基于稀疏分解的微弱多分量LFM信号参数估计

Wigner-Ville分布是线性调频(LFM)信号参数估计方法中的常用方法,但其缺点是对多分量LFM信号有严重的交叉项.文中以稀疏分解方法为基础,利用匹配追踪(MP)算法将微弱多分量LFM信号在过完备原子库上进行分解,由分解得到的原子参数可以估计出各个LFM信号的起始频率和调频斜率,从而实现了微弱多分量LFM信号的参数估计.仿真验证了该方法的有效性.     

Chirp子脉冲频率步进信号目标径向速度估计

频率步进信号是一种重要的距离高分辨信号,但对目标运动比较敏感。对于运动目标成像,必须进行运动补偿。根据频率步进信号的多普勒特征构造一种多普勒匹配滤波器对目标径向速度进行估计。该方法能在一帧信号内估计出目标径向速度。Chirp子脉冲经过脉冲压缩提高了信噪比,保证了估计的精度。同时给出频率步进信号径向速度估计的Cramer-Rao限,并与多普勒匹配滤波仿真数据进行了比较。     

基于相位增量法的合成孔径雷达多普勒中心频率估计

合成孔径雷达(SAR)系统中,多普勒中心频率的精度直接影响着成像的质量。针对合成孔径雷达多普勒中心频率估计问题,提出了基于相位增量的估计方法,并在MATLAB仿真软件环境下进行数据仿真。该算法利用合成孔径雷达回波在方位向上线性调频信号的相频曲线的分布特性,运用反正切定律非线性估计回波相位信息,并利用函数拟合的方法对频率中心进行了有效的估计。该算法降低了运算复杂度,对噪声的干扰具有鲁棒性,并且与已有的符号估计算法具有相当的估计性能。该算法的估计结果可以用于补偿载机运动误差引入的相位误差,从而实现高分辨率成像。     

引信启动效率评估系统数据分析软件设计

针对脉冲多普勒引信视频回波特点提出了一种信号参数提取的方法。首先对脉冲多普勒引信视频回波信号分距离单元分帧作FFT处理，然后采用中心频率法和恒虚警检测方法提取出多普勒频率数据和信噪比数据，得到随时间变化的估计频率曲线和信噪比曲线。估计频率的变化和信噪比的变化趋势从不同的侧面反映了引信工作的历程。     

频率步进雷达ISAR成像包络对齐新方法

逆合成孔径雷达成像常用的运动补偿方法是利用距离像的相关性进行包络对齐.但当目标速度或加速度较大时,散射点走动较大且距离像发散程度严重,此时直接利用距离像的相关性进行包络对齐会有较大的误差.本文分析了频率步进雷达运动目标的回波信号模型,讨论了目标的速度和加速度对距离像的影响,提出了当目标速度和加速度较大时,先用高斯包络线性调频信号自适应分解估计出目标运动的加速度和速度,粗补偿后再用距离像最小熵准则进行精补偿的包络对齐方法.该方法计算量小,估计精度高,且无测速模糊的缺点,仿真结果验证了它能较精确地估计出目标的运动参数,运动补偿效果好.     

一种基于回波数据的运动补偿方法

提出一种基于回波数据进行运动参数提取和运动补偿的方法。该方法首先从回波数据估计多个距离单元的多普勒调频率,再利用这些多普勒调频率估计值对运动参数进行加权最小二乘估计,最后利用估计的运动参数完成视线方向和沿航向运动误差的补偿。无人机SAR实测数据的实验结果表明,在运动误差较大的情况下,该方法仍可以取得良好的成像效果。     

一种单通道SAR对多个地面动目标定位的方法

针对动目标的图像会因为存在径向速度而产生方位偏移问题,即动目标不能成像至正确的方位位置上.采用常规的用于静止目标成像的SAR(Synthetic Aperture Radar)方法对地面动目标成像,对单通道合成孔径雷达(Single-Channel SAR)正侧视工作模式下的多个地面动目标的定位问题进行了研究.首先分析了多个运动目标回波信号的特征,接着根据运动目标回波信号及其频谱的特征估计出了每个运动目标的多普勒中心和多普勒调频率,再利用多普勒参数的估计结果实现了距离走动校正,并计算动目标的运动参数,最后对动目标重新聚焦得到其初始时刻的图像,完成了运动目标的定位.并通过仿真实验验证了方法能准确的估计各个动目标的速度及位置参数,证明了算法的有效性.     

