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An azimuthal-rotation sample holder, with improvements in the rotation-angle accuracy and rotation-axes displacement during azimuthal rotation, was developed for molecular-orientation analysis using scanning transmission X-ray microscopy., In this study, an azimuthal-rotation sample holder compatible with scanning transmission X-ray microscopy was developed. This holder exhibits improvement in the accuracy of rotation angles and reduces the displacement of the rotation axes during azimuthal rotation by using a crossed roller bearing. To evaluate the performance of the holder, the authors investigated the dependence of the optical density around the C K-edge absorption of π-orbital-oriented domains in natural spherical graphite on the rotational angle by using linearly horizontally and vertically polarized undulator radiation. Based on the dependence of the optical density ratio between C 1s → π* and 1s → σ* excitation on the polarization angle of the X-rays, the average two-dimensional orientation angle of the π orbital in each position in a natural spherical graphite sample was visualized.

This paper studies the optimal detection performance of the standard frequency diverse array (FDA) radar and FDA multi-input multioutput (FDA-MIMO) radar in Gaussian clutter and noise. Array signal processing scheme at the receiver is firstly designed to obtain the array steering vector containing range, azimuth, and frequency increment. For the two array configurations, namely, collocated transmit-receive and collocated transmit distributed receive, the likelihood ratio test statistics and the test statistic distributions are derived in the Neyman–Pearson sense. It is then investigated how the number of array elements influences the detection performance of various radar systems at low signal-to-noise ratio (SNR). Several numerical simulations are carried out to demonstrate that the performance improvement is hard for MIMO and FDA-MIMO by only increasing the number of transmit elements, while it is achievable for the FDA. The paper finally makes a comparative analysis for detection performances of five radar configurations under different SNRs.

SUMMARY The horizontal-to-vertical spectral ratio (HVSR) of ambient noise is commonly used to infer a site's resonance frequency (${f_{0,site}}$). HVSR calculations are performed most commonly using the Fourier amplitude spectrum obtained from a single merged horizontal component (e.g. the geometric mean component) from a three-component sensor. However, the use of a single merged horizontal component implicitly relies on the assumptions of azimuthally isotropic seismic noise and 1-D surface and subsurface conditions. These assumptions may not be justified at many sites, leading to azimuthal variability in HVSR measurements that cannot be accounted for using a single merged component. This paper proposes a new statistical method to account for azimuthal variability in the peak frequency of HVSR curves (${f_{0,HVSR}}$). The method uses rotated horizontal components at evenly distributed azimuthal intervals to investigate and quantify azimuthal variability. To ensure unbiased statistics for ${f_{0,HVSR}}$ are obtained, a frequency-domain window-rejection algorithm is applied at each azimuth to automatically remove contaminated time windows in which the ${f_{0,HVSR}}$ values are statistical outliers relative to those obtained from the majority of windows at that azimuth. Then, a weighting scheme is used to account for different numbers of accepted time windows at each azimuth. The new method is applied to a data set of 114 HVSR measurements with significant azimuthal variability in ${f_{0,HVSR}}$, and is shown to reliably account for this variability. The methodology is also extended to the estimation of a complete lognormal-median HVSR curve that accounts for azimuthal variability. To encourage the adoption of this statistical approach to accounting for azimuthal variability in single-station HVSR measurements, the methods presented in this paper have been incorporated into hvsrpy, an open-source Python package for HVSR processing.

A novel low-order integrated guidance and control (LOIGC) design model is deduced, and an original diving integrated guidance and control design approach is proposed in this paper. An analytical model between three-channel body rates and components of acceleration of the hypersonic vehicle in the ballistic frame is derived, and the commanded body rates can be directly obtained by analytic calculation. The LOIGC design model is conducted based on three dimensional (3D) relative dynamics between the hypersonic vehicle and target, and the direct relation with respect to line-of-sight (LOS) angles and control surface fin deflections of the hypersonic vehicle is established. Based on the LOIGC model, the design of six-degree-of-freedom (6DOF) guidance and control system for diving hypersonic vehicles can be converted into an output tracking problem of a low-order nonlinear system, and the commanded control surface fin deflections can be directly obtained by controlling derivatives of elevation and azimuth angles of line-of-sight between the hypersonic vehicle and target. In this paper, the system order and tuning parameters of the 6DOF guidance and control system are both decreased, and the design procedure of 6DOF guidance and control system is simplified. The process of calculating commands of angle of attack and bank angle based on desired guidance overloads, and the tracking loops with respect to Euler angles and body rates of the rotational system can also be omitted. In addition, the newly proposed method can improve the utilization of velocity measurements in the body frame of the hypersonic vehicle. Finally, the effectiveness and robustness of the newly proposed integrated guidance and control design approach are verified and investigated using a 6DOF generic hypersonic vehicle model.

Similar to the conventional squint mode synthetic aperture radar (SAR) imaging processing, the estimation of Doppler centroid is one key problem for the low-squint-mode (within the range of [−5°, 5°]) multichannel in an azimuth high-resolution and wide-swath (HRWS) SAR system. In this paper, based on the electromagnetic scattering model, a novel weighted Doppler centroid estimation approach is proposed for the multichannel in the azimuth HRWS (MC-HRWS) SAR system. First, Maxwell’s equations are employed to derive the echo model for the multichannel SAR system. Then, an improved backscattering model is presented based on the small perturbation method and the available echo model, which is adopted to produce the weights for Doppler centroid estimation. More importantly, in order to improve the precision of Doppler centroid estimation, a weighted ambiguity-free Doppler centroid estimation approach is proposed, where the range-variant characteristic of Doppler centroid is employed to resolve the ambiguity number of Doppler centroid, and the echoes from different range bins with different signal-to-noise ratios are considered. In addition, the Cramer–Rao low bound of the estimated Doppler centroid is also discussed in this paper. The effectiveness of the proposed Doppler centroid estimation approach is verified via simulated and real measured low-squint-mode MC-HRWS SAR data.

