An effective focusing approach for azimuth invariant bistatic SAR processing

This paper proposes a processing method to extend monostatic imaging algorithms for the azimuth invariant bistatic SAR (BISAR) data where the transmitter and the receiver move on parallel tracks with equal velocities. The bistatic range history is approached by a polynomial of the azimuth time. Based on this model, an analytic 2-D signal spectrum derived by the method of series reversion is utilized and a simple one-to-one mapping between the transmitter and the receiver closest ranges is established. In this way, efficient monostatic imaging algorithms which operate in the 2-D frequency domain or the range-Doppler domain are easily modified to handle the BISAR data. In this paper, a chirp scaling algorithm for the BISAR is developed as an application of the new method. By implementing two key operations, range cell migration correction by a chirp scaling, and azimuth compression by a curve fitting technique, this algorithm is able to process the azimuth invariant BISAR data. Simulation results are presented to demonstrate the validity and the efficiency of the proposed algorithm.     

Three-dimensional focusing with multipass SAR data

Deals with the use of multipass synthetic aperture radar (SAR) data in order to achieve three-dimensional tomography reconstruction in presence of volumetric scattering. Starting from azimuth- and range-focused SAR data relative to the same area, neglecting any mutual interaction between the targets, and assuming the propagation in homogeneous media, we investigate the possibility to focus the data also in the elevation direction. The problem is formulated in the framework of linear inverse problem and the solution makes use of the singular value decomposition of the relevant operator. This allows us to properly take into account nonuniform orbit separation and to exploit a priori knowledge regarding the size of the volume interested by the scattering mechanism, thus leading to superresolution in the elevation direction. Results obtained on simulated data demonstrate the feasibility of the proposed processing technique.     

Airborne SAR processing of highly squinted data using a chirpscaling approach with integrated motion compensation

Proposes a new approach for high-resolution airborne SAR data processing, which uses a modified chirp scaling algorithm to accommodate the correction of motion errors, as well as the variations of the Doppler centroid in range and azimuth. By introducing a cubic phase term in the chirp scaling phase, data acquired with a squint angle up to 30° can be processed with no degradation of the impulse response function. The proposed approach is computationally very efficient, since it accommodates the variations of Doppler centroid without using block processing. Furthermore, a motion error extraction algorithm can be incorporated into the proposed approach by means of subaperture processing in azimuth. The new approach, denoted as extended chirp scaling, is considered to be a generalized algorithm suitable for the high-resolution processing of most airborne SAR systems     

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.     

基于Wigner-Hough的合成孔径雷达信号处理

交叉项问题是合成孔径雷达信号处理的主要难题,为了解决常规的合成孔径雷达信号处理中的交叉项问题,从 Wigner-Ville引出 Wigner-Hough变换的原理,及Wigner-Hough变换处理这一问题的方法。通过 Matlab软件仿真实验,比较常规方法与Wigner-Hough变换处理后的合成孔径回波信号效果,经过Wigner-Hough变换处理后的回波信号解决了交叉项问题,凸显Wigner-Hough变换在处理合成孔径信号中的优势。     

Three-dimensional multipass SAR focusing: experiments with long-term spaceborne data

Synthetic aperture radar (SAR) interferometry is a modern efficient technique that allows reconstructing the height profile of the observed scene. However, apart for the presence of critical nonlinear inversion steps, particularly crucial in abrupt topography scenarios, it does not allow one to separate different scattering mechanisms in the elevation (height) direction within the ground pixel. Overlay of scattering at different elevations in the same azimuth-range resolution cell can be due either to the penetration of the radiation below the surface or to perspective ambiguities caused by the side-looking geometry. Multibaseline three-dimensional (3-D) SAR focusing allows overcoming such a limitation and has thus raised great interest in the recent research. First results with real data have been only obtained in the laboratory and with airborne systems, or with limited time-span and spatial-coverage spaceborne data. This work presents a novel approach for the tomographic processing of European Remote Sensing satellite (ERS) real data for extended scenes and long time span. Besides facing problems common to the airborne case, such as the nonuniformly spaced passes, this processing requires tackling additional difficulties specific to the spaceborne case, in particular a space-varying phase calibration of the data due to atmospheric variations and possible scene deformations occurring for years-long temporal spans. First results are presented that confirm the capability of ERS multipass tomography to resolve multiple targets within the same azimuth-range cell and to map the 3-D scattering properties of the illuminated scene.     

