The influence of input parameters on SAR interferometric processing and its implication on the calibration of SAR interferometric data

Synthetic Aperture Radar (SAR) interferometry is a field of rapid development. The processing of SAR interferometric data is complex and influenced, in particular, by the input parameters. A sensitivity study of these input parameters and issues relating to the calibration of SAR interferometric data is presented. The pulse repetition frequency has been identified as a critical parameter during the SAR interferometric processing which, in case of inconsistencies in the CEOS standard data format, leads to erroneous results.     

The preliminary cross-calibration of the HY-2A calibration microwave radiometer with the Jason-1/2 microwave radiometers

This article focuses on the cross-calibration of the Haiyang-2A (HY-2A) calibration microwave radiometer (CMR) with the Jason-1 microwave radiometer (JMR) and the Jason-2 advanced microwave radiometer (AMR). The temporal trends in the CMR brightness temperatures (BTs) are compared with those of the JMR and the AMR in terms of period-averaged BT (averaged over each satellite cycle). The differences between them are observed and then corrected. The data pairs at the crossover points of HY-2A and Jason-1/2 are collected. The differences between the BTs of the CMR and those of the JMR and the AMR are further reduced by a latitude correction. The validation results show that after the time and latitude corrections, the root mean square values of the BT differences are clearly reduced by about 0.8, 0.8, and 0.6 K in the three channels, respectively. Based on the time and latitude corrected data, seven kinds of retrieval model (of vapour-induced wet tropospheric path delay, water vapour, cloud liquid, and sea surface wind speed) are built for the CMR. The results of the retrieval models based on the artificial neural networks show smaller differences from the JMR and AMR data than those of the other models.     

Energy- and spectral-efficiency of zero-forcing beamforming in massive MIMO systems with imperfect reciprocity calibration: bound and optimization

In a time-division duplex (TDD) system with massive multiple input multiple output (MIMO), channel reciprocity calibration (RC) is generally required in order to cope with the reciprocity mismatch between the uplink and downlink channel state information. Currently, evaluating the achievable spectral efficiency (SE) and energy efficiency (EE) of TDD massive MIMO systems with imperfect RC (IRC) mainly relies on exhausting Monte Carlo simulations and it is infeasible to precisely and concisely quantify the achievable SE and EE with IRC. In this study, a novel method is presented for tightly bounding the achievable SE of massive MIMO systems with zero-forcing beamforming under IRC. On the basis of the analytical results, we demonstrate key insights for practical system design with IRC in three aspects: the scaling rule for interference power, saturation region of the SE, and the bound on the SE loss. Finally, the trade-off between spectral and energy efficiencies in the presence of IRC is determined with algorithms developed to optimize SE (EE) under a constrained EE (SE) value. The loss of optimal total SE and EE due to IRC is also quantified, which shows that the loss of optimal EE is more sensitive to IRC in a typical range of transmit power values.     

Setup and calibration of a distributed camera system for surveillance of laboratory space

This paper describes the setup and realization of a distributed camera system designed to survey a laboratory area where humans and mobile manipulator robots collaborate jointly. The system consists of 40 industrial grade cameras surveying a 10 m by 10 m area from a top-down perspective, connected via Gigabit Ethernet (GigE) to a cluster of 40 computers for distributed image processing. The cameras were fully calibrated, achieving an average reprojection error of 0.13 pixels for the complete system, which exceeds state-of-the art accuracy. Current long-term testing has the system running with at least 99.994% availability for up to two weeks. Successful application tests of the system were conducted, where it was used to track the movements of robots and humans across the surveyed area.     

Concurrent adaptive beamforming for standard hexagonal array based on dual norm‐constraint correntropy in the presence of alpha stable noise

This article presents dual norm‐constraint correntropy beamforming methods for standard hexagonal array (SHA) to mitigate the effects of alpha stable noise and maintain the sparsity of filter coefficients. Both goals are achieved simultaneously through the use of norm regularization constraint and the novel convex combination technique. Firstly, we construct constrained optimization equations considered the constraints present in the constrained least‐mean‐square (CLMS) algorithm by incorporating the maximum correntropy criterion (MCC). In addition, in order to decrease the number of active elements for limited power supply array system, we introduce an L1‐norm equation to the list of constraints of the adaptive filter that forces the coefficients with small magnitudes to zero. Then, we utilize the convexity and stability of L2‐norm to devise the constrained maximum correntropy gradient L2‐norm (CMCG‐L2) for further reducing the misadjustment caused by alpha noise and improving the directivity performance of the adaptive beamformer. A novel convex combination scheme is also reported to satisfy the conflicting requirements between the sparsity and mean‐square‐error. Our simulation results demonstrate the superiority of the proposed methods over other previously developed beamforming techniques.     

