Radar Parameters Research Articles

Fine grid model for the dielectric characteristics of ground‐penetrating radar in mixed media

ABSTRACTThe Fisher–Yates random shuffling algorithm combined with the finite‐difference time‐domain method is proposed to construct a fine grid model for the forward simulation of ground‐penetrating radar in mixed media. First, the finite‐difference time‐domain method was used to divide the coarse grid model into several fine grid models by conforming to the boundary conditions of different media, and the corresponding dielectric parameters were assigned to Yee cells in each fine grid model. Then, the Fisher–Yates random shuffling algorithm was used to randomly scramble all Yee cells with equal probability, and the array of scrambled Yee cells was recombined into a coarse grid model. Finally, the geoelectric model of mixed media was generated with the finite‐difference time‐domain method, and a ground‐penetrating radar image excited by electromagnetic wave pulses was obtained. To explore the characteristic signals and dielectric properties of the ground‐penetrating radar electromagnetic response in mixed media, image entropy theory was used to describe the ground‐penetrating radar image, and waveform analysis and wavelet transform mode maximum methods were used to analyse the single‐channel ground‐penetrating radar signal of the mixed media. The results showed that the Fisher–Yates random shuffling–finite‐difference time‐domain method can be used to construct a valid and stable fine grid model for simulating ground‐penetrating radar in mixed media. The model effectively inhibits electromagnetic attenuation and energy dissipation, and the wavelet transform mode maximum method explains the relative dielectric permittivity distribution of the mixed media. The findings of this study can be used as a theoretical basis for correcting radar parameters and interpreting images when ground‐penetrating radar is applied to mixed media.

Can the Correlation between Radar and Cloud-to-Ground Daily Fields Help to Identify the Different Rainfall Regimes? The Case of Catalonia

The rainfall regime is changing in the Catalan territory, likely in most areas in the Mediterranean Basin. This variability, spatial and temporal, means that there may be periods of severe drought combined with periods of heavy rainfall and floods. In this way, the management of water resources is complicated and can produce a high impact on different social aspects. The high convective activity leads to investigating the relationship between the electric discharges and radar parameters (reflectivity, echo top, vertically integrated liquid, and accumulated rainfall). The correlation allows identifying some elements that may be significant in terms of changes in rainfall regimes. Besides, using several radar parameters apart from precipitation accumulation reveals interesting explicit patterns of the previously known. These patterns can help better understand the precipitation behavior and the changes associated with it.

CFAR Detector Based on the Identification of Sea Clutter Distribution Characteristics

To improve the capability of radar detection in a time-varying maritime environment, an algorithm was proposed and analyzed in this paper that can be applied to determine the shape and scale parameters of the K-distributed model using the radar parameters and environmental information under the context of K-distributed sea clutter, and improved the original algorithm to improve the accuracy of the parameter estimation algorithm. Furthermore, a CFAR detector capable of identifying the characteristics of sea clutter distribution was developed. It can estimate the parameters of K-distributed model for sea clutter in real time using both radar parameters and environmental perception information, thus improving the accuracy of clutter background estimation. When the false alarm rate reaches a certain level, the adaptive threshold factor can be obtained for the CFAR detector proposed in this paper, thus improving the effectiveness of control on the CFAR detector. As suggested by the simulation results, the proposed method outperforms the CFAR detector with fixed parameters in the capability of detection and robustness under the context of K-distributed clutter.

Уровни и этапы проектирования и исследования перспективных радиолокационных станций в отечественной специализированной САПР

The article is devoted to the design stages and levels in the developed Russian computer-aided design (CAD) system of radars. The concept of design in CAD is presented. Established three levels of radar design: system, structural, functional-logical. The radar design route is described. It consists of the stages of preliminary assessment of radar parameters, engineering analysis, simulation modeling of the use of radar as part of military defense systems, finding optimal variants of the radar composition.

