Squint Angle Research Articles

Positioning for High-Speed Maneuverable Platform Based on Wrapped InSAR Interferogram

Interferometric Synthetic aperture radar (InSAR) aided inertial navigation system (INS) is developed to introduce terrain elevation into registration, which gives out accumulated error of INS. Unwrapped InSAR interferogram plays a key role in previous InSAR/INS frameworks, while airborne and side-looking assumptions are usually made. However, phase unwrapping is time-consuming and high squint geometry with nonlinear trajectory is common for applications with InSAR/INS. In this article, a novel wrapped InSAR interferogram based positioning method for high-speed maneuverable platform is proposed. A novel back-projection based InSAR (BP-InSAR) signal model for slightly curved diving trajectory with high squint angle is firstly presented. Then process which generates phase gradient template from given DEM is presented, considering both the estimated and measured trajectories. Error analysis is also made to discuss the performance of the proposed method in single dual-channel observation. Finally, a sequential maximum likelihood estimator based on error analysis is implemented to deal with the remained uncertainty in single observation. Numerical experiments verify the proposed method and fully demonstrate the performance of it with curved trajectory and random errors in both position and attitude.

Study on Airborne Near-Nadir TOPS SAR Imaging With Attitude Angle Error

Combined with terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR), near-nadir SAR (N-SAR) system has great potential for the surface water and ocean topography (SWOT) observation. However, one practical problem of the airborne N-SAR is the non-ideal attitude angle caused by the environment. Normally, the influence of attitude angle error can be considered as a constant squint angle of the system. However, in fact, for the near-nadir SAR system with TOPS SAR mode, the attitude angle error will cause a non-ideal 2-dimensional space-variant Doppler centroid for the receiving data and cause the traditional imaging algorithm failure. To deal with such problems, an imaging algorithm with attitude angle estimation for the near-nadir TOPS SAR system is proposed in this paper. Firstly, the influence of attitude angle error and the signal properties are analyzed. Secondly, based on the analysis, an attitude angle estimate algorithm (AAE), utilizing the nonlinear least square method (NLSM) and minimum entropy criterion, is proposed. Then, based on the estimated altitude angle, without data blocking, a full data imaging algorithm (FDA) is proposed. Its main idea is to obtain an un-ambiguous azimuth spectrum and design an appropriate range-variant azimuth filter through frequency chirp scaling (FCS). The numerical simulations and real data processing demonstrate that the proposed algorithm has good performance on attitude angle error estimation and well-focused image obtaining.

Processing of Airborne Video SAR Data Using the Modified Back Projection Algorithm

This article proposes an algorithm framework recently developed for video synthetic aperture radar (SAR), and presents the processing results of the airborne data collected by a W-band radar. This framework aims to accelerate time domain algorithm and produce SAR video that has no change of view angle, which is highly desired in target tracking. The presented framework includes a few modified processing algorithms, where the strategy of subaperture recursion is proposed. The modified acceleration algorithm is used to avoid the interpolation and to adapt to high squint angle without rotation of image grids. Additionally, the conventional autofocus method has been improved to deal with urban data that usually contain strong scatterers. The algorithm framework can achieve SAR video without rotation of view angle with a lower computational load compared to other existing time domain methods, which has been verified on airborne real data. Its processing efficiency becomes impressive if the apertures are highly overlapped in some cases that requires very high frame rate.

Medial rectus disinsertion for management of chronic complete sixth nerve palsy.