The zero-Doppler centroid control in geosynchronous synthetic aperture radar (GEO SAR) is beneficial to reduce the imaging complexity (reduces range-azimuth coupling in received data), which can be realized by adjusting the radar line of sight (RLS). In order to maintain the zero-Doppler centroid throughout the whole orbit of the GEO SAR satellite, the RLS needs to be adjusted in real-time. Due to the ultra-long synthetic aperture time of GEO SAR, the RLS variation during the synthetic aperture time cannot be neglected. However, in the previous related papers, the real-time variation of RLS during the synthetic aperture time was not taken into account in the calculation of Doppler parameters, which are closely related to the RLS, resulting in inaccurate calculation of Doppler parameters. Considering this issue, an accurate Doppler model (the model of relative motion between satellite and ground target) of GEO SAR is proposed in this paper for the accurate calculation of Doppler parameters (Doppler centroid and Doppler bandwidth and other parameters). Finally, simulation experiments are designed to confirm the effectiveness and necessity of the proposed model. The results indicate that the RLS variation during the synthetic aperture time has a considerable effect on Doppler parameters performance of the GEO SAR, and refers to a more stable azimuth resolution performance (the resolution is kept near a relatively stable value at most positions of the elliptical orbit) compared with the case that does not consider the real-time zero-Doppler centroid control.

This paper is the second of two focusing on the analytical solutions for light transport in infinite homogeneous tissue with an azimuth-dependent (m-dependent) anisotropic scattering kernel by two approaches, Case’s singular eigenfuncions (CSEs) expansion and Fourier transform, and proving the consistence of the two solutions theoretically. In this paper, the analytical solution for the m-dependent truncated scattering kernel was derived via the Fourier transform and inversion, and expanded with the m-dependent generalized singular eigenfuncions (GSEs). Two kinds of GSEs that are defined by Ganapol in the case m=0 are extended to arbitrary azimuthal orders and proven to be consistent with CSEs both in expression forms and in intrinsic behaviors. By applying the Fourier transform inversion on the solution for the three-term recurrences, the Green’s function of radiance distributions is obtained successfully, and it conforms perfectly to the CSEs solution in the limit, which has already been discussed in our first accompanying paper. Meanwhile, as a byproduct, a series of identities about the m-dependent Chandrasekhar orthogonal polynomials were presented and will be greatly helpful for further studies.

This paper focuses on the novel approaches for inverse synthetic aperture radar (ISAR) imaging of maneuvering target. It is based on the assumption that the azimuth echoes in a range bin are modeled as multi-component cubic phase signal (CPS) after the translational motion compensation, and the ISAR image quality will be deteriorated by the conventional Fourier transform in the azimuth focusing. In this paper, two novel algorithms for parameters estimation of multi-component CPS based on the local polynomial Wigner distribution (LPWD) and integrated high-order ambiguity function (IHAF) are proposed, and the high-quality instantaneous ISAR image can be obtained by the estimated CPS parameters. The results of simulated and real aircraft data are provided to validate the effectiveness of the proposed methods.

WindSat has provided an opportunity to investigate the first spaceborne passive fully polarimetric observations of the Earth's surface. In this paper, Arctic sea ice was investigated. The passive polarimetric data are provided in the form of the modified Stokes vector consisting of four parameters. The first two components of the modified Stokes vector are the vertically and horizontally polarized brightness temperatures, which have been continuously measured by various radiometers over the last three decades. The third and fourth Stokes components provide in formation on the degree of polarization of the emission. In this paper, three types of analysis are carried out: spatial (maps considering different azimuth angle intervals), temporal (time series of daily averaged Stokes components over a small selected azimuth angle range), and azimuthal (variations w.r.t. the azimuth angle over selected study areas). Analysis has shown the highest brightness temperature variations for the 37-GHz third Stokes component (>; 2 K) during summer. The next highest signals were observed for the 10.7-GHz third and fourth Stokes components (>; 1 K) during summer as well. The 37-GHz fourth Stokes component exhibited the least variability (>; 1 K). Spikes of up to 2 K were identified in the time series of the 37-GHz third Stokes component during mid-January 2004 (winter) over first-year ice regions. The near-surface air temperature of the European Center for Medium-Range Weather Forecasts model data and the Special Sensor Microwave/Imager National Aeronautics and Space Administration Team ice concentrations revealed that, during these events, the surface temperatures reached near melting levels and the retrieved ice concentrations were reduced to about 80%. Moreover, these observations also showed clear evidence of first harmonic azimuthal dependence. Geophysical parameters, such as temperature and ice leads, are likely to be the causes. The larger signals which occurred during summer were identified as being related to the ice surface temperatures being near melting.

To improve the impaired azimuth resolution of the novel Terrain Observation by Progressive Scans (TOPS) mode, a new multi- channel single phase center multiple beam (SPCMB) TOPS mode is proposed in this paper for high-resolution wide-swath (HRWS) imaging. However, the progressive azimuth beam scanning leads to the Doppler spectrum aliasing and both beam center time and Doppler centroid varying with the target's azimuth location. Challenges may arise for processing the SPCMB-TOPS SAR data from these problems. In this paper, an e-cient full aperture imaging approach is proposed to process the raw data. The sketch of the proposed imaging approach is described in detail. Simulation results of point targets validate the proposed imaging approach.

Context. Photon orbital angular momentum (POAM) has been created in the laboratory, yet it is still relatively unknown. How does POAM manifest itself in astronomy? Are there any applications for measuring astrophysical POAM? Aims. In this paper, I 1) explain POAM in an astronomical context; 2) define the POAM observables for astronomy; 3) create generic systems-based calculi that describe how POAM propagates from celestial sphere to detector; 4) use the calculi with several astronomical instruments as examples of their utility; 5) demonstrate an application for astrophysical POAM measurements; and 6) relate POAM to existing astronomical instruments and concepts. Methods. Electric fields are expanded into azimuthal Fourier components, and the intensities are expanded into correlations or rancors. The source electric fields are spatially incoherent. In the systems-based calculi, the inputs are located on the celestial sphere, the system is represented by propagation through free space and instrument, and the outputs are located in a specific plane. The diffraction and point-spread function expansions are very generic and can be used with any type of instrument. I employ these examples to demonstrate the calculi (in order of increasing difficulty): free space, single telescopes, interferometers, coronagraphs, and rancorimeters. Results. The azimuthal Fourier components of the electric field correspond to POAM vortex states. Rancors contain less information than correlations, yet they are easier to measure and can be used in many applications. Propagation through an aberrated telescope applies external torque, which may be expressed in terms of Zernike polynomials. I prove that a sectored phase mask in a focal-plane coronagraph applies torque to the low-order states, producing a null. Also, I prove that a Michelson interferometer is inherently capable of filtering POAM; e.g., tracking 180 ◦ from the central fringe eliminates even states, producing a null. A limited rancorimeter can be created by placing a focal-plane wedge mask in a coronagraph. The resulting rancors can be used to perform super-Rayleigh observations of unresolved unresolved objects, such as binary stars. There are three types of source POAM: intrinsic, structure, and pointing. Instrumental POAM, which must be calibrated, includes optical aberrations and atmospheric turbulence. Conclusions. This paper represents the starting point for future research: 1) making a priori predictions about the intrinsic POAM of astronomical sources; 2) designing ground- and space-based POAM-measuring instruments; 3) understanding existing instruments in terms of POAM; 4) minimizing the effects of random noise on POAM; and 5) calibrating all types of instrumental POAM.

