of aeronautical radio altimeters with increased accuracy in measuring low altitudes. Altitude measurement accuracy is connected with a form of processing [...] Read more.

This manuscript focuses on the analysis of a critical height of radio altimeters that can help for the development of new types of aeronautical radio altimeters with increased accuracy in measuring low altitudes. Altitude measurement accuracy is connected with a form of processing the difference signal of a radio altimeter, which carries information on the measured altitude. The definition of the altitude measurement accuracy is closely linked to the value of a critical height. Modern radio altimeters with digital processing of a difference signal could shift the limit of accuracy towards better values when the basics of the determination of critical height are thoroughly known. The theory results from the analysis and simulation of dynamic formation and the dissolution of the so-called stable and unstable height pulses, which define the range of the critical height and are presented in the paper. The theory is supported by a new method of derivation of the basic equation of a radio altimeter based on a critical height. The article supports the new theory of radio altimeters with the ultra-wide frequency deviation that lead to the increase the accuracy of a low altitude measurement. Complex mathematical analysis of the dynamic formation of critical height and a computer simulation of its course supported by the new form of the derivation of the basic equation of radio altimeter guarantee the correctness of the new findings of the systematic creation of unstable height pulses and the influence of their number on the altitude measurement accuracy. Application of the presented findings to the aviation practice will contribute to increasing the accuracy of the low altitude measurement from an aircraft during its landing and to increasing air traffic safety. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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16 pages, 8464 KiB

Open AccessArticle

Design of a Novel Double Negative Metamaterial Absorber Atom for Ku and K Band Applications

by Saif Hannan, Mohammad Tariqul Islam, Ahasanul Hoque, Mandeep Jit Singh and Ali F. Almutairi

Electronics 2019, 8(8), 853; https://doi.org/10.3390/electronics8080853 - 31 Jul 2019

Cited by 27 | Viewed by 4516

Abstract

This paper presents a multiband metamaterial (MM) absorber based on a novel spiral resonator with continuous, dual, and opposite P-shape. The full wave analysis shows 80.06% to 99.95% absorption at frequencies range for Ku and K bands for several substrate materials of 100 [...] Read more.

This paper presents a multiband metamaterial (MM) absorber based on a novel spiral resonator with continuous, dual, and opposite P-shape. The full wave analysis shows 80.06% to 99.95% absorption at frequencies range for Ku and K bands for several substrate materials of 100 mm² area. The results indicate that the absorption rate remains similar for different polarizing angles in TEM mode with different substrates. With FR4 (Flame Retardant 4) substrate and 64 mm² ground plane, the design acts as single negative (SNG) MM absorber in K band resonance frequencies (19.75–21.37 GHz) and acts as double negative (DNG) absorber in Ku band resonance frequencies (15.28–17.07 GHz). However, for Rogers 3035 substrate and 36 mm² ground plane, it acts as an SNG absorber for Ku band resonance frequency 14.64 GHz with 83.25% absorption and as a DNG absorber for K band frequencies (18.24–16.15 GHz) with 83.69% to 94.43% absorption. With Rogers 4300 substrate and 36 mm² ground plane, it acts as an SNG absorber for Ku band at 15.04 GHz with 89.77% absorption and as DNG absorber for K band frequencies (22.17–26.88 GHz) with 92.87% to 93.72% absorption. The design was fabricated with all three substrates and showed quite similar results as simulation. In comparison with other broadband absorbers, this proposed MM absorber illustrated broad incidence angles in TEM mode. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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21 pages, 5783 KiB

Open AccessArticle

Study of Algorithms for Wind Direction Retrieval from X-Band Marine Radar Images

by Hui Wang, Haiyang Qiu, Pengfei Zhi, Lei Wang, Wei Chen, Rizwan Akhtar and Muhammad Asif Zahoor Raja

Electronics 2019, 8(7), 764; https://doi.org/10.3390/electronics8070764 - 08 Jul 2019

Cited by 6 | Viewed by 2782

Abstract

After decades of research, X-band marine radars have been broadly used for wind measurement. For retrieving the wind direction based on the wind-induced streaks, a lot of effort has been expended on three celebrated approaches—the local gradient method (LGM), the adaptive reduced method [...] Read more.

After decades of research, X-band marine radars have been broadly used for wind measurement. For retrieving the wind direction based on the wind-induced streaks, a lot of effort has been expended on three celebrated approaches—the local gradient method (LGM), the adaptive reduced method (ARM), and the energy spectrum method (ESM). This paper presents a scientific study of these methods. The contrast of retrieving the real measured marine radar images and vane measured results is evaluated, in perspective of the error statistics and algorithm operation efficiency. Interference factors, such as the historical information of the measured area, reference wind speed, and sea condition showing in the monitoring equipment are also concerned. The tentative results showed that LGM is robust, which can be implemented in most radar images, because it allows for a lower selection of requirements compared with the other two methods. For ARM, the better retrieval performance is a tradeoff with extra computation, which is expensive. ESM is superior to the other two algorithms in terms of accuracy and computation load; however, this algorithm is sensitive in rain-contaminated radar images, meaning it is a good choice for data post-processing in the lab. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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12 pages, 5737 KiB

Open AccessArticle

Calculation and Interpretation of Ground Penetrating Radar for Temperature and Relative Water Content of Seasonal Permafrost in Qinghai-Tibet Platea

by Qing Wang and Yupeng Shen

Electronics 2019, 8(7), 731; https://doi.org/10.3390/electronics8070731 - 27 Jun 2019

Cited by 9 | Viewed by 3238

Abstract

Due to the seasonal permafrost thawing, the Qinghai–Tibet Highway has a depression and instability of the roadbed. In order to obtain the ablation interface and water content characteristics of seasonal permafrost areas, non-destructive ground penetrating radars using electromagnetic wave detection methods are widely [...] Read more.