Compression of SAR data through range focusing and variable-ratevector quantization

In spaceborne SAR systems, some form of data compression is required to reduce the bandwidth of the downlink channel. Compressing the raw data is very inefficient because such data exhibit little or no correlation. Data focusing would restore the original dependencies of the image, but it is too complex to be implemented onboard. In this paper we propose to carry out a partial, low-complexity focusing onboard, and then compress the resulting data by means of a suitable algorithm based on variable-rate adaptive vector quantization. Experiments show a performance improvement of 0.5-0.7 dB over compression techniques proposed in the literature     

Adaptive processing using real weights based on a direct data domain least squares approach

In traditional, adaptive signal processing algorithms one change both the amplitude and phase of the weight vectors associated with an array at each of the antenna elements. The use of complex weights offers greater control over the array response at the expense of system complexity. However, it is easier if one requires only amplitude variation with a fixed phase for all the weight vectors associated with all the antenna elements. Because one uses only real arithmetic operations to find the amplitude of the weights connected to the antenna, the computational complexity is reduced considerably. Hence, this paper addresses the use of real weights in an adaptive system. In this paper we describe a new direct data domain least squares (D/sup 3/LS) method using real weights, which utilizes only a single snapshot of the data for adaptive processing. This technique may be useful for real time implementation of the D/sup 3/LS method on a chip.     

New approaches in interferometric SAR data processing

It is known that interferometric synthetic-aperture radar (SAR) images can be inverted to perform surface elevation mapping. Among the factors critical to the mapping accuracy are registration of the interfering SAR images and phase unwrapping. A registration algorithm is presented that determines the registration parameters through optimization. A figure of merit is proposed that evaluates the registration result during the optimization. The phase unwrapping problem is approached through a new method involving fringe line detection. The algorithms are tested with two SEASAT SAR images of terrain near Yellowstone National Park. These images were collected on SEASAT orbits 1334 and 1420, which were very close together in space, i.e. less than 100 m     

An algorithm for interferometric SAR data processing

In this paper, an algorithm of generating INSAR unwrapped phase image from SAR single-look complex images is presented. Besides the general processing technique, this article focuses on the methods of flat-earth phase removal, phase noise reduction and phase unwrapping. The availability is tested by the results of processing ERS-1/2 SAR images.     

双站聚束式合成孔径雷达方位分辨率研究

在双站聚束式合成孔径雷达系统设计中,分辨率是一个关键的参考因素。当发射站和接收站分别位于不同高度但飞行轨迹地面投影平行的两条航迹中时,建立了一种机载双站聚束式合成孔径雷达系统空间几何数学建模。同时对双站聚束式SAR的方位分辨率进行了理论分析和数值仿真,讨论了不同初始条件对双站聚束模式SAR系统分辨率的影响。仿真结果表明,双站聚束式SAR分辨率不仅与雷达工作波长、雷达转视角有关,而且与发射机以及接收机相对位置有关。     

聚束照射合成孔径雷达方位分辨率研究

推导了雷达载体作匀速直线运动时，载体初始位置，速度以及合成孔径时间表示的聚束照射ＳＡＲ等效合成孔径长度的解析式，给出了以雷达工作波长，合成孔径起始及终止时刻速度矢量与天线相位中心到目标瞄准线之间夹角表示的聚束照射ＳＡＲ方位分辨率的理论表达式。     

Compression of SAR raw data through range focusing andvariable-rate trellis-coded quantization

There is an ever-growing interest in the compression of SAR data because of the huge resources required for storage and transmission. This is especially true for spaceborne sensors, given the limited capacity of the downlink channel. Unfortunately, SAR data lack the useful properties on which compression algorithms rely; indeed, these are present in the focused images, but focusing is too complex for on-board implementation at this time. Poggi et al. (2000) proposed to perform on the satellite only the low-complexity range focusing, which increases the data correlation and better concentrates their energy. These properties were then exploited by adopting a variable-rate vector quantizer, with a clear performance improvement with respect to reference techniques. However, vector quantization (VQ) is too complex for actual on-board implementation, and therefore, here we replace VQ with trellis-coded VQ. To limit complexity, only small vectors are used, which reduces VQ's ability to exploit data dependencies; on the other hand, trellis coding allows one to encode large blocks of data at once, and to obtain a better partition of the input space. Experiments on real SAR data show that the overall performance is comparable to that of Poggi et al., but the complexity is much lower, making on-board implementation possible.     