When range ambiguity and range dependence coexist in forward-looking ground moving target indication (GMTI) radar, the traditional space-time adaptive processing (STAP) approaches may fail to work. To cope with this issue, a range-ambiguous clutter suppression approach based on elevation time diverse array (TDA) radar system and azimuth phase coding (APC) technique is presented in this paper. Due to the advantages of frequency scanning, the elevation TDA radar is able to cover all directions by transmitting a single time-shifted waveform. Therefore, a frequency bandpass filter is devised for each single range-bin to achieve the mainlobe echo extraction procedure. In the sequel, the azimuth phase decoding and Doppler filtering are performed to deal with the residual sidelobe ambiguous energy. With two-dimensional filtering, one can extract the unambiguous signals for each range region independently. Then, the traditional clutter compensation and STAP methods are employed to suppress the ground clutter. Finally, the effectiveness of the proposed framework in resolving range ambiguity are verified by the numerical simulation experiments.

As a high resolution airload with accurate rotor wake is pivotal for rotor BVI (Blade-vortex interaction) analysis, a hybrid method with combined Navier-Stokes equation, viscous wake model, and FW-H (Ffowcs Williams-Hawkings) equation is developed for BVI airload and noise in this paper. A comparison with the CFD (Computational Fluid Dynamics)/FW-H method for the AH-1/OLS (Operational Load Survey) rotor demonstrates its capability for favorable accuracy and high computation efficiency. This paper further discusses the mechanisms for the impacts of four flight parameters (i.e., tip-path-plane angle, thrust coefficient, tip Mach number, advance ratio) on BVI noise. Under the BVI condition, several BVI events concurrently occur on the rotor disk. Each interaction has a distinct radiation direction which depends on the interaction azimuth, and its noise intensity is highly associated with the characteristic parameters (e.g., miss-distance, interaction angle, vortex strength). The BVI noise is dominated by the interactions at 30–90° in azimuth on the advancing side, of which the wake angle range is from 180° to 540°. Furthermore, the tip-path-plane angle, thrust coefficient, and tip Mach number change the noise intensity mainly via miss-distance, interaction angle, and vortex strength, but for different advance ratios, the noise intensity and propagation direction are more dependent on the interaction angle and interaction azimuth.

In this paper, we propose an imaging algorithm of m issile-borne SAR in diving and squint mode. The diving acceleration, vertical speed, and squint angle caused a large range cell migration (RCM). The algorithm divides the RCM correction (RCMC) into two steps. Firstly, correcting the main part of range walk in time domain. Secondly, correcting the remaining RCMC in range frequency-azimuth Doppler frequency domain, using an analytical form of the signal 2-D spectrum derived by the method of series reversion. Theoretical analysis and simulation results illustrate its validity, and satisfy the imaging quality of missile-borne SAR in high squint model. Index Terms - Missile-borne SAR, diving and squint mode, RCMC, series reversion. I. Introduction Compared with general airborne or space-borne SAR, missile-borne SAR has significantly different characteristics. In order to attack the target, missile-borne SAR cannot do the uniform line motion, and also it has a certain acceleration and vertical velocity in the diving flight. Moreover, it usually works in a squint mode in order to acquire a period of turning time. Therefore, the general SAR imaging algorithms are no longer suitable for missile-borne SAR (1-2). In (3), the 2-D spectrum of target echo was derived by the method of series reversion, and the RCMC, range and azimuth compression were accomplished in the 2-D frequency domain. But the algorithm was only suitable for the center single point target imaging of the scene in side-looking mode. An imaging algorithm for missile-borne SAR based on azimuth nonlinear chirp scaling (NLCS) was proposed in (4). After finished RCMC and range compression in the 2-D frequency domain by the method of series reversion, azimuth variation of Doppler FM rates for echo signal were compensated with the operation of azimuth NLCS, which could improve focusing depth and effect. However, the computation is too heavy, and it also only worked in side-looking mode. In (5), the spectral overlapping phenomenon in distance was solved by introducing a new CS factor, and the influence caused by velocity and acceleration of the missile were compensated. A deramp method was introduced to cope with the Doppler spectral overlapping phenomenon in azimuth, but this algorithm was too complex to realize. According to the characteristics of the missile-borne SAR platform motion, a space geometry relationship of the diving and squint movement is established in this paper. Then the instantaneous range between radar and target is calculated, and the point target echo signal model is derived. The Doppler frequency center is corrected in range frequency-azimuth time domain (6). The 2-D spectrum of the point target echo signal is deduced using the method of series reversion. After finishing the pulse compression processing, a focused point target image is got. At last, a missile-borne SAR simulation is used to illustrate its validity of the algorithm. II. Geometric Model and Instantaneous Range

With the development of SAR imaging, the efficiency and rapidity of imaging algorithms have always been a research direction, and real-time imaging is a reflection of the speed of the imaging algorithm. For missile-borne SAR, real-time imaging is particularly important because it provides radar with a sense of the battlefield environment. In the case with a highly squinted angle, the azimuth space variance and the coupling between range and azimuth dimension will become serious in imaging, thus an azimuth frequency nonlinear chirp scaling (AFNCS) algorithm is proposed to solve this problem. Based on linear range walk correction, a novel chirp scaling algorithm is adopted to correct the range migration, and then a high-order phase filtering factor is introduced into the azimuth dimension frequency domain to decrease the azimuth space variance. In addition, combined with the SPECtral Analysis method, the image is focused on the Doppler domain. The AFNCS algorithm does not need complex mathematical calculations such as interpolation and can meet the real-time requirement of missile-borne SAR imaging. Simulation results illustrate the effectiveness of the proposed algorithm. The integration of the research in this paper and the deep learning will further pave the way for real-time SAR imaging applications in disaster monitoring, security and surveillance.

