Robust Finite Difference Time Domain Modeling Interface

Three dimensional finite difference time domain modeling (FDTD) has been used for many years in engineering and Earth science applications. The earlier versions were fraught with problems and limitations, including an inability to be used for modeling a broad range of frequencies, difficulty modeling large physical property contrasts between grid cells, and no ability to vary the grid size within the model. The OSU code developed in the Department of Electrical and Computer Engineering (ESL) utilizes an established finite difference time domain (FDTD) approach, with perfectly matched outer boundaries. Therefore, we call our code the PML FDTD algorithm, or simply the PFDTD code. The code has evolved over the years to solve most of the pitfalls of earlier FDTD codes utilizing other types of absorbing boundaries. Our code has been tested over a frequency range from 500 kHz to 2 GHz, and a wide range of conductivities and permittivities. It is ideal for accurate forward modeling of complex subsurface geologic targets. This paper addresses one of the fundamental problems of implementing complex three dimensional modeling schemes, namely the problem of easily assigning physical properties to different parts of the model for input and displaying the three dimensional output of the model. Ideally, we would like to utilize the same graphical interface for: 1) model input, 2) model output, and the display of field data. A graphical interface engine has been developed to overcome the fundamental problem encountered in 3D modeling and display; generating a usable model and displaying the output with ease. The interface utilizes IDL graphical software. The graphical interface enables the user to easily build or edit a model. The modeling interface generates values that can be directly input to the PFDTD modeling routine, and the IDL code is set up so that it can transfer input parameters to the PFDTD code directly. The IDL-based GUI can also be used in a multi-run mode, whereby sequential runs can be submitted to the PFDTD code, with each run modified with a different spatial distribution of electrical properties or a different input frequency.