Theory of Radar Polarimetric Interferometry and Its Application to the Retrieval of Sea Ice Elevation in the Western Weddell Sea, Antarctic

AbstractSea ice elevation plays a crucial role in sea ice dynamic processes driven by winds and waves, for which satellite radar remote sensing becomes indispensable to monitor snow‐covered sea ice across the vast polar regions regardless of darkness and clouds. To measure sea ice elevation, a theory of polarimetric interferometry for both monostatic and bistatic radars is developed based on analytic solutions of Maxwell's equations, accounting for realistic and complicated properties of snow, sea ice, and seawater. This analytic method inherently preserves phase information that is imperative for radar polarimetry and interferometry. Among a multitude of complex radar coefficients in the general polarimetric interferometric covariance matrix, the symmetry group theory is utilized to identify and select appropriate terms pertaining to the retrieval of sea ice elevation while avoiding radar parameters that may inadvertently introduce non‐uniqueness and excessive uncertainty. Theoretical calculations compare well with field observations for rough and old sea ice encountered in the Operation‐IceBridge and TanDEM‐X Antarctic Science Campaign over the Western Weddell Sea. The results show that the magnitude of the coefficient of normalized correlation between co‐polarized horizontal and co‐polarized vertical radar returns is inversely related to sea ice elevation, while the associate phase term is nonlinear and noisy and should be excluded. From these analyses, a protocol is set up to measure Antarctic sea ice elevation to be presented in the next companion paper.

Analysis of Small Sea-Surface Targets Detection Performance According to Airborne Radar Parameters in Abnormal Weather Environments.

Along with the rapid development of marine radar, and particularly those carried on aircraft, the detection of small-sized targets which pose an increasing threat has become one of the main areas of interest. However, by considering an observation chain from an aircraft (such as a drone) in a maritime environment, with the aim of detecting and tracking of low signal-to-clutter ratio (SCR) targets, one of the important points would be the analysis of the radar system performance according to the radar input parameters, the atmospheric propagation medium, the various sea clutter characterization, and the type of targets (RCS, speed, etc.) in this environment. Therefore, it is necessary to obtain the overall path loss including the anomalous atmospheric environment, gas attenuation, clouds attenuation, rainfall attenuation, and beam scanning loss. To consider atmospheric attenuations, ITU-R models are used. On another side, because of spikes and dynamic variation properties, sea clutter is generally described by the statistical distribution with long tail and by its wider Doppler spectrum. Conventional algorithms such as those based on statistical models, MTI, and MTD processing are often limited, especially for the target of low speed and low RCS. Therefore, sea clutter, including empirical and statistical models available, is considered to estimate and simulate the impact of radar input parameters, targets RCS, and sea state on detection performance. The Doppler frequency of target echo which can be exploited for coherent processing is described by assuming an adequate scenario of observation geometry.

The model of radar observation of the surface vibration waves generated by earthquake source (ground vibrator)

This research article is continuation case study based on a model of radar monitoring of vibration waves occurring on the sea surface near the source of a bottom earthquake. The vibration wave is generated parametrically, has near (hydrodynamic) and far (sound) components. The amplitude of the near (generating) wave depends on the bottom vibrator parameters and the depth of the bottom, the far wave propagates in the waveguide formed by the surface and the flat bottom. The vibrator will be installed at a shallow depth (30 m) and the modern aircraft radar will be used to create amplitude and velocity radar images during the experiment. The length of the generated vibration wave will be ~1.5 cm, which corresponds to the frequency of the generating wave ~30 Hz and the “resonant” wave of the radar with a length of ~3 cm (radar X-band). The possibility of monitoring vibration waves in the amplitude and velocity channels of the SAR (synthetic aperture radar) in L, P and UHF-bands is estimated. Also, the expected view of the SAR images is shown. Calculations of the necessary parameters of the aircraft radar are provided, including algorithms for processing the initial signal when creating amplitude and velocity radar images of vibration waves.

An observational analysis of two companion supercell storms over complex terrain

This article analyses two long-lived supercell thunderstorms formed on 11th May 2017 afternoon in a complex topographic area in northern Catalonia (NE Iberian Peninsula). The objectives of this paper are (i) to document a case study that affected a mountainous region in the southern side of the Pyrenees, (ii) to describe thermodynamic and dynamic environmental conditions, (iii) to study how the topography affects the life cycle of both storm cells and (iv) to demonstrate the high correlation between Lightning Jump and radar parameters in complex terrain. ERA5 reanalysis was used to assess the synoptic framework and environmental storm conditions, whereas remote-sensing data (Doppler radar, satellite and lightning observations) and terrain characteristics were considered to study the evolution of both cells. Reanalysis data revealed some differences between preconvective environments for both thunderstorms, showing more favourable conditions for supporting supercells (i.e. stronger deep-layer shear) for the first thunderstorm than for the second one. The analysis suggests substantial interaction between topography and storm cells, influencing their internal dynamics and the development of mesocyclones. The results of this study contribute to enhance our understanding of supercell storms evolution on mountain areas and may be useful to increase the situational awareness of weather forecasters in future similar convective storm events over complex terrain regions.

