Adding Sensitivity to the MLBF Doppler Centroid Estimator

The multilook beat frequency (MLBF) algorithm is the Doppler centroid estimator most commonly used in practice to solve the Doppler ambiguity. However, it still makes errors, notably in medium- or low-contrast scenes. In this paper, we present two ways in which the estimation sensitivity of the MLBF algorithm can be improved. First, we give a more thorough frequency-domain explanation of how the MLBF algorithm works and explain how cross beating and range migration cause estimation difficulties. The first improvement to the algorithm replaces the fast Fourier transform (FFT)-based beat frequency estimator with a more accurate one that uses phase increments. It avoids the FFT limitations of resolution and quantization, especially when the signal is discontinuous in one range cell due to range cell migration or burst mode operation (ScanSAR). A second improvement uses range cell migration correction to straighten the target trajectories before the beat frequency estimator is applied. This has the effect of narrowing the bandwidth of the beat signal and reducing the effect of cross beating. Finally, experiments with RADARSAT-1 data are used to illustrate the improved estimation accuracy of the modified algorithm     

PRF-ambiguity resolving by wavelength diversity

For high-precision synthetic aperture radar (SAR) processing, the determination of the Doppler centroid is indispensable. The Doppler frequency estimated from azimuth spectra, however, suffers from the fact that the data are sampled with the pulse repetition frequency (PRF) and an ambiguity about the correct PRF band remains. A novel algorithm to resolve this ambiguity is proposed. It uses the fact that the Doppler centroid depends linearly on the transmitted radar frequency for a given antenna squint angle. This dependence is not subject to PRF ambiguities. It can be measured by Fourier-transforming the SAR data in the range direction and estimating the Doppler centroid at each range frequency. The achievable accuracy is derived theoretically and verified with Seasat data of different scene content. The algorithm works best with low contrast scenes, where the conventional look correlation technique fails. It needs no iterative processing of the SAR data and causes only low computational load     

解多普勒中心模糊的一种新方法

在合成孔径雷达(SAR)成像的斜视模式下，多普勒中心频率估计往往会出现重频(PRF)模糊。本文提出的能量重心法可以有效地解决多普勒中心模糊问题。这种算法主要利用距离一多普勒城的距离徙动与多普勒中心的惟一对应关系来确定PRF模糊数。Chirp Scaling算法也是从方位傅里叶变换开始的，所以能量重心法可以与它有机地结合起来，从而大大减少运算量。能量重心法同样适用于经过Dechirp压缩处理后的数据，但此时波长差异法不再适用，因为线性调频信号经过Dechirp脉压后将变成单频脉冲信号。此外，能量重心法对大斜视角情况也是有效的。     

A new Doppler ambiguity resolution technique for SAR data based on SPECAN processing

In this paper, we describe an approach for Doppler ambiguity resolution. This approach adopts the fact that unwrapped Doppler centroid is a linear function of range frequency for a given antenna squint angle. On this basis, an alternative azimuth compression method is addressed and performed in range frequency domain to accumulate target energy in the azimuth direction. The resulting trajectories behave as some straight lines with the average slope proportional to absolute Doppler centroid. This slope can be well estimated by image-contrast methods. Theoretical analysis and real measured SAR data show that the proposed approach works well in high- and relatively low-contrast scenes.     

一种脉冲多普勒雷达解距离模糊的新算法

脉冲多普勒雷达在信号检测时存在距离模糊和速度模糊的问题，为了解决模糊问题，在体制上雷达一般采用多重脉冲重复频率（PRF）的工作方式。对于这种体制的雷达，人们已经给出了多种解模糊算法。本文主要阐述了一种解距离模糊的新方法及其实现步骤，并给出了利用该算法解距离模糊的仿真结果。     

雷达信号检测中解模糊的改进算法

模糊问题是脉冲多普勒雷达在信号检测时存在的固有问题,为了解决模糊问题,雷达一般采用多重脉冲重复频率（PRF）的工作方式。对于这种体制的雷达,目前常用的解模糊算法有孙子定理方法、一维集算法和查表法。主要阐述了一种基于一维集算法的改进算法及其实现步骤,并给出了利用该算法解距离模糊的仿真结果。     

Improved slope estimation for SAR Doppler ambiguity resolution

The idea of using the Radon transform to measure the alignment of linear features in synthetic aperture radar (SAR) data has breathed new life into the "look displacement" class of Doppler ambiguity resolution algorithms. In these algorithms, the slope of target energy is estimated to obtain the satellite beam pointing angle accurately enough to resolve the Doppler ambiguity. After explaining the method and adding some minor improvements, it is shown how it can work well on satellite SAR data. Then, an alternate method is developed that combines the ideas of the Radon and look displacement algorithms to obtain a computationally simpler and more accurate algorithm. In addition, the quality checks of the "spatial diversity" approach are used to increase the robustness of the algorithm. Even though the algorithm was conceived for high-contrast scenes, it works remarkably well in low to medium contrast scenes as well.     