Using the active feedback control system on the elastic wave metamaterial, this research concentrates on the sound transmission with the dynamic effective model. The metamaterial is subjected to an incident pressure and immersed in the external mean flow. The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside. The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms. Based on the dynamic equivalent method, the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter. With the coupling between the fluid and structure, the expression of the sound transmission loss (STL) is derived. This research shows the influence of effective mass density on sound transmission properties, and the STL in both modes can be tuned by the acceleration and displacement feedback constants. In addition, the dynamic response and the STL are also changed obviously by different values of structural damping, incident angle (i.e., the elevation and azimuth angles) and Mach number of the external fluid with the mean flow property. The results for sound transmission by two methods are compared, i.e., the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one. This paper is expected to be helpful for understanding the sound transmission properties of both pure single- and double-plate models.

This paper presents an empirical study of the uplink and downlink azimuth angle of arrival (AoA) in an urban micro (UMi) scenario at 28 GHz. At present, most UMi measurements are conducted in the downlink and then the uplink situation is inferred assuming channel reciprocity. Although the channel correlation coefficient of the uplink and downlink can be as high as 0.8, this does not mean that they are the same. Only a real uplink measurement can accurately describe its channel conditions, and this is what this study does. A receiver equipped with a rotatable horn antenna is mounted at the base station and the user terminal, respectively, in simulating the uplink and downlink. To improve the angular resolution, we extract the multipath components (MPCs) using the space-alternating generalized expectation-maximization algorithm. Also, a spatial lobe approach is used to cluster the MPCs in the power angular spectrum. By matching MPCs with objects in the environment, we find that direct propagation and first-order reflections are dominant in line-of-sight and non-line-of-sight cases. By comparing our measurement with those in standard channel models, we verify that the AoA of clusters follows a Gaussian distribution in the uplink and downlink. In addition, a two-dimensional Gaussian distribution for ray AoA and power is established to reflect their correlation.

Thanks to the rapid technological progress in the field of mobile devices, smartphones are increasingly becoming valuable for science. They can serve as photogrammetric measurement devices with built-in cameras, micro-electro-mechanical systems for orientation and position assessment, as well as powerful processing units allowing field-based data acquisition and processing. This paper outlines a comprehensive investigation focusing on the accuracy and stability of smartphone camera rotation parameters determined by built-in smartphone sensors. For that purpose, the rotation parameters were measured under a range of different conditions. Four test scenarios were defined considering indoor- and outdoor measurements using three different devices being in static and dynamic modes. Furthermore, the influence of magnetic perturbations was investigated. The rotation parameters were determined from the measurements applying different sensor fusion approaches. Reference values for accuracy assessment were provided by a superior precision inertial measurement unit that measured the rotation parameters simultaneously to the smartphone in each experiment. The analysis of the smartphone-based rotation parameters, separated in the Euler angles azimuth, pitch and roll, shows average accuracies below 2° for pitch and roll. In comparison, azimuth shows significantly lower accuracies of more than 30° especially when the smartphone is in motion and when it is exposed to magnetic perturbations. In this regard, advanced multi-sensor fusion approaches were examined that handle such interferences to considerably improve the accuracy of azimuth measurements. In conclusion, a summary of accuracies and stabilities to be expected from smartphone sensors is given referring to ambient conditions and investigated sensor fusion strategies.

This paper focuses on the time-difference-of-arrival (TDOA)-based direction finding for a low-altitude source with an acoustic sensor array. The source bearing in space must be estimated by the joint azimuth-elevation estimation. The azimuth may be the only concern for some scenarios, where the elevation is trivial; however, an extra parameter about elevation needs to be estimated in the joint estimation. When a planar array is introduced to replace the spatial array, the azimuth-only estimation solution with the original TDOA measurements is proposed. This solution is simpler than the joint estimation by excluding the elevation calculation. The mathematical relation between the TDOAs of spatial and planar arrays is derived, and their azimuth Cramer–Rao lower bounds (CRLBs) are compared. The CRLBs together with the pseudo-linear estimation and Taylor series least squares method are evaluated for estimating the source azimuth by simulations as well as real-life data. The results demonstrate that the azimuth-only estimation would create a modest precision improvement over the joint azimuth-elevation estimation. The effect of array altitude variation is also examined, suggesting that the relative heights among sensors have little influence on the estimation of source azimuth.

The trajectory estimation problem of a thrusting/ballistic object in three-dimensional (3-D) space has been previously solved with 2-D measurements (azimuth and elevation angles from a fixed passive sensor, either starting from the launch time or with a delayed acquisition) under the assumption of constant mass. However, since the mass decreases as the fuel burns, this should be accounted for. This paper investigates several approaches with different parameter vectors to solve the trajectory estimation and impact point prediction (IPP) with measurements starting after the launch time, i.e., delayed acquisition for both constant mass motion model and mass ejection motion model. For the mass ejection motion model, the mass ejection rate is an extra component of the parameter vector to be estimated. The invertibility of the Fisher information matrix (FIM) of the parameter vectors is also used to confirm the observability (estimability) of the system. The Cramer–Rao lower bound (CRLB) is the inverse of the FIM if it is invertible. The CRLB of the IPP is also derived. We develop the maximum likelihood estimator of the considered motion parameter vectors. Performance comparison between the models considered is given and the statistical efficiency of the best model is confirmed via simulation results.

This paper addresses the problem of three-dimensional target motion analysis from bearing measurements. The established description of uncertain directional data involves azimuth and elevation angles with additive Gaussian noise. Investigation of this widely accepted representation in terms of the corresponding Fisher information matrices reveals that the underlying probability densities are only valid for small absolute elevation angles and precise measurements. Employing spherical statistics, an alternative representation is proposed that is sensible for the whole state space and arbitrarily imprecise bearing sensors. Based on this, a globally valid posterior Cramer–Rao lower bound is derived.

In this paper, effects of the earth’s curvature and lunar revolution on the performance of the moon-based synthetic aperture radar (SAR) are examined by a comprehensive analysis of the motion-induced Doppler frequency and Doppler rate on which azimuthal imaging relies. The motion effects include the earth’s self-rotation related to the earth’s curvature and lunar revolution around the earth. An extended hyperbolic range equation (EHRE) is proposed in line of the equivalent velocity and equivalent squint angle, and then the signal model based on the EHRE is established to simulate the moon-based SAR image from which the imaging performance is analyzed. Theoretical analyses show that the earth’s curvature is a dominant factor in determining the moon-based SAR’s Doppler and azimuthal resolution. Furthermore, the earth’s curvature distorts the SAR image by way of rotating the azimuth imaging from the cross-range direction within a certain skewed angle. The overall effects of lunar revolution generate a velocity correction factor and a deviate squint angle, which subsequently deteriorate the azimuthal resolution and image focusing. Results also show that effects of the earth’s curvature and lunar revolution are in connection with relative positions of the ground target and moon-based SAR. To this end, numerical simulations using point target response is carried out to accentuate the necessary for taking account of the Doppler error induced by the lunar revolution.

