Azimuth Spectrum Research Articles

Quantifying Event‐Specific Radial Diffusion Coefficients of Radiation Belt Electrons With the PPMLR‐MHD Simulation

AbstractUsing the global Lagrangian version of the piecewise parabolic method‐magnetohydrodynamic (PPMLR‐MHD) model, we simulate two consecutive storms in December 2015, a moderate storm on 14–15 December and a strong storm on 19–22 December, and calculate the radial diffusion coefficients (DLL) from the simulated ultralow frequency waves. We find that even though the strong storm leads to more enhanced Bz and Eφ power than the moderate storm, the two storms share in common a lot of features on the azimuthal mode structure and power spectrum of ultralow frequency waves. For both storms, the total Bz and Eφ power is better correlated with the solar wind dynamic pressure in the storm initial phase and more correlated with AE index in the recovery phase. Bz wave power is shown to be mostly distributed in low mode numbers, while Eφ power spreads over a wider range of modes. Furthermore, the Bz and Eφ power spectral densities are found to be higher at higher L regions, with a stronger L dependence in the Bz spectra. The estimated DLL based on MHD fields shows that inside the magnetopause, the contribution from electric fields is larger than or comparable to that from magnetic fields, and our event‐specific MHD‐based DLL can be smaller than some previous empirical DLL estimations by more than an order of magnitude. At last, by validating against in situ observations from Magnetospheric Multiscale spacecraft, our MHD results are found to generally well reproduce the total Bz fields and wave power for both storms, while the Eφ power is underestimated in the MHD simulations.

Processing of Circular-Scanning SAR Data Using Deramping-Based Imaging Approach

With the circular-scanning mode, we can obtain real-time synthetic aperture radar (SAR) images of wide areas including both sides of the nadir line, which considerably benefits the terrain matching procedure. However, due to the continuous rotation of the antenna beam, the azimuth Doppler bandwidth of the circular-scanning SAR data will increase noticeably, which in turn will lead to the azimuth spectrum aliasing phenomenon. Existing approaches for the azimuth processing of the circular-scanning SAR data are based on the subaperture technique. However, when the pulse repetition frequency (PRF) is limited, these approaches result in the loss of azimuth resolution. In this letter, a new circular-scanning approach based on the deramping operation is proposed. The deramping operation could solve the problem of spectrum aliasing and the loss of azimuth resolution can be avoided. The performance of the proposed imaging approach is demonstrated by point targets simulation and real circular-scanning SAR data processing results.

A Range Doppler Imaging Algorithm Based on the MSR Spectrum for the Multi-Aperutre Syntactic Sonar

For ignoring the azimuth variation of the “non-hop-go-hop” time, the existing imaging algorithm for multi-aperture have a poor imaging in moderate squint, so this paper proposes a multi-aperture range Doppler imaging algorithm based on the spectrum of method of series reversion. The exact range history is approximated once, and the error can be adjusted by the order of Taylor series expansion. Then, the analytical expression of the two-dimensional spectrum is obtained by the method of series reversion. In signal processing, the signal of the single aperture is handle with the squint range Doppler imaging algorithm, and the azimuth spectrum is superposed to each aperture, to obtain the image. Finally, the effectiveness and correctness of the algorithm is provided by the simulation experiments.

Neutrino elastic scattering on polarized electrons as a tool for probing the neutrino nature