Due to the seasonal permafrost thawing, the Qinghai–Tibet Highway has a depression and instability of the roadbed. In order to obtain the ablation interface and water content characteristics of seasonal permafrost areas, non-destructive ground penetrating radars using electromagnetic wave detection methods are widely used. Regarding the imaging of the ablation interface in permafrost regions, this paper proposes a high-precision procedure for seasonal permafrost media using waveform difference analysis, electromagnetic wave attenuation attribute calculation and relative wave impedance conversion. It improves the resolution and division accuracy of the imaging. In addition, the study demonstrates a method to calculate the temperature and water content of the ablation zone by mining attenuation attribute, relative wave impedance attribute, absolute instantaneous amplitude attribute and the weighted average frequency attribute parameters under the constraints of the measured data. This method has high accuracy and high efficiency and can be used in the rapid calculation of temperature and water content of seasonal permafrost on the Qinghai–Tibet Highway. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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19 pages, 10374 KiB

Open AccessArticle

Feasibility Study of Passive Bistatic Radar Based on Phased Array Radar Signals

by Jiameng Pan, Panhe Hu, Qian Zhu, Qinglong Bao and Zengping Chen

Electronics 2019, 8(7), 728; https://doi.org/10.3390/electronics8070728 - 26 Jun 2019

Cited by 4 | Viewed by 3274

Abstract

This paper presents the concept of a passive bistatic radar (PBR) system using existing phased array radar (PAR) as the source of illumination. Different from PBR based on common civil illuminators of opportunity, we develop an experimental PBR system using an high-power air [...] Read more.

This paper presents the concept of a passive bistatic radar (PBR) system using existing phased array radar (PAR) as the source of illumination. Different from PBR based on common civil illuminators of opportunity, we develop an experimental PBR system using an high-power air surveillance PAR with abundant signal modulation forms as the transmitter. After the introduction of the PBR system and PAR signals, it can be concluded that the agility of the waveform parameters of PAR signal brings two problems to the signal processing of the PBR systems, which are not discussed in conventional PBR systems. The first problem is the time and frequency synchronization of the system, so we propose a direct wave parameter estimation method based on template matching to estimate the parameters of the transmitted signal in real time to achieve time and frequency synchronization of the system. The second problem is the coherent integration for moving target detection and weak target detection, so we propose a coherent integration method based on Radon–Nonuniform Fast Fourier Transform (Radon-NUFFT) to deal with the problems introduced by the agile waveform parameters. Preliminary results from the field experiment demonstrate the feasibility of the PBR system based on PAR signals, and the effectiveness of the proposed methods is verified. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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18 pages, 9259 KiB

Open AccessArticle

PBR Clutter Suppression Algorithm Based on Dilation Morphology of Non-Uniform Grid

by Qian Zhu, Tao Li, Jiameng Pan and Qinglong Bao

Electronics 2019, 8(6), 708; https://doi.org/10.3390/electronics8060708 - 22 Jun 2019

Cited by 2 | Viewed by 2751

Abstract

Many new challenges are faced by the PBR (passive bi-static radar) employing non-cooperative radar illuminators. After the CFAR (constant false alarm) processor, the appearance of the amount of false alarm clutter points impacts the following tracing performance. To enhance the PBR tracing performance, [...] Read more.

Many new challenges are faced by the PBR (passive bi-static radar) employing non-cooperative radar illuminators. After the CFAR (constant false alarm) processor, the appearance of the amount of false alarm clutter points impacts the following tracing performance. To enhance the PBR tracing performance, we consider to reduce these clutter points before target tracing as soon as possible. In this paper, we propose a PBR clutter suppression algorithm based on dilation morphology of non-uniform grid. Firstly, we construct the non-uniform polar grid based on the acquisition geometry of PBR. Then, with the help of the grid platform, we separate the false alarm clutter points based on the dilation morphology. To efficiently operate the algorithm, we build up its parallel iteration scheme. To verify the performance of the proposed algorithm, we utilize both simulated data and field data to do the experiment. Experimental results show that the algorithm can effectively suppress most of the clutter points. Besides, we respectively combine the proposed suppression algorithm with two typical tracking algorithms to test the performance. Experimental results reveal that the compound tracing algorithm outperforms the traditional one. It can enhance the PBR tracing performance, reduce the occurrence probability of false tracks and meanwhile save time. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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16 pages, 3522 KiB

Open AccessArticle

Application of S-Transform in ISAR Imaging

by Bo Zang, Mingzhe Zhu, Xianda Zhou and Lu Zhong

Electronics 2019, 8(6), 676; https://doi.org/10.3390/electronics8060676 - 14 Jun 2019

Cited by 8 | Viewed by 2731

Abstract

In inverse synthetic aperture radar (ISAR) imaging, time-frequency analysis is the basic method for processing echo signals, which are reflected by the results of time-frequency analysis as each component changes over time. In the time-frequency map, a target’s rigid body components will appear [...] Read more.

In inverse synthetic aperture radar (ISAR) imaging, time-frequency analysis is the basic method for processing echo signals, which are reflected by the results of time-frequency analysis as each component changes over time. In the time-frequency map, a target’s rigid body components will appear as a series of single-frequency signals in the low-frequency region, and the micro-Doppler components generated by the target’s moving parts will be distributed in the high-frequency region with obvious frequency modulation. Among various time-frequency analysis methods, S-transform is especially suitable for analyzing these radar echo signals with micro-Doppler (m-D) components because of its multiresolution characteristics. In this paper, S-transform and the corresponding synchrosqueezing method are used to analyze the ISAR echo signal and perform imaging. Synchrosqueezing is a post-processing method for the time-frequency analysis result, which could retain most merits of S-transform while significantly improving the readability of the S-transformation result. The results of various simulations and actual data will show that S-transform is highly matched with the echo signal for ISAR imaging: the better frequency-domain resolution at low frequencies can concentrate the energy of the rigid body components in the low-frequency region, and better time resolution at high frequencies can better describe the transformation of the m-D component over time. The combination with synchrosqueezing also significantly improves the effect of time-frequency analysis and final imaging, and alleviates the shortcomings of the original S-transform. These results will be able to play a role in subsequent work like feature extraction and parameter estimation. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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17 pages, 4297 KiB

Open AccessFeature PaperArticle

Entropy-Based Low-Rank Approximation for Contrast Dielectric Target Detection with Through Wall Imaging System

by Mandar Bivalkar, Dharmendra Singh and Hirokazu Kobayashi

Electronics 2019, 8(6), 634; https://doi.org/10.3390/electronics8060634 - 05 Jun 2019

Cited by 10 | Viewed by 3349

Abstract

In through wall imaging, clutter plays an important role in the detection of objects behind the wall. In the literature, extensive studies have been carried out to eliminate clutter in the case of targets with the same dielectric. Existing clutter reduction techniques, such [...] Read more.

