Deep neural networks have achieved remarkable accomplishments in practice. The success of these networks hinges on effective initialization methods, which are vital for ensuring stable and rapid convergence during training. Recently, initialization methods that maintain identity transition within layers have shown good efficiency in network training. These techniques (e.g., Fixup) set specific weights to zero to achieve identity control. However, settings of remaining weight (e.g., Fixup uses random values to initialize non-zero weights) will affect the inductive bias that is achieved only by a zero weight, which may be harmful to training. Addressing this concern, we introduce fully identical initialization (IDInit), a novel method that preserves identity in both the main and sub-stem layers of residual networks. IDInit employs a padded identity-like matrix to overcome rank constraints in non-square weight matrices. Furthermore, we show the convergence problem of an identity matrix can be solved by stochastic gradient descent. Additionally, we enhance the universality of IDInit by processing higher-order weights and addressing dead neuron problems. IDInit is a straightforward yet effective initialization method, with improved convergence, stability, and performance across various settings, including large-scale datasets and deep models.

Geometric modeling and imaging mechanisms of turbulent wake have been the focus of research in remote sensing. This paper proposes an interpolation wave-making method (IWMM) to simulate the turbulent wake in the ocean background, which takes into account wave-current interactions rather than using a simple linear superposition method. Combined with the turbulent energy spectrum, the SAR images of the wake at different azimuths are obtained using the semi-deterministic facet scattering model (SDFSM) and velocity bunching (VB) imaging system. The simulation results show that the turbulent wake has a better observation effect only when the radar view direction is parallel to the ship's motion direction. At this angle, the turbulent wake shows the SAR imaging characteristics of one bright side and one dark side.

When a ship moves on a dynamic sea, apart from the translation caused by its velocity, it also has micro rotation motions caused by the interaction between the ship and the ocean waves, i.e. the roll, the pitch and the yaw, which leads to the micro-Doppler features of ships. This paper focuses on the study of the micro-Doppler characteristics of ships on a dynamic sea because it can provide a way for inversion of the target's state of motion, which will benefit the detection and recognition of ships in a marine environment. For this purpose, the radar echo of a ship target is simulated based on its scattering characteristics and the radar parameters. In this process, the scattering characteristics of the target is estimated with the famous geometrical optics and the physical optics (GO-PO) hybrid method. Then, the micro doppler spectrogram is calculated with the short-time Fourier transform (STFT). With this procedure, the micro doppler spectrograms of the ship target with different types of micro motions are simulated. The numerical results show that the amplitude and the period of motion can be estimated with the micro doppler spectrogram, which will benefit the target detection in a marine environment.

Target detection and imaging are important applications of using the BeiDou satellite navigation system reflection signals. This paper proposes a multi-satellite multi-target signal detection model based on Global Navigation Satellite System-Reflection (GNSS-R) bistatic radar technology. Through simulated one-dimensional range images and data curves, it is found that pulse accumulation can effectively suppress noise sidelobes. In addition, the experimental results of the multi-satellite multi-target simulation are given to verify the effectiveness of the proposed model and techniques, and at the same time, the shortcomings of the signal in the influence of multi-target Doppler peak are pointed out.

The spread of misinformation on social media has become a major societal issue during recent years. In this work, we used the ongoing COVID-19 pandemic as a case study to systematically investigate factors associated with the spread of multi-topic misinformation related to one event on social media based on the heuristic-systematic model. Among factors related to systematic processing of information, we discovered that the topics of a misinformation story matter, with conspiracy theories being the most likely to be retweeted. As for factors related to heuristic processing of information, such as when citizens look up to their leaders during such a crisis, our results demonstrated that behaviors of a political leader, former US President Donald J. Trump, may have nudged people's sharing of COVID-19 misinformation. Outcomes of this study help social media platform and users better understand and prevent the spread of misinformation on social media.

Differences in the motion of different parts of a target cause the echo signal to contain specific Doppler modulation information, i.e., the micro-Doppler (m-D) effect. This phenomenon provides an effective way to detect targets in marine environments. In this study, based on the establishment of the micromotion model of a rotating surveillance radar and analysis of the m-D frequency, the geometrical optics and physical optics (GO-PO) method and the time-frequency analysis technique are used to obtain the radar cross section (RCS) and m-D signature of a ship with a shipborne radar at different observation angles. The ship, as the main component of the echo, is associated with the main energy. Finding the optimum angle to observe the shipborne radar is of great importance. The results show that the m-D signatures of the shipborne radar are not clear when the elevation angle is greater than 60° but are clear when the elevation angle is less than 55°. Moreover, some motion parameters can be extracted from the m-D signature, such as the period of the ship micromotion. The rotation speed of the shipborne radar can be obtained and is consistent with the set speed. This can help identify and track the key parts of a ship with local motion.

