High resolution wide swath revisit synthetic aperture radar imaging mode and algorithm

Based on the squint mode, a high resolution wide swath revisit synthetic aperture radar （SAR） imaging mode is pro- posed. The transmitting antennas are configured as the single phase center multiple azimuth beams （SPC MAB）. The formed two beams point to two different directions to obtain two images of the observed scenario. The receiving antennas are configured as displaced phase center multiple azimuth beams （DPC MAB） to decrease the required pulse repetition frequency （PRF）. The de- creased PRF can ensure the high resolution wide swath imaging. Based on the analysis of the character of the return signal, a pro- cessing method named multiple beam multiple channel algorithm （MBMCA） is proposed to separate the aliased sub-beams＇ echoes. The separated echoes are focused respectively to get the revisit imaging to the observed scenario. The simulation experiments ve- rify the validity and correctness of the proposed imaging mode and processing algorithm.

MOTION COMPENSATION FOR WIDE BEAM SAR BASED ON FREQUENCY DIVISION

Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.

Study on the Algorithm to Retrieve Precipitation with X-Band Synthetic Aperture Radar

In order to obtain the global precipitation distribution data,this paper investigates the precipitation distribution model,the normalized radar cross-section model,and the retrieval algorithm with X-band synthetic aperture radar（X-SAR）.A new retrieval algorithm based on the surface-scattering reference attenuation is developed to retrieve the rain rate above the ground surface.This new algorithm needs no statistical work load and has more extensive applications.Calculations using the new algorithm for three cases verify that the rainfall is retrieved with high precision,which proves the capability of the algorithm.

A HIGH RESOLUTION WIDE SWATH SAR METHOD BASED ON INTRA-PULSE NULL STEERING AND MIMO

High Resolution Wide Swath (HRWS) Synthetic Aperture Radar (SAR) often suffers from low Signal-to-Noise Ratio (SNR) due to small transmitting antenna, especially in phased array antenna systems. Digital Beam Forming (DBF) based on Single Input and Multiple Output (SIMO) achieves receiving array gain at the cost of increasing data rate. This letter proposes a new HRWS SAR method, which employs intra-pulse null steering to get receiving gain in elevation and decrease the data rate, and Multiple Input and Multiple Output (MIMO) using Space-Time Block Coding (STBC) in azimuth to get transmitting gain and receiving array gain simultaneously. The feasibility is verified by deduction and simulations.

Algorithm for Gesture Recognition Using an IR-UWB Radar Sensor

This paper introduces a human gesture recognition algorithm using an impulse radio ultra-wide- band (IR-UWB) radar sensor. Human gesture recognition has been one of the hottest research topics for quite a long time. Many gesture recognition algorithms or systems using other sensors have been proposed such as using cameras, RFID tags and so on. Among which gesture recognition systems using cameras have been extensively studied in past years and widely used in practical. While it might show some deficiencies in some cases. For example, the users might not like to be filmed by cameras considering their privacies. Besides, it might not work well in very dark environments. While RFID tags could be inconvenient to many people and are likely to be lost. Our gesture recognition algorithm uses IR-UWB radar sensor which has pretty high resolution in ranging and adjustable gesture recognition range, meanwhile, does not have problems in privacy issues or darkness. In this paper, the gesture recognition algorithm is based on the moving direction and distance change of the human hand and the change of the frontal surface area of hand towards radar sensor. By combining these changes while doing gestures, the algorithm may recognize basically 6 kinds of hand gestures. The experimental results show that these gestures are of quite good performance. The performance analysis from experiments is also given.

Improved Multi-channel Blind Image Restoration Algorithm for UWB Radar

The imaging problem of low signal to noise ratio （SNR）echo is very important for ultra-wide band （UWB） through-wall radar. An improved multi-channel blind image restoration algorithm based on sub-space and constrained least square （CLS） is presented and applied to UWB radar system to deal with this issue. The high resolution of radar image is equivalent to multi-channel blind image restoration based on the improved model of the through-wall radar echo. And a new cost function is proposed to the multi-channel blind image restoration by considering the concept of sub-space as the limitation of blur identification. The proposed algorithm has all advantages of CLS and sub-space, and converts the image estimation to alternating-minimizing the two cost functions. Experimental results prove that the proposed algorithm is effective at improving the resolution of radar image even at low SNR.