In through wall imaging, clutter plays an important role in the detection of objects behind the wall. In the literature, extensive studies have been carried out to eliminate clutter in the case of targets with the same dielectric. Existing clutter reduction techniques, such as the sub-space approach, differential approach, entropy-based time gating, etc., are able to detect a single target or two targets with the same dielectric behind the wall. In a real-time scenario, it is not necessary that targets with the same dielectric will be present behind the wall. Very few studies are available for the detection of targets with different dielectrics; here we termed it “contrast target detection” in the same scene. Recently, low-rank approximation (LRA) was proposed to reduce random noise in the data. In this paper, a novel method based on entropy thresholding for low-rank approximation is introduced for contrast target detection. It was observed that our proposed method gives satisfactory results. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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17 pages, 8994 KiB

Open AccessArticle

Evaluation of a Straight-Ray Forward Model for Bayesian Inversion of Crosshole Ground Penetrating Radar Data

by Hui Qin, Xiongyao Xie and Yu Tang

Electronics 2019, 8(6), 630; https://doi.org/10.3390/electronics8060630 - 04 Jun 2019

Cited by 8 | Viewed by 3116

Abstract

Bayesian inversion of crosshole ground penetrating radar (GPR) data is capable of characterizing the subsurface dielectric properties and qualifying the associated uncertainties. Markov chain Monte Carlo (MCMC) simulations within the Bayesian inversion usually require thousands to millions of forward model evaluations for the [...] Read more.

Bayesian inversion of crosshole ground penetrating radar (GPR) data is capable of characterizing the subsurface dielectric properties and qualifying the associated uncertainties. Markov chain Monte Carlo (MCMC) simulations within the Bayesian inversion usually require thousands to millions of forward model evaluations for the parameters to hit their posterior distributions. Therefore, the CPU cost of the forward model is a key issue that influences the efficiency of the Bayesian inversion method. In this paper we implement a widely used straight-ray forward model within our Bayesian inversion framework. Based on a synthetic unit square relative permittivity model, we simulate the crosshole GPR first-arrival traveltime data using the finite-difference time-domain (FDTD) and straight-ray solver, respectively, and find that the straight-ray simulator runs 450 times faster than its FDTD counterpart, yet suffers from a modeling error that is more than 7 times larger. We also perform a series of numerical experiments to evaluate the performance of the straight-ray model within the Bayesian inversion framework. With modeling error disregarded, the inverted posterior models fit the measurement data nicely, yet converge to the wrong set of parameters at the expense of unreasonably large number of iterations. When the modeling error is accounted for, with a quarter of the computational burden, the main features of the true model can be identified from the posterior realizations although there still exist some unwanted artifacts. Finally, a smooth constraint on the model structure improves the inversion results considerably, to the extent that it enhances the inversion accuracy approximating to those of the FDTD model, and further reduces the CPU demand. Our results demonstrate that the use of the straight-ray forward model in the Bayesian inversion saves computational cost tremendously, and the modeling error correction together with the model structure constraint are the necessary amendments that ensure that the model parameters converge correctly. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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19 pages, 2921 KiB

Open AccessArticle

Focusing of Ultrahigh Resolution Spaceborne Spotlight SAR on Curved Orbit

by Yulei Qian and Daiyin Zhu

Electronics 2019, 8(6), 628; https://doi.org/10.3390/electronics8060628 - 03 Jun 2019

Cited by 5 | Viewed by 2541

Abstract

Aiming to acquire ultrahigh resolution images, algorithms for spaceborne spotlight synthetic aperture radar (SAR) imaging typically confront challenges of curved orbit and azimuth spectral aliasing. In order to conquer these difficulties, a method is proposed in this paper to obtain ultrahigh resolution spaceborne [...] Read more.

Aiming to acquire ultrahigh resolution images, algorithms for spaceborne spotlight synthetic aperture radar (SAR) imaging typically confront challenges of curved orbit and azimuth spectral aliasing. In order to conquer these difficulties, a method is proposed in this paper to obtain ultrahigh resolution spaceborne SAR images on a curved orbit, which is composed of the modified RMA (Range Migration Algorithm) and the modified deramping-based approach. The modified RMA is developed to deal with the effect introduced by a curved orbit and the modified deramping-based approach is utilized to handle the problem of azimuth spectral aliasing. In the modified RMA, the polynomial expression of SAR two-dimensional spectrum on a curved orbit is derived with fourth-order azimuth phase history model and series reversion. Then, the singular value decomposition (SVD) is applied to decompose the expression of SAR two-dimensional spectrum numerically in order to acquire coordinates for Stolt interpolation in the scenario of curved orbit. In addition, the modified deramping-based approach is derived by introducing orbital state vectors in order to accommodate the situation of curved orbit in the proposed method. Experiments are implemented on point target simulation in order to verify the effectiveness of the presented method. In experiments, the range and azimuth resolution can achieve 0.15 m and 0.14 m, with focused scene size of 3 km by 3 km. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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14 pages, 4300 KiB

Open AccessArticle

Multipath Ghost Suppression Based on Generative Adversarial Nets in Through-Wall Radar Imaging

by Yong Jia, Ruiyuan Song, Shengyi Chen, Gang Wang, Yong Guo, Xiaoling Zhong and Guolong Cui

Electronics 2019, 8(6), 626; https://doi.org/10.3390/electronics8060626 - 03 Jun 2019

Cited by 7 | Viewed by 3103

Abstract

In this paper, we propose an approach that uses generative adversarial nets (GAN) to eliminate multipath ghosts with respect to through-wall radar imaging (TWRI). The applied GAN is composed of two adversarial networks, namely generator G and discriminator D. Generator G learns [...] Read more.