The orthogonal frequency division multiplexing (OFDM) chirp signal has its special merits of high-range resolution by exploiting a full bandwidth as multiple input multiple output (MIMO) radar signal. After simulation, there are some high peaks in the autocorrelation function and cross correlation function of conventional OFDM chirp signals, which may increase the correlation interference and reduce the detection performance of MIMO radar signal. This letter proposes to reduce the autocorrelation sidelobe peak (ASP) of OFDM chirp signal by subsection imitating the nonlinear frequency modulation (NLFM) signal's time-frequency structure. Since a suitable difference should be made between the subchirp rates and subchirp carrier frequencies of each of the two designed OFDM chirp signals for reducing the cross correlation peaks (CP), the imitated NLFM waveforms' design problem is solved by the proposed optimized method. At last, subchirps of the designed signals are coded by a group of optimized codes. The simulation shows the designed OFDM chirp signals have lower ASP and CP than the conventional ones and referenced previous OFDM signals, and their ASP decreases as the number of subchirps increases.

A modified range-Doppler algorithm (M-RDA) for processing high squint synthetic aperture radar (SAR) echoes is proposed in this letter. Unlike the original RDA, the M-RDA directly corrects the range cell migration in the range frequency domain without interpolation, which greatly enhances its computational efficiency. When analyzing a high squint SAR echo signal, the approximation of the distance between the SAR antenna and the scene of interest leads to error in azimuthal compression. To address this problem, a fourth-order phase model is considered in the proposed algorithm to achieve accurate azimuthal compression. Finally, geometry correction is performed to obtain the final focused SAR images. The simulation results show that the proposed algorithm can process high squint SAR echoes effectively.

The study on the scattering mechanism of breaking ship waves provides important theoretical basis to the ship detection and radar imaging in a marine environment. This paper presents a new procedure for evaluating the electromagnetic scattering field of breaking ship waves over a perfect electric conductor sea surface. In this paper, different forms of the near-field ship waves are obtained by the computational fluid dynamics (CFD) method, which provides a new means of analyzing a fully coupled fluid-structure interaction system in a detailed manner. Sufficient grids are used in the CFD numerical simulation to obtain the flow field information of the breaking waves. The accuracy of the breaking wave geometry has been improved obviously, which will lead to a better understanding of the electromagnetic scattering characteristics of breaking ship waves. Considering the multiple scattering between the ship hull and the breaking waves, the scattering field of the sea surface and the ship hull are evaluated by the forward-backward iterated physical optics algorithm. Both scattering characteristics of the breaking ship waves and distribution of the scattering coefficients are obtained. By comparing the bistatic scattering field in different situations, the numerical results show some important effects of the breaking ship waves, which are quite different from the effects of ship models. What is more, the time varying radar cross section of the breaking ship waves are presented based on the dynamic ship waves.

In simulations of different kinds of radar clutter or scattering intensity distribution of terrain or sea surroundings, the memoryless nonlinear transform (MNLT) method is one of the most widely used approach for the simulation of non-Gaussian stochastic process or high-dimensional field, especially for the requirement of high-efficiency purpose. Concerning the MNLT method, the estimation of power spectral function usually exerts a strong impact on the quality of the implementation, which is not discussed in the previous literatures. This letter gives a study on the comparison of the 3-D correlated map simulations of sea-surface scattering using different ways of power spectral function estimation in the small to large sea scattering data simulation. From comparisons of the simulation results, it is observed that the interpolation-based expanding method is the optimal way to conduct power spectral function estimation, which can make a significant contribution to the scattering predictions and remote sensing simulations concerning the large maritime scenes.

The mixture of wind wave and swell is simulated based on a bimodal spectrum and nonlinear hydrodynamic theory, and the investigation of the Doppler spectra of backscattered signals from such sea surfaces in time-varying marine environment is performed by applying the second-order small-slope approximation model. The results are also compared with some popular data sets, and based on the comparison it can be found that the variation trends of Doppler shift and Doppler spectral bandwidth are different for mixed waves with various weights, which reflect qualitatively the distinct ways of influences that wind wave components and swell ones exert on Doppler signature.

