Three-dimensional Full-time Airborne TEM Modeling with Shift-and-Invert Krylov Subspace Method and Response Characteristic Analysis

doi:10.19657/j.geoscience.1000-8527.2022.075

Abstract

Abstract:

To study the fulltime response characteristics of airborne TEM with complex geoelectric models, it is necessary to develop a 3D forward algorithm with transmitted waveform consideration. Based on the unstructured tetrahedral mesh and the Shift-and-Invert Krylov subspace (SAI Krylov) method, we achieve the fulltime 3D edge finite-element simulation of airborne transient electromagnetic, by using the source processing technology-based dipole discretization technique. We simulate the shape of the transmitting loop by topography, and then the instantaneous current pulse technology is used to simulate the transmitting waveform. The numerical simulation algorithm developed here is verified by the analytical solutions of the uniform half-space model, under the excitation of step wave, half-sine wave, triangle wave, and trapezoidal wave, and by the calculation results of the 3D FETD algorithm of the VTEM actual transmitting waveform. The anomaly spherical model with uplifted terrain is designed, and the characteristics of airborne transient electromagnetic response are calculated and analyzed. The fulltime 3D numerical simulation algorithm of airborne TEM (based on SAI Krylov subspace) is suitable to calculate the response of complex geoelectric models, and is highly accurate.

Key words: airborne TEM, 3-D modeling, fulltime waveform, SAI Krylov subspace, edge finite-element

CLC Number:

P631

DONG Yan, TAN Handong, FU Xing. Three-dimensional Full-time Airborne TEM Modeling with Shift-and-Invert Krylov Subspace Method and Response Characteristic Analysis[J]. Geoscience, 2023, 37(01): 74-83.

Figures/Tables 15

Fig.1 Schematic diagram of the arbitrary transmitting waveform

Fig.2 Schematic diagram of unstructured grid schematics in the study area

Fig.3 Edge electric field distribution (of tetrahedral element) diagram

Fig.4 Rational Arnoldi approximation

Fig.5 Schematic diagram of transmission waveforms

Fig.6 Homogenous half-space model

Fig.7 Comparison of SAI Krylov and analytic solution for step waveform model

Fig.8 Comparison of SAI Krylov and analytic solution for half-sine waveform model and triangle waveform model

Fig.9 Comparison of SAI Krylov and analytic solution for trapezoidal waveform model

Fig.10 ATEM dbz/dt response of step, triangular, half-sine and trapezoidal waves during off-time

Fig.11 Model of cubic anomaly body

Fig.12 Realistic transmitting waveform for VTEM system and its ATEM response

Fig.13 Schematic diagram of spherical model with upliftedterrain

Fig.14 dbz/dt response of half-sine waveform model during off-time

Fig.15 ATEM dbz/dt response at 0.255 ms for homogeneous half-space model, sphere model without terrain, and sphere model with uplifted terrain

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