In this paper, we propose an approach that uses generative adversarial nets (GAN) to eliminate multipath ghosts with respect to through-wall radar imaging (TWRI). The applied GAN is composed of two adversarial networks, namely generator G and discriminator D. Generator G learns the spatial characteristics of an input radar image to construct a mapping from an input to output image with suppressed ghosts. Discriminator D evaluates the difference (namely, the residual multipath ghosts) between the output image and the ground-truth image without multipath ghosts. On the one hand, by training G, the image difference is gradually diminished. In other words, multipath ghosts are increasingly suppressed in the output image of G. On the other hand, D is trained to improve in evaluating the diminishing difference accompanied with multipath ghosts as much as possible. These two networks, G and D, fight with each other until G eliminates the multipath ghosts. The simulation results demonstrate that GAN can effectively eliminate multipath ghosts in TWRI. A comparison of different methods demonstrates the superiority of the proposed method, such as the exemption of prior wall information, no target images with degradation, and robustness for different scenes. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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16 pages, 9767 KiB

Open AccessArticle

Weak Signal Extraction from Lunar Penetrating Radar Channel 1 Data Based on Local Correlation

by Zhuo Jia, Sixin Liu, Ling Zhang, Bin Hu and Jianmin Zhang

Electronics 2019, 8(5), 573; https://doi.org/10.3390/electronics8050573 - 23 May 2019

Cited by 7 | Viewed by 2925

Abstract

Knowledge of the subsurface structure not only provides useful information on lunar geology, but it also can quantify the potential lunar resources for human beings. The dual-frequency lunar penetrating radar (LPR) aboard the Yutu rover offers a Special opportunity to understand the subsurface [...] Read more.

Knowledge of the subsurface structure not only provides useful information on lunar geology, but it also can quantify the potential lunar resources for human beings. The dual-frequency lunar penetrating radar (LPR) aboard the Yutu rover offers a Special opportunity to understand the subsurface structure to a depth of several hundreds of meters using a low-frequency channel (channel 1), as well as layer near-surface stratigraphic structure of the regolith using high-frequency observations (channel 2). The channel 1 data of the LPR has a very low signal-to-noise ratio. However, the extraction of weak signals from the data represents a problem worth exploring. In this article, we propose a weak signal extraction method in view of local correlation to analyze the LPR CH-1 data, to facilitate a study of the lunar regolith structure. First, we build a pre-processing workflow to increase the signal-to-noise ratio (SNR). Second, we apply the K-L transform to separate the horizontal signal and then use the seislet transform (ST) to reserve the continuous signal. Then, the local correlation map is calculated using the two denoising results and a time–space dependent weighting operator is constructed to suppress the noise residuals. The weak signal after noise suppression may provide a new reference for subsequent data interpretation. Finally, in combination with the regional geology and previous research, we provide some speculative interpretations of the LPR CH-1 data. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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12 pages, 2399 KiB

Open AccessArticle

Bistatic-ISAR Linear Geometry Distortion Alleviation of Space Targets

by Lin Shi, Baofeng Guo, Ning Han, Juntao Ma, Xiaoxiu Zhu and Chaoxuan Shang

Electronics 2019, 8(5), 560; https://doi.org/10.3390/electronics8050560 - 20 May 2019

Cited by 5 | Viewed by 2484

Abstract

The linear geometry distortion caused by time variant bistatic angles induces the sheared shape of the bistatic inverse synthetic aperture radar (bistatic-ISAR) image. A linear geometry distortion alleviation algorithm for space targets in bistatic-ISAR systems is presented by exploiting prior information. First, we [...] Read more.

The linear geometry distortion caused by time variant bistatic angles induces the sheared shape of the bistatic inverse synthetic aperture radar (bistatic-ISAR) image. A linear geometry distortion alleviation algorithm for space targets in bistatic-ISAR systems is presented by exploiting prior information. First, we analyze formation mathematics of linear geometry distortions in the Range Doppler (RD) domain. Second, we estimate coefficients of first-order polynomial of bistatic angles by least square error (LSE) method through exploiting the imaging geometry and orbital information of space targets. Third, we compensate the linear spatial-variant terms to restore the linear geometry distortions. Consequently, the restored bistatic-ISAR image with real shape is obtained. Simulated results of the ideal point scatterers dataset and electromagnetic numerical dataset verify the performance of the proposed algorithm. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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24 pages, 6181 KiB

Open AccessArticle

Narrowband Interference Separation for Synthetic Aperture Radar via Sensing Matrix Optimization-Based Block Sparse Bayesian Learning

by Guojing Li, Wei Ye, Guochao Lao, Shuya Kong and Di Yan

Electronics 2019, 8(4), 458; https://doi.org/10.3390/electronics8040458 - 25 Apr 2019

Cited by 6 | Viewed by 3030

Abstract

High-resolution synthetic aperture radar (SAR) operating with a large bandwidth is subject to impacts from various kinds of narrowband interference (NBI) in complex electromagnetic environments. Recently, many radio frequency interference (RFI) suppression approaches for SAR based on sparse recovery have been proposed and [...] Read more.