To report the outcomes of the medial rectus (MR) disinsertion procedure for the management of refractory esotropia (ET) with or without Abnormal head posture (AHP) in chronic complete sixth nerve palsy. This is a retrospective case series of patients with sixth nerve palsy who suffered from residual ET and diplopia following the conventional strabismus surgeries and underwent MR disinsertion procedure between April 2017 and February 2020. This procedure was offered to the patients who declined to use prism and did not wish to perform surgery on the fellow eye. The demographic and clinical data, including sex, age, visual acuity, pre and postoperative angle of strabismus, duction limitations, results of forced duction and force generation tests, details of prior strabismus surgeries, orbital CT scan findings, and follow up duration were collected from the medical records. Six patients were enrolled in this study. Mean age was 35.0 ± 14.0 years, and mean follow-up was 15.3 ± 5.9 months. The ET at the Primary position (PP) was 35.0 ± 18.4 prism dioptre (PD) before MR disinsertion, which decreased to 14.2 ± 17.4 PD after MR disinsertion procedure. Four cases needed additional complementary surgeries to improve residual ET in PP. No case developed overcorrection. Abduction deficiency was -5.0 ± 1.3 before MR disinsertion, which improved to - 2.8 ± 0.5 units at last follow-up. The mean of induced adduction deficiency was - 2.9 ± 0.4 at last follow-up. MR disinsertion can be considered in patients with chronic complete sixth nerve palsy and refractory diplopia when the conventional methods have failed.

An Improved Equivalent Squint Range Model and Imaging Approach for Sliding Spotlight SAR Based on Highly Elliptical Orbit

As an emerging orbital system with flexibility and brand application prospects, the highly elliptical orbit synthetic aperture radar (HEO SAR) can achieve both a low orbit detailed survey and continuous earth surface observation in high orbit, which could be applied to marine reconnaissance and surveillance. However, due to its large eccentricity, two challenges have been faced in the signal processing of HEO SAR at present. The first challenge is that the traditional equivalent squint range model (ESRM) fails to accurately describe the entire range for the whole orbit period including the perigee, the apogee, and the squint subduction section. The second one is to exploit an efficient HEO SAR imaging algorithm in the squinted case which solves the problem that traditional imaging algorithm fails to achieve the focused imaging processing of HEO SAR during the entire orbit period. In this paper, a novel imaging algorithm for HEO SAR is presented. Firstly, the signal model based on the geometric configuration of the large elliptical orbit is established and the Doppler parameter characteristics of SAR are analyzed. Secondly, due to the particularity of Doppler parameters variation in the whole period of HEO, the equivalent velocity and equivalent squint angle used in MESRM can no longer be applied, a refined fourth-order equivalent squint range model(R4-ESRM) that is suitable for HEO SAR is developed by introducing fourth-order Doppler parameter into Modified ESRM (MESRM), which accurately reconstructs the range history of HEO SAR. Finally, a novel imaging algorithm combining azimuth resampling and time-frequency domain hybrid correlation based on R4-ESRM is derived. Simulation is performed to demonstrate the feasibility and validity of the presented algorithm and range model, showing that it achieves the precise phase compensation and well focusing.

Accurate detection method of moving target based on sequential SAR images with multiple azimuth squint angles

In this paper, a novel moving target detection method for sequential Synthetic Aperture Radar (SAR) images with different azimuth-squint angles is proposed. In sequential SAR images, due to the movement of the target, the imaging position of moving targets among different frames differs. The method proposed in this paper uses this kind of motion characteristics to achieve the detection of moving targets in multi-frame SAR images. This algorithm can be divided into two parts: block-level detection and pixel-level detection. Block-level detection is achieved by stacked denoising autoencoders to extract the high-dimensional features of the moving target. Pixel-level detection consists of Local Binary Similarity Patterns (LBSP) coding as well as grayscale background subtraction. Pixel-level detection only needs to consider the pixels of foreground image pieces which contain moving targets. This method can not only increase the detection speed, but also suppress the false alarm problem caused by clutter. Experiments are carried out for verifying the validation of the method and the comparison are made between the proposed method and the traditional Constant False Alarm Rate (CFAR) algorithm.

Ground Moving Target Imaging for Highly Squint SAR by Modified Minimum Entropy Algorithm and Spectrum Rotation