Signal Simulation of Dual-Polarization Weather Radar and Its Application in Range Ambiguity Mitigation

In this paper, a dual-polarization weather radar echo signal simulation method is proposed for the evaluation of the performance enhancement of dual-polarization weather radar systems, the optimization of signal processing algorithms and the improvement of scanning strategies. The actual weather radar base data are used in the simulation as the reference weather scene, which avoids using a complex algorithm for weather modeling. Moreover, based on radar weather equations, the radar system parameters are added into the radar echo signal modeling to establish the relationship between the simulated echo signal and radar system. As a result, the final simulated echo signal not only shows both the time and frequency domain characteristics of the weather target, but also includes the effects of the important performance of the dual-polarization weather radar system. In addition, to evaluate the performance of range ambiguity mitigation using phase coding and batch working modes, two different simulation methods for the radar signal are established on the method above; one is for batch working mode with long-PRT (pulse repetition time) and short-PRT transmission and receiving, and the other is for phase-coded mode with phase-coded transmission and phase-uncoded receiving. Under the same weather scene, the observation of these two different methods of range ambiguity mitigation are simulated and compared. Results show that the performance of the phase coding mode for mitigating range ambiguity is better than that of the batch mode. Obviously, the simulation method can be used to directly show the observation of different algorithms for mitigation range ambiguity under the same weather process, and quickly compare and evaluate the algorithm’s performance, which is not possible for real radars.

Radar Signal Intrapulse Modulation Recognition Based on a Denoising-Guided Disentangled Network

Accurate recognition of radar modulation mode helps to better estimate radar echo parameters, thereby occupying an advantageous position in the radar electronic warfare (EW). However, under low signal-to-noise ratio environments, recent deep-learning-based radar signal recognition methods often perform poorly due to the unsuitable denoising preprocess. In this paper, a denoising-guided disentangled network based on an inception structure is proposed to simultaneously complete the denoising and recognition of radar signals in an end-to-end manner. The pure radar signal representation (PSR) is disentangled from the noise signal representation (NSR) through a feature disentangler and used to learn a radar signal modulation recognizer under low-SNR environments. Signal noise mutual information loss is proposed to enlarge the gap between the PSR and the NSR. Experimental results demonstrate that our method can obtain a recognition accuracy of 98.75% in the −8 dB SNR and 89.25% in the −10 dB environment of 12 modulation formats.

Neural Network-Based Control of an Adaptive Radar

This article demonstrates the use of a neural network to replace the nonlinear optimization at the core of a fully adaptive radar (FAR) system. Use of the neural network is shown to reduce computational complexity, leading to faster updates of the radar parameters. The feed-forward neural networks used were trained using the Levenberg–Marquardt algorithm along with a generalized regression neural network architecture. Training data was obtained from an existing FAR optimization system using the system’s parameter selections and target states for single-target tracking in range and velocity. The trained networks were then used to perform radar parameter selection based on the predicted (forward propagation of prior probabilities) probabilities represented by the target state (target range, velocity, and signal-to-noise ratio) and error variance (target range and velocity variance). The trained neural network was able to reduce the average optimization time by an order of magnitude while obtaining on average a lower resource consumption and similar radar task performance.

Улучшение характеристик космических РСА в режимах высокого разрешения

The methods of increasing the size of the radar image obtained by space radars with synthesized aperture in high-resolution mode are analyzed. The image size increase is achieved due to the extended scanning of the antenna beam in the azimuthal plane. The basis of the considered methods is the classical searchlight mode. The modes of composite (multi-frame) searchlight shooting and sliding searchlight shooting are compared. The dependences of azimuthal resolution and frame size on the size of the scanning sector are estimated. Numerical examples are based on the parameters of COSMO-SkyMed and TerraSAR-X radars. A list of the main ways to increase scanning is provided. A brief description of the Staring Spotlight mode is given, as an example, which allows to significantly increase the detail and quality of images.

Adaptive Time-Space Resource and Waveform Control for Collocated MIMO Radar with Simultaneous Multi-Beam

Collocated multiple input multiple output (MIMO) radar, which has agile multi-beam working mode, can offer enhanced multiple targets tracking (MTT) ability. In detail, it can illuminate different targets simultaneously with multi-beam or one wide beam among multi-beam, providing greater degree of freedom in system resource control. An adaptive time-space resource and waveform control optimization model for the collocated MIMO radar with simultaneous multi-beam is proposed in this paper. The aim of the proposed scheme is to improve the overall tracking accuracy and meanwhile minimize the resource consumption under the guarantee of effective targets detection. A resource and waveform control algorithm which integrates the genetic algorithm (GA) is proposed to solve the optimization problem. The optimal transmitting waveform parameters, system sampling period, sub-array number, binary radar tracking parameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\chi_i(t_k)$</tex> , transmitting energy and multi-beam direction vector combination are chosen adaptively, where the first one realizes the waveform control and the latter five realize the time-space resource allocation. Simulation results demonstrate the effectiveness of the proposed control method.