High-resolution synthetic aperture radar (SAR) operating with a large bandwidth is subject to impacts from various kinds of narrowband interference (NBI) in complex electromagnetic environments. Recently, many radio frequency interference (RFI) suppression approaches for SAR based on sparse recovery have been proposed and demonstrated to outperform traditional ones in preserving the signal of interest (SOI) while suppressing the interference by exploiting their intrinsic structures. In particular, the joint recovery strategy of SOI and NBI with a cascaded dictionary, which eliminates the steps of NBI reconstruction and time-domain cancellation, can further reduce unnecessary system complexity. However, these sparsity-based approaches hardly work effectively for signals from an extended target or NBI with a certain bandwidth, since neither of them is sparse in a prescient domain. Moreover, sub-dictionaries corresponding to different components in the cascaded matrix are not strictly independent, which severely limits the performance of separated reconstruction. In this paper, we present an enhanced NBI separation algorithm for SAR via sensing matrix optimization-based block sparse Bayesian learning (SMO-BSBL) to solve these problems above. First, we extend the block sparse Bayesian learning framework to a complex-valued domain for the convenience of radar signal processing with lower computation complexity and modify it to deal with the separation problem of NBI in the contaminated echo. For the sake of improving the separated reconstruction performance, we propose a new block coherence measure by defining the external and internal block structure, which is used for optimizing the observation matrix. The optimized observation matrix is then employed to reconstruct SOI and NBI simultaneously under the modified BSBL framework, given a known and fixed cascaded dictionary. Numerical simulation experiments and comparison results demonstrate that the proposed SMO-BSBL is effective and superior to other advanced algorithms in NBI suppression for SAR. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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17 pages, 6224 KiB

Open AccessArticle

Remote Sensing Image Fusion Based on Sparse Representation and Guided Filtering

by Xiaole Ma, Shaohai Hu, Shuaiqi Liu, Jing Fang and Shuwen Xu

Electronics 2019, 8(3), 303; https://doi.org/10.3390/electronics8030303 - 08 Mar 2019

Cited by 16 | Viewed by 3264

Abstract

In this paper, a remote sensing image fusion method is presented since sparse representation (SR) has been widely used in image processing, especially for image fusion. Firstly, we used source images to learn the adaptive dictionary, and sparse coefficients were obtained by sparsely [...] Read more.

In this paper, a remote sensing image fusion method is presented since sparse representation (SR) has been widely used in image processing, especially for image fusion. Firstly, we used source images to learn the adaptive dictionary, and sparse coefficients were obtained by sparsely coding the source images with the adaptive dictionary. Then, with the help of improved hyperbolic tangent function (tanh) and

l_{0} - \max

, we fused these sparse coefficients together. The initial fused image can be obtained by the image fusion method based on SR. To take full advantage of the spatial information of the source images, the fused image based on the spatial domain (SF) was obtained at the same time. Lastly, the final fused image could be reconstructed by guided filtering of the fused image based on SR and SF. Experimental results show that the proposed method outperforms some state-of-the-art methods on visual and quantitative evaluations. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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19 pages, 6898 KiB

Open AccessArticle

Coherent Integration for Radar High-Speed Maneuvering Target Based on Frequency-Domain Second-Order Phase Difference

by Ke Jin, Tao Lai, Yubing Wang, Gongquan Li and Yongjun Zhao

Electronics 2019, 8(3), 287; https://doi.org/10.3390/electronics8030287 - 04 Mar 2019

Cited by 23 | Viewed by 5322

Abstract

In recent years, target detection has drawn increasing attention in the field of radar signal processing. In this paper, we address the problem of coherent integration for detecting high-speed maneuvering targets, involving range migration (RM), quadratic RM (QRM), and Doppler frequency migration (DFM) [...] Read more.

In recent years, target detection has drawn increasing attention in the field of radar signal processing. In this paper, we address the problem of coherent integration for detecting high-speed maneuvering targets, involving range migration (RM), quadratic RM (QRM), and Doppler frequency migration (DFM) within the coherent processing interval. We propose a novel coherent integration algorithm based on the frequency-domain second-order phase difference (FD-SoPD) approach. First, we use the FD-SoPD operation to reduce the signal from three to two dimensions and simultaneously eliminate the effects of QRM and DFM, which leads to signal-to-noise ratio improvement in the velocity-acceleration domain. Next, we estimate the target motion parameters from the peak position without the need for a search procedure. We show that this algorithm can be easily implemented by using complex multiplications combined with fast Fourier transform (FFT) and inverse FFT (IFFT) operations. We perform comparisons with several representative algorithms and show that the proposed technique can be used to achieve a good trade-off between computational complexity and detection performance. We present both simulated and experimental data to demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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24 pages, 6258 KiB

Open AccessArticle

Retrieval of Three-Dimensional Surface Deformation Using an Improved Differential SAR Tomography System

by Zhigui Wang, Mei Liu and Kunfeng Lv

Electronics 2019, 8(2), 174; https://doi.org/10.3390/electronics8020174 - 02 Feb 2019

Cited by 2 | Viewed by 3086

Abstract

Conventional differential synthetic aperture radar tomography (D-TomoSAR) can only capture the scatterers’ one-dimensional (1-D) deformation information along the line of sight (LOS) of the synthetic aperture radar (SAR), which means that it cannot retrieve the three-dimensional (3-D) movements of the ground surface. To [...] Read more.

Conventional differential synthetic aperture radar tomography (D-TomoSAR) can only capture the scatterers’ one-dimensional (1-D) deformation information along the line of sight (LOS) of the synthetic aperture radar (SAR), which means that it cannot retrieve the three-dimensional (3-D) movements of the ground surface. To retrieve the 3-D deformation displacements, several methods have been proposed; the performance is limited due to the insufficient sensitivity for retrieving the North-South motion component. In this paper, an improved D-TomoSAR model is established by introducing the scatterers’ 3-D deformation parameters in slant range, azimuth, and elevation directions into the traditional D-TomoSAR model. The improved D-TomoSAR can be regarded as a multi-component two-dimensional (2-D) polynomial phase signal (PPS). Then, an effective algorithm is proposed to retrieve the 3-D deformation parameters of the ground surface by the 2-D product high-order ambiguity function (PHAF) with the relax (RELAX) algorithm. The estimation performance is investigated and compared with the traditional algorithm. Simulations and experimental results with semi-real data verify the effectiveness of the proposed signal model and algorithm. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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18 pages, 16195 KiB

Open AccessFeature PaperArticle

Multi-Sensor Satellite Data Processing for Marine Traffic Understanding

by Marco Reggiannini and Luigi Bedini

Electronics 2019, 8(2), 152; https://doi.org/10.3390/electronics8020152 - 01 Feb 2019

Cited by 12 | Viewed by 3136

Abstract

The work described in this document concerns the estimation of the kinematics of a navigating vessel. This task can be accomplished through the exploitation of satellite-borne systems for Earth observation. Indeed, Synthetic Aperture Radar (SAR) and optical sensors installed aboard satellites (European Space [...] Read more.