Calibration of satellite radiometers and the comparison of vegetation indices

Satellite technology provides a steadily improving capability to monitor surface land use and vegetation. However, the increasing number of satellite sensors has led to a variety of spectral indices which may be used to characterize vegetation. A basis is developed for comparing results from different sensors using instrument calibration coefficients, and the derived radiances are related to reflectances, principal component variables such as greenness, and spectral vegetation indices.     

Indirect method for estimation of the errors in measurements of sky radiance by Sun–sky radiometers of CIMEL type: calibration by molecular scattering

The results of measurements of the aerosol optical thickness (AOT) of the atmosphere by CIMEL Sun–sky radiometers are analysed. In arid zones, days with values of AOT not greater than 0.02 are common. In these cases, the sky radiance in backward hemisphere in the visible wavelength range is practically fully determined by the molecular scattering, which is well studied up to date. This fact opens up possibilities to estimate the errors in measuring sky radiance comparing observed and calculated data, as well as to separate them into random and systematic.     

服务机器人智能空间中顶棚投影器建模与外参数标定

研究服务机器人智能空间中顶棚投影器的运动学建模和外参数标定问题.首先,利用D-H方法对投影器进行运动学建模;然后,给出一种全新的求解一类关于旋转矩阵方程组的非线性迭代优化算法,以完成投影器的外参数标定;最后进行了实验验证.实验结果表明,所提出的投影器建模方法和外参数标定算法具有很高的精度,经过标定后的投影器能够在地面上投射出完全按期望路径引导机器人运动的激光斑点,从而实现低成本服务机器人高效和精确地导航.     

波束形成算法研究与改进

近年来,智能天线在抗干扰方面应用广泛,多种不同的自适应波束成形算法被相继提出。首先讨论了LMS、GSC、MMSE三种波束形成算法的性能,对于均匀线性阵列天线,在相同条件的情况下,通过计算机仿真比较了三种算法的特点。最后提出了对MMSE算法的改进,通过对单个天线逐个权值的调整,使阵列输出信号与参考信号差异最小,减少计算复杂度,自适应地产生最优权值,实现了很好的抗干扰效果。     

双冗余CAN总线模块的设计与实现

为满足恶劣环境下计算机系统的高可靠性需求,将冗余技术结合到CAN总线模块的硬件与软件开发中,介绍其总体方案、硬件及软件设计方法,重点描述了在VxWorks系统下的驱动软件实现,给出了部分实现细节及设计流程。测试结果表明,此设计可成功实现CAN冗余模块在总线故障情况下的冗余切换,提高了设备可靠性。     

嵌入式冗余计算机的设计与实现

根据用户要求,针对高可靠性多余度容错计算机的可靠性设计要点,介绍一种嵌入式冗余计算机的组成和工作原理,论述冗余技术的选择和应用,主要包括冗余模式、同步方式的选择和表决器的设计,给出硬件的可靠性设计措施和软件设计思路,并用相关试验证明该冗余计算机的可靠性。     

Benefits and Drawbacks of Redundant Batch Requests

Most parallel computing platforms are controlled by batch schedulers that place requests for computation in a queue until access to compute nodes is granted. Queue waiting times are notoriously hard to predict, making it difficult for users not only to estimate when their applications may start, but also to pick among multiple batch-scheduled platforms the one that will produce the shortest turnaround time. As a result, an increasing number of users resort to “redundant requests”: several requests are simultaneously submitted to multiple batch schedulers on behalf of a single job; once one of these requests is granted access to compute nodes, the others are canceled. Using simulation as well as experiments with a production batch scheduler we evaluate the impact of redundant requests on (1) average job performance, (2) schedule fairness, (3) system load, and (4) system predictability. We find that some of the popularly held beliefs about the harmfulness of redundant batch requests are unfounded. We also find that the two most critical issues with redundant requests are the additional load on current middleware infrastructures and unfairness towards users who do not use redundant requests. Using our experimental results we quantify both impacts in terms of the number of users who use redundant requests and of the amount of request redundancy these users employ. This work was supported by the NSF under Award 0546688.     

