Backscattering Radar Cross Section Research Articles

Backscatter Radar Cross Section Analysis of Chaff Using the Sequential Loading Method

Backscatter Radar Cross Section Analysis of Chaff Using the Sequential Loading Method

Microwave Radar Sensing of Sea Waves: An Effective Reflection Coefficient

At the small incidence angles, the dominant backscattering mechanism for sea waves is the quasi-specular backscattering mechanism. The power of the reflected signal depends on the distribution function of the slopes of large-scale waves (in comparison with radar wavelength) and on the effective reflection coefficient, which is introduced instead of the Fresnel coefficient. In this paper, we discussed a new method for calculating the effective reflection coefficient from the wave scatterometer SWIM data. For the first time, measurements are performed by a radar at different azimuth angles at small incidence angles. This makes it possible to measure the effective reflection coefficient. An original algorithm was developed for data processing and determination of the total mean square slopes of large-scale sea waves and the azimuth dependence of the backscattering radar cross section at zero incidence angle. In the result of subsequent processing, the azimuth dependence of the effective reflection coefficient is retrieved. SWIM data were used to evaluate the developed algorithm. Processing of the test data set confirmed the efficiency of the algorithm. The azimuth anisotropy coefficients for the mean square slopes of large-scale waves and the effective reflection coefficient are calculated

Numerical Simulation of the Radar Cross Section of UHV/EHV Power Lines Illuminated by X-, C-, L-, and P-Band Spaceborne SAR

Many spaceborne synthetic aperture radars (SARs), which operate separately in the X, C, and L bands, have been employed to monitor ultra-high-voltage (UHV) and extra-high-voltage (EHV) power lines. However, a full interpretation of the scattering characteristics of these power lines in spaceborne SAR images remains a challenging task. A numerical simulation of the radar cross-section (RCS) of UHV/EHV power lines in the X, C, L, and P bands over a wide range of incidence angles is presented in this paper. A physical model of the UHV/EHV power line is first built. Here, two practical shapes of the UHV/EHV power line are considered, which include the symmetrical catenary when two suspension points have the same height and the inclined catenary when the heights of two suspension points are different. Then, the multilevel fast multipole algorithm (MLFMA) is used for the analysis of the backscatter behavior of UHV/EHV power lines in the X, C, L, and P bands. The effects of several parameters of practical importance on the backscatter RCS of UHV/EHV power lines are also studied, which include the carrier frequency, polarization type, aspect angle of illumination, span length, height difference between two suspension points, conductor sag, and cable diameter. In addition, several comparisons made between simulated and practical observation results demonstrate that the obtained theoretical results can be used to interpret the scattering characteristics of UHV/EHV power lines in spaceborne SAR images and can provide some useful suggestions for monitoring UHV/EHV power lines using spaceborne SAR images.

Electromagnetic Scattering Characteristics of Blunt Cone Aircraft Under THz Waves Based on PO Method

The physical optics (PO) method based on subregional triangular patch division was used to study the electromagnetic (EM) scattering characteristics of a blunt cone hypersonic vehicle under terahertz (THz) waves in different environments. First, the backscattering radar cross section (RCS) of a metal blunt cone under gigahertz and THz waves was calculated separately; the results show that the RCS under the THz wave has higher accuracy and can better reflect the structural characteristics of the target. Then, the RCS of a blunt cone covered with a plasma sheath at different reentry heights was calculated; the results show that the existence of the plasma sheath will reduce the target RCS, and the degree of reduction is related to the maximum electron density, the frequency of incident waves, and other factors, but THz waves can alleviate this effect. Finally, the RCS of a blunt cone covered with a plasma sheath and radar absorbing material (RAM) at different incident EM wave frequencies were also studied, and some interesting conclusions are preliminarily obtained. Our work can provide a meaningful reference for advancing research on the stealth and anti-stealth capabilities of hypersonic vehicles.