Influence of Public Mobile Communication System on the Frequency of S-Band Radars

Given the interference between public mobile communication system and S-band radars, an applicable interference analysis model was established, the typical frequency parameters of radar and the key parameters of the base station were sorted out, the radiation parameters of the mobile terminal (MT) were tested practically, and the interferences of the base station and MT to radar were calculated. Further, the Monte Carlo method was taken to simulate the system-level lumped interference of the communication system to radar, and an analysis was made on the influence of the communication system on the frequency of radar. The results revealed that the public mobile communication system had severe lumped interference with radar, which may affect radar frequency. Therefore, it is necessary to take measures to protect radar.

Numerical Simulation of SAR Image for Sea Surface

Based on the simulated signal, a numerical simulation method of synthetic aperture radar (SAR) imaging for time-varying sea surfaces is proposed, which is helpful to study the SAR imaging mechanism of time-varying sea surfaces so as to better extract ocean wave parameters from SAR images. Not only are the modulation of ocean waves, speckle noise, and temporal decorrelation of the small-scale waves considered, but the velocity bunching (VB) effect caused by the motion of large-scale waves is also effectively added to the simulation of the SAR echo signal. To verify the reliability of the simulation method, the simulated SAR images using the parameters of the RADARSAT-2 SAR, the corresponding wind wave information measured by an in-situ buoy, and the reanalysis wave spectra have been compared with the actual RADARSAT-2 SAR images. The comparisons demonstrate that the characteristics of simulated SAR images, such as the intensity distribution and the image spectra, are consistent with those of actual RADARSAT-2 SAR images. Based on the numerical simulation method proposed by us, SAR images of ocean waves for different marine environments and radar platform parameters are simulated. The imaging results indicate that the texture feature of the wind waves would be severely damaged due to the VB effect, while the texture of swells in the simulated SAR images may not be damaged or even becomes clearer. From the simulated SAR image spectrum, it can be found that the azimuth wavenumber is cut off when the VB effect is considered in the simulation process, and the azimuth cut-off wavelength increases with the range-to-velocity ratio.

Multi-Layer Overlapped Subaperture Algorithm for Extremely-High-Squint High-Resolution Wide-Swath SAR Imaging with Continuously Time-Varying Radar Parameters

Extremely-high-squint (EHS) geometry of the traditional constant-parameter synthetic aperture radar (SAR) induces non-orthogonal wavenumber spectrum and hence the distortion of point spread function (PSF) in focused images. The method invented to overcome this problem is referred to as new-concept parameter-adjusting SAR. It corrects the PSF distortion by adjusting radar parameters, such as carrier frequency and chirp rate, based on instant data acquisition geometry. In this case, the characteristic of signal is quite different from the constant-parameter SAR and therefore, the traditional imaging algorithms cannot be directly applied for parameter-adjusting SAR imaging. However, the existing imaging algorithm for EHS parameter-adjusting SAR suffers from insufficient accuracy if a high-resolution wide-swath (HRWS) performance is required. Thus, this paper proposes a multi-layer overlapped subaperture algorithm (ML-OSA) for EHS HRWS parameter-adjusting SAR imaging with three main contributions: First, a more accurate signal model with time-varying radar parameters in high-squint geometry is derived. Second, phase errors are compensated with much higher accuracy by implementing multiple layers of coarse-to-fine spatially variant filters. Third, the analytical swath limit of the ML-OSA is derived by considering both the residual errors of signal model and phase compensations. The presented approach is validated via both the point- and extended-target computer simulations.

Increasing self-protection jammer efficiency using radar cross section adaptation

Increasing jamming effectiveness in self-protection electronic warfare systems is a crucial research area for air operations. Of all the factors affecting jamming performance, two parameters that increase jamming efficiency without changing the design parameters of radar and jammer systems are RCS and distance. Changing the distance between radar and target to increase the jamming effect is not sensible. Because disobeying the path for distance concern may ruin the operation aim. Adapting the RCS to the situation appears to be a suitable method to increase the jamming efficiency. In this study, a novel method is proposed for enhancement the jamming effectiveness by changing RCS appropriately. Hence, a heading calculator unit is integrated into the self-protection electronic warfare system. The heading calculator interacts with the radar warning receiver and jammer and points an appropriate heading direction during jamming. The heading variances are limited to as slight changes as possible.