Airborne forward-looking radar (AFLR) imaging has raised many concerns in fields of Earth observation, independent of weather and daytime. Constrained by imaging principles, conventional high-resolution radar imaging techniques such as synthetic aperture radar (SAR) and Doppler beam sharpening (DBS) are incapable of AFLR imaging. The real aperture radar (RAR) can obtain AFLR images using a scanning antenna, but suffers from coarse cross-range resolution. Recently, there has been much attention paid to the iterative adaptive approach (IAA), which draws from the benefits of RAR imaging and provides improved cross-range resolution. However, earlier work on the IAA imposed a convolution model on the received azimuth echo, neglecting the effect of the Doppler phase. This model mismatch degrades the imaging performance for moving platforms. To settle this problem, this paper first establishes a Doppler-convolution model of AFLR imaging, where both Doppler phase and antenna convolution effects are considered, allowing more accurate reconstruction when applying the IAA to formulate a super-resolution image. Then, a data-depended approach for Doppler centroid estimation is proposed to circumvent the problem of low estimation precision using platform motion parameters delivered by navigational devices mounted on the radar platform. Simulation results demonstrate that the proposed implementation of the IAA based on the Doppler-convolution model and Doppler centroid estimation can overcome the deficiencies of the SAR and DBS techniques in the forward-looking imaging direction, and present a noticeably superior performance as compared with conventional AFLR imaging methods.

In this paper, we propose a long-time coherent integration method for a maneuvering target with the first-, second-, and third-order range migrations, and the complex Doppler frequency migration. In this method, after range compression, the echo signal is first transformed into the range-frequency and Doppler domain based on series reversion, and then an azimuth matched filtering procedure is implemented in the 2-D frequency domain. It can eliminate the coupling effects between range and azimuth jointly caused by the radial velocity, radial acceleration, and radial acceleration rate of a moving target. Due to the linear transform property, the proposed method can work well under low signal-to-clutter and noise ratio. In addition, the Doppler ambiguities, when target azimuth spectrum either is within a pulse repetition frequency (PRF) or spans over neighboring PRF bands, can be well solved. Both simulated and real synthetic aperture radar data processing results are provided to validate the effectiveness of the proposed algorithm.

In geosynchronous spaceborne–airborne bistatic synthetic aperture radar (GEO-BiSAR) system, the airborne platform achieves high-resolution imaging by passively receiving the signal from the interested scenario. In this paper, the Doppler characteristics of GEO-BiSAR and the individual contribution of the transmitter and the receiver are first analyzed. The airborne receiver is found to be the dominant contributor for the total Doppler bandwidth, which will lead to Doppler spectrum aliasing regarding the low pulse repetition frequency (PRF) adopted by the GEO-SAR. In order to suppress the Doppler ambiguity without adjusting the PRF of GEO-SAR, azimuth multichannel receiving technique is introduced to the airborne receiver. The multichannel transfer function is derived based on the method of series reversion and the spectrum reconstruction algorithm is then modified for multichannel GEO-BiSAR. Moreover, the reconstruction performance is closely related to the corresponding spacing between each channel (i.e., channel configuration). Therefore, the channel configuration design for GEO-BiSAR aims at optimizing the azimuth ambiguity-to-signal ratio with a satisfactory level of signal-to-noise ratio scaling factor by adjusting the channel configuration. The channel configuration design is modeled as a constrained single objective optimization problem (CSOP). Then, a channel configuration design method based on differential evolution and feasibility rule is proposed to solve the CSOP and obtain the channel configuration for the receiver with the optimal reconstruction performance. Finally, simulations results are presented to verify the effectiveness of the proposed method, and characteristics of channel configuration are analyzed in detail, which can be a practical guide for the implementation of multichannel GEO-BiSAR systems.

This paper presents a simple and novel formulation for the design and analysis of a generic cubic array with a single real coefficient for each antenna element, to steer the developed beam toward a certain desired angle in both azimuth (totally $360^{\circ}$) and elevation (totally $180^{\circ}$) directions. This configuration demonstrates frequency invariance of the directional patterns of the array within a relatively large fractional bandwidth which makes this array a potential candidate for wideband and ultra wideband applications. The required real coefficients are calculated based on matrix manipulation methods. However, the dimension of the matrices and vectors used in the computations are much less than the total number of antenna elements. Computer simulation shows the performance of the array with respect to the resolution of the main beam and frequency independence of the patterns and also in terms of the complexity and frequency range. Moreover, we will present a comparison between the proposed algorithm and the Fourier transform based methods and adaptive least mean square algorithm.

This paper discusses on the heat and fluid flow around two co-rotating cylinders in the tandem arrangement. The non-dimensional rotating speed (R.S) varies in the range of 0 ≤ R.S ≤ 4 and different non-dimensional gap spaces such as G/D = 1.5, 2.0, and 3.0 are considered between the cylinders. Computations are performed at the Reynolds number of 200 with constant Prandtl number of 7.0. It is demonstrated that rotating the cylinders deforms the recirculating regions of both upstream and downstream cylinders in which the rate of this deformation changes as a function of the R.S and G/D. On the other hand, co-rotating the cylinders shows some additional events such as the azimuthal displacement of the front stagnation points and development of the negative lift coefficient for both cylinders. It is found that the instabilities of the shear layer for both upstream and downstream cylinders are maximum at R.S = 1 and with increasing the R.S, the vortex shedding suppresses around the cylinders due to dominating the fluid rotating zone. Finally, it is revealed that at higher R.S values, a uniform Nusselt number distribution can be observed on both cylinders regardless of the gap space between the upstream and downstream cylinders.

Full-coverage synthetic-aperture radar (SAR) imaging and human target identification in complex scenes are very important for security and rescue applications. In this paper, a drone-based vital-SAR-imaging hybrid radar system is proposed to realize targets’ imaging and human identification simultaneously. Carried by an operational custom-built drone with a designed S-shaped trajectory, 2-D SAR images of the entire region could be obtained through the frequency-modulated continuous-wave mode, and the “vital Doppler” effect of human target can be searched through the Doppler mode. Then, the vital-SAR-imaging could be achieved. Several experiments including cart-based SAR imaging with three trajectories, cart-based vital-SAR-imaging, and drone-based multitrajectory vital-SAR-imaging were carried out to reveal the capability and distinct operational features of the proposed system. Experimental results demonstrate that the system has the ability to obtain SAR imaging results in different scenes with multiple trajectories, and the human target could be effectively distinguished from other stationary objects. The results show that the lowest human target location error is 0.06 m in a $4\,\,\text {m} \times 9$ m indoor region, which illustrates the great potential for search and rescue applications.