Application of the Doppler Spectrum of the Backscattering Microwave Signal for Monitoring of Ice Cover: A Theoretical View

In the radar remote sensing of sea ice, the main informative parameter is the backscattering radar cross section (RCS), which does not always make it possible to unambiguously determine the kind of scattering surface (ice/sea waves) and therefore leads to errors in estimating the area of the ice cover. This paper provides a discussion of the possibility of using the Doppler spectrum of the reflected microwave signal to solve this problem. For the first time, a semi-empirical model of the Doppler spectrum of a radar microwave signal reflected by an ice cover was developed for a radar with a wide antenna beam mounted on a moving carrier at small incidence angles of electromagnetic waves (0°–19°). To describe the Doppler spectrum of the reflected microwave signal, the following parameters were used: shift and width of the Doppler spectrum, as well as skewness and kurtosis coefficients. Research was conducted on the influence of the main parameters of the measurement scheme (movement velocity, width of antenna beam, sounding direction, incidence angle) and the sea ice concentration (SIC) on the parameters of the Doppler spectrum. It was shown that, in order to determine the kind of scattering surface, it is necessary to use a wide or knife-like (by the incidence angle) antenna. Calculations confirmed the assumption that, when measured from a moving carrier, the Doppler spectrum is a reliable indicator of the transition from one kind of scattering surface to another. The advantage of using the coefficients of skewness and kurtosis in the analysis is that it is not necessary to keep the radar velocity unchanged during the measurement process.

Enhancement of backscattering cross section from an equivalent human cylinder under oblique incidence

An analysis about the enhancement of backscattering radar cross section from an equivalent human body cylinder using a specific type of coating is presented. The types of coatings considered for the human body are taken to inductive meta surface (MS), inductive MS followed by a dielectric layer and an epsilon negative (ENG) metamaterial. An eigenfunction expansion method has been used to derive analytical expressions for the scattered electric and magnetic fields. It is investigated that inductive MS and inductive MS followed by a dielectric layer type of coatings cannot be used to enhance the backscattering radar cross section from the human body. It is found that an ENG metamaterial coating having specific permittivity and coating thickness can be used to significantly enhance the back-scattering radar cross section from the human body under oblique incidence. Therefore, an ENG metamaterial coating is selected for the proposed model and finally, the modelling of the proposed design is suggested.

Wind speed retrieval from Chinese Gaofen-3 synthetic aperture radar using an analytical approach in the nearshore waters of China’s seas

ABSTRACT Empirical wind-retrieval algorithms for synthetic aperture radar (SAR), such as the geophysical model function (GMF) CMOD5N in the C-Band, are currently well developed. The retrieval accuracy of GMFs, however, is lower in the presence of marine phenomena such as oceanic fronts and mesoscale eddies, making SAR wind retrieval challenging under these conditions. In this study, we proposed a scheme for wind retrieval from Chinese Gaofen-3 (GF-3) SAR images using an analytical approach to obtain the wind speed in the nearshore waters of China’s seas. Approximately 300 images were acquired from 2018 to 2021 in the copolarization channels [vertical–vertical (VV) and horizontal–horizontal (HH)]. The images were collocated with the measurements from the Advanced Scatterometer (ASCAT) and the Chinese Haiyang-2B (HY-2B) scatterometer. Our analytical approach was based on the Bragg resonant and non-Bragg (NB) scattering model for the calculation of the normalized radar backscatter cross-section (NRCS), which accounted for the influence of wave-current interactions and breaking waves in nearshore waters. We used the sea surface currents obtained from the HYbrid Coordinate Ocean Model (HYCOM) to simulate the Bragg resonant roughness. We derived the contribution of the NB breaking waves from the SAR-measured NRCS values in both the VV and HH channels. By comparing the retrieval results obtained using the analytical approach with the scatterometer products, we concluded that the root mean square error (RMSE) of the wind speed was 2.01 m s−1 with a 0.91 correlation coefficient (COR), which was less than the 2.93 m s−1 RMSE and 0.72 COR for the GMF CMOD5N. The variation in the bias of the HYCOM currents was approximately 1 m s−1 for current speeds greater than 0.3 m s−1. These findings verified the stability of the analytical approach for SAR wind retrieval in complex sea states.

