Sensitivity Analysis and Calibration of Hydrological Modeling of the Watershed Northeast Brazil

Mathematical models of the quantity and quality of water in hydrographic basins enable simulation of a wide variety of processes, including the production of water and sediments, and the dynamics of point and nonpoint sources of pollution. These models have become increasingly complex, requiring large amounts of input data, which can increase the uncertainty of the results of simulations. For this reason, it is essential to perform calibration and validation procedures. The objective of this work was to conduct sensitivity analysis and calibration of a distributed hydrological model (SWAT) applied to the flows of water in the watershed of the Poxim River. Satisfactory performance of the model was indicated by the values obtained for the Nash-Sutcliffe efficiency coefficient (0.77), the percent bias (5.05), the root mean square error (0.48), and the ratio of the RMSE to the standard deviation of the observations (RSR) (0.49). The set of parameters identified here could be used for the simulation and evaluation of other scenarios.

Efficiency and Feasibility of an Integrated Algorithm for Distributed Hydrological M odel Calibration

Increasing complexity of distributed hydrological model （DHM） has lowered the efficiency of convergence.In this study,global sensitivity analysis （SA） was introduced by combining multiobjective （MO） optimization for DHM calibration.Latin Hypercube-once at a time （LH-OAT） was adopted in global parameter SA to obtain relative sensitivity of model parameter,which can be categorized into different sensitivity levels.Two comparative study cases were conducted to present the efficiency and feasibility by combining SA with MO（SA-MO）.WetSpa model with non-dominated sorting genetic algorithm-Ⅱ （NSGA-Ⅱ） algorithm and EasyDHM model with multi-objective sequential complex evolutionary metropolis-uncertainty analysis （MOSCEM-UA）algorithm were adopted to demonstrate the general feasibility of combining SA in optimization.Results showed that the LH-OAT was globally effective in selecting high sensitivity parameters.It proves that using parameter from high sensitivity groups results in higher convergence efficiency.Study case Ⅰ showed a better Pareto front distribution and convergence compared with model calibration without SA.Study case Ⅱ indicated a more efficient convergence of parameters in sequential evolution of MOSCEM-UA under the same iteration.It indicates that SA-MO is feasible and efficient for high dimensional DHM calibration.

IMPROVED CALIBRATION METHOD FOR AIRBORNE ATI-SAR BASELINE

Airborne Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) baseline error is a main error resource affecting the precision of velocity measurement of moving objects and therefore should be calibrated externally. The Jet Propulsion Laboratory (JPL) has proposed a calibration scheme for tasks of PacRim98 and PacRim2000 based on several static objects on the ground. In this paper, the influence of phase center uncertainty on baseline determination by using PacRim method proposed by JPL is analyzed. According to the analysis, the phase center uncertainty can cause a constant part of error to the result of baseline calibration. In order to deal with this problem, an improved calibration method on the basis of sensitivity equations and some ground moving targets, whose velocities are already known, is proposed in this paper. The simulation results show that our proposed calibration method has improved the accuracy of baseline calibration and has obviously prohibited the effect of antennas' phase center uncertainty.

An Adaptive Image Calibration Algorithm for Steganalysis

In this paper,a new adaptive calibration algorithm for image steganalysis is proposed.Steganography disturbs the dependence between neighboring pixels and decreases the neighborhood node degree.Firstly,we analyzed the effect of steganography on the neighborhood node degree of cover images.Then,the calibratable pixels are marked by the analysis of neighborhood node degree.Finally,the strong correlation calibration image is constructed by revising the calibratable pixels.Experimental results reveal that compared with secondary steganography the image calibration method significantly increased the detection accuracy for LSB matching steganography on low embedding ratio.The proposed method also has a better performance against spatial steganography.

Dark Current Compensation and Sensitivity Adjustment on Gallium Arsenide Linear Array Detector for X-Ray Imaging

For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.

Application of 2-D Position Sensitive Detector in Spatial Straightness Measurement of Guide Rails

A laser collimating system based on 2-D position sensitive detector (PSD) is presented in this paper. The working principle of PSD is depicted in detail. A calibration device was developed to check the nonlinearity errors of PSD and a multilayer feedforward neural network based on error back-propagation algorithm was used to compensate errors. With the aid of computer-based data acquisition system, an automatic dynamic measuring process was realized. A series of experiments, including comparison tests with laser interferometer, were done to evaluate the performance of the measuring system. The experimental results show that the spatial straightness errors of guide rails can be measured with high accuracy. The maximum differences between the device and laser interferometer are 0.027 mm in Y direction, and 0.053 mm in X direction in the measuring distance of 6 m.