In previous works, it has been shown that the motion of a thrusting/ballistic object in a three-dimensional (3-D) space is observable with 2-D measurements from a stationary passive sensor. The measurements can either start from the launch point or can be delayed. The observability was investigated by testing the invertibility of the Fisher Information Matrix (FIM). This paper discusses the observability via the uniqueness of the target state vector for a certain sequence of 2-d angle-only measurements from a single fixed passive sensor. The discussion starts with polynomial motion from which the results are extended to nonlinear thrusting/ballistic motion. To illustrate the observability of a thrusting/ballistic target, the estimation problem of such a target with delayed acquisition after burn-out time is solved with a 7-d parameter vector (velocity vector azimuth angle and elevation angle, drag coefficient, 3-d acquisition position, and target speed at the acquisition time). A maximum likelihood (ML) estimator is used for the motion parameter estimation at acquisition time. The impact point prediction is then carried out with the ML estimates. The FIM is investigated via simulations to prove the observability numerically and the maximum likelihood estimator is shown to be efficient.

Based on a two-dimensional phase coding, a novel range ambiguity suppression technique is proposed in this paper. By transmitting two-dimensional phase coded signals, the two-dimensional spectrum of the range ambiguous signals will be shifted along both range and azimuth directions compared with that of desired signals. Then, part of the two-dimensional spectrum of the range ambiguous signals will be located outside the two-dimensional spectral support, which is known in priori, of the desired signals. Considering the range frequency and Doppler oversamplings, a filter corresponding to the two-dimensional spectral support of the desired signals is applied, which suppresses the range ambiguity. Simulation results of both point targets and distributed targets validate the effectiveness of the proposed method.

This paper provides an experimental investigation on the internal shear layers and the edges of the uniform momentum zones (UMZs) in a turbulent pipe flow. The time-resolved stereoscopic particle image velocimetry data are acquired in the cross-section of the pipe, and span the range of Reynolds number Reτ=340--1259. In the first part of the study, internal shear layers are detected using a three-dimensional detection method, and both their geometry as well as their fingerprint in the flow statistics are examined. Three-dimensional conditional mean flow analysis revealed a strong low-speed region beneath the average shear layers. This low-speed region is associated with positive wall-normal fluctuations, and it is accompanied by two swirling motions having opposite signs on either side in the azimuthal direction. Moreover, the shear layers are stretched by the two opposite azimuthal motions. In the second part of the study, the shear layers are treated as the continuous edges of the UMZs, which are detected using the histogram method following Adrian et al. (J. Fluid Mech., vol. 422, 2000, pp. 1–54) and de Silva et al. (J. Fluid Mech., vol. 786, 2016, pp. 309–331). For this part, two different orientation of the planes are used, i.e. the wall-normal–streamwise plane and the wall-normal–spanwise plane (cross-section of the pipe). Comparison of the detected structures shows that the shear layers mostly overlap with a UMZ edge (in either plane).

In this paper we present an analytical model for estimating the uncertainty of the horizontal wind speed based on dual-Doppler lidar measurements. The model follows the propagation of uncertainties method and takes into account the uncertainty of radial velocity estimation, azimuth and elevation pointing angles, and ranging. The model is achieved by coupling ranging and elevation angle to uncertainty of the probed wind speed through a simple power-law shear model. The model has been implemented in Python and made freely available through as the Python package YADDUM.

Ground moving targets may be smeared in a synthetic aperture radar (SAR) image due to the range migration, Doppler ambiguity and azimuth spectrum split caused by target unknown motion parameters. To handle these problems, we propose a fast non-searching method for maneuvering target refocusing and motion parameters estimation in this paper. First, the azimuth-deramp is conducted, which is capable of eliminating the azimuth spectrum splitting. In the sequel, the second-order keystone transform (SOKT) based on the scaling principle is applied to further correct the residual range curvature. Then, the phase difference (PD) is performed to eliminate the range walk and estimate the motion parameters, which does not require the prior knowledge of Doppler ambiguity number. Finally, the moving target can be well focused with the estimated parameters. This method has high computational efficiency and improved parameter estimation accuracy. Both simulated and real data are processed to demonstrate the effectiveness of the proposed method.

In this paper, a sparse reconstruction based approach to estimate Stokes parameters and 2-D DOAs of polarized sources is proposed in case of unknown number of sources. An L-shaped coprime array composed of dipole-dipole pairs, where a dipole in the dipole-dipole pair is placed on x-axis and the other is placed on z-axis, is used to reduce the mutual coupling across two dipoles in the dipole-dipole pair. In order to estimate the elevation of polarized sources, an orthogonal matching pursuit algorithm with the identification of the sources' number (OMP-isn) is proposed. In our proposed approach, the quasi deterministic maximum likelihood (qDML) test step is added in each iteration of algorithm. In addition, a refining grid step is also added in each iteration to reduce the estimation error incurred by the grid mismatch. The OMP algorithm and sparse iterative covariance-based estimation (SPICE) method are employed to estimate the azimuth of polarized sources. In order to pari the azimuth with the elevation, a pair-matching method is proposed based on the l 2 -norm and l 1 -norm ( l 2 / l 1 ) minimization. Based on the pairing azimuth and elevation, Stokes parameters of polarized sources are estimated by using Least Squares (LS) or Total Least Squares (TLS). The stochastic CRB is derived for the 2-D DOAs and Stokes parameters of polarized sources. Simulations are used to verify the performance of the proposed approach.

In this paper, the motion parameters’ estimation problem in synthetic aperture radar (SAR) imaging is extended to the multidimensional case, and the azimuth signal of a moving target with velocities and accelerations in three directions is modeled as a polynomial-phase signal (PPS). To estimate the multidimensional motion parameters of the moving target from the azimuth PPS, a multi-SAR system is required. On this basis, a new method based on the cubic phase function (CPF) is proposed to estimate the Doppler phase coefficients (DPCs) of the PPS. And, all the first- and second-order motion terms can be derived from the DPC. Experimental results have shown that, using the proposed scheme, the motion parameters can be accurately estimated in high signal-to-noise ratio scenarios.