Microsized Graphene Helmholtz Resonator on Circular Dielectric Rod: A Tunable Sub-THz Frequency-Selective Scatterer

A novel miniature THz resonator consisting of a finite-length slotted graphene cylinder wrapped around an infinite circular dielectric rod is proposed. A full-wave 3-D electromagnetic scattering model is built using the method of moments (MoM) solution of the electric-field integral equation (EFIE) in the spectral domain. In order to gain a better understanding of the associated physical effects, the obtained results are compared with a 2-D model where the slotted graphene cylinder is assumed infinite. A good agreement between the 3-D and 2-D models is found. The dependence of the backscattering radar cross section on the frequency is analyzed. It is found that in both cases this scatterer displays quasi-static Helmholtz resonance (HR) response in the sub-THz frequency range, a behavior previously known for perfectly electrically conducting (PEC) slotted cylinders. For both models, in-resonance surface current distributions and far-zone radiation patterns are given. The most important innovation is that due to the use of graphene the Helmholtz-mode resonance becomes electrically tunable.

Scattering Characteristics of an Electrically-Large Aircraft Object Illuminated by Bessel Vortex Beams

Based on the excellent and broad prospect of the vortex beams in military application, it is necessary to evaluate the scattering characteristics of classical Bessel beam upon a perfect electrical conductor (PEC) blunt cone model of aircraft structure. First, a Bessel beam is expanded by a series of plane wave spectra. Then, combining the physical optics (PO) method, the scattered field of the object fitted by facet elements can be calculated. The amplitude, phase, and orbital angular momentum (OAM) spectra of scattered field for different object attitudes are discussed in detail. The results show that the backward scattering still retains good OAM characteristics, and which are distorted with the increase of oblique angle. Besides, the backscattering radar cross section (BRCS) of aircraft are also calculated and analyzed, and the scattering results of degenerated zero-order Bessel beam and plane wave are compared to verify the correctness of the proposed theory. Compared with plane waves, object scattering of vortex beams provides a new degree of freedom, providing more information for object detection.

Measurements of Total Sea Surface Mean Square Slope Field Based on SWIM Data

The total mean square slope (mss) of large-scale (in comparison with the scale of radar wavelengths) ocean waves can describe the roughness of the ocean surface. This important parameter has found many applications and can be determined by the dependence of large-scale mss on azimuthal angles. The Surface Waves Investigation and Monitoring instrument onboard the China France Oceanography Satellite (CFOSAT) can provide a two-dimensional (2D) normalized backscattering radar cross section (NRCS) for 2D global ocean-surface wave detection. In this paper, the 2D NRCS is used to calculate the total large-scale mss via two methods. The first method is constructed from regression, while the second scheme is derived from a three-solution method. Finally, the total large-scale mss are calculated using these methods, and the map of the distribution of the global total mss is presented for the first time. Our results show that the two sources of total large-scale mss obtained are consistent with each other. CFOSAT can provide a 2D total large-scale mss map and be used as a new data resource for global applications.

Electromagnetic waves scattering from an infinite elliptical metal cylinder covered by a plasma layer in presence of external magnetic field

In this paper, scattering of the electromagnetic waves from a metal elliptical cylinder covered by a plasma layer is investigated by the Finite Element-Boundary Integral (FE-BI) method. The under study object that can be supposed as an elliptic complex antenna is located in a constant magnetic field. The inner cylinder can be rotated to plasma cover so that they are nonconfocal. Generally, elliptic antennas have azimuthal asymmetry and their response to electromagnetic waves is sensitive to incident angle of landing wave. This effect is more severe in under study antenna due to its geometrical configuration that depends on the rotating angle of the conducting core related to plasma cover. Furthermore, presence of constant magnetic field along the antenna axis causes permittivity tensor of the plasma as an influential factor in radar cross section, becomes anisotropic. Here, backscattering radar cross section (BRCS) of the antenna is calculated when irradiated by TE and TM waves under different incident angles. It will be shown how one can control BCRS of the antenna by varying its configuration and the external magnetic field intensity. Validation of numerical computations applied in this work is demonstrated by comparing it with an analytical method for a special case.