Possibility of using the polarized electron target (PET) for testing the neutrino nature is considered. It is assumed that the incoming nu _e beam is the superposition of left chiral (LC) states with right chiral (RC) ones. Consequently the non-vanishing transversal components of nu _e spin polarization may appear, both T-even and T-odd. nu _es are produced by the low energy monochromatic (un)polarized emitter located at a near distance from the hypothetical detector which is able to measure both the azimuthal angle and the polar angle of the recoil electrons, and/or also the energy of the outgoing electrons with a high resolution. A detection process is the elastic scattering of nu _es (Dirac or Majorana) on the polarized electrons. LC nu _es interact mainly by the standard V - A interaction, while RC ones participate only in the non-standard V + A, scalar S_R, pseudoscalar P_R and tensor T_R interactions. All the interactions are of flavour-conserving type (FC). We show that a distinction between the Dirac and the Majorana nu _es is possible both for the longitudinal and the transversal nu _e polarizations. In the first case a departure from the standard prediction of the azimuthal asymmetry of recoil electrons is caused by the interferences between the non-standard complex S and T couplings, proportional to the angular correlations (T-even and T-odd) among the polarization of the electron target, the incoming neutrino momentum and the outgoing electron momentum. It is shown that such a deviation would indicate the Dirac nu _e nature and the presence of time reversal symmetry violation interactions. It is remarkable that the result is conclusive for all Majorana non-standard couplings. In the second case the azimuthal asymmetries, polar distribution and energy spectrum of scattered electrons are sensitive to the interference terms between the standard and exotic interactions, proportional to the various angular correlations among the transversal nu _e spin polarization, the electron target polarization, the incoming nu _e momentum and the outgoing electron momentum. In the particular case of the V–A and S couplings the precise measurement of some observables, e.g. the spectrum, can distinguish between the Dirac and the Majorana nu _es as long as the incoming nu _e beam has non-vanishing transversal polarization. Our model-independent study is carried out for the flavour nu _e eigenstates in the relativistic nu _e limit.

On the SAR Imaging Performance Analysis of Alternate Transmitting Mode Based on Waveform Diversity: Theory and Simulation

For synthetic aperture radars (SARs), an alternate transmitting mode based on waveform diversity is widely discussed for suppressing range-ambiguity in many letters, because it is easy to implement and there is no need to improve the pulse repetition frequency (PRF). These studies mainly focus on the discussion of pseudo-orthogonal waveform design, such as up–down chirp waveforms and orthogonal-frequency-division-multiplexing (OFDM) waveforms; however, the effect on imaging caused by waveform diversity is ignored. This letter, for the first time, provides a demonstrative derivation of imaging for the alternate transmitting mode, which will deepen the understanding of this mode and be helpful for the future research. In this letter, we point out that transmitting different waveforms will introduce a phase-amplitude periodic modulation in the azimuth domain; furthermore, it will cause the aliasing of the azimuth spectrum. In addition, the simulation experiment is performed for verifying the correctness of the theoretical analysis.

A High-Squint TOPS SAR Imaging Algorithm for Maneuvering Platforms Based on Joint Time-Doppler Deramp Without Subaperture

The beam steering of high-squint terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) mounted on maneuvering platforms causes azimuth spectrum aliasing and nonlinear variation of the Doppler center with target azimuth position. A joint time-Doppler deramp (JTDD) based method is proposed and mainly contains two parts. First, for the azimuth spectrum aliasing, the unfolded 2-D spectrum is obtained by a modified linear deramp function in the azimuth time domain constructed from the 3-D motion parameters. After range cell migration correction (RCMC), the data supporting area in the azimuth time domain is expanded, and thus, aliased because of the nonlinear variation of Doppler center. Then, a nonlinear deramp operation in the Doppler domain is further proposed to obtain a nonaliasing signal. The proposed algorithm is efficient with less zero-padding due to the consideration of nonlinear components of Doppler center variation. Simulation and real SAR data processing are presented to validate the proposed algorithm.

Image Formation of Azimuth Periodically Gapped SAR Raw Data with Complex Deconvolution

The phenomenon of periodical gapping in Synthetic Aperture Radar (SAR), which is induced in various ways, creates challenges in focusing raw SAR data. To handle this problem, a novel method is proposed in this paper. Complex deconvolution is utilized to restore the azimuth spectrum of complete data from the gapped raw data in the proposed method. In other words, a new approach is provided by the proposed method to cope with periodically gapped raw SAR data via complex deconvolution. The proposed method provides a robust implementation of deconvolution for processing azimuth gapped raw data. The proposed method mainly consists of phase compensation and recovering the azimuth spectrum of raw data with complex deconvolution. The gapped data become sparser in the range of the Doppler domain after phase compensation. Then, it is feasible to recover the azimuth spectrum of the complete data from gapped raw data via complex deconvolution in the Doppler domain. Afterwards, the traditional SAR imaging algorithm is capable of focusing the reconstructed raw data in this paper. The effectiveness of the proposed method was validated via point target simulation and surface target simulation. Moreover, real SAR data were utilized to further demonstrate the validity of the proposed method.

