磁场光学成像及矢量场层析方法研究

【作者】 李小牛；

【导师】 白晋涛；

【作者基本信息】 西北大学 ， 光学， 2013， 博士

【摘要】 地磁场测量在不但在科学探索、航空、航天、航海、国防军事等方面都有着重要的应用,也和人们的生产生活紧密地联系在一起,因此对地磁场的测量和研究的意义就显得更为重要。然而随着对地球磁场的应用和研究的深入,现有的地面磁测、航空磁测、海洋磁测、地磁台磁测等地球磁场测量方法已经暴露出一些不小的局限性。其中主要的原因是现有的测量方法所采用的测量仪器在每一时间只能针对它自己所在位置的磁场进行单点测量。为了克服现有磁测方法的不足,探索新的地磁测量方法,本课题组提出了磁旋光成像地球磁场测量方法,借助于地面反射太阳光的偏振特性及地球大气层的磁旋光效应,在卫星高度测量偏振光穿越大气层后的旋光度,获取地球磁场信息并利用CT算法重建地磁场。这一测量方法具有测量速度快、显示直观等优点,适合作为一种地磁普查测量手段。本论文基于磁旋光成像地球磁场测量方法,首先对磁场光学成像方法的可行性进行实验验证。设计了二维磁场光学成像方法,建立了成像光路系统、检偏系统、图像数据采集系统,采集了一系列包含磁场信息的灰度图像；建立了图像数据处理算法,编制相应的图像数据处理程序,用图像处理程序将成像元件采集到的图像数据进行处理,得到了磁场的二维图像。对实验得出的磁场二维图像的成像效果进行观察和分析,根据图像所包含噪声的特点进行相应的后处理,有效降低了图像中的噪声影响,突出了磁场作用效果,为后续图像处理提供了思路。由磁光二维成像实验结果出发,分析实验系统的误差因素,并从两个角度加以改进。一方面设计出了新的改进方案,另一方面改进原有用于磁光偏转角度测量的倍频法,特别注意到,在磁光调制偏振测量方法中,如果用矩形波代替正弦波作为调制信号,能够提高检测精度,故而以矩形波为调制信号重新设计了磁场光学成像系统,有效地提高了磁光测试和成像的精度。论文在仔细研究标量场CT和矢量场CT投影数据获取的区别的基础上,首先构造了模拟矢量分布图,对其分量作Radon变换和特定处理后获得模拟矢量场的Radon变换数据(即投影数据),随后以此为基础对解析重建算法和代数方程重建算法进行了比较,确认了解析方法在矢量场CT重建中的有效性和代数方法的重要性。更多还原

【Abstract】 The geomagnetic field measurement is not only important in scientific exploration, aviation, spaceflight, navigation, national defense military, etc, but also closely linked with people’s Production and living, this make measurement and study on the geomagnetic field even more important. However, with the deepening of the application and study of the earth’s magnetic field, the existing geomagnetic field measurement measures, such as groumd survey, Aerial survey survey, Marine survey and geomagnetic station survey etc. have exposed some considerable limitations. The main reason is the measuring instrument adopted by the existing measurement methods can only made single point measurement on its own location each time.In order to overcome the shortage of the existing geomagnetic field measurement method and explore new geomagnetic measurement method, we puts forward the magnetic rotation imaging method of the geomagnetic field. With the aid of the polarization characteristics of reflected sunlight and the magnetic rotation effect of the earth’s atmosphere, this method attempt to measure rotation angle of polarized light after it pass through the atmosphere on satellite, and rebuild the the geomagnetic field by CT algorithm reconstruction of geomagnetic field. The merit of this measurement method such high speed and visualization etc. made it suitable for general survey of geomagnetic field.This paper based on the magnetic rotation imaging method of the geomagnetic field. First, experimental research and analysis of two-dimensional magneto-optic imaging method is carried out. Establish imaging optical path system, polarization analyzing system, image data acquisition system, image data processing algorithms, and the corresponding image data processing program; Process image data collected by imaging element with the processing program to get two-dimensional image of the magnetic field; Evaluate the image and make post-processing accordingly.Find error factors and try to recover them from two perspectives on the basis of experimental results of existing magneto-optic two-dimensional imaging. On one hand to design improvement project, and on the other to improve measuring method. Find that rectangle wave lead to a high accuracy then sine wave in frequency multiplication method test, and replace sine wave with rectangle wave as magneto-optic modulation signal in magneto optical test (imaging).After having found out difference of CT projection between scalar field and vector field, vector field is structured by Computer simulation. After made direct Radon transform and process of its component of the vector field, the real Radon transform (projection data) of simulated vector field is obtained. Compare analytic reconstruction methods and algebraic reconstruction technique and have verified the validity of the the former and the importance of the latter in vector field CT reconstruction.更多还原