Exploitation of Electromagnetic Models for Sea Wind Speed Estimation from C-Band Sentinel-1 Images

Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can give high wind resolution cells. For this purpose, one can find two principal approaches: via electromagnetic (EM) models and empirical (EP) models. In both approaches, the Geophysical Model Functions (GMFs) are used to describe the relation of radar scattering, wind speed, and the geometry of observations. By knowing radar scattering and geometric parameters, it is possible to invert the GMFs to retrieve wind speed. It is very interesting to compare wind speed estimated by the EM models, general descriptions of radar scattering from sea surface, to the one estimated by the EP models, specific descriptions for the inverse problem. Based on the comparisons, some ideas are proposed to improve the performance of the EM models for wind speed retrieval.

方位向调制干扰对高分宽幅多通道SAR的影响

多通道合成孔径雷达(synthetic aperture radar,SAR)能够利用方位向多通道重构处理去除多普勒模糊,获得高分宽幅SAR图像。针对此特殊的多通道重构处理方式,研究了传统SAR方位向调制干扰对高分宽幅多通道SAR的影响,包括多普勒调制干扰和脉冲延迟转发干扰两种类型的方位向调制干扰方式,为高分宽幅多通道SAR干扰决策提供理论基础。理论分析指出,多普勒调制干扰信号经成像处理后将在方位向生成等间隔分布的虚假目标,并且幅度受与多普勒调制频率相关的正弦函数和匹配滤波损失联合调制;而脉冲延迟转发干扰信号在成像后将只有单个干扰目标出现,且目标的方位位置仅与延迟的脉冲数有关。仿真实验验证了理论分析的正确性。

微波光子W波段宽带雷达成像技术研究

W波段逆合成孔径雷达(inverse synthetic aperture radar,ISAR)具有成像分辨率高、成像距离远、体积小、重量轻等特点,适用于机载、弹载、星载等应用领域,是雷达系统中的一个重要的研究方向。微波光子技术由于具有高频、大带宽、低传输损耗等优势,是克服传统雷达面临“电子瓶颈”效应的主要手段。本文提出一种基于微波光子技术实现的W波段调频信号体制ISAR成像系统。在发射端,使用微波光子倍频技术实现了瞬时带宽为8 GHz的W波段线性调频(linearly frequency-modulated,LFM)信号生成。在接收端,基于微波光子去斜技术实现回波信号去斜处理。ISAR成像仿真结果表明,不同姿态下的目标轮廓清晰可辨。

基于超宽带雷达回波短时傅里叶变换的土壤含水率检测

土壤体积含水率监测对提高农业生产效率和制定合理土壤管理措施具有重要意义。超宽带雷达由于其高距离分辨率、强穿透能力在农业土壤动态信息实时监测中得到广泛应用。但以往对超宽带雷达信号的处理主要关注时域特征,忽略了同样具有丰富信息的频域特征,使得回波信号在土壤体积含水率反演过程中无法得到充分利用,限制了土壤体积含水率的反演精度。本文基于超宽带雷达获取的土壤回波信号,对其进行预处理并提取与土壤体积含水率有关的回波信号,对该信号采用短时傅里叶变换(Short-time Fourier transform,STFT),分析与土壤体积含水率有关的回波信号随时序变化的时频谱特征,进而结合卷积神经网络(Convolutional neural network,CNN)建立土壤体积含水率分级以及回归预测模型。实验结果表明,基于添加高斯白噪声后的数据,对于土壤体积含水率的分级,将时频特征和CNN模型相结合时,分级总体精度和Kappa系数分别为98.69%和0.9849,相较于10个时域特征与植被指数NDVI(Normalized difference vegetation index)建立的支持向量机模型(Support vector machine,SVM),分级总体精度提升21.78个百分点,Kappa系数提高0.2515。对于土壤体积含水率的回归预测,将时频特征和CNNR(Convolutional neural network regression)模型相结合时,预测结果与真实值之间的决定系数(R^(2))为0.9872,均方根误差(RMSE)为0.0048 cm^(3)/cm^(3),相对分析误差(RPD)为6.2738,相较于10个时域特征结合植被指数NDVI建立的CNNR模型,R^(2)提升0.2316,RMSE降低1.3377 cm^(3)/cm^(3),RPD提高4.2714。综上,在土壤体积含水率分级和回归预测方面,本文所提方法较传统信号检测处理方法具有明显优势。