Angular decorrelations in γ + 2jets events at high energies in the parton Reggeization approach

We study associated production of prompt photon and two jets at high energies in the framework of the parton Reggeization approach (PRA), which is based on multi-Regge factorization of hard processes and Lipatov’s effective theory of Reggeized gluons and quarks. In this approach, initial-state off-shell effects and transverse momenta of initial partons are included in a gauge-invariant way. We compute azimuthal angle difference spectra in [Formula: see text] + 2[Formula: see text]jets events and compare results with data from D0 Collaboration at the Tevatron. It was found that agreement between predictions and data can be achieved only under assumption on strong violation in transverse momentum ordering during initial-state quantum chromodynamics (QCD) evolution which corresponds multi-Regge kinematical regime instead of DGLAP picture.

A Phase-Preserving Focusing Technique for TOPS Mode SAR Raw Data Based on Conventional Processing Methods

We present a new solution for the phase-preserving focusing of synthetic aperture radar (SAR) raw data acquired through the Terrain Observation with Progressive Scan (TOPS) mode. The proposed algorithm consists of a first interpolation stage of the TOPS raw data, which takes into account the Doppler Centroid frequency variations due to the azimuth antenna steering function, and allows us to unfold the azimuth spectra of the TOPS raw data. Subsequently, the interpolated signals are processed by using conventional phase-preserving SAR focusing methods that exploit frequency domain and spectral analyses algorithms, which are extensively used to efficiently process Stripmap and ScanSAR data. Accordingly, the developed focusing approach is easy to implement. In particular, the presented focusing approach exploits one of the available frequency domain Stripmap processing techniques. The only modification is represented by the inclusion, within the 2D frequency domain focusing step, of a spurious azimuth chirp signal with a properly selected azimuthal rate. This allows us to efficiently carry out the TOPS azimuth focusing through the SPECAN method. Furthermore, an important aspect of this algorithm is the possibility to easily achieve a constant and tunable output azimuth pixel size without any additional computing time; this is a remarkable feature with respect to the full-aperture TOPS-mode algorithms available in the existing literature. Moreover, although tailored on Sentinel-1 (S1) raw data, the proposed algorithm can be easily extended to process data collected through the TOPS mode by different radar sensors. The presented experimental results have been obtained by processing real Sentinel-1 raw data and confirm the effectiveness of the proposed algorithm.

Parameter Estimation and Error Calibration for Multi-Channel Beam-Steering SAR Systems

Multi-channel beam-steering synthetic aperture radar (multi-channel BS-SAR) can achieve high resolution and wide-swath observations by combining beam-steering technology and azimuth multi-channel technology. Various imaging algorithms have been proposed for multi-channel BS-SAR but the associated parameter estimation and error calibration have received little attention. This paper focuses on errors in the main parameters in multi-channel BS-SAR (the derotation rate and constant Doppler centroid) and phase inconsistency errors. These errors can significantly reduce image quality by causing coarser resolution, radiometric degradation, and appearance of ghost targets. Accurate derotation rate estimation is important to remove the spectrum aliasing caused by beam steering, and spectrum reconstruction for multi-channel sampling requires an accurate estimate of the constant Doppler centroid and phase inconsistency errors. The time shift and scaling effect of the derotation error on the azimuth spectrum are analyzed in this paper. A method to estimate the derotation rate is presented, based on time shifting, and integrated with estimation of the constant Doppler centroid. Since the Doppler histories of azimuth targets are space-variant in multi-channel BS-SAR, the conventional estimation methods of phase inconsistency errors do not work, and we present a novel method based on minimum entropy to estimate and correct these errors. Simulations validate the proposed error estimation methods.

