Satellite imagery based adaptive background models and shadow suppression

Accurate segmentation of foreground objects in video scenes is critical for assuring reliable performance of vision systems for object tracking and situational awareness in outdoor scenes. Most existing techniques for background modeling and shadow suppression require that a number of parameters be “hand-tuned” based on environmental conditions. This paper presents two contributions to overcome such limitations. First, we develop and demonstrate a satellite imagery based approach for selecting appropriate background and shadow models. It is shown that the illumination conditions (i.e. cloud cover) of a scene can be reliably inferred from visible satellite images in the local region of the camera. The second contribution presented in the paper is introduction and evaluation of a Hybrid Cone-Cylinder Codebook (HC3) model which combines an adaptive efficient background model with HSV-color space shadow suppression into a single coherent framework. The structure of the HC3 model allows for seamless fusion of the satellite data. We are thereby able to exploit the fact that, for example, shadows are more pronounced on sunny days than cloudy days, allowing for more sensitive detection. The paper presents a set of experiments using day long sequences of videos from an operational surveillance system testbed. Results of these experimental analyses quantitatively illustrate the benefits of using satellite imagery to inform and adaptively adjust background and shadow modeling.     

SAR图像目标和阴影径向积分特征评估

为了评价理论建模建立合成孔径雷达（Synthetic Aperture Radar,SAR)图像模板的准确性,利用SAR图像中两个典型区域（目标和阴影）,建立仿真与实测图像之间相似性的定量评估方法.该方法预先分割出目标和阴影区域,并分别提取目标轮廓、目标强度分布和阴影轮廓的极化映射径向积分特征,基于这三种特征计算仿真图像和实测图像的相关系数.对三种车辆目标（BMP2、BTR70、T72）的仿真SAR图像与运动和静止目标获取与识别（Moving and Stationary Target Acquisition and Recognition, MSTAR)实测SAR图像进行相似性比对和分类识别,结果表明,目标轮廓、目标强度分布、阴影轮廓的极化映射径向积分特征评估方法具有较好的相似性和分类性能.     

Mixture models with skin and shadow probabilities for fingertip input applications

This paper proposes an accurate moving skin region detection method for video-based human–computer interface using gestures or fingertips. Using Gaussian mixture models as groundwork, the proposed method expresses the features of skins in a probability form and incorporates them into the mixture-based framework. Moreover, to alleviate the influence of shadows, the properties of shadows are also formulated as probabilities and used for shadow detection and elimination. In addition to moving skin region detection, this paper also develops two practical fingertip input applications to demonstrate the accuracy of the proposed detection method. The two applications are Mandarin Phonetic Symbol combination recognition system and single fingertip virtual keyboard implementation. Experimental results have shown the advantages of the proposed detection method and the effectiveness of the two application implementations.     

Self-organizing feature maps and hidden Markov models formachine-tool monitoring

Vibrations produced by the use of industrial machine tools can contain valuable information about the state of wear of tool cutting edges. However, extracting this information automatically is quite difficult. It has been observed that certain structures present in the vibration patterns are correlated with dullness. We present an approach to extracting features present in these structures using self-organizing feature maps (SOFMs). We have modified the SOFM algorithm in order to improve its generalization abilities and to allow it to better serve as a preprocessor for a hidden Markov model (HMM) classifier. We also discuss the challenge of determining which classes exist in the machining application and introduce an algorithm for automatic clustering of time-sequence patterns using the HMM. We show the success of this algorithm in finding clusters that are beneficial to the machine-monitoring application     

Fast and robust generation of feature maps for region-based visual attention.

Visual attention is one of the important phenomena in biological vision which can be followed to achieve more efficiency, intelligence, and robustness in artificial vision systems. This paper investigates a region-based approach that performs pixel clustering prior to the processes of attention in contrast to late clustering as done by contemporary methods. The foundation steps of feature map construction for the region-based attention model are proposed here. The color contrast map is generated based upon the extended findings from the color theory, the symmetry map is constructed using a novel scanning-based method, and a new algorithm is proposed to compute a size contrast map as a formal feature channel. Eccentricity and orientation are computed using the moments of obtained regions and then saliency is evaluated using the rarity criteria. The efficient design of the proposed algorithms allows incorporating five feature channels while maintaining a processing rate of multiple frames per second. Another salient advantage over the existing techniques is the reusability of the salient regions in the high-level machine vision procedures due to preservation of their shapes and precise locations. The results indicate that the proposed model has the potential to efficiently integrate the phenomenon of attention into the main stream of machine vision and systems with restricted computing resources such as mobile robots can benefit from its advantages.     