不同目标函数对新安江模型参数的敏感性和不确定性影响分析

目标函数的选择影响流域水文模型的参数率定结果。为深入探究不同目标函数对水文模型参数的敏感性和不确定性及径流模拟结果的影响,本文以福建省金溪池潭流域日径流模拟为例,采用SCEM-UA优化算法率定三水源新安江模型,选择纳什效率系数f_(1)、均方根误差f_(2)和Kling-Gupta效率系数f_(3)作为参数率定的目标函数,同时构建分别偏好f_(1)、f_(2)、f_(3)三者的组合多目标函数F_(1)、F_(2)和F_(3)共6个率定目标,比较不同率定目标下的径流模拟精度差异,采用Sobol全局敏感性分析方法定量对比分析不同目标函数下的新安江模型参数敏感性,最后基于GLUE方法分析丰枯水期和不同流量级别下的径流模拟不确定性。结果表明:(1)6个目标函数下,新安江模型的主要敏感参数识别结果一致;(2)F_(1),F_(2),F_(3)较单目标函数展现出更高的径流模拟精度;(3)在不同水文时期和不同流量级别下,f_(1)表现出较其他目标函数更高的覆盖率和较小的不确定性区间。不同目标函数下均呈现枯水期参数不确定性最小,且随流量级别的增大而径流模拟不确定性增加的规律。

极化敏感阵列方位依赖误差校正算法

在实际应用中多种类型阵列误差同时存在,针对这种情况下阵列误差方位依赖的特点,提出了一种基于流形分离技术(manifold separation technique,MST)的改进多重信号分类(multiple signal classification,MUSIC)算法,可以有效解决多种阵列误差影响下的波达方向估计问题。利用MST获得包含阵列非理想特性的采样矩阵,从而进行精准测向;通过二维傅里叶变换求解二维空间谱,与现有MUSIC校正算法相比,减少了谱峰搜索的运算量。理论分析和仿真验证了该算法的有效性,可为实际问题的解决提供参考。

一维光学位置传感器融合的非接触多自由度位姿测量系统

为实现机器人末端位姿多自由度实时测量反馈,融合一维光学位置传感器(Position Sensitive Detector,PSD)建立了平面3自由度非接触测量系统,对其测量原理,信号处理电路,环境光干扰去除和非线性标定算法等进行研究。根据PSD传感器测量特性和平面3自由度测量要求设计了4-PSD测量系统,并建立测量系统数学模型。研究了PSD传感器的信号处理电路,通过运放和除法器实现了单个PSD的信号处理,结合单片机与A/DC采样电路,实现了上位机的高频率信号采集。对4-PSD测量系统进行预实验,为消除环境光干扰,通过激光调制和数字滤波等方法进行验证。最后,通过激光位移传感器标定4-PSD测量系统,介绍了4-PSD的标定步骤(原点、转角、长度和二阶非线性标定),测定了系统标定后的误差分布。该测量系统具有较高的测量频率(50 Hz)。标定实验结果表明:标定后的4-PSD测量系统在70 mm×70 mm内,测量精度平均为0.49 mm,比标定前降低了90%的误差,能满足大部分高速、高精度机器人末端的非接触式实时测量反馈需求。

一种考虑g敏感性的MIMU系统级标定方法研究

针对微机械惯性测量单元(micro-electro-mechanical-system inertial measurement unit,MIMU)中存在陀螺漂移的g敏感性以及因漂移误差大而无法进行自主方位对准问题,建立了MIMU系统级标定Kalman滤波状态空间模型,考虑g敏感性误差状态的影响,在量测方程中加入方位失准角变化率以增强g敏感性的状态估计可观性;直接采用外输入粗略初始方位角进行导航解算,降低地球自转角速度的影响,提高陀螺漂移估计精度。设计了一套完整的系统级标定转位编排方案,陀螺标定和加速度计标定相互依赖,共同协作完成MIMU系统级标定,能够有效分离出所有30个标定参数,利用某型号弹载MIMU进行了实物标定试验验证,分别用标定前后数据进行导航解算,对比导航结算结果发现标定后的3个方向的导航速度都降低了,加速度计的刻度因数和零偏标定精度更高。特别在MIMU存在多轴大角度转动情况下,近10 min内达到优于30 m/s的导航速度精度,验证了系统级标定具有较高的精度。