双频一体化超宽带探地雷达天线设计

针对目前探地雷达(Ground Penetrating Radar,GPR)产品单一频段工作所导致的耗时费力、效率低等缺点,文中设计实现了一种中心频率分别为400 MHz、1000 MHz且带宽为200~1500 MHz的双频一体化复合阵列天线,并将其应用于超宽带(Ultra-Wide Band,UWB)探地雷达系统中。阵列天线包含3个中心频率为400 MHz和6个中心频率为1000 MHz的蝶形天线,具备双频段同时探测能力,可实现一条测线含两种不同频段的探测结果,克服了传统探地雷达不同频率的重复探测问题,增强了探地雷达系统的实用性。所提出的双频一体化探地雷达天线具有超宽带、高增益、波束窄等特点,其相对带宽为153%,整个带宽内最高实现17.6 dBi峰值增益,半功率波束宽度最窄为7.6°,为高分辨率、高效率探地雷达应用提供了一种新的天线方案。

微波光子SAR最优子带融合的全分辨伪彩图生成方法

微波光子(MWP)雷达是一种通过光子器件对传统微波雷达硬件架构进行改进的新型雷达系统。借助光子器件卓越的物理特性,MWP雷达能够发射超宽带、高线性度的高质量线性调频信号,从而实现对目标的超高分辨率探测与成像。在目标成像与探测过程中,不同结构和特性的目标区域对不同频率信号的响应存在差异。因此,微波光子雷达具备通过散射差异生成伪彩图像的潜力,从而进一步提升微波光子合成孔径雷达(MWP-SAR)的信息获取能力。传统的遥感技术生成的伪彩图像分辨率较低,无法达到厘米级的分辨。因此,该文提出了一种在保证MWP-SAR高分辨率的前提下合成伪彩图像的方法。该算法首先建立了最优子带回波搜索模型,随后采用最优子带搜索算法对超宽带回波进行处理,以获取散射特性相差最大的子带回波通道。再对多子带差异图像进行色彩合成,通过这一处理步骤,能够生成对目标散射特性最佳描述的伪彩图像。同时,为了确保MWP-SAR的分辨率不受到损失,建立了一个融合模型,将全分辨率的SAR图像与多子带图像相融合,以维持伪彩图像的高分辨率。最终,通过实测的机载MWP-SAR数据成功地合成了全分辨率的伪彩色图像,从而验证了该算法的有效性。该算法可以使得MWP-SAR在成像时获取更多的目标信息,为成像雷达微波视觉的实现提供辅助。

W波段机载视频合成孔径雷达系统

合成孔径雷达(SAR)能够全天时全天候工作,在对地遥感领域具有广泛和深入的应用。视频SAR将SAR成像获得的空间维度信息拓展到时-空维度,可以获取更加丰富的遥感信息。传统SAR频段较低,导致合成孔径时间长,数据计算量大,高帧频输出难度很大;而低频段太赫兹波对目标细节感知能力强,合成孔径短,特别适合于微弱目标的视频感知。本文设计了一种工作在W波段的视频SAR系统,采用收发分置连续波固态前端体制,输出峰值功率1 W,最大发射带宽可达1 GHz;采用极坐标格式算法(PFA)结合GPU架构实现高帧率低延时成像。仿真试验表明,系统成像分辨力可达0.15 m,成像帧率约5 Hz。

