SIDE-LOOKING ECHO DATA TRANSFORM TO SQUINT MODE SAR IMAGING

Nowadays the side-looking SAR echo data can be obtained easily from the commercial channel, while that of other SAR imaging modes such as squint, spotlight are difficult to be acquired. This paper presents a new scheme to transform the side-looking returns to squint ones, in a direct and an indirect approach respectively. Direct transformation uses the data with a wide azimuth beam angle. The maximum of the required squint angle is limited under several degrees. Squint data under indirect transformation can be obtained by adding a platform velocity along slant range according to the required squint angles. Then the squint data is determined by the angle between the new forward velocity and line-of-sight direction. This method results in higher squint angle compared with the first one. Verification shows the feasibility of these approaches with illustration of side-looking E-SAR raw data processing. The future work will be on the precise Doppler centroid estimation and effective imaging algorithm development.

CROSS-TRACK THREE APERTURES MILLIMETER WAVE SAR SIDE-LOOKING THREE-DIMENSIONAL IMAGING

The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.

STUDY ON THE SIGNATURE OF GROUND MOVING TARGET FOR AIRBORNE SQUINT SAR IMAGING

Compared with the side-looking Synthetic Aperture Radar (SAR), the flexible beampointing of squint SAR makes great application value. This paper derives the image signature of the ground moving target after the processing of Range-Doppler (RD) algorithm, the SAR signatures of ground moving targets are analyzed, including the geometry correction, the offsets and defocusing in both range and azimuth direction. Finally, computer simulation results validate its effectiveness. The research results are especially significant for moving targets detection and parameters estimation in squint mode SAR.

Compact wideband microstrip array antenna with beam squint

A compact wideband microstrip array antenna with a squint beam is introduced without the matched load. Its measured beam is at 10° offset to the broadside with a measured gain of 12 dB at 10 GHz. The measured impedance bandwidth （voltage standing wave ratio （VSWR）≤2） is over 16%, which agrees well with the simulated one. It is a low-cost wideband design with compact simple structure, suited for military and commercial application.

An approach to wide-field imaging of linear rail ground-based SAR in high squint multi-angle mode

Ground-based synthetic aperture radar(GB-SAR) has been successfully applied to the ground deformation monitoring.However, due to the short length of the GB-SAR platform, the scope of observation is largely limited. The practical applications drive us to make improvements on the conventional linear rail GB-SAR system in order to achieve larger field imaging. First, a turntable is utilized to support the rotational movement of the radar.Next, a series of high-squint scanning is performed with multiple squint angles. Further, the high squint modulation phase of the echo data is eliminated. Then, a new multi-angle imaging method is performed in the wave number domain to expand the field of view. Simulation and real experiments verify the effectiveness of this method.

NOVEL APPROACH BASED ON DERAMPING TECHNIQUE FOR SQUINTED SLIDING SPOTLIGHT SAR IMAGING

This paper investigates a novel approach based on the deramping technique for squinted sliding spotlight Synthetic Aperture Radar (SAR) imaging to resolve the azimuth spectrum aliasing problem. First of all, the properties of the azimuth spectrum and the squint angle impacts on the azimuth spectrum aliasing problem are analyzed. Based on the analysis result, an operation of filtering is added to the azimuth preprocessing step of traditional Two-Step Focusing Approach (TSPA) to resolve the azimuth folding problem and remove the influence of the squint angle on the azimuth spectrum aliasing problem. Then, a modified Range Migration Algorithm (RMA) is performed to obtain the precise focused image. Furthermore, the focused SAR image folding problem of traditional TSPA is illuminated in this paper. An azimuth post-processing step is proposed to unfold the aliased SAR image. Simulation experiment results prove that the proposed approach can solve the spectrum aliasing problem and process squinted sliding spotlight data efficiently.