Effect Analysis of Antenna Vibration on GEO SAR Image

Existing effect analyses of antenna vibration (AV) on synthetic aperture radar (SAR) image, which are all aimed for low-earth-orbit SAR and based on the linear trajectory, second-order azimuth spectrum, and range time-invariant as well as azimuth time-variant antenna gain, are not feasible in geosynchronous SAR (GEO SAR), because GEO SAR has an obviously curved trajectory, high-order azimuth spectrum, and two-dimensional (2-D) time-variant antenna gain. To overcome these problems and analyze the effects of AV on GEO SAR image, a modified analysis is proposed in this paper. First, based on the curved trajectory, the high-order ideal echo signal model and the ideal point spread function (PSF) of GEO SAR are, respectively, established and deducted, and the AV that consists of antenna translational vibration (ATV) and antenna rotation motion (ARV) and the 2-D time-variant antenna gain in squint mode are also, respectively, modeled. Then, based on the series expansion, the paired echo theory, and the aforementioned models, the echo signal model affected by ATV, the corresponding PSF affected by ATV, the antenna gain model affected by ARV, and the corresponding PSF affected by ARV are obtained, and the effects of ATV and ARV on GEO SAR image are, respectively, analyzed in detail. Compared with existing effect analyses of AV on SAR image, the modified analysis considers the influences of curved trajectory, high-order azimuth spectrum, and 2-D time-variant antenna gain simultaneously, and it has much more accuracy and adaptability correspondingly. Finally, computer simulations validate the correctness of the proposed analysis.

Long-Time Coherent Integration Algorithm for Radar Maneuvering Weak Target With Acceleration Rate

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.

Spatial Characteristics of Wideband Channels Using Leaky Coaxial Cables in Tunnel Scenario

This paper presents the spatial domain and propagation characteristics of different wideband channels using leaky coaxial cables (LCXs) for underground environment at 1.8GHz corresponding to the Long Term Evolution for Metro (LTE-M) standards. Angular dispersion of the signal significantly affects the channel capacity, and it can be exactly predicted in both the near and far fields for underground environments by means of a multimode waveguide. A ray tracing phenomenon was exploited to visualize the wave propagation for different transmitter and receiver antenna distances by using the time domain approach for both the horizontally and vertically polarized LCXs. In order to achieve this goal, we characterized the power azimuth spectrum (PAS) and power angle profile (PAP) for different tunnel dimensions and found that the PAS can be demonstrated by a zero-mean Gaussian distribution whose angular spread (AS) is dependent on the transmitter-receiver distances and the tunnel dimensions. The results demonstrate that the horizontally polarized LCX has higher angular spread values than the vertically polarized one, and the correlation coefficient follows the decreasing function with the increment of angular spread.

Azimuthal organization of large-scale motions in a turbulent minimal pipe flow

Direct numerical simulation data for turbulent minimal pipe flows with Reτ = 927, 1990, and 2916 are examined to explore the azimuthal (or spanwise) organization of their large-scale structures. We chose a streamwise-minimal unit with a streamwise domain length of Lx+≈1000, which is the characteristic streamwise length of near-wall streaks. The spanwise scales of most of the energetic motions and their contributions to the total energy are comparable with those of the streamwise long-domain simulation. In the azimuthal energy spectra of the streamwise velocity fluctuations (u), the large-scale energy increases with Reτ and three outer peaks (λθ = 0.7–0.8, π/2 and π) become evident when Reτ = 2916. The presence of the outer peaks at λθ = 0.7–0.8 and π/2 is consistent with the results of the long-domain simulation. The peak at λθ = 0.7–0.8 is associated with large-scale motions and the other two peaks are associated with very-large-scale motions (VLSMs). The maximum spanwise wavelength increases linearly with the wall-normal distance from the wall. A kz−1 region is evident in the range 0.3R < λz (=rλθ) < R, which indicates the presence of self-similar motions. The conditional two-point correlation with a cut-off wavelength of λz = 0.9R shows that there is a strong correlation between the enhanced energy in the outer region and the wall-attached structures, which were extracted from the time evolution of the streamwise-averaged u field (u2D). The spanwise sizes (lz) of the attached u2D structures scale with their height (ly) in the log region and their time scales (lt) follow ltuτ/lz = 2, which is consistent with the bursting time scale. Their spanwise sizes lie in the range R < lz < 3R, for which lt increases significantly, which indicates that these structures are associated with VLSMs and make the dominant contributions to the enhanced energy in the outer region. These structures penetrate to the wall region as a manifestation of the footprint and modulate the small-scale energy. The negative-u2D structures induce congregative motions in the near-wall region.

