Predicting an upper bound on SAR ATR performance

We present a method for predicting a tight upper bound on performance of a vote-based approach for automatic target recognition (ATR) in synthetic aperture radar (SAR) images. In such an approach, each model target is represented by a set of SAR views, and both model and data views are represented by locations of scattering centers. The proposed method considers data distortion factors such as uncertainty, occlusion, and clutter, as well as model factors such as structural similarity. Firstly, we calculate a measure of the similarity between a given model view and each view in the model set, as a function of the relative transformation between them. Secondly we select a subset of possible erroneous hypotheses that correspond to peaks in similarity functions obtained in the first step. Thirdly, we determine an upper bound on the probability of correct recognition by computing the probability that every selected hypothesis gets less votes than those for the model view under consideration. The proposed method is validated using MSTAR public SAR data, which are obtained under different depression angles, configurations, and articulations     

一种提高SAR目标识别率的有效方法

在合成孔径雷达自动目标识别SAR ATR中，SAR像的预处理是提高识别率的关键技术之一。给出了一种简单有效的SAR图像预处理方法，该方法首先对SAR目标像进行对数变换后，再做傅立叶变换。经预处理后的SAR像用支持矢量机SVM分类器进行目标识别。实验结果表明：本方法不但有效地提高了目标识别率，而且保证了目标的平移不变性并具有良好的推广能力。     

SAR ATR performance using a conditionally Gaussian model

A family of conditionally Gaussian signal models for synthetic aperture radar (SAR) imagery is presented, extending a related class of models developed for high resolution radar range profiles. This signal model is robust with respect to the variations of the complex-valued radar signals due to the coherent combination of returns from scatterers as those scatterers move through relative distances on the order of a wavelength of the transmitted signal (target speckle). The target type and the relative orientations of the sensor, target, and ground plane parameterize the conditionally Gaussian model. Based upon this model, algorithms to jointly estimate both the target type and pose are developed. Performance results for both target pose estimation and target recognition are presented for publicly released data from the MSTAR program     

Feature enhancement and ATR performance using nonquadratic optimization-based SAR imaging

We present an evaluation of the impact of a recently proposed synthetic aperture radar (SAR) imaging technique on feature enhancement and automatic target recognition (ATR) performance. This image formation technique is based on nonquadratic optimization, and the images it produces appear to exhibit enhanced features. We quantify such feature enhancement through a number of criteria. The findings of our analysis indicate that the new feature-enhanced SAR image formation method provides images with higher resolution of scatterers, and better separability of different regions as compared with conventional SAR images. We also provide an ATR-based evaluation. We run recognition experiments using conventional and feature-enhanced SAR images of military targets, with three different classifiers. The first classifier is template based. The second classifier makes a decision through a likelihood test, based on Gaussian models for reflectivities. The third classifier is based on extracted locations of the dominant target scatterers. The experimental results demonstrate that the new feature-enhanced SAR imaging method can improve the recognition performance, especially in scenarios involving reduced data quality or quantity.     

Improving slant-range resolution with multiple SAR surveys

Across-track resolution of a spaceborne synthetic aperture radar (SAR) system is limited by power and data rate constraints. The authors derive and discuss a new technique for increasing the across-track resolution of objects that do not change with time, using multiple surveys of the same area from different off-nadir angles. Precise information on the spaceborne trajectories are not requested since they can be derived from SAR interferometry. Simulated data show that theoretical derivations are in good agreement with practice     

SAR resolution in the presence of phase errors

The author analyzes the effects of phase errors on synthetic aperture radar (SAR). The theory is applied to the following question: how does the achievable resolution vary with the carrier frequency when optimum quadratic focus and/or optimum processing interval (synthetic aperture length) are used? Numerous related results are given, so that much of the material is tutorial. For phase errors corresponding to uncompensated motion, the best achievable RMS resolution with any phase error spectrum satisfies the derived equation. For motion-induced phase errors it is seen that resolution improves with increasing carrier frequency when the first term in the expression applies (e.g. for phase errors concentrated at low frequencies) and resolution is independent of carrier frequency when R δ/v/v is the smaller term (e.g. with broad band or high frequency phase errors)     