Ground moving target (GMT) is displaced and defocused in conventional synthetic aperture radar (SAR) image due to the residual phase error of non-cooperative GMT motion. In this study, a GMT imaging (GMTIm) method is proposed for highly squint SAR. As the squint angle become large, the displace and defocus effect of the GMT image become severe and the geometry distortion of the GMT image cannot be ignored. The proposed method first deduced the two-dimensional (2-D) frequency domain signal of the GMT and the bulk compression function of the Range Migration Algorithm (RMA) in highly squint SAR. Then GMT ROI data are extracted and a modified minimum entropy algorithm (MMEA) is proposed to refocus the GMT image. MMEA introduces the idea of bisection into the iteration process to converge more efficiently than the previous minimum entropy method. To overcome the geometry distortion of the GMT image, an equivalent squint angle spectrum rotation method is proposed. Finally, to suppress the GMT image sidelobe, the sparse characteristic of GMT is considered and a sparse enhancement method is adopted. The proposed method can realize GMTIm in highly squint SAR where the squint angle reaches to 75 degrees. The PSNR and ISLR of point target in highly squint SAR is close to that in side-looking SAR. The simulated point target data and ship data are used to validate the effectiveness of the proposed method.

Strip-Map SAR Image Formulation Based on the Modified Alternating Split Bregman Method

Conventional compressive sensing (CS)-based imaging methods allow images to be reconstructed from a small amount of data, while they suffer from high computational burden even for a moderate scene. To address this problem, this paper presents a novel two-dimensional (2D) CS imaging algorithm for strip-map synthetic aperture radars (SARs) with zero squint angle. By introducing a 2D separable formulation to model the physical procedure of the SAR imaging, we separate the large measurement matrix into two small ones, and then the induced algorithm can deal with 2D signal directly instead of converting it into 1D vector. As a result, the computational load can be reduced significantly. Furthermore, thanks to its superior performance in maintaining contour information, the gradient space of the SAR image is exploited and the total variation (TV) constraint is incorporated to improve resolution performance. Due to the non-differentiable property of the TV regularizer, it is difficult to directly solve the induced TV regularization problem. To overcome this problem, an improved split Bregman method is presented by formulating the TV minimization problem into a sequence of unconstrained optimization problem and Bregman updates. It yields an accurate and simple solution. Finally, the synthesis and real experiment results demonstrate that the proposed algorithm remains competitive in terms of high resolution and high computational efficiency.

Observation on the Curative Effect of Microsurgery in 154 Children with Strabismus and Analysis of Its Influencing Factors.

Strabismus is a common ophthalmic disease in the process of child body development, in which the two eyes cannot gaze at the target at the same time, and the incidence of this disease of children is higher. In children with esotropia, exotropia, and up and down strabismus and other typical symptoms, the cause is genetic, innerve, and refractive and regulated, and not receiving timely treatment may lead to stereo vision and diplopia and other phenomena, affecting their learning and life. Surgical treatment is the main treatment for strabismus at present. Traditional orthodontic surgery is performed by doctors under the naked eye, often due to improper operation or suture error and other factors, resulting in more postoperative complications, such as more tissue damage, conjunctival congestion, and muscle suture reaction, which seriously affect the clinical effect of surgical treatment. In recent years, with the continuous development of microsurgical technology, the correction of strabismus under a microscope has been widely carried out in clinic. The operation under the microscope makes the operation more delicate and accurate, overcomes the defects of traditional surgery, and highlights the advantages of minimally invasive surgery. The purpose of this study was to investigate the effect of microsurgical techniques in the treatment of strabismus in children and to analyze the factors influencing the outcome. The results showed that microsurgical strabismus correction in the treatment of strabismus children has short operation time, less intraoperative blood loss, short hospital stay, high efficiency, and less complications, which is worthy of popularization. Age, preoperative strabismus angle, refractive error, distance stereopsis injury, near stereoscopic injury, and duration of disease were all independent influencing factors of postoperative efficacy.

Optimal Attitude Maneuvering Analyses for Imaging at Squint Staring and Sliding Spotlight Modes of SAR Satellite