计算机网络中冗余链路及设备的管理

结合实际案例 ,以 Cisco产品为主线 ,介绍了计算机网络中冗余链路及网络设备使用方法和配置方法 ,利用冗余技术建立一个健壮的计算机网络。介绍了几个 Cisco独到而特有的技术 ,如 :生成树协议、快速转发、循环冗余链路及冗余路由等。     

迈克尔逊干涉型光纤水听器研究与实现

设计了对偏振衰落不敏感的迈克尔逊干涉型光纤水听器,系统通过使用直接调制光源的相位载波零差检测方式实现了光纤水听器相位载波(PGC)解调,并给出了实验测试结果。由2个水听器组成水听器阵进行了水池实验,结果显示:该干涉型光纤水听器有明显的指向性,具有一定的潜在实际应用前景。     

冗余数据约简的研究与设计

Z. Pawlak于1982年提出的Rough集理论有效地分析了不确定、不精确、不一致等各种不完备信息,其优点是无需任何关于数据的初始的或附加的信息,如统计学中的概率分布。该文介绍了Rough集的基本理论在数据约简中的应用。在分析基于信息系统的粗糙集理论的基础上,描述了一种基于核与重要度的约简算法,从降低约简算法计算复杂度角度出发,修改了属性约简算法,计算了算法修改前后的复杂度。实验结果表明,修改后的算法在降低时间复杂度的同时得出了次优属性集的约简。     

Process and conduction of interferometric phase for satellite images

The Digital Elevation Model (DEM) is used in many fields of earth science. It is generated from interferometry SAR (InSAR) using two co-registered radar Single Look complex (SLC) [1], [2] and [3]. This work concerns the exploitation of radar images SLC of the Algiers area acquired on 03 January and 04 January 1994. The former is taken as a master image and the latter as a slave image. We have developed an interferometric process starting with the implementation of a co-registration algorithm for our images, then the elimination of flat-earth phase from the interferogram and at the end we developed a filter in order to minimize the existing noise to have good results after the unwrapping step using our own developed method.     

激光偏振干涉纳米定位系统的设计与实验研究

为适应工业发展和计量界对精密定位提出的越来越高的要求,本文提出了基于偏振激光干涉技术的纳米定位方法。在该干涉测长系统中,用偏振计取代传统单频激光干涉仪的光电传感器并配置偏振分光元件、起偏镜等,可将干涉仪出射光的干涉条纹相位细分为36000份,使用波长为633nm的激光源,可将理论测量分辨率提高到 10pm。将完成的偏振干涉测长系统与商用SIOS干涉仪的实验测量结果做了比对。本文还就完成的实验系统的各误差源做了实验研究,得到量化值。经不确定度评估计算,在标准实验室环境条件下,对于微米级行程的位移,其位置测量不确定度小于1.4nm。该方法可应用于纳米定位的各个领域。     

Analysis of Tsai calibration method using two- and three-dimensional calibration objects

Camera calibration is a fundamental process for both photogrammetric and computer vision. Since the arrival of the direct linear transformation method and its later revisions, new methods have been developed by several authors, such as: Tsai, Heikkilä and Zhang. Most of these have been based on the pinhole model, including distortion correction. Some of these methods, such as Tsai method, allow the use of two different techniques for determining calibration parameters: a non-coplanar calibration technique using three-dimensional (3D) calibration objects, and a coplanar technique that uses two-dimensional (2D) calibration objects. The calibration performed by observing a 3D calibration object has good accuracy, and produces very efficient results; however, the calibration object must be accurate enough and requires an elaborate configuration. In contrast, the use of 2D calibration objects yields less accurate results, is much more flexible, and does not require complex calibration objects that are costly to produce. This article compares these two different calibration procedures from the perspective of stereo measurement. Particular attention was focused on the accuracy of the calculated camera parameters, the reconstruction error in the computer image coordinates and in the world coordinate system and advanced image-processing techniques for subpixel detection during the comparison. The purpose of this work is to establish a basis and selection criteria for choosing one of these techniques for camera calibration, according to the accuracy required in each of the many applications using photogrammetric vision: robot calibration methods, trajectory generation algorithms, articulated measuring arm calibration, and photogrammetric systems.     

六方纳米氧化钨的制备及其表征

氧化钨无机半导体材料因其特有的物理化学性能以及在气敏、光催化、光致变色、电致变色和场发射等领域的广泛应用,得到人们的普遍关注.以钨酸钠为前驱体,硫酸钠为结构导向剂,采用水热合成法制备了六方相三氧化钨,并应用X射线衍射(XRD),扫描电镜(SEM),高分辨透射电镜(HRTEM),傅里叶变换(FFT)等微观分析手段对三氧化钨粉体进行表征和分析.结果表明:在pH≈1,最终反应温度160℃,反应时间12 h可得到平均直径约为85 nm,长度约为2.2μm六方相氧化钨纳米线.并由HRTEM和FFT图像可分析得知,六方相三氧化钨纳米线晶体生长方向主要沿着[001]轴向,其晶面间距为0.3880 nm.