A Fast Inversion Method for Interpreting Crosshole Electromagnetic Data
Hee Joon Kim(1), Ki Ha Lee(2) and Michael J. Wilt(3)
(1) Pukyong National University, Korea. (2) Lawrence Berkeley National Laboratory, U.S.A.. (3) ElectroMagnetic Instruments, Inc., U.S.A..
Contacts: hejkim@pknu.ac.kr (Hee Joon Kim)
Abstract
The extended Born or localized nonlinear (LN) approximation of integral equation (IE) solutions has been applied to inverting crosshole EM data using a cylindrically symmetric model. The LN approximation is less accurate than a full solution but much superior to the simple Born approximation. When applied to the cylindrically symmetric model with a vertical magnetic dipole source, however, the LN approximation works well because electric fields are scalar and continuous everywhere. One of the most important steps in the inversion is the selection of a proper regularization parameter for stability. The LN solution provides an efficient means for selecting an optimum regularization parameter, because Green's functions, the most time consuming part in IE methods, are repeatedly re-usable throughout the selection process. In addition, the IE formulation readily contains a sensitivity matrix, which can be revised at each iteration at little expense. This fast inversion scheme has been tested on its stability and efficiency using synthetic and field data.
raeg2003@tansa.kumst.kyoto-u.ac.jp
Last modified: Mon Oct 28 10:15:37 2002