Finite element modeling of heating phenomena of cracks excited by high-intensity ultrasonic pulses     

陈赵江  郑江  张淑仪  米小兵  郑凯 《海洋学报(英文版)》2010,29(11)

A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.  相似文献   

结合强度信息的LIDAR数据滤波方法     

袁枫  张继贤  张力  高井祥 《测绘科学》2010,35(5):39-40,34

机载激光扫描系统可以直接生成扫描区域的数字表面模型,但是为了提取数字地面模型还须对LIDAR数据进行滤波处理。本文分析了用坡度法对机载LIDAR数据进行滤波的不足,并结合LIDAR数据中的强度信息,提出了一种结合强度信息的LIDAR数据滤波方法。与坡度法相比,该方法提高了滤波的精度和效率。试验结果表明该方法计算速度快,并能够有效地滤除LIDAR数据中的地物。  相似文献   

精密单点定位在机载GPS中的应用     

叶修松  徐广袖  王玉振 《测绘学院学报》2010,(1)

推导了精密单点定位PPP(Precise Point Positioning)的基本原理及其解算流程。为达到分米级甚至厘米级的PPP精度,给出了基于传统模型PPP技术,PPP数据必须处理的几个关键问题。最终,在Matlab程序设计语言软件平台下开发了APTags 1.0软件包,并通过机载GPS动态数据测试得出了如下结论:序列历元的事后动态定位精确度在B,L,H方向优于25 cm(RMS);85%定位结果的精度优于15 cm的动态定位结果。APTags软件包获取的动态精密单点定位结果与传统差分定位结果基本吻合。  相似文献   

机载激光雷达单机检校方案研究   总被引：1，自引：1，他引：0  

刘凯华  张建霞  左建章 《测绘科学》2010,35(6):62-64,69

针对目前LiDAR的精度标定环节,本文分析了激光雷达的测距原理和影响测距精度的因素后,提出了对测距精度影响较大的激光器二极管电流强度、扫描半角、扫描频率、扫描距离以及灰度值的自身误差检测方法,展示了交通标志的特殊点云图像,并以此组织了完整的检校工作,验证了该检校方法的可行性,提出了可供参考的检测注意事项,为在测量结果中加入误差校正提供了理论依据。  相似文献   

Exploring hyperspectral bands and estimation indices for leaf nitrogen accumulation in wheat     

Xia Yao  Yan ZhuYongChao Tian  Wei FengWeiXing Cao 《International Journal of Applied Earth Observation and Geoinformation》2010

Hyperspectral sensing can provide an effective means for fast and non-destructive estimation of leaf nitrogen (N) status in crop plants. The objectives of this study were to design a new method to extract hyperspectral spectrum information, to explore sensitive spectral bands, suitable bandwidth and best vegetation indices based on precise analysis of ground-based hyperspectral information, and to develop regression models for estimating leaf N accumulation per unit soil area (LNA, g N m⁻²) in winter wheat (Triticum aestivum L.). Three field experiments were conducted with different N rates and cultivar types in three consecutive growing seasons, and time-course measurements were taken on canopy hyperspectral reflectance and LNA under the various treatments. Then, normalized difference spectral indices (NDSI) and ratio spectral indices (RSI) based on the original spectrum and the first derivative spectrum were constructed within the range of 350–2500 nm, and their relationships with LNA were quantified. The results showed that both LNA and canopy hyperspectral reflectance in wheat changed with varied N rates, with consistent patterns across different cultivars and seasons. The sensitive spectral bands for LNA existed mainly within visible and near infrared regions. The best spectral indices for estimating LNA in wheat were found to be NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆), and the regression models based on the above four spectral indices were formulated as Y = 26.34x^1.887, Y = 5.095x − 6.040, Y = 0.609 e^3.008x and Y = 0.388x^1.260, respectively, with R² greater than 0.81. Furthermore, expanding the bandwidth of NDSI (R₈₆₀, R₇₂₀) and RSI (R₉₉₀, R₇₂₀) from 1 nm to 100 nm at 1 nm interval produced the LNA monitoring models with similar performance within about 33 nm and 23 nm bandwidth, respectively, over which the statistical parameters of the models became less stable. From testing of the derived equations, the model for LNA estimation on NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆) gave R² over 0.79 with more satisfactory performance than previously reported models and physical models in wheat. It can be concluded that the present hyperspectral parameters of NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆) can be reliably used for estimating LNA in winter wheat.  相似文献   

机载三线阵传感器航空摄影测量的坐标转换方法研究     

耿迅  杨天克  缪剑 《测绘科学》2010,35(4):65-67

由于机载GPS获取的数据是WGS84坐标系,定向测图时首先要进行坐标转换。本文讨论了7参数平面转换模型与GPS水准测量拟合高程异常的方法,研究了数字航空摄影测量的像控点布设问题,并对数字航空摄影测量只在测区四角布设控制点即可满足空三精度要求的观点进行了分析。实验结果表明,机载三线阵航空摄影测量中高精度的7参数转换与似大地水准面精化成果是获取高精度空三的前提。  相似文献   