In numerous researching fields involving sea scattering problems, the electromagnetic (EM) scattering model becomes a better alternative rather than a direct experiment due to its low cost and easy realization. Nevertheless, the EM scattering model still appears to be slow and laborious when encountering the large scene or the long time case. This letter proposes an effective and efficient approach for 3-D space-time correlated sea scattering map simulation, an important step in real clutter simulation, which is based on the statistical characteristics from the EM scattering model. Namely, this approach can give a fast simulation of the large scene or long time space-time correlated sea scattering map through the statistic characteristics of that with a small scene or short time acquired by the EM scattering model. From the comparisons of the texture feature and the statistical characteristics between the results derived from the EM model and the proposed approach, it is demonstrated that the proposed approach can give a fast and effective simulation of the 3-D space-time correlated sea scattering map.

A complete facet model for the backscattering from rough sea surface with breaking waves is proposed in this paper. In consideration of the spatial distribution of breaking waves on sea surface, the model is able to give a good interpretation to the “super events” under high sea states, such as sea spikes and high polarization ratios. Based on the proposed model, normalized radar cross section plots of sea surface under backscattering configuration are calculated and compared with measured data. The comparisons show that the proposed model is tractable to estimate the scattering from electrically large ocean surface under high sea states with accuracy and efficiency. In addition, the non-Gaussian statistics and spatial correlation properties of sea clutter are analyzed under different range resolutions and incident angles. The results show that high kurtosis value, which means a sea spike phenomenon, mostly happens in lower grazing angle and higher range resolution cases. The comparisons of simulated SAR images of sea surface with and without breaking waves also reveal that sea spikes and high polarization ratios are caused by breaking waves. All the simulation results prove that our model not only is able to explain the physical mechanism of the scattering but also can be applied to the analyses of statistical properties of sea clutter under high sea states.

The Bragg hypothesis provides a simplified representation of the complex real ripples that contribute to sea clutter returns. We propose to describe the microscopic profile of large-scale long waves by a set of sinusoidal ripples, which are assumed to be with the Bragg wavelength that satisfies the resonant condition, and travel along the local scattering lines of sight pointing towards and away from the radar. This simplification shows a reasonable way to obtain a rather simple representation of Bragg waves on sea surfaces. More importantly, it allows us to derive a simple asymptotic expression of integration in the far-field scattering amplitude formula, which facilitates the development on a compact model of the instantaneous complex reflective function of a time-deterministic sea surface. Good agreements shown in numerical examples validate the proposed model, which is very efficient to simulate the coherent sea clutters in 2D case up to X band.

An improved facet model for the predication of the normalized radar cross section (NRCS) of electrically large rough sea surface was proposed based on the first-order small slope approximation (SSA-1) method, the Bragg scattering mechanism, and the specular scattering mechanism. The proposed method is able to evaluate both the complex reflective function and NRCS of electrically large sea surfaces from as low as ultrahigh frequency band to as high as Ka-band. The main idea is that a tilt sea facet can be regarded as the superposition of a planner facet and the microscopic profile; the latter is assumed to be a set of sinusoidal ripple patches. Thus, the integration kernel in SSA-1 over several small facets can be replaced by a large facet with a short wave modification. The efficiency increases because of the much larger mesh size than SSA. Then, both the backscattering and bistatic scattering NRCS results calculated by the proposed method were compared with those predicated by SSA-1, and all of the results show that the proposed method has the merits of high calculation efficiency as well as calculation accuracy.

In the former model for sand surface electromagnetic (EM) scattering, the sand ripples are generally viewed as a standard sine-shaped wave surface, which artificially deprives many inherent properties of natural sand ripples. For example, the ripples have two pretty distinct sides: Y-junctions and variable texture directions. For these reasons, these corresponding scattering models deserve doubts to final calculated results. On the other hand, the former models usually are statistical models, which are not favorable in target coupling scattering problems and synthetic aperture radar (SAR) imaging simulations. In this paper, based on the physical mechanism governing the formation of aeolian landforms, sand ripples of actual shape are generated under the discrete models. Furthermore, as the slope of the ripple surface is fully small, facet-based small-slope approximation (SSA) method is unquestionably utilized in the EM scattering studies of sand ripples. Finally, significant differences are shown between the results based on sine-shaped wave surface and practical ripple surface, which proves the necessity of the new model for EM scattering of sand ripples.