Ambiguity-free Doppler centroid estimation technique for airborne SAR using the Radon transform

In synthetic aperture radar (SAR) signal processing, the Doppler centroid estimation technique, called the "clutter-lock", is important because it is related to the signal-to-noise ratio, geometric distortion, and radiometric error of the final SAR image. Conventional algorithms have either ambiguity problems or somewhat high computational load. Using the fact that the Doppler centroid and the squint angle are directly related, we propose an ambiguity-free Doppler centroid estimation technique using Radon transform, named geometry-based Doppler estimator. The proposed algorithm is computationally efficient and shows good performance of estimating the absolute Doppler centroid.     

一种中重频下联合解距离速度模糊的新算法

脉冲多普勒雷达在中重频下存在距离模糊、速度模糊问题,传统算法先解距离模糊再解速度模糊。在复杂电磁环境（存在杂波、干扰）下,上述算法存在如何选择距离门配对解模糊的难题。本文针对这种情况提出一种新算法,在距离维和速度维联合解模糊,并通过仿真验证了算法的有效性。     

Application of the multiple PRF technique to resolve Dopplercentroid estimation ambiguity for spaceborne SAR

The range correlation technique for resolution of Doppler centroid estimation ambiguity for a spaceborne SAR is reviewed. A new technique using multiple pulse repetition frequencies (PRFs) is presented. An algorithm employing simple integer arithmetic for radar systems, such as moving target indicator radar (MTIR) systems, where the PRFs contain a large common divisor, is formulated. For SAR systems, where other performance factors control selection of the PRFs, an algorithm that uses PRFs of arbitrary numerical values is devised to resolve the ambiguity. The performance of this multiple PRF technique is analyzed using a statistical error model. An example is presented for the Shuttle Imaging Radar-C (SIR-C) C-band SAR     

基于距离-多普勒补偿的多基雷达协同抗主瓣压制干扰

针对多基地雷达系统中多普勒频差导致干扰信号的去相关的问题,该文提出一种基于距离-多普勒补偿的多基雷达协同抗主瓣压制干扰方法。首先,通过不同雷达平台接收到的干扰信号的互相关函数,分析了多普勒频差对多平台干扰信号的相关性影响。其次,通过最大化时间-多普勒2维相关函数对传播延时差与多普勒频差进行估计和补偿,实现主瓣干扰抑制。然后,为了降低运算量,先利用幅度相关估计出传播延时差,再估计出多普勒频差。仿真结果表明,通过多普勒频率补偿后进行干扰信号级相消处理,可有效抑制主瓣压制干扰。     

基于压缩感知理论的多普勒解模糊处理

多目标的多普勒解模糊处理是低脉冲重复频率(PRF)雷达的关键技术之一,论文提出一种新的基于压缩感知(CS)理论的多普勒解模糊处理方法,利用多重PRF方式下相参处理间隔内的时域欠采样特性及多普勒频谱的稀疏特性,构造了多普勒解模糊的CS模型,采用正交匹配追踪(OMP)算法直接估计出无模糊多普勒谱的幅度响应,可实现PRF分组参差方式下对多个目标的解多普勒模糊处理,仿真结果验证了算法的有效性。     

一种基于查表的解速度模糊算法

根据奈奎斯特第一采样定理,采样频率要大于信号频率的两倍,信号才会不模糊。但是雷达的脉冲重复频率和目标的多普勒频率并不一定会满足此定理,这样就产生了速度模糊。解速度模糊并准确地估计目标的速度是雷达的一个重要任务,但通常的解模糊算法存在算法复杂、运算量大、精度不高等问题。提出了一种基于查表的解速度模糊算法,该方法在保证精度和容错的前提下,大大降低了运算量,是一种工程化的方法。最后仿真结果验证了该方法的有效性。     

Real-time synthetic aperture radar (SAR) processing with a newsubaperture approach

A time-domain subaperture approach that is suitable for real-time synthetic aperture radar (SAR) processing and that produces high-quality, full-resolution images is presented. The real-time subaperture algorithm is based on an approximation of the phase history correction in each subaperture with a simple linear correction, which can be carried out by an up/down-conversion of the received signal followed by a moving average operation. The characteristics of the impulse response function are improved considerably by means of a frequency overlap of the subapertures and become comparable to a conventional matched filter response. Special algorithms for high-quality SAR processing, such as autofocus, Doppler centroid estimation, and range migration correction, can be efficiently implemented. High flexibility is achieved for multilook processing and no secondary range compression is needed, even for high squint angles     