折射/谐衍射红外双波段成像光谱仪系统研究     

刘英  孙强  卢振武  曲锋  吴宏圣  李淳 《海洋学报》2010,32(10):6980-6987

为了获取足够的目标信息,充分利用中波红外和长波红外的光谱信息,建立了谐衍射中、长波红外超光谱成像系统.利用谐衍射元件独特的色散特性,将谐衍射透镜应用于中、长波红外超光谱成像系统中,使系统在中波红外3.7—4.8 μm和长波红外8—12 μm的2个红外大气窗口内获取数百个光谱图像.设计结果表明,中波红外波段,在18对线/mm处光学系统的调制传递函数(MTF)大于0.55;长波红外波段,在13对线/mm处光学系统的MTF大于0.5;光学系统的衍射环绕能,在中波红外波段30 μm半径范围内大于85%,在长波红外  相似文献   

Hyperspectral feature analysis of chlorophyll a and suspended solids using field measurements from Taihu Lake,eastern China     

《水文科学杂志》2013,58(4):808-824

Abstract

We report results of three field campaigns conducted at 39 stations. At each station, we measured reflectance spectra in situ and collected water samples for measuring chlorophyll a (CHL) and suspended solids (SS) concentrations in the laboratory. To identify the indicative bands and develop suitable estimation models for CHL (C _CHL) and SS (C _SS) concentrations in Taihu Lake, a spectral-feature method and a derivative method were applied. The following conclusions were drawn: (a) the critical C _CHL and C _SS probably causing their spectral variation are, respectively: 0, 10, 50 and 75 μg L^?1, and 0, 10, 50 and 100 mg L^?1; (b) the derivative method is better than the spectral-feature method for estimating C _CHL and C _SS; (c) the optimal variable for CHL is a reflectance second-order derivative at 501 nm or a reflectance first-order derivative at 698 nm; the optimal variable for SS can change when its concentration is low and the range is narrow; otherwise, the optimal variable is a reflectance first-order derivative at 878 nm; and (d) the CHL and SS have an effect on one another's retrieval. The C _CHL estimation accuracy would benefit from narrowing the C _SS range. With C _CHL increasing and its range broadening, the corresponding C _SS estimation accuracy decreases gradually.  相似文献   

士兵胫骨应力性骨折的影像评分与临床表现相关分析          下载免费PDF全文

张秋怡  徐凯  陈凯  刘忱  文磊 《CT理论与应用研究》2017,26(6):783-790

目的:明确士兵胫骨应力性骨折患者不同影像学评分与临床表现之间的相互关系,增强对士兵胫骨应力性骨折的认识。方法:本研究共纳入34例参加军事训练出现胫骨应力性骨折的士兵患者,所有对象平均年龄为19.1岁。所有患者分别由骨科医生及影像科医生采用X线、MRI扫描及CT扫描来评价胫骨应力性骨折的严重程度。同时由骨科医生对临床严重程度评分进行评价。统计学分析不同影像学检查评分与临床严重程度之间的相互关系,影像学检查评分与治愈时间之间的关系以及评价不同医生采用不同影像学设备评价患者的可靠性。结果:临床严重程度与患者的X线(r=-0.529,P=0.029)、MRI扫描(r=-0.641,P=0.006)及CT (r=-0.573,P=0.016)影像学评分存在负相关。治愈时间与患者的X线及CT影像学评分无相关性,与MRI扫描的影像学评分虽无相关性,但有相关的趋势(P=0.09)。MRI扫描的可靠性最佳(α=0.849),CT次之(α=0.779),X线第三(α=0.623)。结论:胫骨应力性骨折临床严重程度与X线、磁共振及CT扫描影像学评分存在负相关。X线、磁共振及CT扫描影像学评分与治愈时间无相关性。   相似文献   

高分辨率机载SAR影像判读实验   总被引：3，自引：0，他引：3  

肖洲  赵争  黄国满 《测绘科学》2006,31(2):42-43

近年来机载SAR系统在国内得到快速发展。由于SAR系统具有不同于光学传感器的成像机理,因而可以提供全新的数据获取手段和不同的地物信息。利用高分辨率机载SAR影像进行解译时必须熟悉其成像机理和图像信息特点,充分了解SAR图像解译标志的特点和各类地物的解译规律。本文以高分辨率机载SAR数据为基础,对比光学影像,从SAR成像特点和地物散射特性出发,对SAR影像进行了目视解译,分析了SAR影像在地形地物要素识别中的应用潜力。  相似文献