基于数据挖掘的快速记录存储器数据处理技术

针对目前国内缺少专门分析快速记录存储器(QAR)数据的有效手段的情况,研究了一种新的基于数据挖掘的QAR数据的分析方法。首先结合聚类和概率分析对k-means算法进行改进,解决了聚类数目难以确定的难题,形成了良好的聚类效果;然后,在此基础上结合加权最小距离分类器及概率分析的方法,对待分类的QAR数据的类别属性进行判断以确定异常数据;最后给出了仿真实验,验证了该方法的可行性和有效性。     

基于级数反演法的聚束式广义双基成像算法研究

该文将级数反演法应用于聚束式广义双基成像。对于广义双基,其2维频谱表达式较普通双基更加复杂,很难用精确的解析关系表达,这对后续成像处理造成了极大的困难。通过级数反演法,可以得到信号的2维频谱展开式,在2维频域进行2次距离压缩,同时在距离多普勒域进行距离徙动校正。该算法保留了单基距离多普勒算法的高效性,由于2次距离压缩考虑到了方位向的影响,因此该算法对大合成孔径情况比较适合。用该算法对仿真数据进行处理,得到了良好的成像结果。     

姿态指向稳定度对聚束SAR成像的影响

姿态指向稳定度是合成孔径雷达卫星平台设计的重要参数。文中在卫星姿态指向抖动数学模型的基础上，利用成对回波理论推导了姿态指向抖动对聚束SAR点目标冲激响应函数的影响，分析了姿态指向抖动与聚束SAR成像质量指标的关系，推导了姿态指向稳定度与聚束SAR图像质量之间定量关系的解析表达式，为聚束模式星载SAR卫星总体分析和设计提供了理论依据。最后通过计算机仿真验证了分析的正确性。     

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     

A new subaperture approach to high squint SAR processing

A high squint subaperture (HSS) algorithm was developed from the perspective of a strip map synthetic aperture radar (SAR) system and has the ability to focus SAR data at extremely high squint angle of 55° with less than 1.27% mainlobe expansion or even higher squint angles if larger mainlobe expansion can be tolerated. The unique characteristic of this algorithm is that the subapertures are formed by multiplying the received signal with a set of overlapped complex conjugated reference signals where the chirp rate varies in the azimuth direction. This is done to solve the range focus problem that arises after the azimuth input signal undergoes the range walk removal procedure. As the IISS algorithm only involves short fast Fourier transforms (FFTs) and avoids interpolation, it is computationally efficient and allows for small data buffers and facilitates hardware real-time implementation. The distinct feature of this algorithm is its simplicity of implementation, which is vital in real time processing and motion compensation when the squint angle may be changing continuously     

WIDE SWATH FMCW SAR DATA PROCESSING IN SQUINT MODE简

This paper concentrates on the data processing of Frequency Modulation Continuous Wave （FMCW）, Synthetic Aperture Radar （SAR） in the case of wide swath and squint mode. In the mode, the Doppler centroid dramatically varies along slant range compared to conventional pulsed-SAR. This poses a challenge for system design and signal processing since a very large azimuth bandwidth would be introduced. In the paper, we accommodate the Doppler centroid variations with range by an im- proved spectral-length extension method, where a bulk range shift and updated Doppler centroid variations are introduced to greatly reduce the azimuth aliasing with respective to the existing methods Moreover, an image formation approach that integrates wave number domain algorithm is presented to focus the raw data of FMCW SAR in the case of wide swath and squint mode. Point target simulation experiment demonstrates the advantages of the presented method.     

星载大斜视聚束SAR变PRI成像技术研究

星载SAR大斜视聚束可以实现高分辨率宽覆盖成像和目标多方位信息获取,但斜视情况下大距离徙动会造成回波数据获取效率下降、波位选择困难等问题。变PRI技术可以跟踪聚束成像过程中目标斜距变化,提高数据获取效率、降低波位选择难度。该文对星载大斜视聚束SAR的变PRI工作机理进行了研究,提出了一种PRI变化序列迭代设计方法和波位选择策略,研究了样条插值和NUFFT两种非周期非均匀采样重建方法,并首次通过机载飞行试验对所提出的变PRI的SAR系统工作体制进行了验证。