一种改进多分量LFM信号时频分布估计方法

传统时频分布方法在估计多分量线性调频信号时,交叉项影响导致时频估计精度低。因此,提出建立信号调频斜率因子库,对时频分布核函数进行改进,使核函数能有效抑制由多分量信号引起的交叉项干扰。通过分析核函数与信号模糊函数交叉项及自身项的关系,将时频估计问题转化为求解最优调频斜率因子库来对核函数进行改进,使信号的广义模糊函数能量最大。以多分量线性调频信号为例进行仿真,结果证明与传统时频分布方法相比,改进的时频估计方法可以在有效抑制交叉项干扰的同时保留大部分自身项,提高了多分量信号时频估计的精度和抗噪声能力。     

基于三参数Chirplet变换的ARM检测

根据反辐射导弹(ARM)回波信号的特征,选择Chirplet变换5个参数中的3个,得到三参数Chirplet变换,并结合自适应线性预测滤波算法,提出一种基于三参数Chirplet变换的ARM检测方法。该方法可有效缩小搜索范围和降低输入信噪比要求,且可借助FFT实现。仿真结果表明其可在大载机回波干扰和低信噪比环境下快速准确地检测出ARM回波,实现实时告警。     

基于多路欠采样的多分量LFM信号参数估计

针对多分量线性调频(Linear frequency modulated,LFM)信号,提出了一种基于多路欠采样的参数估计方法。采样过程由多个采样速率相同、采样时刻不同的模数转换器实现,总采样率可以低于信号的奈奎斯特采样率。基于欠采样序列乘积型模糊函数的单频特性,可以通过峰值检测实现调频斜率的估计。根据估计出的调频斜率对各路欠采样序列进行解线调处理,可得到多频正弦信号。结合矩保持问题的求解方法以及对超定方程组的求解,可以根据解线调后的各路序列估计出原始LFM信号各分量的初始频率。本文方法能够根据亚奈奎斯特采样样本实现LFM信号的参数估计,并且运算简单、易于实现。仿真实验验证了其有效性和准确性。     

大斜视双基地SAR的二维可分离成像算法

提出了大斜视双基地SAR的二维可分离成像算法.首先建立了大斜视双基地SAR回波信号模型,并对其距离徙动和方位调频率的变化特性进行了分析;在此基础上,将二维可分离成像算法推广应用到了双基地SAR领域,解决了大斜视双基地SAR回波信号线性距离徙动补偿后方位调频率在方位向出现的空变性问题.算法采用了由平移不变双基地SAR几何关系所确定的新匹配函数,并考虑了3次相位项对成像效果的影响,改善了成像的效果.最后通过点目标仿真验证了算法的有效性.     

Improving SAR data processing with polarimetric reference functions in the range Doppler algorithm

Synthetic aperture radar (SAR) is a form of radar that can be used to create images of objects and landscapes. The main important application of the polarimetric SAR can be found in surface and target decomposition process of its image processing. In this article, we propose a method of polarimetric SAR data processing using two new polarimetric reference functions of canonical targets with the intention to apply in coherent decompositions. Our experiment uses polarimetric backscatter characteristics of the dihedral and trihedral reflectors as the targets under a ground-based SAR geometry to create the polarimetric reference functions for azimuth compression in the SAR data processing. We process the data using Pauli decomposition to investigate the effect of our functions on the RGB (red, green, and blue) properties of the processed images. The results show that Pauli decomposition using our functions produces images with different distribution and intensity of RGB colours in the image pixels with some signs of improvement over the traditional range Doppler algorithm. This demonstrates that our polarimetric reference function can be used in the decomposition steps of the traditional SAR data processing and can potentially be used to reveal some useful quantitative physical information of target points of interest and improve image and surface classification.     

Improved Doppler parameter estimation of squint SAR based on slope detection

For high-quality synthetic aperture radar (SAR) processing, Doppler parameter estimation is an essential procedure. In this article, first the relationship between slope and Doppler parameter of squint SAR is established, and then an improved slope-detection-based Doppler parameter estimation scheme is proposed. In the scheme, the intensity data are first converted into binary data by setting a threshold using the Ostu algorithm, and then a Radon transform is conducted on the binary data in two steps: the coarse and fine Radon transform. Using the proposed scheme, the binary data will have sparse features, and the number and interval of search for the Radon transform can be greatly reduced. Hence, the Doppler parameter can be estimated with more speed than conventional Radon-transform-based methods. Besides, Doppler centroid and Doppler rate can be estimated with the same scene. Simulations and experiments with real data validate the effectiveness of the scheme.     