Location-Based Hybrid Precoding Schemes and QoS-Aware Power Allocation for Radar-Aided UAV–UGV Cooperative Systems

Unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) complement each other, promising a variety of benefits for unmanned cooperative systems. When infrastructures for communication are unavailable, such as disaster relief and patrol mission in sparsely populated areas, UGVs can be controlled to go to the esignated areas with the aid of a UAV. Specifically, the UAV hovers over the UGVs, sending commands to the UGVs and obtaining location information from the UGVs. In this paper, we consider integrating millimeter wave communication and UAV–UGV cooperative system. For high mobile unmanned cooperation systems, we develop two joint radar-aided hybrid precoding schemes, which are suitable for a fully connected (FC) hybrid precoding structure and partially connected (PC) hybrid precoding, respectively. Specifically, an effective hybrid precoding scheme is first proposed by using location information to jointly design hybrid precoding and power allocation. Moreover, we also derive the radar parameter estimation problem Cramér-Rao lower bound (CRLB). In order to ensure the minimum quality-of-service (QoS) of UGVs, we propose a QoS-aware power allocation scheme based on the difference-of-two-convex-function (D.C.) programming. Finally, a heuristic hybrid precoding design algorithm, where the analog precoding matrix is usually implemented by low-resolution phase shifters (PSs), is proposed based on antenna dynamic grouping and radar parameter acquisition, with the aim of maximizing the sum-rate of the UAV–UGV cooperative systems. Extensive computer simulation results indicated the validity of the proposed radar-aided location-based hybrid precoding schemes in the UAV–UGV heterogeneous cooperative system.

Scattering Mechanism Analysis of Man-Made Targets via Polarimetric SAR Observation Simulation

Scattering mechanism analysis of a man-made target is critical for polarimetric synthetic aperture radar (PolSAR) image feature extraction and image interpretation. The most straightforward method for scattering mechanism investigation of man-made target is to analyze a huge amount of measured data under various conditions. However, the acquirement of measured data is extremely expensive and time consuming, coupled with its poor reusability, which makes the investigation inefficient and costly. The electromagnetic (EM) simulation is an effective and convenient way to obtain PolSAR data by solving equations describing the EM scattering from target of interest. It is adaptable to any observation condition, targets or environments, which have become a powerful tool commonly used for the study of EM scattering mechanism of target. In this article, an efficient simulation framework for the emulation of PolSAR operation and imaging is proposed. This framework is based on ray tracing integrated with geometrical optics, physical optics, and Kirchhoff approximation. The simulated image of a family car is in good agreement with the measured data of MiniSAR platform. Besides, images of T-72 tank under various observation conditions, radar parameters and terrains are simulated. Freeman decomposition is employed and scattering component percentages of target under different conditions are presented to analyze the scattering mechanism in detail.

Quantitative Evaluation of the Effects of Large-Scale Sea Wave Components on Microwave Backscattering From Ocean Surface

This paper quantitatively examined the effect of these long-wave components with wavelength larger than the Bragg component on radar backscattering using the series-expanded first-order small slope approximation (SSA-1) and the Hwang sea wave spectrum model. Firstly, some roughness with various scales are constructed using different long-wave sea spectrum components and subsequently are cast into SSA-1 to obtain the corresponding normalized backscattering cross-section (NBCS) at different radar frequency, incidence angles, and wind speeds, respectively. Then, the effect of large-scale wave components on radar backscattering is revealed by analyzing the NBCSs with different roughness. Finally, the existing wavelength filtering theory explained the effect of large-scale waves on radar backscattering. It was also verified by another scattering model, i.e., the advanced integral equation model (AIEM) and radar measurements. Besides, we also investigate the effects of sea states and swell waves on the numerical simulation results. The effect of long-scale waves on NBCS clarifies the source of backscattering from the multiscale sea surface, which is helpful for both analytical and numerical scattering models to explore the sea surface scattering properties and better interpret the radar sensing of sea surface. Also, the examination of the effect of sea states and swell waves on radar backscatter is instructive for reducing the inversion errors of sea surface wind speed from radar measurements by means of configuring the appropriate radar parameters (e.g., high frequencies and large incidence angles).