The work described in this document concerns the estimation of the kinematics of a navigating vessel. This task can be accomplished through the exploitation of satellite-borne systems for Earth observation. Indeed, Synthetic Aperture Radar (SAR) and optical sensors installed aboard satellites (European Space Agency Sentinel, ImageSat International Earth Remote Observation System, Italian Space Agency Constellation of Small Satellites for Mediterranean basin Observation) return multi-resolution maps providing information about the marine surface. A moving ship represented through satellite imaging results in a bright oblong object, with a peculiar wake pattern generated by the ship’s passage throughout the water. By employing specifically tailored computer vision methods, these vessel features can be identified and individually analyzed for what concerns geometrical and radiometric properties, backscatterers spatial distribution and the spectral content of the wake components. This paper proposes a method for the automatic detection of the vessel’s motion-related features and their exploitation to provide an estimation of the vessel velocity vector. In particular, the ship’s related wake pattern is considered as a crucial target of interest for the purposes mentioned. The corresponding wake detection module has been implemented adopting a novel approach, i.e., by introducing a specifically tailored gradient estimator in the early processing stages. This results in the enhancement of the turbulent wake detection performance. The resulting overall procedure may also be included in marine surveillance systems in charge of detecting illegal maritime traffic, combating unauthorized fishing, irregular migration and related smuggling activities. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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15 pages, 5814 KiB

Open AccessArticle

Improved ISRJ-Based Radar Target Echo Cancellation Using Frequency Shifting Modulation

by Qihua Wu, Feng Zhao, Junjie Wang, Xiaobin Liu and Shunping Xiao

Electronics 2019, 8(1), 46; https://doi.org/10.3390/electronics8010046 - 01 Jan 2019

Cited by 25 | Viewed by 4260

Abstract

Target echo cancellation is an ingenious method that protects the target of interest (TOI) from being detected by radar. Interrupted-sampling repeater jamming (ISRJ) is a novel deception jamming method for linear frequency modulation (LFM) radar countermeasures, which has been applied in target echo [...] Read more.

Target echo cancellation is an ingenious method that protects the target of interest (TOI) from being detected by radar. Interrupted-sampling repeater jamming (ISRJ) is a novel deception jamming method for linear frequency modulation (LFM) radar countermeasures, which has been applied in target echo cancellation recently. Compared with the conventional cancellation method, not only can the target echo be successfully cancelled at radar receiver, but a train of false targets is also produced and forms deception jamming by applying the ISRJ technique. In this paper, an improved radar target echo cancellation method based on ISRJ is proposed that utilizes an extra frequency shifting modulation on the intercepted LFM radar signal. The jammer power is more efficiently utilized by the proposed method. Moreover, more flexible multi-false-target deception jamming can be obtained by adjusting the interrupted sampling frequency. The real target remains effectively protected by the false preceding target in the presence of amplitude mismatch of cancellation signal and target echo. Numerical simulations and measured data experiments are conducted to demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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15 pages, 9891 KiB

Open AccessFeature PaperArticle

A Synthetic Aperture Radar (SAR)-Based Technique for Microwave Imaging and Material Characterization

by Yuri Álvarez López, María García Fernández, Raphael Grau and Fernando Las-Heras

Electronics 2018, 7(12), 373; https://doi.org/10.3390/electronics7120373 - 02 Dec 2018

Cited by 9 | Viewed by 4346

Abstract

This contribution presents a simple and fast Synthetic Aperture Radar (SAR)-based technique for microwave imaging and material characterization from microwave measurements acquired in tomographic systems. SAR backpropagation is one of the simplest and fastest techniques for microwave imaging. However, in the case of [...] Read more.

This contribution presents a simple and fast Synthetic Aperture Radar (SAR)-based technique for microwave imaging and material characterization from microwave measurements acquired in tomographic systems. SAR backpropagation is one of the simplest and fastest techniques for microwave imaging. However, in the case of heterogeneous objects and media, a priori information about the constitutive parameters (conductivity, permittivity) is needed for an accurate imaging. In some cases, a first guess of the constitutive parameters can be extracted from an uncorrected SAR image, and then the estimated parameters can be introduced in a second step to correct the SAR image. The main advantage of this methodology is that there is little or no need for a priori information about the object to be imaged. Besides, calculation time is not significantly increased with respect to conventional SAR, thus allowing real-time imaging capabilities. The methodology has been validated by means of measurements acquired in a cylindrical setup. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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18 pages, 9414 KiB

Open AccessArticle

Unmanned Aerial Vehicle Recognition Based on Clustering by Fast Search and Find of Density Peaks (CFSFDP) with Polarimetric Decomposition

by Hao Wu, Bo Pang, Dahai Dai, Jiani Wu and Xuesong Wang

Electronics 2018, 7(12), 364; https://doi.org/10.3390/electronics7120364 - 01 Dec 2018

Cited by 10 | Viewed by 3030

Abstract

Unmanned aerial vehicles (UAV) have become vital targets in civilian and military fields. However, the polarization characteristics are rarely studied. This paper studies the polarization property of UAVs via the fusion of three polarimetric decomposition methods. A novel algorithm is presented to classify [...] Read more.