The ground moving target's radial velocity estimation based on the interferometric phase in a multichannel synthetic aperture radar (SAR) system suffers from 2π modulo folding, resulting in the target's azimuth location ambiguity in the SAR image. To address this problem, a novel coprime adjacent arrays SAR (CAA-SAR) is proposed in this paper. The two sparse uniform subarrays constituting the CAA are arranged adjacently with a conjunct element, then a virtual array can be obtained with much more virtual elements and smaller element spacing, which will help to solve the azimuth location ambiguity. After ground clutter suppression, multiple pixels’ samplings are utilized based on the MUSIC algorithm for estimating radial velocity as well as azimuth shift by exploiting all virtual elements of CAA-SAR. Compared with the existing nonuniform linear array SAR method based on Chinese remainder theorem, the CAA-SAR can obtain a better accuracy with the same number of elements in a larger sparse configuration, or use fewer elements to obtain an approximate accuracy in almost the same physical aperture. Compared with the coprime arrays SAR, the CAA-SAR has a better accuracy due to its larger number of unique virtual elements and longer physical aperture. Finally, some results of numerical experiments are provided to demonstrate the effectiveness of the proposed method.

Generally, the influence of initial phase of polarization distribution of incident vector beams always is ignored in its tight focusing, because it just induce the whole rotation of polarization distribution. In this paper, we show some distinctive effects induced by the initial azimuthal phase of polarization distribution in the tight focusing of radially polarized and azimuthal-variant hybrid vector beams. For these two types of vector beams, the initial azimuthal phase of polarization distribution induces two types rotation, the whole polarization rotation and the combined polarization rotation including the polarization distribution rotation and phase difference rotation, respectively. Furthermore, two methods are presented for modulating energy flow density and spin angular momentum density in the focal region, the synchronous and asynchronous rotation, which denote two polarization unit vectors with the same or different initial phase. Our results indicate the light–matter interaction can be induced by the polarization distribution rotation of incident vector beams in its tight focusing, and provide a possible connection with the rotational Doppler effect of optical vector beams.

This paper presents the experimental identification of the dynamic interaction between three fluctuations excited by different thermodynamical forces in a linear plasma. The observed fluctuations are characterized as an axial symmetric mode, a drift wave, and an azimuthally symmetric potential fluctuation from the spatiotemporal structures measured with Langmuir probe arrays. The intermittent burst of the axial symmetric mode is observed by the instantaneous wave number spectrum. The energy transfer analysis revealed that the axially symmetric mode gains energy from the other mode during the burst while the drift wave loses energy. The intermittent burst synchronizes with the azimuthal symmetric potential fluctuation.

In this paper, a passive ranging problem with elevation angle, azimuth angle, and signal intensity measurements is presented. The signal intensity is inversely proportional to the squared distance between target and sensor. All measurements are obtained from a single fixed sensor and the emitted signal intensity is unknown. The observability is investigated through the Fisher information matrix (FIM) and Cramer–Rao lower bound. The maximum-likelihood (ML) estimator is used for the estimation of the trajectory of the target and the FIM is calculated numerically. The simulation results prove the feasibility of passive ranging using signal intensity measurements from a single stationary passive sensor. The estimates are shown to be statistically efficient.

It is well known that ground moving targets may be smeared in a synthetic aperture radar (SAR) image due to the range migration, Doppler phase broadening, and velocity ambiguity caused by target unknown motion parameters, especially for the accelerating targets within a long observation time. To deal with these problems, a maneuvering target refocusing method based on keystone transform (KT) and coherently integrated cubic phase function (CICPF) is proposed in this paper. First, an azimuth deramp function is constructed along the slow-time dimension at each range-frequency gate to reduce the order of envelope migration and phase response over the slow-time. Then, the residual range walk and the time-varying Doppler phase are eliminated by the KT and the CICPF, respectively. With the estimated motion parameters, moving targets can be finely refocused. Both simulated and real SAR data processing results are presented to validate the proposed algorithm.

In this paper, a new analytic decomposed transfer function (DTF) for spaceborne synthetic aperture radar processing is calculated using the stationary phase approximation and Taylor's series expansion. The DTF copes with large Doppler centroid variations and executes range cell migration correction, secondary range compression, azimuth compression, and higher order effects. A fourth-order (DTF4) and fifth-order (DTF5) algorithms have been implemented using segmented block processing. It is shown that the DTF4 yields high quality 3-look target responses at azimuth resolution 0.3 m and range resolution 0.5 m at low squint (yaw = 0.3°) for X -band. At higher squint (yaw = 7.5°) the DTF5 has to be used to obtain adequate image quality.

This paper analyzes the effect of polarization and the incident angle on the contrasts of interference patterns in three-beam interference lithography. A non-coplanar laser interference system was set up to simulate the relationship between contrast, beam polarization, and the incident angle. Different pattern periods require different incident angles, which means different contrast losses in interference lithography. Two different polarization modes were presented to study the effects of polarization with different incident angles based on theoretical analysis simulations. In the case of the co-directional component TE polarization mode, it was demonstrated that the pattern contrast decreases with the increase in the incident angle and the contrast loss caused by the polarization angle error also grew rapidly. By changing the mode to azimuthal (TE-TE-TE) polarization, the contrast of the interference pattern can be ensured to remain above 0.97 even though the incident angle is large. In addition, TE-TE-TE mode can accept larger polarization angle errors. This conclusion provides a theoretical basis for the generation of high-contrast light fields at different incident angles, and the conclusion is also applicable to multi-beam interference lithography.

Imaging position shift based on the multiple azimuth squint angles (MASA) mode is effective for target azimuth velocity estimation, whereas accuracy is low when target range velocity is high. In this paper, the estimation problem for both target azimuth and range velocities is considered based on the multi-channels MASA (MC-MASA) mode. Firstly, the acquisition geometry of MC-MASA mode and Doppler characteristics of a moving target are analyzed in detail, especially in squint mode. Then, for better moving target estimation, the stationary background clutter is removed using the displacement phase center antenna (DPCA) technique, and the failure in range velocity estimation with sequential SAR images is also discussed. Furthermore, a modified along-track interferometry (ATI) is proposed to preliminarily reconstruct the azimuth-and-range velocity map based on the MC-MASA mode. Since the velocity estimation accuracy is dependent on squint angle and signal-to-clutter ratio (SCR), the circumstances are divided into three cases with different iteration estimation strategies, which could expand the scene application scope of velocity estimation and achieve a high estimation accuracy along both azimuth and range directions. Finally, the performance of the proposed method is demonstrated by experimental results.