For a better understanding of the inverse synthetic aperture radar (ISAR) image, cross-range scaling is an essential step. To deal with the scaling problem of ISAR image, this letter proposes a novel cross-range scaling algorithm for ISAR image. This method consists of three steps. In the first step, joint time-frequency method is employed to compensate the rotational motion and generate 2-D ISAR images at two selected times. Theoretically, after rotating the angular shift between the two images, they present the same appearance. However, conventional image rotation is computationally inefficient and complex for implementation. Thus, in the second step, we propose a 2-D unitary estimation of parameters via rotation invariance technique (ESPRIT) superresolution ISAR imaging technique to extract isolated scatterers instead of conventional ISAR image. In the last step, we search rotation velocity (RV) and rotate the image by angular shift to find the right RV that makes the two selected images match each other best. Finally, simulated and real ISAR data are provided to demonstrate the effectiveness and correctness of the proposed cross-range scaling algorithm.

Based on the scattering mechanisms of multipath, a bistatic synthetic aperture radar (Bis-SAR) image intensity model for the composite ship-ocean (or other metallic targets with ocean) scene is developed in this paper through reasonably dealing with the path lengths of transmitter and receiver to the ship target. To get a Bis-SAR image intensity model for the composite ship-ocean scene, the Bis-SAR image intensity distribution for the ocean surface is analyzed, and the facet scattering model is used to give the individual returns from separate facets. In addition, the influence of velocity bunching (VB) modulation of long ocean waves on the distribution of radar cross section is also discussed. Finally, Bis-SAR imagery simulations of ocean wave and the composite ship-ocean scene are illustrated, and the results show that the proposed Bis-SAR image intensity model can be reasonable and the interaction effects between the ship and sea surface can make significant contributions to the Bis-SAR intensity.

Two-dimensional exponential correlation rough surfaces characterized by textures are combined with the small-slope approximation (SSA) method to comparatively study electromagnetic (EM) scattering features of textured surfaces. The normalized copolarized radar cross section from 2-D exponential correlation rough surfaces characterized by stripe texture and block texture, respectively, is analyzed. Several numerical results show the effects of incident angle, texture angle, correlation length, and root-mean-square height on the copolarimetric scattering from the textured rough surface. The validity of the SSA method is verified by comparisons of theoretical value and measured data. Moreover, normalized amplitude distributions of backscattering fields from cells in a scene are studied through its statistical distribution and space correlation function, which are particularly useful for analysis and simulation of remote sensing images. Finally, based on the statistical distribution and space correlation function, the zero memory nonlinear transformation method is utilized to simulate EM scattering from very large scenes. The simulated scene coincides with the original one quite well.

This paper presents a study of the microwave backscattering from 2-D time-evolving nonlinear surfaces of a sea with finite depth by using the second-order small-slope approximation. According to the shallow-water dispersion relation, the revised nonlinear hydrodynamic choppy wave model in connection with an experiment-verified sea spectrum for finite-depth water is employed to construct the wave profiles in the finite-depth sea. The numerical results show that the discrepancy between the choppy surfaces of the infinite-depth sea and their finite-depth counterparts for monostatic normalized radar cross section is much smaller than that between the linear surfaces and the nonlinear choppy surfaces. Furthermore, the comparison of the Doppler spectra of the backscattered echoes from the linear and nonlinear choppy sea surfaces shows that the nonlinear hydrodynamic features significantly impact the Doppler spectrum. In particular, the Doppler spectrum for nonlinear finite-depth sea presents much higher second-order peaks and increased spectral amplitudes in the frequency range around the Doppler peak frequency, which reiterates the importance of the role that the nonlinear hydrodynamic effect of waves played in the interpretation of backscattering from finite-depth nearshore seas from the qualitative point of view.

This paper is aimed at developing an applicable and feasible facet model, which formulation should be tractable and time saving for personal computers to take charge of the efficient evaluation on the complex reflective function of large-scope 2-D oceans, either in the monostatic or bistatic case. The sea surface is envisaged as a two-scale profile on which the long waves are locally approximated by planar facets. The microscopic profile within a facet is assumed to be represented by a set of sinusoidal ripple patches. The complex reflective function of each modified facet is evaluated by a modified formula of the original Bass and Fuks' two-scale model, in which the phase factor of each facet is with the capillary wave modification. Several examples with application to the frozen or time-evolving case are given to prove the implementation.