Retrieval of Polarimetric Azimuthal Angular Characteristics via the Application of Target Decomposition to Spectral Domain Circular SAR Images

In this paper, we discuss the application of polarimetric target decomposition (TD) theorems to circular synthetic aperture radar (CSAR) images to retrieve the polarimetric azimuthal angular characteristics of the targets. In CSAR systems, radar-carrying aircraft moves along a circular path. The antenna beam is pointed toward the center of the circular path during the data acquisition to irradiate the spotlighted area from various azimuthal or aspect angles. Therefore, the resultant polarimetric CSAR images contain information about the polarimetric scattering mechanisms of the targets at each aspect angles. To recover this information, we propose the use of spectral decomposition of CSAR images in combination with several TD algorithms. The spectral domain CSAR images can be viewed as the azimuthal angular spectrum images. Thus, the application of TD algorithms to the spectral domain images is expected to be able to obtain the angular dependence and polarimetric scattering properties of the targets simultaneously. We carried out a simple numerical simulation and an indoor laboratory experiment to validate the proposed TD scheme.

Color reconnection as a possible mechanism of intermittency in the emission spectra of charged particles in PYTHIA-generated high-multiplicity pp collisions at energies available at the CERN Large Hadron Collider

Nonstatistical fluctuation in pseudorapidity ($\ensuremath{\eta}$), azimuthal ($\ensuremath{\phi}$), and pseudorapidity-azimuthal ($\ensuremath{\eta}\text{--}\ensuremath{\phi}$) distribution spectra of primary particles of PYTHIA Monash (default) generated $pp$ events at $\sqrt{s}=2.76$, 7, and 13 TeV have been studied using the scaled factorial moment technique. A weak intermittent type of emission could be realized for minimum-bias (MB) $pp$ events in $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ space and a much stronger intermittency could be observed in high-multiplicity (HM) $pp$ events in all $\ensuremath{\chi}(\ensuremath{\eta})$, $\ensuremath{\chi}(\ensuremath{\phi})$, and $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ spaces at all the studied energies. For HM $pp$ events, at a particular energy, the intermittency index ${\ensuremath{\alpha}}_{q}$ is found to be largest in two-dimensional $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ space and least in $\ensuremath{\chi}(\ensuremath{\eta})$ space, and no center of mass energy dependence of ${\ensuremath{\alpha}}_{q}$ could be observed. The anomalous dimensions ${d}_{q}$ are observed to be increased with the order of the moment $q$, suggesting a multifractal nature of the emission spectra of various studied events. While, the coefficient ${\ensuremath{\lambda}}_{q}$ is found to decrease monotonically with the order of the moment $q$ for two-dimensional analysis of MB $pp$ events as well as for one-dimensional analysis of HM $pp$ events, a clear minimum in ${\ensuremath{\lambda}}_{q}$ values could be observed from the two-dimensional HM $pp$ data analysis. For PYTHIA Monash generated sets of data, the strength of the intermittency is found to vary significantly with the variation of the strength of the color reconnection (CR) parameter, i.e., reconnection range RR, for $\mathrm{RR}=0.0$, 1.8 and 3.0, thereby, establishing a strong connection between the CR mechanism and the observed intermittent type of emission of primary charged particles of the studied high-multiplicity $pp$ events.

Algorithm Optimization and Model Comparison in MIMO OTA Testing

3GPP, CTIA and COST name the testing method for evaluating the performance of multi-antenna terminals as multiple input multiple output over the air test. In serval proposed methods, multiple probe anechoic camber-based testing method for MIMO capable equipment is attractive due to its ability to reconstruct spatial-temporal characteristic in controllable way. In this paper, power allocation among multiple probes will be investigated to emulate a given channel model, specified by its power azimuth spectrum (PAS), accurately. In the optimization algorithm, an effective power allocation algorithm is obtained by introducing the constraint of the maximum deviation (average angle of arrival AOA and azimuth extension AS) between the target PAS and the simulated PAS. After adding the constraints, the research can turn the problem into a convex optimization problem and solve it in the CVX convex optimization toolkit in Matlab. In the simulation, the proposed algorithm is compared with the reference algorithm least squares method in the related literature. The simulation results show that the proposed optimization algorithm is better than the reference algorithm and the optimization performance of the proposed algorithm is confirmed.