一种基于频率调制的时域相关多普勒估计算法

对SAR成像中多普勒中心频率进行研究,指出传统多普勒中心估计,在解卷绕过程中,会存在不稳定问题。针对这一问题,提出了一种基于频率调制的时域相关估计算法。该算法将多普勒中心搬移到非卷绕区,避免了卷绕出现;估计过程中使用最小二乘法更新调制频率,适应多普勒中心变化,保证了估计的稳定性,该算法相比传统估计算法,解决了传统算法不稳定问题,具有更强的适用性。最后通过真实的机载SAR数据,验证了该算法的有效性。     

基于GPU的星载SAR多普勒中心频率估计处理技术

针对星载SAR多普勒中心频率估计算法复杂及运算量大的特点,基于GPU技术手段开展实时数据处理技术研究。选用Tesla C1060构建GPU专用科学计算平台,针对雷达卫星数据进行了数据处理实验,完成了系统结构设计。完成了多普勒中心频率估计算法分析\,基于CUDA编程模型构建以及MLCC算法优化设计等关键技术。结果表明:在不考虑全局拟合数据处理的情况下,实现了多普勒中心频率估计的处理速度达到Radarsat\|1卫星下行速率的12倍以上。为进一步进行精确的多普勒中心估计及实时SAR成像处理系统的研制提供了依据。     

Estimating tropical rain attenuation on the Earth-satellite path using radar data

Radar-return echoes, known as ‘reflectivity’, are exploited in the course of estimating rain attenuation along a slant path. Relevant radar gates or ‘range bins’ are identified to correlate a specific satellite path. The reflectivity value of each range bin is converted to rainfall rate using established radar reflectivity values – rainfall rates, (Z–R relation). Specific attenuation is then derived for all associated range bins. The attenuation for each bin is the product of specific attenuation and its effective path length. The summation of attenuation endured by all range bins is inferred as the attenuation along the slant path. In this study, an X-band slant path rain attenuation was estimated using 2.85 GHz (S-band) Terminal Doppler Weather Radar (TDWR) data. A technique to estimate rain attenuation by exploitation of radar information is elaborated in this article. Comparisons between the radar-derived attenuation estimations and actual satellite signal measurements are also presented. The findings were verified by comparing the generated values to the directly measured rain attenuation from the Razak satellite (RazakSAT). Radar reflectivity data were obtained from Kuala Lumpur International Airport (KLIA) radar station operated by the Malaysian Meteorology Department (MMD). Preliminary findings using the most recent Z–R relation (i.e. the generated radar-derived rain attenuation estimations) appear to show lower values than the actual measurements.     

An exact wide field digital imaging algorithm

Abstract

A new imaging algorithm is presented for Synthetic Aperture Radar (SAR) that is exact in the sense that it is capable of producing a complex image with excellent geometrical, radiometrical and phase fidelity. No interpolations or significant approximations are required, yet the method accomplishes range curvature correction over the complete range swath. The key to the approach is a quadratic phase perturbation of the range linearly frequency modulated signals while in the range signal, azimuth frequency transform (Doppler) domain. Range curvature correction is completed by a phase multiply in the two-dimensional frequency domain. Other operations required are relatively conventional. The method is generalizable to imaging geometries encountered in squint and spotlight SAR, inverse SAR, seismics, sonar, and tomography.     

Resolution and parameters estimations for multiple maneuvering targets

Resolution and parameters estimations for multiple maneuvering targets in the same range cell is addressed in this work. The low-resolution radar cannot distinguish multiple targets in both distance and angle, but the detection of Doppler frequency variation of the multiple maneuvering targets can be used to resolve this problem. At present, most of researches on detection of Doppler frequency variation are carried out with time-frequency analysis methods, such as Fractional Fourier transformation （FRFT）, Adaptive Chirplet transformation （ACT）, and Wigner-Ville distribution （WVD） and so on, which need satisfy enough time duration and sampling theorem. This paper proposes a new method of resolution and parameters estimation for multiple maneuvering targets based on Compressive Sensing （CS） and clustering technique, which samples at low rate and short time duration without sacrificing estimation performance. Simulation results validate the effectiveness of the proposed algorithm, and also show that the performance of the proposed method is superior to that of FRFT in the condition of multiple targets.     

An approach for refocusing of ground fast-moving target and high-order motion parameter estimation using Radon-high-order time-chirp rate transform

Long synthetic aperture time can improve the imaging quality of a ground moving target, whereas a moving target may be severely smeared in the cross-range image due to the range migration and the Doppler frequency migration. In this paper, the effects of the third-order Doppler broadening and Doppler ambiguity of a fast-moving target are considered. To address these issues, a novel motion parameter estimation method named high-order time-chirp rate transform (HTRT) is proposed, and then a new synthetic aperture radar (SAR) imaging method based on Radon-HTRT (RHTRT) for a ground moving target is developed. The major contributions are as follows: 1) The proposed SAR imaging method can eliminate the Doppler ambiguity effect. 2) The proposed method can realize longer time coherent integration than Radon–Fourier transform (RFT) and Radon–fractional Fourier transform (RFRFT) methods. 3) The proposed method is computationally efficient since HTRT can obtain the motion parameters of a moving target via performing the 2-dimensional (2-D) fast Fourier transform (FFT). Both the simulated and real data processing results show that the proposed method can finely image a ground moving target in a high signal-to-clutter and noise ratio (SCNR) environment.