THE STRIP IMAGING OF AIRBORNE SQUINT SIDELOOKING MODE SAR

Airborne squint side-looking strip imaging mode SAR has the advantages of better flexibility and larger field in applications than the classic side-looking mode SAR. Because of the large range migration and serious range-azimuth coupling terms, the imaging processing of squint mode SAR is a full two-dimensional (2-D) phenomenon. In this paper, different algorithms, which can be used for the imaging processing of squint mode SAR, are compared with each other in terms of their focusing quality and their ability to handle the large range migration of the squint side-looking mode SAR. And their abilities of real-time imaging are also discussed. The algorithms contained here are 2-D FFT method, fast polynomial transform(FPT) method, and the direct correcting method based on range-Doppler focusing algorithms. Other new methods are also discussed here briefly.

Study of a millimeter-wave squint indirect holographic algorithm suitable for imaging with large field-of-view

In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.

栅格空间Squint/Opera墨尔本办公室

动画与视觉艺术工作室Squint/Opera是墨尔本具有领先水平的动漫创作机构之一。它的新办公总部位于一个商业中心的地下一层。尽管这家公司的动画师们每天都要创造大量的虚拟场景,却仍然脱离不了物质世界带来的桎梏。今年年初,Squint/Opera找到SIBLING建筑事务所,希望设计师为他们打造一个全新的工作场所,使公司性质与空间特征能够融合在一起,让办公室成为虚拟与现实的交汇之地。

改良耳穴压豆联合局部按摩治疗儿童特发性异常瞬目症的临床研究

目的 观察改良耳穴压豆联合局部按摩治疗儿童特发性异常瞬目症的临床疗效。方法 纳入2019年10月—2022年4月在上海市松江区中心医院眼科门诊确诊的4~12岁特发性异常瞬目症患儿90例,随机分成观察组(A组)、中医组(B组)和对照组(C组)各30例(60只眼)。分别予改良耳穴压豆、经典耳穴压豆和常规心理—行为疗法配合滴眼液治疗。3组均观察21 d。分别于治疗前、治疗后测量患儿瞬目频率、学习能力的数据。结果(1)瞬目频率评分:3组治疗前瞬目频率评分比较,差异无统计学意义(P>0.05)。治疗后A组与B组瞬目频率评分均较治疗前降低,差异均有统计学意义(t_(A组)=19.313、t_(B组)=15.000,均P=0.000),C组较治疗前,差异无统计学意义(P>0.05)。治疗后3组间比较,差异有统计学意义(F=1093.886,P=0.000)。与C组比较,A组和B组瞬目频率评分均较低,差异均有统计学意义(t_(A组)=-11.655,t_(B组)=-11.171,均P=0.000);A组和B组比较,差异无统计学意义(P>0.05)。(2)阅读速度比较:治疗后A组与B组阅读速度均较治疗前增加,差异均有统计学意义(t_(A组)=-60.647,t_(B组)=-61.465,均P=0.000),C组较治疗前,差异无统计学意义(P>0.05)。治疗后3组间阅读速度比较,差异有统计学意义(F=19.150,P=0.000)。与C组比较,A组与B组阅读速度均较快,差异均有统计学意义(t_(A组)=4.744、t_(B组)=4.033,均P=0.000);A组与B组比较,差异无统计学意义(P>0.05)。(3)听写速度比较:治疗后A组与B组听写速度均较治疗前增加,差异均有统计学意义(t_(A组)=-115.348、t_(B组)=-109.133,均P=0.000),C组较治疗前,差异无统计学意义(P>0.05)。治疗后3组间比较,差异有统计学意义(F=91.933,P=0.000)。与C组比较,A组与B组听写速度均较快,差异均有统计学意义(t_(A组)=9.751、t_(B组)=8.203,均P=0.000);A组与B组听写速度比较,差异无统计学意义(P>0.05)。(4)中医症候积分:3组治疗前中医症候积分比较,差异无统计学意义(P>0.05)。治疗后A组与B组中医症候积分均较治疗前降低,差异均有统计学意义(t_(A组)=-4.365、t_(B组)=-4.062,均P=0.000),C组较治疗前,差异无统计学意义(P>0.05)。治疗后3组间比较,差异有统计学意义(F=17.259,P=0.000)。与C组比较,A组和B组中医症候积分均较低,差异均有统计学意义(t_(A组)=-4.979、t_(B组)=-4.625,均P=0.000);A组和B组比较,差异无统计学意义(P>0.05)。(5)临床疗效:A组(96.67%)与B组(93.33%)总有效率均优于C组(66.67%),差异均有统计学意义(χ^(2) A组=9.017,P=0.003;χ^(2) B组=6.667,P=0.010),而A组与B组比较,差异无统计学意义(P>0.05)。(6)复发率:A组(10.34%)与B组(14.29%)复发率均低于C组(80.00%),差异均有统计学意义(χ^(2) A组=24.191、χ^(2) B组=20.728,均P=0.000);而A组与B组比较,差异无统计学意义(P>0.05)。结论 改良耳穴压豆联合局部按摩治疗儿童特发性异常瞬目症临床疗效较好,具有操作简单、疗效可靠、复发率低等优势,值得临床推广。