Super resolution SAR imaging via parametric spectral estimationmethods

Super resolution synthetic aperture radar (SAR) image formation via sophisticated parametric spectral estimation algorithms is considered. Parametric spectral estimation methods are devised based on parametric data models and are used to estimate the model parameters. Since SAR images rather than model parameters are often used in SAR applications, we use the parameter estimates obtained with the parametric methods to simulate data matrices of large dimensions and then use the fast Fourier transform (FFT) methods on them to generate SAR images with super resolution. Experimental examples using the MSTAR and Environmental Research Institute of Michigan (ERIM) data illustrate that robust spectral estimation algorithms can generate SAR images of higher resolution than the conventional FFT methods and enhance the dominant target features     

Automatic target recognition using enhanced resolution SAR data

Using advanced technology, a new automatic target recognition (ATR) system has been developed that provides significantly improved target recognition performance compared with ATR systems that use conventional synthetic aperture radar (SAR) image-processing techniques. This significant improvement in target recognition performance is achieved by using a new superresolution image-processing technique that enhances SAR image resolution (and image quality) prior to performing target recognition. A computationally efficient two-level implementation of a template-based classifier is used to perform target recognition. The improvement in target recognition performance achieved using superresolution image processing in this new ATR system is quantified     

Effects of Reduced SAR Azimuth Processing

Several approaches are evaluated for reducing the large data handling and processing loads associated with synthetic aperture radar (SAR) imaging systems. The effects of data abbreviation on SAR images were studied theoretically as well as experimentally with SEASAT-A data. Image degradation was measured in terms of azimuth resolution and signal-to-clutter ratio. It was found that the degradation of image quality to data rate reduction is graceful. With high time-bandwidth product signals, little or no azimuth resolution degradation was noticed with several data bandwidth reduction techniques that achieve data reduction factors of up to 8. The signal-to-clutter ratio was found to decrease slowly with increasing reduction in data rate.     

ATR发动机燃烧室波瓣混合器张角及瓣宽比对掺混、燃烧特性的影响

为了促进空气涡轮火箭发动机燃烧室内来自压气机的空气和流经涡轮的富燃燃气的掺混、提高燃烧效率,本文基于空气涡轮火箭发动机燃烧室入口结构参数设计了波瓣混合器,并采用数值模拟方法通过调整张角及瓣宽比对波瓣结构进行优化。结果表明：1）保持外张角不变,增大波瓣内张角可以有效改善内涵燃料在燃烧室中心轴附近区域燃烧不完全的状况;2）在内、外张角相同的条件下,通过减小瓣宽b2使瓣宽比 大于1可以提升掺混及燃烧效率;3）相对于非反应流动,波瓣诱导流向涡在反应流中强度更高,沿径向向外移动的速度也更快;4）带有波瓣结构的燃烧室内,因内、外涵气流掺混造成的总压损失很小,80%以上的总压损失是由加热造成的。     

A technique for enhanced slant range resolution for SAR systems inknowledge-based environment

Synthetic Aperture Radar (SAR) is an airborne (or spaceborne) radar mapping technique for generating high resolution maps of surface target areas including terrain. High resolution is achieved by coherently combining the returns from a number of radar transmissions. The resolution of the images is determined by the parameters of the emissions, with more data giving greater resolution. A requirement of the Microwave Radar Division's SAR radar is to provide classification of targets. This paper presents a technique for enhancing slant range resolution in SAR images by dithering the carrier centre frequency of the transmitted signal. The procedure controls the radar waveforms so they will optimally perform the classification function, rather than provide an image of best quality. It is shown that a Knowledge-Based engineering approach to determining the waveform of the radar gives considerably improved performance as a classifier of targets (of large radar cross-section), even though the corresponding image is degraded     

Effects of Navigation Errors in Maneuvering SAR

A maneuvering synthetic aperture radar in squint mode, during a loosely piloted maneuver, is simulated with presence of various navigation system errors. The error sources investigated place emphasis on short-term effects, involving platform servo transients, noise and quantization in accelerometers, interaction of angle pickoff uncertainty with the displacement from platform to radar antenna, and uncertainty in this displacement itself. Simulation results are accompained by interpretive discussion, and followed by suggested areas for further study.     