Unmanned aerial vehicles (UAV) have become vital targets in civilian and military fields. However, the polarization characteristics are rarely studied. This paper studies the polarization property of UAVs via the fusion of three polarimetric decomposition methods. A novel algorithm is presented to classify and recognize UAVs automatically which includes a clustering method proposed in “Science”, one of the top journals in academia. Firstly, the selection of the imaging algorithm ensures the quality of the radar images. Secondly, local geometrical structures of UAVs can be extracted based on Pauli, Krogager, and Cameron polarimetric decomposition. Finally, the proposed algorithm with clustering by fast search and find of density peaks (CFSFDP) has been demonstrated to be better than the original methods under the various noise conditions with the fusion of three polarimetric decomposition methods. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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23 pages, 1111 KiB

Open AccessArticle

Sparse DOD/DOA Estimation in a Bistatic MIMO Radar With Mutual Coupling Effect

by Peng Chen, Zhenxin Cao, Zhimin Chen and Chunhua Yu

Electronics 2018, 7(11), 341; https://doi.org/10.3390/electronics7110341 - 21 Nov 2018

Cited by 21 | Viewed by 3392

Abstract

The unknown mutual coupling effect between antennas significantly degrades the target localization performance in the bistatic multiple-input multiple-output (MIMO) radar. In this paper, the joint estimation problem for the direction of departure (DOD) and direction of arrival (DOA) is addressed. By exploiting the [...] Read more.

The unknown mutual coupling effect between antennas significantly degrades the target localization performance in the bistatic multiple-input multiple-output (MIMO) radar. In this paper, the joint estimation problem for the direction of departure (DOD) and direction of arrival (DOA) is addressed. By exploiting the target sparsity in the spatial domain and formulating a dictionary matrix with discretizing the DOD/DOA into grids, compressed sensing (CS)-based system model is given. However, in the practical MIMO radar systems, the target cannot be precisely on the grids, and the unknown mutual coupling effect degrades the estimation performance. Therefore, a novel CS-based DOD/DOA estimation model with both the off-grid and mutual coupling effect is proposed, and a novel sparse reconstruction method is proposed to estimate DOD/DOA with updating both the off-grid and mutual coupling parameters iteratively. Moreover, to describe the estimation performance, the corresponding Cramér–Rao lower bounds (CRLBs) with all the unknown parameters are theoretically derived. Simulation results show that the proposed method can improve the DOD/DOA estimation in the scenario with unknown mutual coupling effect, and outperform state-of-the-art methods. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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16 pages, 537 KiB

Open AccessArticle

Direct Position Determination of Coherent Pulse Trains Based on Doppler and Doppler Rate

by Guizhou Wu, Min Zhang, Fucheng Guo and Xuebing Xiao

Electronics 2018, 7(10), 262; https://doi.org/10.3390/electronics7100262 - 22 Oct 2018

Cited by 10 | Viewed by 3077

Abstract

Direct Position Determination (DPD) of coherent pulse trains using a single moving sensor is considered in this paper. Note that when a large observation window and relative maneuvering course between emitter and receiver both exist, the localization accuracy of Doppler frequency shift only [...] Read more.

Direct Position Determination (DPD) of coherent pulse trains using a single moving sensor is considered in this paper. Note that when a large observation window and relative maneuvering course between emitter and receiver both exist, the localization accuracy of Doppler frequency shift only based DPD will decline because of the noticeable Doppler frequency shift variations. To circumvent this problem, a Doppler frequency shift and Doppler rate based DPD approach using a single moving sensor is proposed in this paper. First, the signal model of the intercepted coherent pulse trains is established where the Doppler rate is taken into consideration. Then, the Maximum Likelihood based DPD cost function is given, and the Cramer–Rao lower bound (CRLB) on localization is derived whereafter. At last, the Monto Carlo simulations demonstrate that in one exemplary scenario the Doppler frequency shift variations are noticeable with a large observation window and the proposed method has superior performance to the DPD, which is only based on the Doppler frequency shift. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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13 pages, 513 KiB

Open AccessArticle

Position Estimation of Automatic-Guided Vehicle Based on MIMO Antenna Array

by Zhimin Chen, Xinyi He, Zhenxin Cao, Yi Jin and Jingchao Li

Electronics 2018, 7(9), 193; https://doi.org/10.3390/electronics7090193 - 11 Sep 2018

Cited by 12 | Viewed by 3426

Abstract

The existing positioning methods for the automatic guided vehicle (AGV) in the port can not achieve high location precision, Therefore, a novel multiple input multiple output (MIMO) antenna radar positioning scheme is proposed in this paper. The positioning problem for AGV is considered, [...] Read more.

The existing positioning methods for the automatic guided vehicle (AGV) in the port can not achieve high location precision, Therefore, a novel multiple input multiple output (MIMO) antenna radar positioning scheme is proposed in this paper. The positioning problem for AGV is considered, and the joint estimation problem for direction of departure (DoD) and direction of arrival (DoA) is addressed in the multiple-input multiple-output (MIMO) radar system. With the radar detect the transponder and estimate the DoA/DoD, the relative location between the transponder and the AGV can be obtained. The corresponding Cramér–Rao lower bounds (CRLBs) for the target parameters are also derived theoretically. Finally, we compare the positioning accuracy of the traditional global position system (GPS) with the proposed MIMO radar system. Simulation results show that the proposed method can achieve better performance than the traditional GPS. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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12 pages, 3324 KiB

Open AccessArticle

Saliency Preprocessing Locality-Constrained Linear Coding for Remote Sensing Scene Classification

by Lipeng Ji, Xiaohui Hu and Mingye Wang

Electronics 2018, 7(9), 169; https://doi.org/10.3390/electronics7090169 - 30 Aug 2018

Cited by 3 | Viewed by 2886

Abstract

Locality-constrained Linear Coding (LLC) shows superior image classification performance due to its underlying properties of local smooth sparsity and good construction. It encodes the visual features in remote sensing images and realizes the process of modeling human visual perception of an image through [...] Read more.