In this study, we analyzed the imaging maneuver time, retargeting maneuver time, and attitude maneuvering characteristics in the imaging section (Phase 1) and retargeting maneuver section (Phase 2) when taking multiple-target images in squint spotlight mode in a single pass of a passive SAR satellite. In particular, the synthetic aperture time and attitude maneuvering characteristics in the staring and sliding spotlight modes that can image the wider swath width while maintaining high resolution were compared and analyzed. In the sliding spotlight mode, the rotation center was located below the ground surface when the satellite was maneuvering towards the target. Steering and sliding maneuvers were performed when targeting, and the synthetic aperture time of the sliding spotlight was longer than that of the staring spotlight because overlapping imaging was performed on the point target. The satellite maneuvering during imaging can be considered as a time-fixed problem, because it was performed within synthetic aperture time according to resolution, incidence angle, swath width, etc., by minimizing the Doppler centroid variation. In order to optimize the retargeting maneuver time, an optimal analysis of the attitude maneuvering was carried out and the validity of the optimal analysis algorithm was confirmed. Finally, the scenario was analyzed by assuming a problem of imaging four targets with 5 × 5 km swath width in a 20 km × 20 km densely populated area. It was confirmed that if a squint angle of ±12 degrees is provided in a single pass, four high resolution images of 5 km × 5 km can be imaged in the sliding spotlight mode.

Effect of Vertical Transposition of the Horizontal Muscles on Vertical Strabismus Associated with Exotropia

Purpose: To evaluate the correction of vertical strabismus associated with exotropia by vertical transposition of the horizontal muscle to an extent equal to half the muscle width combined with muscle recession-resection. Methods: We enrolled patients with vertical strabismus of 4-15 prism diopters (PD) associated with exotropia who were not scheduled for vertical rectus or oblique muscle surgery. Regardless of the strabismus angle, the insertion site of the horizontal muscle was vertically transposed by half the muscle width during surgery. Success was defined as a vertical strabismus angle of 2 PD or less. Results: The preoperative mean exodeviation far angle in 41 patients was 27.8 PD and the average vertical strabismus far angle 8.1 PD. The success rate of exotropia surgery was 68.3%. The mean vertical strabismus angle was 2.8 PD on postoperative day 1 and the success rate of vertical strabismus surgery 92.7%. Undercorrection was evident in 4.9% of patients and overcorrection in 2.4%. The preoperative vertical strabismus angle was strongly associated with the residual angle after surgery (r = 0.386, <i>p</i> = 0.013). Receiver operating curve analysis revealed that the preoperative vertical strabismus far angle cutoff was 11 PDs. No patient factor significantly influenced vertical strabismus correction. Conclusions: Vertical transposition of the horizontal muscle by half of the muscle width may correct vertical strabismus of far angle 11 PDs or less.

Effect of an oculomotor rehabilitation program for subacute brain injury patients with ophthalmoplegia: a case-control study

Purpose Examining the effects of an oculomotor rehabilitation program in subacute brain injury patients presenting with external ophthalmoplegia. Methods This case-control study included 33 patients with subacute brain injury accompanied by external ophthalmoplegia (15 cases, 18 controls) from a hospital rehabilitation ward. Participants underwent comprehensive rehabilitation for 8 weeks. The patients participated in an oculomotor rehabilitation program, which involved inducing pursuit, fixation, saccade, and vergence for 20 min daily, 6 days a week for 8 weeks. We assessed improvements in the angle of strabismus; visual function index (VFI), which evaluates inconvenience in daily life; and diplopia after 8 weeks in the two groups using statistical methods. Results The program resulted in an immediate strabismus angle improvement (p < 0.001). Strabismus angle change over the 8-week period was significantly higher (p < 0.001) in patients (22.9 ± 12.3°) than in control participants (8.3 ± 7.6°). VFI change was significantly greater (p = 0.003) in patients (7.1 ± 5.1 points) than in control participants (2.7 ± 2.4 points). The patients exhibited significantly higher diplopia improvement rates while looking straight ahead and in the direction of paralysis than did control participants (p = 0.021 and p = 0.037, respectively). Conclusion This program improved external ophthalmoplegia without any specialized environmental configurations or personnel, which ensures wide clinical applications. IMPLICATIONS FOR REHABILITATION Our oculomotor rehabilitation program improved external ophthalmoplegia in subacute brain injury patients. The program promotes pursuit, fixation, saccades, and vergence. The patients lay in the supine position and it places a little burden on them. The program can be completed within 20 min daily, requires no special environmental configurations, and can be performed by anyone.