剪应力压电智能骨料灵敏度便捷标定方法

大量混凝土结构在地震中出现显著剪切破坏特征,有必要开展混凝土剪应力监测。以PZT压电陶瓷为敏感传感元件的剪应力压电智能骨料传感器已被学者们证实能够实现混凝土内部剪应力的监测。然而,目前剪应力压电智能骨料的灵敏度标定试验依赖于高精密加载设备或大型结构构件,存在试验复杂、成本高以及标定后传感器无法重复使用等问题。本研究首先提出了一种基于单摆装置循环加载的剪应力压电智能骨料灵敏度便捷标定方法;其次,通过有限元和试验方法研究了加载位置变化对及单摆面外运动对灵敏度标定的影响;最后,通过该方法标定了一批剪应力压电智能骨料的灵敏度,并与精密加载获得的灵敏度进行了对比。本研究对提高混凝土结构剪应力监测精度具有重要意义。

冗余驱动并联机械手运动精度校准方法研究

针对冗余驱动并联机械手(RAPM)的运动精度,以某三自由度主轴头为例,提出了一种基于最小误差模型的运动精度校准方法。首先通过消除冗余几何源误差,建立包含最少几何源误差的最小误差模型,采用蒙特卡罗模拟进行几何源误差灵敏度分析,研究各几何源误差对终端精度的相对影响。在此基础上提出了粗校准和精校准相结合的分层辨识策略,以实现冗余驱动并联机械手的精度校准。最后通过校准实验测试表明,所提出的校准方法能够大幅降低冗余驱动并联机械手的终端误差,验证了所提校准方法的有效性。

一种隧道磁电阻电流传感器的旁路自校准技术

应用于智能电网的隧道磁电阻(tunnel magnetoresistance,TMR)电流传感器的灵敏度易受环境温度的影响发生变化,从而严重影响TMR电流传感器的测量精度。从TMR电流传感器基本测量原理出发,对传感器芯片的灵敏度进行了理论分析。在传感器下方增设了周期注入式直流自校准回路,计算注入前后传感器输出电压的差值平均值,实时追踪校准当前环境温度下灵敏度的真实值,并设计闭环运算控制电路对传感器进行实时调整。最后搭建实验测试平台进行了直流注入实验、温控实验和线性度实验,测试结果证明了旁路自校准技术可以提高开环式TMR电流传感器测量的准确性和稳定性。

基于导通压降的大容量IGBT模块结温观测与误差分析研究

压接式绝缘栅双极性晶体管PP-IGBT(press-pack insulated gate bipolar transistor)模块因其优越的电气性能和可靠性,广泛应用于柔性直流换流阀等大功率应用场景。IGBT芯片结温的准确观测对于其运行状态的监测与剩余寿命的评估都非常重要。已有结温观测方法多是针对键合引线式IGBT,未考虑到压接式模块的特性,无法直接应用。首先,针对大容量换流阀中的压接式IGBT,提出了一种实用的模块导通压降与结温标定方法,并对结温在线估计的误差进行了全面分析。然后,基于ABB公司5SNA 3000K452300压接式IGBT模块(4500 V,3000 A)设计了结温标定方案,包括实验电路、温度标定范围选择、结温控制方式、测量电路及标定实验步骤。最后,基于脉冲测试平台,对所提方法进行了验证。实验结果表明,所提结温标定与观测方案有效,结温观测误差在±5℃以内,且能适用压接式IGBT模块存在差异的情况。

基于冲击法的压电式力传感器灵敏度研究

为了开展冲击力校准装置下压电式力传感器动态灵敏度的校准,介绍了基于自由落体的落锤冲击力模型和基于空气轴承悬浮支撑的水平式质量块冲击碰撞的模型;通过4阶Butterworth低通滤波,研究加速度信号波形的滤波平滑,比较了不同截止频率的滤波效果;通过激光测振仪和标准加速度计测量加速度的对比试验,研究加速度绝对测量法与比较测量法对力传感器动态灵敏度校准精度的影响。试验结果表明,激光测振仪测量加速度须通过微分解调,要选择合适上限截止频率的4阶Butterworth低通滤波器进行滤波平滑处理;激光干涉绝对法复现的动态力精度为2%,加速度计比较法复现的动态力精度为4%;激光干涉绝对法校准的灵敏度波动性比加速度计比较法校准的灵敏度波动性小。