Advanced View at the Ocean Surface

AbstractImprovement of methods for satellite monitoring of the world ocean state is one of the most important areas of the remote sensing because of the influence the oceans have on the Earth's climate. Currently, only one parameter is measured on a regular basis on a global scale: the significant wave height which is obtained from spaceborne radar altimeter data. It is known that at small incidence angles within the framework of Kirchhoff approximation, the backscattering radar cross section depends mainly on the mean square slope (mss) of the sea surface; therefore, this parameter can be measured. The performed studies lead to the improvement of the methods for processing the data from a precipitation radar. We demonstrate that the mss of the large‐scale (compared to the radar wavelength) sea waves can be restored within the swath, that is, about 115 km wide. The aim of this work is to communicate these new possibilities to the broad research community involved in the studies of the oceans. In this paper, a review of the results is performed and the prospects for global monitoring are first shown. On the basis of the precipitation radar data, it becomes possible to measure global fields of sea wave slopes, which in turn will help scientists to analyze the processes of air‐sea interaction. Availability of this new mss parameter essentially doubles the amount of available descriptors of sea waves, which will advance the understanding of the processes occurring in the oceans.

Simulation and Feature Extraction of the Dynamic Electromagnetic Scattering of a Hypersonic Vehicle Covered with Plasma Sheath

Based on the detection platform of space-borne radar (SBR), the dynamic electromagnetic (EM) scattering characteristics of a hypersonic vehicle covered with plasma sheath are calculated and analyzed by the physical optics (PO) method. Using the angle-time conversion method, the dynamic radar cross section (DRCS) of the vehicle in horizontal flying path and different flying states is solved in the range of L-band to X-band. The relevant effective statistical features are extracted from the time-scale matrix of DRCS based on continuous wavelet transform (CWT). The numerical results show that: At different flying altitudes, the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath has irregular fluctuation and large range reduction in the head region of the vehicle. Generally, the higher the incident EM wave frequency is, the more detailed the fluctuation characteristics of the DRCS can be reflected. Within the same radar illuminate angle range, the time consumed by the vehicle DRCS is inversely proportional to the flying height and flying speed and is directly proportional to the detection altitude of the SBR. Besides, the different kinds of statistical eigenvalues extracted from DRCS will play an important role in hypersonic targets classification and recognition.

Analyzing the Electromagnetic Scattering Characteristics of a Hypersonic Vehicle Based on the Inhomogeneity Zonal Medium Model

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from L-band to X-band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the S-band and the band range of 7-11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets.

Microstrip array antenna in-band RCS reduction using polarization reconfigurable elements

ABSTRACTAn efficient approach for in-band radar cross section (RCS) reduction of microstrip patch array antenna without employing extra-low RCS artificial materials is proposed and analysed. The element of the array has a simple structure, consisting of a corner-cut square patch and two tiny perturbation elements. By controlling two independently biased PIN diodes, it can produce linear polarization (LP), left- and right-handed circular polarization (LHCP/RHCP) radiation waves. The backscattering RCS reduction of the array can be achieved by changing the polarization status of array elements. For verification, the performance of a polarization reconfigurable microstrip array with different polarization modes is designed, compared and analysed. From the simulation and measurement results, the peak RCS of the array can be reduced by more than 7 dB without affecting its radiation performance.

RCS reduction of reflectarray using new variable size FSS method

This study focuses on the reduction of the Radar Cross Section (RCS) for planar reflectarray antenna by using Frequency Selective Surface layers. For this study, a novel broadband reflectarray antenna is designed. The designed reflectarray antenna is composed of a broken circular ring and a cogwheel geometry. With variable size geometry, the proposed unit cell has more than 400° phase range which provides a broader bandwidth of the antenna. The RCS reduction of the reflectarray antenna is provided using variable size elements of the FSS technique and modification of reflectarray antenna ground plane. Therefore, the backscattering RCS of FSS backed modified reflectarray antenna is reduced up to 10 dB in the whole frequency band. This RCS reduction cost a reduction in terms of antenna gain level. The scattering characteristics, radiation patterns and RCS of both metallic grounded and FSS backed antennas are simulated and experimentally verified.