快速扫描机载气象雷达多普勒解模糊算法

本文针对机载气象雷达前视快速扫描下的多普勒模糊问题,提出了两种多普勒解模糊算法：基于改进方位向波束形成算法和基于阻塞矩阵算法。基于改进方位向波束形成算法在传统的Capon波束形成的基础上,利用空间谱积分的方法对非期望信号协方差矩阵进行重构和对导向矢量进行估计,进一步提高了算法的鲁棒性,降低方位角估计误差;基于阻塞矩阵算法需要估计导向矢量,并利用导向矢量计算阻塞矩阵,将接收信号进行多普勒模糊相消预处理,阻塞每个多普勒频点的模糊多普勒分量,以达到解模糊的目的。通过仿真实验证明,两种方法均可以有效地恢复信号的多普勒信息,其中基于阻塞矩阵算法与基于改进方位向波束形成算法相比,有更优良的性能,并有更小的运算量。     

基于相位补偿的BPSK相参脉冲串信号多普勒频率变化率估计算法

目标与观测平台之间径向加速度引起的接收信号多普勒频率变化率的精确估计对于高精度单站无源定位与跟踪具有重要意义。该文针对脉内相位调制信号的频率变化率不能直接表征多普勒频率变化率的问题,首先引入相位补偿的方法消除BPSK相位调制序列的影响,然后针对固定脉冲重复频率和脉冲重复频率抖动两种情况分别提出了径向加速度引起的多普勒频率变化率的精确估计方法,并且给出了多普勒频率变化率与采样频率、观测时间及脉冲重复频率之间的约束关系。仿真结果表明,典型参数条件下该文提出算法的信噪比门限比已有算法低约4~6 dB。     

一种基于距离-多普勒二维联合的群目标分辨方法

编队飞机由于间距很小,常规低分辨雷达无法直接从距离和方位上分辨架次.本文提出一种基于距离—多普勒二维联合处理的群目标分辨方法.发射线性调频脉冲信号,将观测时间内的若干次回波在距离维和多普勒维分别转换为单频信号的叠加,再联合距离－多普勒二维信息估计协方差矩阵,用超分辨信源数估计算法——新的改进盖氏圆盘法分辨目标架次.这种方法可以直接地给出判决结果,适用于各种飞行状态、低信噪比环境或波束驻留时间较短的情况,而且和重频参差工作模式相兼容,尤其适合中、高重频工作方式.     

Blind deconvolution for Doppler centroid estimation in highfrequency SAR

For high-quality SAR (synthetic aperture radar) processing, the Doppler centroid frequency is needed. However, SAR data are sampled along the azimuth direction at the pulse repetition frequency (PRF); the estimation of the Doppler centroid frequency by means of spectral analysis techniques may produce ambiguous results due to aliases. The mathematical expression of the residual error that occurs when SAR data are focused with an incorrect alias of the PRF is thus derived. Then, a blind deconvolution technique is used to estimate the actual PRF replica from the focused image. Squinted X-band data, corresponding to those that will be generated by the SIR-C mission, have been generated from the JPL-AirSAR L- and C-band data by means of an inversion of the focusing process. Even if the real data may show differences with respect to the simulated data, the blind deconvolution method appears to be more precise and robust than the other conventional techniques tested     

基于多组重频相参积累的多普勒解模糊方法

脉冲多普勒体制雷达一般需要对多组不同脉冲重复频率(PRF)的脉冲组分别进行处理和检测,该文研究了多组PRF相参积累的方法,将不同PRF的脉冲组作为一组进行处理,使各PRF脉冲组回波能够相参积累,只需要对一帧数据进行检测即可解模糊,改善了传统方法由于分别检测造成低信噪比时检测性能较差的问题。分析了各参数对检测结果的影响并以处理结果的主副瓣比作为适应度评价值,通过遗传算法快速搜索满足需要的参数组合,减少了搜索数目。仿真实例说明了使用遗传算法可有效获得具有优良性能的参数组合,不仅检测性能得到有效提升,还较大幅度地降低了成功解模糊所需的信噪比。     

一种基于多循环频率的韧性时延与多普勒频移联合估计算法

本文提出了一种基于分数低阶循环模糊函数的多循环频率时延与多普勒频移联合估计算法.该方法将分数低阶矩与循环平稳特性相结合,能够在SαS(Symmetric α Stable)脉冲噪声条件下检测信号的循环平稳特性.算法充分利用了信号的循环频率信息,具备较强的抑制干扰能力.仿真结果表明,在脉冲噪声和干扰环境中本文提出的算法均...