星载SAR在炮兵侦察中运用问题的探讨

星载合成孔径雷达(SAR)的迅速发展和技术优势,满足了当下高分辨宽幅成像、高精度测绘及地面监视的需求,具有重要的科学、军事及商业价值。文章总结了星载SAR技术的发展和运用现状,在此基础上讨论其在炮兵侦察中的关键技术,并分析相关技术在运用中的优势和不足,而后深入研究和探讨了星载SAR在炮兵侦察领域可承担的职责及运用前景。文章通过分析和总结,认为随着星载SAR技术的不断创新,工程化、实用化持续推进,其必能进一步扩大应用领域,成为炮兵侦察中的一支“奇兵”。

太赫兹极高分辨力雷达成像试验研究

给出了一种载频0.14 THz、带宽5 GHz的极高分辨力太赫兹雷达成像系统样机。系统采用Ka波段毫米波信号二倍频后作为样机收发链路的谐波混频本振,以线性调频连续波信号作为发射信号,接收时采用去斜接收。利用该太赫兹雷达进行了成像试验并得到了1维距离像与逆合成孔径雷达(ISAR)成像结果。结果表明,THz雷达样机实现了3 cm的高分辨力,其ISAR像清晰,反映了目标的细微特征。

基于距离向多孔径接收的宽测绘带SAR成像方法的研究

该文提出了一种新的基于距离向多孔径接收宽测绘带合成孔径雷达(SAR)成像方法。首先对这种成像方法进行了严格的论证,并证明了运算中的加权矩阵为良态矩阵,然后分析了这种成像方法的计算量,讨论了这种宽测绘带SAR的信噪比,最后给出了仿真结果。

高功率超宽带同轴双锥天线的设计和实验

用口径场的方法对有限长同轴双锥天线进行了分析和设计。同轴双锥天线能工作在电压±１００ｋＶ、重复频率１００Ｈｚ、单周期脉冲全底宽３．６ｎｓ和输出阻抗５０Ω的超宽带脉冲辐射源上，辐射功率大于１００ＭＷ；天线带宽１５０ＭＨｚ～１ＧＨｚ；输入阻抗５０Ω。Ｅ平面和Ｈ平面平行极化半功率点全宽度分别为５０°和３６０°；天线的功率效率约为６５％。

毫米波合成孔径雷达的发展及其应用

分析了毫米波SAR高分辨成像的基本原理,阐述了毫米波SAR的优点,并结合目前国际上典型的毫米波SAR系统,综述了毫米波SAR技术与系统的发展状况,讨论了毫米波SAR的应用前景、存在的问题以及未来的发展趋势.

新型集成超宽带开槽天线的研制及其应用

研制出一种用于超宽带短脉宽辐射和接收的新型集成超宽带（ＵＷＢ）槽天线，该天线采用共面波导到槽线的宽带过渡方式馈电，实验结果显示了其高保真的宽带特性及高增益高效率特性．利用所研制的ＵＷＢ天线建立起超宽超带雷达（ＵＷＢＲ）实验系统，测量几种简单目标特性及涂层目标特性，证明了该种天线可用作实际的ＵＷＢＲ天线．

多子带并发的MIMO-SAR高分辨大测绘带成像

提出多子带并发的多发多收(MIMO)SAR成像方法,在扩大测绘带宽度的同时实现高分辨成像。首先采用低的脉冲重复频率保证大测绘带距离不模糊,然后利用每一个子带对应的多颗接收卫星的空间信息对该子带回波信号进行空域滤波解多普勒模糊,再对解过模糊的各子带信号进行频带合成实现距离高分辨。该方法可以有效利用多颗卫星的空间自由度。仿真实验验证了该方法的有效性。