探地雷达中的逆时偏移及速度估计

【作者】 张彬；

【导师】 戴前伟；

【作者基本信息】 中南大学 ， 地球探测与信息技术， 2010， 硕士

【摘要】 偏移技术是探地雷达数据处理中一项重要的技术环节,其目的是使绕射波收敛和倾斜反射波归位,而寻求雷达高频电磁波所遵循的上行波方程又是波动方程偏移技术的关键。本文从几种常规的雷达偏移技术入手,讨论了它们的实现过程及优缺点,再从传统15°有限差分偏移算法遵循的波动方程出发,分析了该算法难以使陡倾角反射界面偏移归位的产生根源,进而引入了不同于浮动坐标变换或延时坐标变换的线性变换,通过对原波动方程进行了精确推导而未采用任何近似,得到了与15°偏移方程形式相同的均匀介质中线性变换有限差分偏移方程,在不同的差分格式及边界条件约束下实现雷达波场的逆时外推,论文在前人研究的基础之上,研究了该偏移算法在非均匀层状变速介质中的实现情况,通过对加入了速度参数的波动方程进行推导,得到非均匀变速介质中含混合因子项的线性变换差分逆时偏移方程,解决了原偏移算法在非均匀介质中对速度参数的高敏感性问题,并编写了相应的Matlab实现程序,应用该程序对复杂的非均匀变速介质地电模型的正演剖面和实测剖面进行了偏移处理,分析得到的偏移结果体现了混合因子项的作用,即在非均匀介质中同时存在主要反射体和多次反射质点的情况下,可以根据勘探目的,选择是否考虑差分方程式中的混合项来对其进行偏移处理。在此基础上,而在运行线性变换差分逆时偏移程序进行波场外推,需要输入速度矩阵,实际操作中常是根据偏移成像后图像的效果,对输入的速度矩阵进行不断的修正,这样来逐渐逼近地下介质真实的速度参数,这就给该算法的偏移结果带来一定误差,所以准确速度参数是该偏移算法实现的关键,文章深入研究了波速估计,提出了一种较精确的适合该偏移算法的波速估计方法,它结合输入得到的准确速度矢量矩阵,再次对前面实测资料的偏移效果进行优化,通过对比二者的偏移效果,基于波速估计的非均匀介质中线性变换差分逆时偏移算法极大地提高了原算法的偏移精度。本文得到国家自然科学基金项目、教育部博士点新教师基金资助项目、湖南省自然基金重点项目、湖南省科技计划项目的联合支助。更多还原

【Abstract】 Migration techniques is a crucial step in Ground penetrating radar data processing, the aim of which is to make the diffraction wave converged and let the tilt reflection homing, and the key of this techniques is the to find the upcoming wave equation solution, firstly, the paper discussed the migration of several conventional method as well as the merit and disadvantages of each method, then the paper analyzes the traditional 15 degree equation migration algorithm, of which is unable to correctly migrate steep-dip reflections(reflections propagating at large angle),then the linearly transformed ideology is derivated, of which is essentially different from the time-retarded coordinates transformation, through more accurate and stable computation, a none-approximate equation is obtained with special difference scheme to achieve steep-dip reflection migration in constant-velocity media, then the paper extends the application it into laterally inhomogeneous media to improve the former case, a new equation is derivated with a mixed factor items added, and the preparation of the corresponding Matlab program. Then apply it to dealing with a more complicated variable-velocity model and measured data, the imaging results shows the advantage of the improved linear transformation of the migration algorithm is more flexible in dealing with the geological model of main reflector or multiple reflection particles.On this basis, the paper discusses the velocity estimates, for the velocity matrix is needed to input when running the former migration program, while, the actual operation is through repeated input attempt to approximate the true velocity matrix value, which is based on the migration effect, thus a more accurate velocity estimation method is used to reduce the errors in the process of velocity matrix importing, through which to optimize the accuracy of final migration effect with the migration program in the former case.The paper was funded by a joint support of the National Natural Science Fund, the Ministry of Education Doctoral Foundation of new teachers, the key project of Hunan Natural Science Foundation, the Science and technology projects of Hunan Province.更多还原