机载SAR 实时成像处理系统设计

介绍了机载SAR 实时信号处理器的体系结构和实时信号处理的算法流程, 通过对载机平台实测数据进行成像处理, 给出了高分辨率的SAR 图像, 验证了该系统的可靠性。
     

实时SAR成像系统矩阵转置方法研究与实现

合成孔径雷达（SAR）是一种高分辨率成像雷达,而矩阵转置是实时SAR成像信号处理中一个很重要的操作,矩阵转置的效率高低将直接决定整个SAR成像信号处理系统的性能。对于矩阵转置,可采用行进列出或列进行出、两页式或三页式转置等方法进行处理,但这些方法处理时间较长,转置效率较低。在现有矩阵转置方法的基础上,提出了一种新的矩阵转置方法。在实际硬件平台上利用提出的矩阵转置方法进行了实时SAR成像处理,所得结果的矩阵转置效率为78%,整个SAR成像处理时间为10秒。测试结果表明,该方法对解决矩阵转置问题是行之有效的。     

机载SAR实时成像系统自聚焦方法研究

发展我国自主产权的机载SAR（合成孔径雷达）实时成像系统，对于军事国防、资源探测、灾害预报等领域均具有重要的意义，在SAR成像算法中，自聚焦的好坏是影响图像分辨率的关键因素，但是因为自聚焦算法的复杂性，国内目前尚未有效地解决它在实时环境中的实现问题，从而使得实时成像的质量比较差，提出了一种利用GPS（全球定位系统）数据改善机载SAR实时成像系统自聚焦性能的实现方法，并在自主研制的机载SAR实时成像系统上实现，使该系统的成像分辨率得到明显改善。     

基于FPGA的小型化实时CMOS成像处理系统

针对成像处理系统的实时性和小型化的问题,设计了一种基于Cyclone IV系列FPGA的CMOS数据采集处理系统,实现了图像的实时采集、处理和双通道输出;通过体系结构上的优化实现了系统的小型化设计。介绍了系统总体框架、硬件体系结构、FPGA功能模块以及图像预处理算法等。最后对系统进行了功能性实验,在满足双通道实时显示的情况下,可以实现图像增强等实时处理,表明该系统具有一定的实用价值。     

用FPGA实现星载SAR实时成像处理器的工程方法

根据星载SAR成像算法的原理，提出了一种用FPGA实现该成像处理器的有效方法。该处理器的体系结构由算法直接映射而来，同时根据算法内在的时间关系将流水处理和并行处理相结合，从而极大地减少了处理时间。根据算法各运算对数据的精度要求不同，将浮点运算和定点运算结合在一块，既满足了成像的精度要求又节省了硬件开销。该系统工作在100MHz时，33s左右能完成16k^＊16k星载样本点的成像，并对加拿大Radarsat的雷达原始信号进行成像处理，成像质量能达到要求。     

星载SAR成像处理器中转置存储器的FPGA实现

论述了合成孔径雷达(Synthetic aperture radar，SAR)成像处理器转置存储器(Corner turning memory，CTM)的功能和原理，提出了一种基于FPGA的星载SAR成像处理器CTM设计方案，分析了系统的参数及输入输出接口时序，给出了详细的硬件实现，并进行了功能和时序仿真。方案主要部分由一片XC2V500 FPGA和三片K6F3216T6M SRAM组成，采用三页式结构和输入输出并行处理方法，考虑了星上环境条件对器件的限制，可以实现星上SAR实时成像处理器的CTM系统。实验结果表明该CTM系统可行。     

基于SAR成像算法的高性能信号处理模块

针对SAR成像算法高速实时处理、宽幅海量存储的特点,设计并实现一种基于多PowerPC处理器的高性能并行信号处理模块.该处理模块利用多种高速串行总线构成不同层次的互联网络以适应不同类型的数据流传输,结合具有混合并行结构的底层处理节点以完成SAR成像算法在该处理模块上的映射.应用结果表明,基于该处理模块构建的信号处理系统...     

星载SAR的噪声干扰分析

由于在星载SAR干扰功率计算中,采用传统的雷达干扰方程很难得到某些参数,因此计算结果可能不合理。根据星载SAR的成像原理和噪声干扰机理,从定性和定量两个方面分析了对星载SAR实施噪声干扰的可行性。在不考虑成像算法及传输损耗的影响下,提出了与星载SAR的方位、距离分辨率及其运行轨道等参数有关的干扰方程,分析了与传统干扰方程的不同及影响因素。依据星载SAR系统波位设计原理,分析了雷达天线端口及其接收机通道的信干比变化,并进行了仿真、计算。研究结果适用于星载SAR干扰的工程设计及计算。     