自选择混合分布模型的CFAR用于SAR图像舰船检测

为了解决恒虚警率检测算法（CFAR检测）在合成孔径雷达图像舰船检测中,用已有分布建模,不能应对所有的场景,对于一些复杂场景建模拟合效果不理想的问题,本文使用一种自选择混合分布的CFAR检测方法:首先,对图像进行预处理,减少目标像素对海杂波的影响;其次,利用学习出来的混合分布模型对预处理后的每一块图像进行建模,计算全局阈值,并根据阈值把图像像素分为目标和背景杂波;然后,为防止漏检,重新对场景像素进行建模、检测,重复此过程直到背景杂波中检测不到目标为止;最后加入后处理,减少虚警的产生。这一方法不仅能得到更好的海杂波模型,同时还能提取舰船的更多细节,实验结果证明了这一方法的有效性。      

Generation of digital terrain models with a ground-based SAR system

A novel technique for the retrieval of a digital terrain model (DTM) with a ground-based synthetic aperture radar (GB-SAR) system is described. A set of SAR images collected over a test site located at Salice d'Ulzio, Italy, is used to validate experimentally the proposed DTM retrieval technique. The topographic height is obtained using an algorithm specifically tailored for a GB-SAR system equipped with two receive antennas. The comparison with an existing DTM of the test site area shows that the retrieved DTM is accurate, with root mean square height differences between the two DTMs below 5 m.     

高波段SAR与UWB SAR运动补偿效果分析

对于相同的分辨力要求,高波段SAR合成孔径较短,因此运动补偿处理相对较为容易,而超宽带(UWB)SAR,却需要较长的合成孔径,运动补偿处理难度较大.本文分析了高波段SAR和UWB SAR的特点,采用同一次飞行试验中高波段SAR和UWB SAR实测数据,提取出基于多普勒调频率的运动补偿前后高波段SAR和UWB SAR图像中点目标的相位误差及其频谱,分析了运动补偿的效果,得出了基于多普勒调频率的运动补偿对高波段SAR和UWB SAR聚焦性能的改善程度.     

电磁兼容测量场地从OATS、SAR到FAR的演变

试验场地对电磁兼容测试至关重要.本文对常用的几种实验场地:开阔试验场OATS、半电波暗室SAR、全电波暗室FAR存在的问题,尤其是限值的转换问题作了较为详细精确的分析,对实际的测试工作具有参考价值.     

Synthesis of magnetic material images using SAR models withirregular neighbour sets

The application of SAR models to the synthesis of magnetic material images is presented. The effects of the structure of neighbour sets on the statistical properties of synthesised images are investigated. Supported by the content-based image retrieval technique, the work demonstrates that using a neighbour set with its shape corresponding to the orientations and coarseness of the underlying texture allows the generation of realistic synthetic images     

合成孔径雷达的某些性能及其简析

合成孔径雷达（SAR）系统的性能与许多方面有关。文中讨论方位鉴别力、距离鉴别力、鉴别力与覆盖区域的限制、SAR雷达方程、对SAR平台的要求、SAR工作模式、多频率与多极化、ISAR和未来的SAR与有源相控阵等问题。     

Towards generation of efficient test cases from UML/OCL models for complex safety-critical systems

This paper describes a new approach for model-based test case generation (MBTCG) for large systems, which not only supports the expression of complex requirements (constraints) using OCL, but also lays ground for improving the efficiency (i.e. maximum coverage with minimal number of test cases) of the generated test case set. For that purpose, UML/OCL models are transformed to (object-oriented) action systems, where test cases are generated by means of mutation. The resulting "abstract" test cases represent input/output sequences with possible branches according to valid alternatives in system responses. They have finally to be transformed to "concrete" test cases which can be applied to the target application. The described work is part of the European project MOGENTES.     

The optical second-harmonic generation from porous silicon

Second-harmonic generation from porous silicon with a magnitude of two orders greater than that from the original silicon crystalline wafers is discussed. The measured effective second-order nonlinear susceptibility X⁽²⁾_ps.eff for a p-type porous silicon is 1.96×10^-7 esu. The susceptibility is estimated on the base of a bulk property rather than on quantum confinement owing to its large surface to volume ratio     

航空图像中阴影区域的检测

航空图像中的阴影区域可以提供大量的关于目标形状、相对位置、表面特性、高度的相关信息,本文首先对阴影的特征进行了研究,认为阴影对图像的影响是使所投射地表的表面光照强度降低,但不改变原有地表,目标表面的光照特征,如纹理特征及光照强度方向统计特征等。阴影区域内的灰度方差一般小于其他非阴影区域,不同阴影区域之间的灰度值具有较强的一致性。然后,本文利用基于二维直方图的最大熵门限化方法求得边缘图像,并对边缘图像进行了细化和跟踪,删除那些对比很弱、或者虽然对比度较强,但是不满足光照条件的边缘,得到阴影边缘。在门限化过程中使用了邻域函数和过渡区域,既保留了弱边缘,又最大程度地抑制了噪声对边缘的干扰。根据阴影边缘构出假想的阴影区域,并统计这些区域的灰度直方图,求得阴影区域的灰度区间。根据该灰度区间可以得到阴影区域,这些区域具有对比度较高、至少有一侧比较规则、光学性质类似的特点。     

Phase unwrapping for large SAR interferograms: statistical segmentation and generalized network models