This paper investigates optimal sensor placement strategies for angle-of-arrival (AOA) localization in three-dimensional space. We adopt the A-optimality criterion to determine optimal sensor placements under the Gaussian measurement noise. A comprehensive analysis of optimal sensor-target geometries is provided with no restriction on the number of AOA sensors, sensor-target range, and noise variances. A resistor network analogy is also presented to enable quick determination of optimal sensor-target geometries. The analytical results are verified by extensive simulation studies. Refereed/Peer-reviewed

For high-resolution wide-swath synthetic aperture radar imaging algorithms, signal reconstruction is a key step. The steering vector plays an important role in signal reconstruction, which can be constructed by the ambiguity components. The information of the ambiguity components, e.g., number and index, is usually regarded to be constant and known. However, we find that the information of ambiguity components is always a piecewise function of the baseband frequency. This means that the steering vector cannot be preconstructed accurately and it will negatively affect the signal reconstruction. This paper presents an improved signal reconstruction method based on the Doppler spectrum estimation. The proposed method can estimate the variant ambiguity components to form the steering vector exactly by the Capon estimation. As a result, the method is able to restore the Doppler spectrum entirely and performs well on the noise reduction. Moreover, the baseband Doppler centroid and antenna pattern can be obtained in the proposed method. Simulated data and airborne raw data are processed to validate the algorithm.

In this paper, the relationships of the plunges and azimuths of T and P axes versus the strikes, dips, and rakes of two seismic nodal planes were derived to provide reference for earthquake researchers. The independence of the plunges and azimuths of T, B, and P axes in focal mechanism solution was discussed, and it was concluded that three parameters, i.e., the azimuths of T, B and P axes, are completely independent. The focal mechanism solution representation based on Euler rotation was introduced, using three Euler angles in place of the plunges and azimuths of T, B, and P axes, and three focal mechanism solution representations were briefly compared and analyzed in respect of accuracy on the basis of the assumption of rounding; it was concluded that the Euler angle representation has better accuracy, compared with the azimuth representation and the traditional representation with T, B, and P axes.

Space resolution is one of the most important characteristics of radar systems. In multi-position surface movement radar (SMR) systems, resolution depends on the properties of radar sensors, their location and co-processing methods of radar data. The subject of experimental studies was a range and angular resolution of the X-band surface surveillance radar sensor "MRS-1000" as a part of the multi-position SMR system. The radar sensors were located on the airfield. The size of the range strobe to be analysed was 0.79 m, and the azimuth width was 1 0 . As to the radiation pattern width, the MRS-1000 does not satisfy the specialised SMR system requirements for 0.4 0 at most. The analysis objective was to estimate the range and angular resolution of radar sensors across maneuvering area of the artificially covered airfield surface and, using these data, give justification for further analysis of the multi-position SMR system characteristics. The paper describes a general technique to estimate the range and angular resolution of the radar sensor using a radar sensor and a pair of reference corner reflectors (RCR) with radar cross-section (RCS) of 1 m 2 and record the radar sensor output signals and provide their post-processing. The resolution was estimated by approximating the samples of the recorded signals with a Gaussian function using the least squares method. The results of range and angular resolution estimates are presented as follows: 1.5 ... 2 m in range, 1 ... 1.5 0 in azimuth. The relevance of the outcomes achieved is motivated by the need to conduct further analysis of the multi-position SMR system comprising relatively simple and low-cost radar sensors with characteristics, which are beneath the requirements for specialised SMR radars.

A new ground moving target focusing method for airborne synthetic aperture radar (SAR) is introduced in this paper. Firstly, first-order discrete polynomial-phase transform (DPT) is used to reduce the target phase order. Secondly, Keystone transform (KT) is applied to correct the residual range walk, and then the target second-order motion parameter can be estimated after performing the azimuth fast Fourier transform (FFT). Finally, the target first-order motion parameter can be estimated after the Doppler frequency migration (DFM) compensation and a well-focused result of a moving target can be obtained. Compared with the conventional SAR imaging methods, the proposed method can eliminate the effects of Doppler ambiguity and azimuth spectrum split. In addition, the proposed method is computationally efficient since the target motion parameter searching procedure is avoided, which can satisfy the target real-time imaging requirements. Real data processing results are provided to validate the effectiveness of the proposed algorithm.

We address the performance analysis of the maximum likelihood (ML) direction-of-arrival (DOA) estimation algorithm in the case of azimuth/elevation estimation of two incident signals using the uniform circular array (UCA). Based on the Taylor series expansion and approximation, we get explicit expressions of the root mean square errors (RMSEs) of the azimuths and elevations. The validity of the derived expressions is shown by comparing the analytic results with the simulation results. The derivation in this paper is further verified by illustrating the consistency of the analytic results with the Cramer-Rao lower bound (CRLB).

In this paper, a physically based numerical electromagnetic approach, by solving Maxwell's equations, is developed to investigate the scattering and the emission from double-layered media, where both the top and bottom interfaces are random sastrugi surfaces with a random horizontal shift between the two corresponding negative-slope facets of both interfaces. Numerical simulations are illustrated for bistatic scattering and four Stokes parameters at L-, C-, X-, and K-bands. Results indicate that the bistatic scattering and Stokes parameters are asymmetric for the double-sastrugi media, whereas for the other two structures, sastrugi surface alone and sastrugi surface with a planar bottom boundary, their scattering and the first two Stokes parameters are even symmetric relative to the azimuthal angle of 90°, and the third and fourth Stokes parameters are odd symmetric. In particular, the Stokes results no longer have the strong coherent fluctuations in angular variations shown in periodic double-layered structures because the random double-layered structure eliminates the coherent interference. It is interesting to observe that the internal total reflection may cancel if the coupled interactions between the two sastrugi interfaces are very strong, which results in decreasing scattering at the L-band, and its Stokes parameters are similar to those of the sastrugi alone. Numerical results also reveal that the maxima of cross-polarized specular scattering from double-sastrugi structures can be observed at cross incidence; however, they are at a deep dip for the latter two statistical symmetric structures. The sastrugi-sastrugi structure, being geometrically anisotropic, is capable of generating strong cross-polarized scattering and, subsequently, significant amounts of the third and fourth Stokes. The azimuthal patterns, at a viewing angle of 55°, of four Stokes parameters, although more complex, are feature rich where two striking extrema of third and fourth Stokes are presented. Compared with the L-band, the C-band presents strong azimuthal dependence of four Stokes. The simulation results offer deeper insights into the scattering and emission process in sastrugi surface and may lead to better retrieval of surface parameters from radar or radiometric measurements.