基于改进混合坐标系的大斜视俯冲机动平台SAR快速时域成像算法

多级子图像融合是加速合成孔径雷达(Synthetic Aperture Radar,SAR)时域成像的关键手段.然而,机动平台SAR的大斜视采集增强了频谱支持区域的不规则特性,降低图像融合的效率和精度.针对这些问题,本文设计了一种改进的混合坐标系,在此基础上开发了大斜视俯冲机动平台SAR快速时域成像算法.得益于改进混合坐标系中建立的等效斜距模型,频谱对斜视角的敏感度降低,消除了频谱空变现象.因此,设计频谱预处理函数可以有效压缩和拼接频谱,提升图像融合的效率和精度.通过仿真和原始数据处理,验证了提出算法性能的优越性.

基于椭球模型的斜视星载SAR距离模糊仿真

距离模糊比是星载SAR图像的一项重要指标,与正侧视成像相比,大斜视成像星地几何关系更为复杂,传统距离模糊计算与仿真中将地球视为球体的假设会对计算结果造成较大偏差,不能准确评估SAR图像质量。本文采用更为准确的地球椭球模型代替球体模型,并提出了一种基于斜视天线坐标系的模糊区计算方法,利用此方法对距离模糊比沿距离向测绘带的变化进行仿真,同时对距离模糊比沿方位向的空变性也进行研究。本文研究成果对星载SAR系统设计具有重要参考价值。

一种适用于星载大斜视聚束SAR的改进距离徙动算法

星载大斜视聚束合成孔径雷达(Synthetic Aperture Radar,SAR)探测范围大、目标驻留时间长,有广泛的应用前景,但会带来较大的距离徙动,使得回波信号耦合严重。传统算法使用固定窗接收数据,为了采集完整,则需要较大的采样窗,但采得数据中存在大量的无效数据,采样效率很低。为解决时域采样效率低等问题,可使用滑窗接收模式,但该模式一般结合时域算法或极坐标格式算法使用,而在星载SAR大场景成像的情况下,时域算法计算效率低下,极坐标格式算法的聚焦半径较小,因此本文提出了一种改进的距离徙动算法来解决大斜视滑窗接收模式下的高效精确成像问题。本文建立了滑窗接收模式下的时域回波模型,利用傅里叶变换的性质推导出精确两维解析频谱,并基于上述两维解析频谱,提出雷达视线坐标系下的两维空间域解耦方法并给出对应的完整成像处理流程,最后通过仿真实验验证算法的有效性。本文提出的新方法既能解决大斜视两维频谱扭曲带来的频域采样效率低下问题,又可避免传统方法在大斜视模式下的残留距离徙动放大问题,为后续的自聚焦处理提供便利。

基于分数阶傅里叶变换和图像加权熵的chirp scaling算法

针对传统的基于傅里叶变换和匹配滤波实现的chirp scaling(CS)成像算法中多普勒参数随斜距变化以及成像分辨率低的问题,提出利用分数阶傅里叶变换(FRFT)对CS成像算法进行优化。首先建立斜视合成孔径雷达(SAR)回波信号模型,理论推导利用FRFT代替匹配滤波进行信号压缩。针对方位向最优旋转角的搜索问题,对得到的图像基于加权最小熵建立代价函数,利用动量法的梯度下降优化算法进行迭代计算,最终得到分辨率更高的SAR图像。为验证算法的有效性,分别在点目标仿真数据和实测SAR数据集上进行实验。结果表明,与传统CS成像算法相比,该算法的成像结果成像主瓣宽度更窄、旁瓣更低、成像更加清晰。

机载SAR斜视区域成像研究

本文研究机载合成孔径雷达（SAR）斜视区域成像,提出在一维距离像上对地面像素逐个进行距离对准和相位补偿的运动补偿方法.该方法在完成斜地校正的同时,还能有效地改善方位聚焦并减小几何失真.用上述运动补偿方法和线性R-D成像算法,某型机载SAR在试飞实验中成功实现了斜视区域成像.