机载SAR实时成像系统中的数据可视化研究

SAR实时成像系统在国防等很多领域都有着重要的应用,系统对数据可视化方面的要求也越来越高,但目前国内对SAR实时成像系统的数据可视化方面的研究还不多,提出了一种针对SAR实时成像系统的新的数据可视化方案,并已在实际的飞行成像中得到了检验,新方案实时提供的信息更全面、更直观、可分析性更强,具有较强的信息表现能力和双向实时交互能力,能够较好地辅助对图像的在线分析,还对方案的重要组成部分－缩略图的原理和实现算法做了概括介绍。     

流水线结构的高效SAR快视成像处理器

本文由快视成像算法的特点出发,提出了一种流水线结构SAR快视成像处理机的实现方法.这种方法充分考虑到了DSP和FPGA的运算特点,突出了快视成像处理的实际需求.系统硬件实现的复杂度较低,仅仅采用加减操作即可完成方位向信号的处理,易于实时成像,在观测大范围现象以及图像预览等方面有广阔的应用前景.     

A novel spaceborne SAR wide-swath imaging approach based on Poisson disk-like nonuniform sampling and compressive sensing

Since the range swath width in the conventional single channel spaceborne synthetic aperture radar(SAR)is restricted by the system parameters,there is a trade-off between the azimuth resolution and the swath width in order to satisfy the Nyquist sampling criterion.In this paper,we propose a novel spaceborne SAR wide-swath imaging scheme based on compressive sensing(CS)for the sparse scene.The proposed method designs a Poisson disk-like nonuniform sampling pattern in the azimuth direction,which meets the demand of wider swath by restricting the smallest time interval between any two azimuth samples,with the conventional sampling pattern preserved in the range direction.By a similar way to the processing procedure of spectral analysis(SPECAN)algorithm,the linear range migration correction(RMC)is realized while carrying out range compression,which can meet the demand for focusing with middle level resolution.To reduce the computation load of CS reconstruction,we propose a novel fast reconstruction algorithm based on nonuniform fast Fourier transform(NUFFT),which greatly reduces the computation complexity from O(2M N)to O(4N log N).Experiment results validate the effectiveness of the proposed methods via the point target simulation and the Radarsat-1 raw data processing in F2 mode.     

FPGA implementation of collaborative representation algorithm for real-time hyperspectral target detection

Hyperspectral image contains various wavelength channels and the corresponding imagery processing requires a computation platform with high performance. Target and anomaly detection on hyperspectral image has been concerned because of its practicality in many real-time detection fields while wider applicability is limited by the computing condition and low processing speed. The field programmable gate arrays (FPGAs) offer the possibility of on-board hyperspectral data processing with high speed, low-power consumption, reconfigurability and radiation tolerance. In this paper, we develop a novel FPGA-based technique for efficient real-time target detection algorithm in hyperspectral images. The collaborative representation is an efficient target detection (CRD) algorithm in hyperspectral imagery, which is directly based on the concept that the target pixels can be approximately represented by its spectral signatures, while the other cannot. To achieve high processing speed on FPGAs platform, the CRD algorithm reduces the dimensionality of hyperspectral image first. The Sherman–Morrison formula is utilized to calculate the matrix inversion to reduce the complexity of overall CRD algorithm. The achieved results demonstrate that the proposed system may obtains shorter processing time of the CRD algorithm than that on 3.40 GHz CPU.     

Estimation of tree growth in a conifer plantation over 19 years from multi-satellite L-band SAR

The general capability of synthetic aperture radar (SAR) for monitoring forest ecosystems is well documented. However, the majority of SAR studies of forest dynamics use only imagery acquired by one SAR system and are thus limited to the lifecycle of a particular satellite. The synergistic analysis of SAR data from one of the earliest spaceborne SAR missions, the SEASAT mission, with the Japanese JERS-1 satellite-borne SAR is presented. Biophysical parameters frequently retrieved from SAR are tree biomass using backscatter and tree height from the interferometric phase. One potential application that has not been thoroughly examined is mapping of incremental tree growth from SAR backscatter changes. Tree growth measures biomass changes over time, and is correlated to the amount of carbon sequestered by the trees. This paper examines the retrieval of tree growth from multitemporal spaceborne L-band SAR. A SEASAT SAR image from 1978 and a JERS-1 SAR image from 1997 over Thetford forest, UK are used to retrieve tree growth of Corsican Pine stands. Incremental growth was estimated from the changes in backscatter coefficient, and compared to the expected tree growth from general yield class models used by the UK Forestry Commission. The accuracy of the retrieval algorithm depends on the minimum forest stand size included in the analysis. For managed forest plantations, multitemporal L-band SAR has some potential for detecting incremental biomass to support sustainable forest management.     

FPGA实时实现PGA算法的研究

合成孔径雷达(SAR)成像具有数据量巨大、算法比较复杂等特点.如何实时实现SAR成像的相关算法是嵌入式高性能计算领域一个值得研究的问题.FPGA以其高性能、可重构等优势,被越来越多地应用到嵌入式高性能计算领域中作为一种高效低成本的解决方案.针对SAR成像中多普勒调频率估计的经典算法--PGA算法,以FPGA作为实现平台,通过对算法的本质的挖掘,提出了适于FPGA实时实现的对于经典算法的改进算法.同时也阐述了将改进算法映射到FPGA实现的设计过程.实验结果表明,改进的算法较经典的PGA算法明显地减少了迭代次数,在SOC中通过硬件的运算精度能够满足系统的要求.     