Effects of finite weight resolution and calibration errors on theperformance of adaptive array antennas

Adaptive antennas are now used to increase the spectral efficiency in mobile telecommunication systems. A model of the received carrier-to-interference plus noise ratio (CINR) in the adaptive antenna beamformer output is derived, assuming that the weighting units are implemented in hardware, The finite resolution of weights and calibration is shown to reduce the CINR. When hardware weights are used, the phase or amplitude step size in the weights can be so large that it affects the maximum achievable CINR. It is shown how these errors makes the interfering signals “leak” through the beamformer and we show how the output CINR is dependent on power of the input signals. The derived model is extended to include the limited dynamic range of the receivers, by using a simulation model. The theoretical and simulated results are compared with measurements on an adaptive array antenna testbed receiver, designed for the GSM-1800 system. The theoretical model was used to find the performance limiting part in the testbed as the 1 dB resolution in the weight magnitude. Furthermore, the derived models are used in illustrative examples and can be used for system designers to balance the phase and magnitude resolution and the calibration requirements of future adaptive array antennas     

局部进气ATR涡轮性能影响因素数值模拟研究

为研究局部进气条件下ATR涡轮内的流动特性,对局部进气涡轮进行定常和非定常数值模拟.定常计算采用冻结转子方法,改变动叶与静叶的周向相对位置研究涡轮内流场特征;改变进气扇区布局、进口参数和局部进气度,研究其对涡轮性能的影响.研究结果表明,对于给定局部进气度,进气扇区整体布局时,涡轮性能的优越性最大;在局部进气ATR涡轮的设计中,需要综合考虑流量、效率和功率3个因素来决定局部进气度.不同位置定常流动结果的平均值与非定常流动的时均值存在差异,非定常计算更好地展示了静叶尾迹和流动积累效应的影响,因而更加可靠.     

Theory and experiments on hard-limited SAR imaging

Known results in the area of hard-limited array theory are extended and generalized for synthetic aperture radar (SAR) applications in order to obtain a significant reduction of the required transmission channel bandwidth. The results provide a theoretical basis for subsequent numerical experiments related to the SIR-B mission. The SAR signal is hard-limited (at the offset frequency, after the heterodyne process) and filtered, and the restored signal is processed in the conventional way to obtain the image of the pertinent scene. Results of this experiment may be useful in assessing image degradation due to 1-b coding     

固体碳氢推进剂ATR二次燃烧特性实验研究

为了探索常温来流条件下补燃室稳定燃烧的工作条件,设计并加工了一套专门用于研究掺混燃烧的试验装置,验证了模拟落压机构的效果,探索了只有简单掺混器状态下碳氢推进剂的二次燃烧特性。实验发现,只有简单掺混装置的情况,在比冲较优空燃比状态下未能实现二次燃烧,因此在发动机参数设计中不仅要考虑比冲性能还要兼顾可燃条件;实验中采用的固体碳氢推进剂在直接掺混方式下稳定燃烧的空然比上限为4.4左右;简单掺混方式燃烧效率不理想,今后需要探索适合碳氢燃料的火焰稳定器和增强掺混燃烧方法。      

SAR干扰效果研究

研究了对干扰前不同图像质量的合成孔径雷达(SAR)的干扰效果问题。从干扰前SAR图像质量指标积分旁瓣比(ISLR)入手,提出等效信干比的概念,建立积分旁瓣比与等效信干比的关系,分析等效信干比与发现概率、错误概率的关系,最后确定不同图像质量所对应的所需信干比。     

基于北斗卫星导航的搜救系统原理与构型

为使基于北斗卫星的导航搜救系统比现有全球卫星搜救系统（COSPAS-SARSAT）更具先进性、优越性、更适应我国国情,在全球卫星搜救系统基础上构建基于北斗卫星搜救系统的原理和构型,使其具备提供全天候、全天时、高精度、高可靠的定位、导航和授时服务,并充分利用短消息服务有效缩短救生搜索和定位时间,提高了搜救效率,同时加强卫星定位保密程度,为未来军事用途打下基础。     

鲁棒成形极化敏感阵列波束的方法及极化估计

基于极化敏感阵列,提出了一种鲁棒成形阵列波束的方法。该方法首先将阵列的数据模型进行了重新描述,从而获得了信号波达角(DOA)和极化解耦的模型。借助于该模型并对信号的两个极化方向分别进行鲁棒约束,设计出了一个新的鲁棒空域波束空间成形矩阵,利用该矩阵可以获得信号两个极化分量的鲁棒估计。基于特征值分解的方法,最后给出了估计信号极化参数的方法。分析和数值仿真实验均表明:提出的方法,在对DOA估计误差以及阵列位置误差等造成的阵列失配具有较强鲁棒性的同时,也能有效抑制干扰和噪声,进而提升了极化参数估计的性能。