斜视SAR运动补偿研究

该文建立了斜视SAR的运动误差模型,分析了不同斜视角度和波束宽度情况下运动误差造成的影响,提出了小斜视和大斜视情况下各自的运动补偿方法,分析表明该方法较常规运动补偿方法适用范围更广。仿真和实测数据的处理结果表明了该方法的有效性。

基于SPECAN处理的斜视SAR实时成像算法及其FPGA实现

斜视合成孔径雷达(synthetic aperture radar,SAR)成像具有广阔的应用前景。首先提出一种基于SPECAN算法的斜视SAR实时成像处理方法,具有运算量小、操作简单的特点。针对SPECAN处理带来的图像扇形畸变,提出采用Sinc插值校正方位采样间隔空变性的方法,实现图像扇形畸变的校正。在此基础上采用FPGA(field programmable gate arrays,FPGA)实时编程实现,重点阐述基于"空域滤波"思想的Sinc插值模块设计。实测数据处理结果验证了该算法的有效性及FPGA实时实现的可行性。

间歇性外斜视手术前后立体视和眼位变化影响因素的分析

目的探讨间歇性外斜视手术前后立体视觉及术后眼位变化的影响因素。方法选择2010年1月至2014年12月中国医科大学附属第一医院眼科间歇性外斜视患者70例,根据术前视远斜视度测量结果设计手术,采用非主导眼外直肌后徙或外直肌后徙结合内直肌缩短术。依术前有无近立体视及手术年龄、发病年龄、斜视角,分别观察手术前后双眼的裸眼及矫正视力、屈光状态、立体视觉、斜视角度及眼位等的变化。结果与术前比较,术后具有立体视觉者显著增多(P<0.05);与手术年龄>9岁组比较,手术年龄≤9岁组患者立体视觉恢复率及眼位正位率亦显著升高(P<0.05);与发病年龄>9岁组比较,发病年龄≤9岁组患者立体视觉恢复率及眼位正位率无统计学差异(P>0.05);与斜视度≤45△组比较,>45△组患者立体视觉恢复率及眼位正位率均无统计学差异。结论手术治疗间歇性外斜视可有效提高立体视觉,恢复眼位。手术效果与手术年龄有关,视觉发育期的间歇性外斜视患者术后立体视觉的恢复率更高。斜视度无论大小,早期手术均有利于立体视功能的恢复。

弹载SAR子孔径大斜视成像方位空变校正新方法

斜视成像是弹载合成孔径雷达(Synthetic Aperture Radar,SAR)的一种重要工作模式,从实际应用出发,弹载SAR为实现快视成像常采用子孔径处理.由于在大斜视模式下,距离方位严重耦合,常规算法成像处理的第1步是采用时域校正距离走动的方法来消除距离方位的耦合,这会带来方位相位随方位位置空变问题,造成方位无法统一处理,影响方位聚焦深度.文中详细分析了弹载SAR大前斜瞬时斜距模型,针对子孔径数据,提出一种基于高次相位滤波的方位空变校正新方法,实现方位统一聚焦处理.点目标仿真数据处理验证了文中所提方法的有效性和实用性.

俯冲斜视SAR成像分辨力分析

针对雷达平台在俯冲条件下的SAR成像几何关系及成像原理,分析了俯冲条件下斜视SAR在斜平面内的分辨力,根据几何关系给出了从斜平面转换到地面的斜地转换系数,最后推导了俯冲斜视段的地面方位向和距离向的分辨力数学表达式。在此基础上对影响分辨力的主要因素进行了分析,分析结果表明,该成像分辨力数学模型不仅适合俯冲阶段,也适合平飞阶段,对工程应用具有一定参考价值。