星载SAR原始数据普适性分块自适应矢量压缩算法

传统矢量量化器的码本普适性差,需要在线更新,难以在星载SAR系统中实现.文中针对星载SAR原始数据的统计特性,以多维空间上的失真函数为代价函数,根据输入数据的联合概率密度函数设计得到了具有普适性的矢量量化码本,分析了原始数据矢量量化编码以及解码方案.在此基础上,深入研究了矢量量化级联熵编码方案的可行性以及码字索引在信道传输发生误码时算法的稳健性.实际数据处理结果表明,文中算法具有普适性,矢量量化码本的普适性使得码本可以进行离线设计,为矢量量化的星载实用化提供了理论指导.     

A universal adaptive vector quantization algorithm for space-borne SAR raw data

Codebook of conventional VQ cannot be generally used and needs real time onboard updating,which is hard to implement in spaceborne SAR system.In order to solve this problem,this paper analyses the characteristic of space-borne SAR raw data firstly,and then utilizes the distortion function of multidimensional space as criterion,and finally the adaptive code book design algorithm is proposed according to the joint probability density function of the input data.Besides,the feasibility of the new algorithm in cascade with entropy coding and the robustness of the algorithm when error occurs during transmission are analysed based on the encoding and decoding scheme.Experimental results of real data show that codebook deriving from the new algorithm can be generally used and designed off-line,which makes VQ a practical algorithm for space-borne SAR raw data compression.     

High performance FPGA-based image correlation

Image correlation is widely used for image and picture processing. Typical applications of image correlation are object location, image registration and sub-image similarity measurement. However, image correlation requires the comparison of a large number of sub-images implying a large computational effort that may prevent its use for real-time applications. On the other hand, correlation computation is very well suited for FPGA implementations. In this work we present efficient architectures for the implementation of Zero-Mean Normalized Cross-Correlation using FPGAs with application to image correlation. In particular, we compare the implementations of correlation in the spatial and spectral domains. Experimental results demonstrate that FPGAs improve performance by at least two orders of magnitude with respect to software implementations on a modern personal computer. This speed-up makes the performance of correlation computation suitable for real-time image processing. The proposed architectures have been applied to a correlation-based fingerprint-matching algorithm, demonstrating that real-time processing requirements can be well satisfied with an FPGA-based implementation.     

基于稀疏重构框架下剪切波的SAR图像去噪

SAR图像很容易被乘性噪声多污染,进而影响SAR图像后序的分析与处理。本文中提出了一种基于剪切波稀疏编码的SAR图像移除乘性噪声的新模型。首先通过压缩感知理论建立SAR图像去噪模型;其次通过剪切波变换获得剪切波系数,每个尺度的系数视为一个单元;对于每个单元,通过剪切波域的贝叶斯估计对稀疏系数进行迭代估计。重现的单元最后结合起来构造去噪后的图像。SAR图像去噪效果显示了该算法有良好的表现性,对噪声具有鲁棒性;本文提出的算法不仅有较好的去噪效果,而且还保存了更多的边界信息。     

BAQ算法在SAR原始数据压缩中的应用研究

研究了用块自适应量化（BAQ）算法压缩合成孔径雷达（SAR）原始数据,考虑了实际SAR数据的非零均值。文中给出了算法在信号域内的信号对量化噪声比（RSQN）和均方根相位误差这两个性能指标的评估结果;并给出了SAR原始数据经BAQ处理后的成像结果;最后提出了一种可与雷达接收机增益控制电路相结合的、压缩比灵活可变的BAQ方案,适合于在压缩比和图像质量之间作折衷选择。     

一种星载InSAR高精度快速DEM重建方法

面对全球干涉测量的海量实测数据,在保持精度的情况下,如何提高处理速度是星载干涉合成孔径雷达(interferometric synthetic aperture radar,InSAR)数据处理必须考虑的重要问题.数字高程模型(digital elevation model,DEM)重建是InSAR数据处理中较为耗时的一个关键环节.针对星载InSAR处理中DEM快速重建的难题,从DEM重建原理出发,分析揭示了干涉相位与目标点三维坐标映射关系的两个基本特性,一是目标点的三维坐标与干涉相位的关系可以分别用多项式来进行拟合,二是SAR图像上相近像素各自对应的多项式变化不大,并从理论上对特性的成立进行了论证.基于此,提出了一种快速DEM重建方法,给出了快速算法的详细步骤及关键参数的取值方法.最后,利用德国最先进的在轨雷达卫星TerraSAR-X获取的重复轨道干涉数据进行快速DEM重建,处理结果表明在重建精度损失较小的情况下,显著提高了重建速度,验证了该方法的高效性和正确性.