Two-dimensional (2-D) phase unwrapping is a key step in the analysis of interferometric synthetic aperture radar (InSAR) data. While challenging even in the best of circumstances, this problem poses unique difficulties when the dimensions of the interferometric input data exceed the limits of one's computational capabilities. In order to deal with such cases, we propose a technique for applying the statistical-cost, network-flow phase-unwrapping algorithm (SNAPHU) of Chen and Zebker (2001) to large datasets. Specifically, we introduce a methodology whereby a large interferogram is partitioned into a set of several smaller tiles that are unwrapped individually and then divided further into independent, irregularly shaped reliable regions. These regions are subsequently assembled into a full unwrapped solution, with the phase offsets between regions computed in a secondary optimization problem whose objective is to maximize the a posteriori probability of the final solution. As this secondary problem assumes the same statistical models as employed in the initial tile-unwrapping stage, the technique results in a solution that approximates the solution that would have been obtained had the full-size interferogram been unwrapped as a single piece. The secondary problem is framed in terms of network-flow ideas, allowing the use of an existing nonlinear solver. Applying the algorithm to a large topographic interferogram acquired over central Alaska, we find that the technique is less prone to unwrapping artifacts than more simple tiling approaches.     

Automatic generation of accurate low-order models for magnetic devices

A method to automatically create low order state-space models for magnetic devices is set forth. The method begins with geometrical and materials data from which the finite element analysis (FEA) is used to build a high order state-space model. It is shown that this model contains far more state variables than are necessary to achieve the nearly the same results in the frequency band of interest. It is shown that the full-order model can be reduced methodically without additional physical assumptions. The reduction method is applicable directly to magnetically linear systems, but applies to a wide range of power electronics applications and can be a basis for future nonlinear device modeling. The method reduced an example inductor model from 882 state variables to two. To confirm correct model derivation, the full-order model is checked against and agrees with experimental data to the extent that the FEA and materials data are accurate. The reduced-order model agrees very well with the full-order model, particularly in computing impedance.     

Study of the SAR signature of internal waves by nonlinear parametric autoregressive models

In this paper, we propose a method for estimating the nonlinear differential equation governing the propagation of internal waves (IWs) in a stratified water column of the ocean. This estimation of the kind of nonlinear differential equation and the coefficients of this equation is performed from profiles of the synthetic aperture radar signature at the ocean surface. Theoretically, the equation is based upon the Korteveg-de Vries (KdV) equation or one of its improved versions. The estimation of the differential equation version is based on nonlinear polynomial autoregressive models up to the third order. The estimation of the parameters of these models is performed simply by solving a set of linear equations using higher order statistics. This general approach allows us to identify the best model of propagation, i.e., the kind of nonlinearity as well as the structure of each kernel (linear, quadratic, cubic), without determining an analytic solution to the equation of propagation. Moreover, the physical oceanic parameters (such as the thermocline depth) are deduced from the estimated coefficients of the KdV equation (assuming an underlying model of the water column). Results on simulated profiles generally lead to an exact model identification (i.e., the one used for simulation with the exact order of nonlinearity and the exact structure of each kernel) and lead to satisfying geophysical parameter estimates. Finally, the geophysical parameters estimated from three sets of ERS-1 profiles are generally coherent with the parameters observed in the IW propagation mechanism but have not been validated by "in situ" measurements.     

Improved models for the generation of multiple uncorrelatedRayleigh fading waveforms

An improved sum-of-sinusoids simulation model is proposed for Rayleigh fading channels. The new model employs random initial phase, and conditional random Doppler frequency for all individual sinusoids. The second-order statistics of the new simulator match the desired ones exactly even if the number of sinusoids is a single-digit integer. Other key statistics of the new simulator approach the desired ones of Clarke's (1968) reference model as the number of sinusoids approaches infinity, while good convergence is achieved when the number of sinusoids is small. Moreover, the new simulator can be directly used to generate multiple uncorrelated fading waveforms; it is also pointed out that a class of 16 different simulators, which have identical statistical properties, can be developed for Rayleigh fading channels     

基于条带式SAR与聚束式SAR内在联系的SAR成像研究

针对条带式合成孔径雷达（stripmap sar）与聚束式合成孔径雷达（spotlight sar）的方位向频谱结构,讨论了两种模式SAR之间的区别与联系,利用两者之间的内在联系,提出斜视条件下将条带式SAR数据分块,进行聚束式处理的方法,并对聚束式成像区域大小参数的选择进行了分析.对于相同尺寸的成像区域,对条带式SAR进行聚束式处理可以减小运算量.采用空间频率插值成像算法实现了条带式SAR与聚束式SAR成像算法上的统一,最后应用外场实测数据完成成像,成像结果证实了理论分析的正确性.     

基于高分辨率SAR图像的建筑物高度提取

分析了高分辨率SAR图像中建筑物的成像特征:叠掩及角反射器效应,获取了SAR图像中建筑物屋顶像点位移,最后根据相应的公式计算了建筑物的高度。与实际高度数据相比较,发现计算结果精度较高,是一种可行的建筑物高度获取方法,可为以后发射的高分辨率星载SAR图像的应用提供很好的借鉴。