航空电磁法三维电阻率反演成像技术

3-D resistivity inversion imaging of airborne EM data.

航空电磁测量三维电阻率成像方法能快速测定地下电阻率的分布。给出了三维电阻率成像方法的基本原理,该方法包括近似三维反演因子和综合子空间解算器两部分,三维反演因子可用于近似正向线性电阻率的解译；综合子空间法实质为共轭梯度法的变换,可以通过综合子空间法把大型的线性方程系统简化为较小的、易求解的非线性系统。三维成像法属线性反演法,可直接用于测定三维电阻率分布,通过模型试验对该方法进行了可靠性验证,结果表明三维电阻率成像能更好显示地质体的导电性,同时可提供大量地质构造信息。

This technique has been developed to provide fast esti- mates of resistivity distributions in airborne EM surveys. This proposed 3-D imaging method consists of an approxi- mate 3 D linear inversion operator and a generalized sub- space soIver.The 3-D inversion operator can be generated using any forward approximation that is linear in resistivi- ty.The generalized subspace method is an alternative to the conjugate gradient method,and it reduces the original large linear equations system to a smaller but nonlinear one that is solved iteratively.The 3-D imaging technique is a linear inverse method and can be used directly to estimate 3-D resistivity distribution or to provide a model update during an intermediate iteration in a nonlinear 3-D inver- sion.Synthetic examples indicate that the 3-D imaging can provide quantitative geology structure information about the resistivity and spatial distributions of the 3-D tar- gets.