Fixation eye movement abnormalities and stereopsis recovery following strabismus repair

We evaluated the effects of strabismus repair on fixational eye movements (FEMs) and stereopsis recovery in patients with fusion maldevelopment nystagmus (FMN) and patients without nystagmus. Twenty-one patients with strabismus, twelve with FMN and nine without nystagmus, were tested before and after strabismus repair. Eye-movements were recorded during a gaze-holding task under monocular viewing conditions. Fast (fixational saccades and quick phases of nystagmus) and slow (inter-saccadic drifts and slow phases of nystagmus) FEMs and bivariate contour ellipse area (BCEA) were analyzed in the viewing and non-viewing eye. Strabismus repair improved the angle of strabismus in subjects with and without FMN, however patients without nystagmus were more likely to have improvement in stereoacuity. The fixational saccade amplitudes and intersaccadic drift velocities in both eyes decreased after strabismus repair in subjects without nystagmus. The slow phase velocities were higher in patients with FMN compared to inter-saccadic drifts in patients without nystagmus. There was no change in the BCEA after surgery in either group. In patients without nystagmus, the improvement of the binocular function (stereopsis), as well as decreased fixational saccade amplitude and intersaccadic drift velocity, could be due, at least partially, to central adaptive mechanisms rendered possible by surgical realignment of the eyes. The absence of improvement in patients with FMN post strabismus repair likely suggests the lack of such adaptive mechanisms in patients with early onset infantile strabismus. Assessment of fixation eye movement characteristics can be a useful tool to predict functional improvement post strabismus repair.

Improved Relative Range Equation in Squint SAR for Moving Targets Refocusing

Moving target detection is difficult for synthetic aperture radar (SAR). As SAR is designed for imaging of stationary ground scene, the moving targets would be blurred and displaced in conventional SAR imaging. To increase the signal clutter ratio, the moving targets should be refocused while detecting. Based on relative range equation, one can refocus and detect the moving targets simultaneously by searching the relative velocity. This method has been derived and applied for side looking SAR. In this paper, we extend the relative range equation to squint mode. The procedures of the refocusing method are also illustrated. By introducing a parameter of relative squint angle, the imaging position of the moving target is derived. The refocusing method is validated by simulations. The moving target can be optimally refocused, and the refocused position can be parametrized by the relative motion parameters.

Comparison of Two Conjunctival Incision Techniques in Strabismus Operations: Analysis of the Patient Population in 2008, 2010 - 2014.

Until 2010, the Halle university hospital used the limbal approach in strabismus operations to open the conjunctiva, as first described by Harms in 1949. In 2010, this was changed the to a modified radial incision technique, as inspired by the fornix incision of Harms and the "minimally invasive strabismus surgery" (MISS) technique of D. S. Mojon. The indication is the reduction in complications and protection of the conjunctiva. A retrospective analysis was performed of cases between 2008 and March 2014 was performed, including a total of 258 patients. 109 patients were treated with the limbal approach and 149 patients with the radial cut. The following aspects were included for comparison: the medium-term control of the squint angle after three months, intra- and postoperative number of complications, duration of the operations. A survey collected the reasons for not taking part in follow-up checks and the alignment of these patients. To compare binary variables, the chi-square-test was used and to compare average terms the unpaired t test, with a level of significance of 0.05%. The results of the postoperative square angles were comparable to both each other as to the literature. The number of complications was kept low in both techniques. The duration of the operations under the radial incision technique was clearly higher. However, throughout the observed years the duration of operations turned out to have decreased. The reasons for not taking part in controls were diverse and the alignment of these patients was high, regardless of the incision technique. The limbal approach was a well-proven method to open the conjunctiva. After changing to the radial incision technique, there was never a negative influence on the results of the surgeries or the rate of complications. The duration of the operations was extended. Superiority of the new technique was not shown. It could however be an alternative, as it spares the conjunctiva and permits glaucoma operations.

Тактика и сроки проведения хирургического лечения у ребенка с врожденной эссенциальной эзотропией. Клинический случай

Purpose. To evalute the effective of the proposed volume of surgical treatment for the progressive course of infant esotropia. Material and мethods. A premature baby with congenital esotropia, which was diagnosed at the sith month of life. The patient was assigned a spectacle correction taking into account the par of ametropia and constant alternating occlusion. In connection with the subsequent increase in horizontal esodeviation and the appearance of a paretic component, a bilateral recession of the internal rectus muscle by 5mm was carried out in combination with an injection of Botox in a volume of 2.0. IU. Results and discussion. After the first stage of surgical treatment, a stable decrease of horizontal esodeviation and an increase of the amount of abduction were achieved. Conclusion. Bilateral combined weakening of medial rectus muscles (classical recession and chemorecession) allows to achieve predicted good results in case of large strabismus angles, combined with limi of abduction. Key words: congenital esotropia, chemodenervation, chemorecession.