$L$ -Band Ocean Surface Roughness

Surface wave spectral properties of centimeter to decameter (cmDm) wavelengths are of great interest to microwave remote sensing of the ocean. They are obviously different from the high-frequency extension of the wind-wave spectrum models developed for ocean science and engineering applications, which focus on the longer waves in the energetic peak region of the wave spectrum. For more than six decades, the cmDm waves are generally considered to be in the equilibrium range, and its spectral function has a constant slope: −5 or −4 in the 1-D frequency spectrum, and −3 or −2.5 in the 1-D wavenumber spectrum. The observed wind-wave spectral slopes, however, are not constant. As a result, the cmDm wave properties are significantly different from those inferred from an equilibrium spectrum model. Surface slope measurements are more suited for studying the cmDm waves. Microwave radar backscattering cross sections have been used to study the shorter range of cmDm waves. L-band lowpass-filtered mean square slope (LPMSS) is contributed by waves longer than about 0.6 m, here referred to as the decimeter to decameter (dmDm) waves. The analysis of LPMSS has improved the modeling of dmDm waves. Ultimately, the spectral slope variation is a critical characteristic of cmDm waves. The wave spectrum model formulated with the variable spectral slope consideration produces very good agreement with L-band scatterometer and reflectometer measurements.

Researches on the scattering characteristics in THz band of conductor cylinder coated with parabolic distribution and time-varying plasma media

It is widely acknowledged that inhomogeneous and time-varying plasma can effectively reduce the back scattering radar cross section (RCS) and THz wave has the potential to penetrate the plasma and against the plasma stealth. Therefore, the backscattering and bistatic radar cross section (RCS) of conductor cylinder coated with parabolic distribution and time-varying plasma media in THz wave band are studied by the Runge-Kutta Exponential Time Differencing-Finite Difference Time Domain (RKETD-FDTD) method in this paper. The influences of plasma parameters are analyzed. From both the backscattering and bistatic RCS simulations, it is obviously that inhomogeneous and time-varying plasma cloaking system makes a significant difference on reducing the RCS and improve the plasma stealth while electromagnetic wave in THz region can successfully weaken its influence and contribute to the anti-stealth.

Effect of Bispectrum on Radar Backscattering From Non-Gaussian Sea Surface

The upwind-downwind asymmetry in normalized radar backscattering cross section (NRBCS) from ocean surface is well known; one acceptable and convincing reasoning is explained by the fact that the surface height distribution deviates from Gaussian one, which causes a nonzero skewness function, and consequently affects the radar cross section in up and down wind directions. Specific forms of skewness function, in between Gaussian and exponential, have been proposed in previous studies to account for the upwind/downwind asymmetry in radar backscatter. Attempt is made, through numerical simulation, in this article to examine the impact of these two types of skewness functions on NRBCS. The simulated NBRCSs, with and without skewness contributions, are compared with measured data in upwind and downwind directions at L-, C-, and Ku-bands for different wind speeds. The results indicate that the Gaussian-type skewness function works better to account for the upwind/downwind asymmetry of NBRCS by choosing an appropriate root mean square (RMS) height appearing in skewness function and as the wind speed or radar frequency increases, the RMS height increases but regardless of wind direction and radar incidence angle.

The Doppler Spectrum of the Microwave Radar Signal Backscattered From the Sea Surface in Terms of the Modified Bragg Scattering Model

Significant progress has been made in the study of electromagnetic wave scattering from the sea surface. Essential results were obtained in solving applied problems, but there are still unsolved problems in the scattering theory. The radar backscatter cross section is usually used to solve remote sensing tasks, although the Doppler spectrum (DS) of the scattered microwave signal contains more information about sea waves. The concept of a two-scale model of the scattering surface is used in this article. Correct allowance for large-scale waves, in comparison with radar wavelength, in deriving theoretical formulas enabled us to develop a modified Bragg scattering model. It is based on the previously developed scattering model that is refined here to take into account the contribution of the horizontal component of the orbital velocity to the DS. It is shown that allowance for large-scale waves limits the growth of the radar cross section of the Bragg component with a decrease in the incidence angle, which allows using the resonant scattering model at small incidence angles. An additional result is that the modified model of the DS can also be used in the range of middle incidence angles because it takes into account the contribution of the horizontal component of the orbital velocity. It is shown that if the correlation between large-scale and small-scale components of sea waves is neglected, the new formulas pass into the known formulas for the DS within the framework of the Bragg scattering model.