Estimating structure and geoacoustic parameters of sub-bottom by using spatial characteristics of ocean ambient noise in shallow water

The field of ocean ambient noise contains numerous information about the water column, especially the information about the sub-bottom. The geoacoustics parameters of sub-bottom are very important factors influencing the spatial characteristics of ocean ambient noise field. For different layered structures of the sub-bottom, the bottom-loss shows different critical angles according to sound speed of each layer, while the structure of interference fringe is dependent on the thickness of the sediment. Flux theory of ocean ambient noise proposed by Harrison is used in this paper. Using this theory, the curve of bottom-loss can be extracted by computing the ratio between the energy of the upward wave and the downward wave. From the ideal reflection coefficient, the influence of sound speed, density and attenuation coefficient on reflection coefficient are discussed in the situation of the sub-bottom of acoustic half space, while the reflection coefficient of 1 layer of sediment is simplified. Initially, the reflection coefficient is the sum of sound waves reflect from the sub-bottom transmitted from the same source at the same angle. Only the first two terms are reserved, so that the mechanism of the interference fringe can be easily discussed. The structure of interference fringe can be explained which is affected by the thickness of the sediment. The curve of bottom-loss oscillates periodically with the increase of the thickness of the sub-bottom. Also by the reciprocity principle, the interference fringe of the reflection coefficient can be explained by considering the sound transmitted from two point sources at the surface of the sea. In this way the same result can be obtained as that from the method of simplification. The result of the experiment in China Yellow Sea shows that the information about the reflection coefficient of the sub-bottom can be extracted by the vertical azimuth spectrum of ocean ambient noise. In this way, the critical angle can be obtained, so that the sound speed of the sub-bottom can be estimated by using Snell law. The structure of the interference fringe is also contained in the bottom-loss curve estimated by ocean ambient noise. Therefore the layered structure, sound speed and the thickness of the layer of the sub-bottom can be estimated.

Axisymmetric rotating flow with free surface in a cylindrical tank

The flow induced by a disk rotating at the bottom of a cylindrical tank is characterised using numerical techniques – computation of steady solutions or time-averaged two-dimensional and three-dimensional direct simulations – as well as laser-Doppler velocimetry measurements. Axisymmetric steady solutions reveal the structure of the toroidal flow located at the periphery of the central solid body rotation region. When viewed in a meridional plane, this flow cell is found to be bordered by four layers, two at the solid boundaries, one at the free surface and one located at the edge of the central region, which possesses a sinuous shape. The cell intensity and geometry are determined for several fluid-layer aspect ratios; the flow is shown to depend very weakly on Froude number (associated with surface deformation) or on Reynolds number if sufficiently large. The paper then focuses on the high Reynolds number regime for which the flow has become unsteady and three-dimensional while the surface is still almost flat. Direct numerical simulations show that the averaged flow shares many similarities with the above steady axisymmetric solutions. Experimental measurements corroborate most of the numerical results and also allow for the spatio-temporal characterisation of the fluctuations, in particular the azimuthal structure and frequency spectrum. Mean azimuthal velocity profiles obtained in this transitional regime are eventually compared to existing theoretical models.

A Frequency Domain Backprojection Algorithm Based on Local Cartesian Coordinate and Subregion Range Migration Correction for High-Squint SAR Mounted on Maneuvering Platforms

Accurate range modeling, cross-range-dependent range migration, and space-variant Doppler parameter are main issues to be solved in processing high-squint synthetic aperture radar (SAR) data acquired from maneuvering platforms. A frequency domain backprojection algorithm, based on local Cartesian coordinate (LCC) and subregion range cell migration correction, is proposed to deal with these problems. With the proposed algorithm, the range model is built in an LCC system to accurately match the signal characteristics after range walk correction. Then, the compensation of cross-range-dependent range migration is implemented based on properly divided subregions after azimuth spectrum filtering. Finally, the space-variant Doppler parameter and higher order phase terms are coherently integrated in range-Doppler domain to get the focused subregion images with full resolution of the synthetic aperture. The final image of the entire scene is obtained by directly connecting all subregion images. The results of simulated and real SAR data validate the proposed algorithm.