New slant range model and azimuth perturbation resampling based high-squint maneuvering platform SAR imaging

Strong spatial variance of the imaging parameters and serious geometric distortion of the image are induced by the acceleration and vertical velocity in a high-squint synthetic aperture radar (SAR) mounted on maneuvering platforms. In this paper, a frequency-domain imaging algorithm is proposed based on a novel slant range model and azimuth perturbation resampling. First, a novel slant range model is presented for mitigating the geometric distortion according to the equal squint angle curve on the ground surface. Second, the correction of azimuth-dependent range cell migration (RCM) is achieved by introducing a high-order time-domain perturbation function. Third, an azimuth perturbation resampling method is proposed for azimuth compression. The azimuth resampling and the time-domain perturbation are used for correcting first-order and high-order azimuthal spatial-variant components, respectively. Experimental results illustrate that the proposed algorithm can improve the focusing quality and the geometric distortion correction accuracy of the imaging scene effectively.

Новые возможности хирургического лечения паралитического косоглазия у детей

Purpose. To assess the clinical effectiveness of the developed surgical method for treating paralytic strabismus. Material and methods. The operation was performed on 32 patients with paralytic strabismus (32 eyes) aged 3 to 12 years. All patients had diplopia in the primary gaze position or in a small abduction. Convergent strabismus was diagnosed in 26 children (81%), divergent strabismus – in 6 patients (19%), in 34% of cases (11 people) strabismus was with a vertical component. Strabismus angle according to Hirshberg before surgery: horizontal deviation from 10 to 30°, vertical – from 5 to 15°. Results. On the 7–10th day after the operation, orthotropy and the appearance of mobility of the eyeball towards the affected muscle were achieved in all operated patients. In the long term (6–12 months) after surgery, 23 children (72%) fully recovered the mobility of the eyeball in 8 directions and formed stable binocular vision, and orthotropy remained. In 9 patients (28%), there was a limitation of the mobility of the eyeball to 5–7°. Conclusion. The proposed method for the surgical treatment of paralytic strabismus makes it possible to achieve in one stage the correction of the deviation angle and the improvement of mobility with the elimination of diplopia, avoids the appearance of postoperative vertical deviation and eliminates large deviation angles. Using the proposed method, it is possible to simultaneously correct both horizontal and vertical deviations. Key words: paralytic strabismus, deviation angle, horizontal deviation, vertical deviation.

A Fast Back-Projection SAR Imaging Algorithm Based on Wavenumber Spectrum Fusion for High Maneuvering Platforms

In this paper, a fast back-projection (BP) synthetic aperture radar (SAR) imaging algorithm based on wavenumber spectrum fusion is proposed for high maneuvering platforms with high squint angles and high dive angles. When the platforms have nonlinear trajectory errors, the trajectory errors will introduce significant spectrum displacement, which varies with the target position. If the influence of trajectory error is not considered, the trajectory’s deviation from the ideal SAR imaging geometry will degrade the focusing performance. The dive angle will further enlarge the influence on SAR focusing. In this paper, the center function of the spatially variable sub-aperture wavenumber spectrum is derived, firstly, which is the basis for reasonably setting the oversampling rate. Then, the accurate spectrum fusion method is proposed, which is efficiently implemented by fast Fourier transform (FFT) and circular shifting. The proposed algorithm is called high-squint and high-dive accelerated factorized back-projection (HSHD-AFBP). Compared to the commonly used spectrum fusion method, HSHD-AFBP not only improves the imaging quality, but also expands the image width. Finally, the effectiveness of the proposed algorithm is verified by simulation data.

A Moving Target Velocity Estimation Method Based on the MC-MASA SAR Mode

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.