振动液柱管中不同尺度水听器灵敏度补偿方法

针对不同尺度的球型和圆管型测量水听器,通过仿真软件COMSOL建立管中声场模型,分析不同尺度水听器对声场的干扰,进而对不同尺度水听器声压灵敏度补偿修正。通过振动液柱校准装置,在校准频段100~1000 Hz对不同尺度水听器灵敏度标定,与补偿后的水听器灵敏度值比对结果表明:水听器的尺寸会扰乱周围声场分布,导致管中声场分布不均匀;当敏感元件尺寸接近声管内径时,圆管型测量水听器甚低频段干扰接近2.28 dB,而高频段干扰最高达5 dB。同尺寸的圆管水听器相较于球型水听器对声场的干扰较大。补偿后的水听器灵敏度不确定度在0.52 dB以内,满足振动液柱法校准的指标要求。

磁电式低频振动传感器原位校准改进型系统的设计与实现

针对拾振器的原位校准在高频段的灵敏度误差大的问题,构建了改进校准电路后系统模型。通过实验,得到原位校准与激光干涉法的归一化灵敏度的相对误差,发现改进电路后的相对误差小于改进电路前的相对误差。此外,在实验过程中,水平向传感器对于安装角度有较高的要求,分别改变传感器与水平面的夹角,获得了激光干涉法与原位校准法的校准结果,发现当传感器与水平面有一定夹角时,使用改进后校准的方法后,低频灵敏度与高频灵敏度的误差变大。

关键本构模型识别与不确定性量化方法研究

典型基于输入的最佳估算加不确定性(BEPU)分析方法需要全面考虑各种来源的不确定性,但作为重要不确定性来源之一的最佳估算程序内部本构模型不确定性却很难得到准确量化。针对传统BEPU方法的不足,采用函数型数据分析加次序敏感性分析方法识别重要模型,贝叶斯校准方法加高斯过程代理模型量化模型参数不确定性,得到了一种准确的关键本构模型识别与不确定性量化方法。使用该方法量化了FLECHT-SEASET实验中重要模型的不确定性,并将量化的不确定性抽样传播至包壳温度。另外对该方法与传统的关键本构模型识别方法进行对比。结果表明,该方法可以准确识别瞬态过程中的关键本构模型,传播计算结果能够很好地包络实验值。

基于运动轨迹约束的静水压激励法水听器校准

针对传统静水压激励法水听器校准系统中,由于连通软管欠约束导致连通软管内水体振动时惯性力对等效声压的影响不一致,从而引起由测量重复性引入的不确定度偏大,影响水听器灵敏度校准不确定度的问题,提出了基于运动轨迹约束的静水压激励法水听器校准方法。该方法设计了运动约束装置控制连通软管在振动时产生相同的运动轨迹,基于此建立数学模型确定了连通软管部分振动对等效声压的影响,推导出不受限于水听器开路电压测量数据的等效高度计算公式。搭建了基于运动轨迹约束的静水压激励法水听器校准装置,并与传统方法进行了比对。实验结果表明:相较于传统静水压激励法,该方法将水听器灵敏度校准的不确定度由0.34 dB(k=2)减小到0.25 dB(k=2),其中由测量重复性引入的不确定度从0.12 dB减小到0.02 dB。

基于旋转弹体的非理想阵列测向技术研究

[目的]针对旋转弹测向系统在飞行过程中由强杂波环境带来的误差干扰进行研究,提出一种实时校正的波达方向(DOA)估计算法。[方法]该算法利用阵列旋转角度这一先验条件,基于最大似然(ML)准则,实现对共形阵列误差和信号空域-极化域参数的联合估计。[结果]仿真实验表明,该算法对存在方位依赖的幅相不一致性误差的阵列系统,可以实现在线的误差和信号参数联合估计,且该算法的估计性能均与阵列平台旋转次数和信噪比(SNR)相关,当旋转次数达到24以上时,在低信噪比为10 dB情况下空域参数估计误差在1°以下。[结论]所提算法采用分维交替处理的思路来解决多参数估计问题,在保证参数收敛的同时大幅降低了运算的复杂度。