【作者】 裴建新；

【导师】 张维冈； 周辉；

【作者基本信息】 中国海洋大学 ， 地球探测与信息技术， 2004， 硕士

【摘要】 至今，在使用显式外推算子的地质雷达数据叠前深度偏移中几乎都忽略了电磁波的吸收，受野外数据采集方法的限制，常用的偏移方法也主要解决共偏移距数据问题。本文提出了一种在叠前深度偏移方法中考虑吸收效应的方法，该方法为基于波动方程理论且考虑介质吸收特性的有限差分算法。在获得模型的正演模拟结果后，在多偏移距数据的波场外推中同时使用速度和吸收模型，以实现考虑吸收特性的偏移处理。 本文在模拟雷达波数据剖面时，从麦克斯韦方程组出发，利用微分形式方程组的旋度方程推导正演模拟的FDTD差分格式。求得满足数值稳定性的Courant条件后设定时间、空间网格的单位元胞尺寸，采用Yee网格进行网格的剖分，设置正演模型的空间电磁参数。为了在有限的研究区域获得无限空间的波场模拟，在区域边界处引入PML吸收边界，并获得了较好的效果。 分别在无吸收性和中等吸收性介质中获得模拟结果，比较剖面差异知，在雷达数据研究中考虑吸收问题是十分重要的。另一方面，本文由波动方程推导有限差分波场外推算子。该算子包含吸收衰减与复速度的函数关系，由它获得反延拓算子，进而实现有限差分叠前深度偏移。对输出的深度剖面，分析考虑介质吸收特性与否对成像效果的影响。 本文通过考虑具有中等吸收性的介质模型，目的是要展示在地质雷达偏移方法中考虑吸收的必要性和效果。试验结果表明，文中的偏移方法可获得较好横向分辨率的同时，还能实现吸收补偿，所得到的图像要好于用没有考虑吸收的外推算子得到的图像，可见它是切实可行的。随着该方法的进一步研究，我们还将获得更为丰富的关于近地表介质特性和结构的高分辨率信息。更多还原

【Abstract】 In prestack depth migration using explicit extrapolators, the attenuation of the electromagnetic wave for ground penetrating radar (GPR) has been almost neglected so far. Conventional migration techniques aim at processing common-offset data. This paper presents one kind of migration method for considering absorption effect. The finite difference algorithm in this paper is based on wave equation theory and the character of absorption. After getting simulation result of a model, both phase velocity and absorption coefficient are used in the wave extrapolation in order to take absorption effect into account in the migration method.The finite-difference time-domain (FDTD) scheme for wave field simulation can be derived from the Maxwell’ s curl equations. The size of a cell and the interval of time are determined by Courant condition that is a numerical stability condition. In order to eliminate the effects of boundaries, the perfectly matched layer (PML) absorption boundary condition is used in this paper. The absorption effect of the PML boundary is very nice.It is known that it is necessary to consider absorption in GPR by comparing profile properties obtained from absorption-free and middle absorption models. The finite difference wave field extrapolation operator, which contains a functional relation of attenuation and complex velocity, can be derived from wave equations. The inverse operator can be derived from the finite difference wave field extrapolation operator. Finite differential prestack depth migration can be realized using theinverse operator.To show the necessity and effectiveness of taking absorption into account in migration, middle absorption models are used in this paper. The migration in this paper can get the higher lateral resolution and realize absorption compensation. The migration image obtained from the method for compensating absorption is better than others obtained from the methods without considering absorption. The quality and high-resolution information about the near surface media can be more accurately obtained through this migration method that compensates absorption.更多还原