Locality-constrained Linear Coding (LLC) shows superior image classification performance due to its underlying properties of local smooth sparsity and good construction. It encodes the visual features in remote sensing images and realizes the process of modeling human visual perception of an image through a computer. However, it ignores the consideration of saliency preprocessing in the human visual system. Saliency detection preprocessing can effectively enhance a computer’s perception of remote sensing images. To better implement the task of remote sensing image scene classification, this paper proposes a new approach by combining saliency detection preprocessing and LLC. This saliency detection preprocessing approach is realized using spatial pyramid Gaussian kernel density estimation. Experiments show that the proposed method achieved a better performance for remote sensing scene classification tasks. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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12 pages, 418 KiB

Open AccessArticle

Designing Constant Modulus Sequences with Good Correlation and Doppler Properties for Simultaneous Polarimetric Radar

by Fulai Wang, Chen Pang, Yongzhen Li and Xuesong Wang

Electronics 2018, 7(8), 153; https://doi.org/10.3390/electronics7080153 - 20 Aug 2018

Cited by 8 | Viewed by 3154

Abstract

Simultaneous polarimetric radar transmits a pair of orthogonal waveforms both of which must have good auto- and cross-correlation properties. Besides, high Doppler tolerance is also required in measuring the highly maneuvering targets. A new method for the design of sequences with good correlation [...] Read more.

Simultaneous polarimetric radar transmits a pair of orthogonal waveforms both of which must have good auto- and cross-correlation properties. Besides, high Doppler tolerance is also required in measuring the highly maneuvering targets. A new method for the design of sequences with good correlation and Doppler properties is proposed. We formulate a fourth-order polynomial, but unconstrained, minimization problem. An iterative algorithm based on the gradient method on the phases is applied to solve it. Numerical results demonstrate the superiority of the proposed algorithm compared to the previous state-of-the-art method. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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20 pages, 5731 KiB

Open AccessArticle

An Inverse Synthetic Aperture Ladar Imaging Algorithm of Maneuvering Target Based on Integral Cubic Phase Function-Fractional Fourier Transform

by Yakun Lv, Yanhong Wu, Hongyan Wang, Lei Qiu, Jiawei Jiang and Yang Sun

Electronics 2018, 7(8), 148; https://doi.org/10.3390/electronics7080148 - 15 Aug 2018

Cited by 11 | Viewed by 3840

Abstract

When imaging maneuvering targets with inverse synthetic aperture ladar (ISAL), dispersion and Doppler frequency time-variation exist in the range and cross-range echo signal, respectively. To solve this problem, an ISAL imaging algorithm based on integral cubic phase function-fractional Fourier transform (ICPF-FRFT) is proposed [...] Read more.

When imaging maneuvering targets with inverse synthetic aperture ladar (ISAL), dispersion and Doppler frequency time-variation exist in the range and cross-range echo signal, respectively. To solve this problem, an ISAL imaging algorithm based on integral cubic phase function-fractional Fourier transform (ICPF-FRFT) is proposed in this paper. The accurate ISAL echo signal model is established for a space maneuvering target that quickly approximates the uniform acceleration motion. On this basis, the chirp rate of the echo signal is quickly estimated by using the ICPF algorithm, which uses the non-uniform fast Fourier transform (NUFFT) method for fast calculations. At the best rotation angle, the range compression is realized by FRFT and the range dispersion is eliminated. After motion compensation, separation imaging of strong and weak scattering points is realized by using ICPF-FRFT and CLEAN technique and the azimuth defocusing problem is solved. The effectiveness of the proposed method is verified by a simulation experiment of an aircraft scattering point model and real data. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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Review

Jump to: Editorial, Research

18 pages, 13829 KiB

Open AccessFeature PaperReview

Review of the Comprehensive SAR Approach to Identify Scattering Mechanisms of Radar Backscatter from Vegetated Terrain

by Motofumi Arii, Hiroyoshi Yamada, Shoichiro Kojima and Masato Ohki

Electronics 2019, 8(10), 1098; https://doi.org/10.3390/electronics8101098 - 29 Sep 2019

Cited by 8 | Viewed by 5774

Abstract

In a field of polarimetric synthetic aperture radar (SAR) remote sensing, various kinds of polarimetric decomposition techniques have been proposed. However, poor validations prevent them from operational applications. A true composition ratio of scattering mechanisms within a radar backscatter plays a key role. [...] Read more.

In a field of polarimetric synthetic aperture radar (SAR) remote sensing, various kinds of polarimetric decomposition techniques have been proposed. However, poor validations prevent them from operational applications. A true composition ratio of scattering mechanisms within a radar backscatter plays a key role. To overcome the issue, a novel comprehensive SAR approach to accurately identify a contribution of each scattering mechanism has been introduced. This is based on multiparametric SAR observation combined with a numerical model simulation. In this article, a comprehensive SAR approach is concisely reviewed to accelerate the research in this field. First, popular model-based polarimetric decompositions are introduced and their limitations are shown. Then, a behavior of scattering mechanisms is analyzed by the discrete scatterer model with some results using real multiparametric SAR data. A comprehensive SAR approach must be essential to realize an operational use of polarimetric SAR data. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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23 pages, 2125 KiB

Open AccessReview

Analytical Approach in the Development of RF MEMS Switches

by Igor E. Lysenko, Alexey V. Tkachenko, Elena V. Sherova and Alexander V. Nikitin

Electronics 2018, 7(12), 415; https://doi.org/10.3390/electronics7120415 - 10 Dec 2018

Cited by 24 | Viewed by 5448

Abstract

Currently, the technology of microelectromechanical systems is widely used in the development of high-frequency and ultrahigh-frequency devices. The most important requirements for modern and advanced devices of the ultra-high-frequency range are the reduction of weight and size characteristics, power consumption with an increase [...] Read more.

Currently, the technology of microelectromechanical systems is widely used in the development of high-frequency and ultrahigh-frequency devices. The most important requirements for modern and advanced devices of the ultra-high-frequency range are the reduction of weight and size characteristics, power consumption with an increase in their functionality, operating frequency and level of integration. Radio frequency microelectromechanical switches are developed using the technology of the manufacture of CMOS-integrated circuits. Integrated radio frequency control circuits require low control voltages, the high ratio of losses to the isolation in the open and closed condition, high performance and reliability. This review is devoted to the analytical approach based on the knowledge of materials, basic performance indices and mechanisms of failure, which can be used in the development of radio-frequency microelectromechanical switches. Full article

(This article belongs to the Special Issue Advanced Technology Related to Radar Signal, Imaging, and Radar Cross-Section Measurement)

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