Z-Axis Tipper Electromagnetics

Jump to: navigation, search
GEOTHERMAL ENERGYGeothermal Home

Exploration Technique: Z-Axis Tipper Electromagnetics

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Electrical Techniques
Parent Exploration Technique: Magnetotelluric Techniques
Information Provided by Technique
Lithology:
Stratigraphic/Structural:
Hydrological:
Thermal:
Cost Information
Low-End Estimate (USD): 4,827.00482,700 centUSD
4.827 kUSD
0.00483 MUSD
4.827e-6 TUSD
/ mile
Median Estimate (USD): 6,206.14620,614 centUSD
6.206 kUSD
0.00621 MUSD
6.20614e-6 TUSD
/ mile
High-End Estimate (USD): 17,239.291,723,929 centUSD
17.239 kUSD
0.0172 MUSD
1.723929e-5 TUSD
/ mile
Z-Axis Tipper Electromagnetics:
Z-Axis Tipper Electromagnetic Technique (ZTEM) survey is an airborne natural source electromagnetic survey that relates the vertical magnetic field to the horizontal magnetic fields measured at a reference station on the ground.
Other definitions:Wikipedia Reegle

Introduction

Natural source electromagnetics have an important role in understanding the electrical conductivity of upper regions of the earth. Their primary advantage, compared to controlled source methods, is the large depth of penetration that is a consequence of the plane wave excitation. In the ZTEM technique, the vertical component of the magnetic field is recorded above the entire survey area, while the horizontal magnetic fields are recorded at a ground based reference station.

Use in Geothermal Exploration

Large ZTEM data sets can be effective exploration tools, particularly when exploring on the district and regional scale where subsurface geology is hidden under cover.

Physical Properties

ZTEM data are transfer functions that relate the vertical magnetic fields computed above the earth to the horizontal magnetic field at some fixed reference station. This relation is given by

$H_z=T_zx (r,r_0 ) H_x (r_0 )+ T_zy (r,r_0 ) H_y (r_0)$

where r is the location for the vertical field, r0 is the location of the ground based reference station $Tzx$ and $Tzy$ and are the vertical field transfer functions. Solving for the transfer functions requires that the vertical fields are known for two independent polarizations. The transfer functions for each polarization are given by

$H_z^(1) =T_zx . H_x^(1)+ T_zy . H_y^ (1)$

$H_z^(2)=T_zx . H_x^(2)+ T_zy . H_y^(2)$

where the superscripts (1) and (2) refer to the source field polarization in the x and y directions respectively. In order to forward model the transfer functions, one must have the capability to solve the natural source field problem for different polarizations of the source field. Briefly, Maxwell's equations in the quasi-static regime, when combined with the constitutive relations of charge conservation and Ohm's law, form the necessary equations for ZTEM modeling.

References

Holtham E. and D. W. Oldenburg 2012 Large-scale inversion of ZTEM data Geophysics Vol. 77 No. 4;

Holtham E. and D. W. Oldenburg 2010 Three-dimensional inversion of ZTEM data: Geophysical Journal International Vol. 182 p.168–182;

Print PDF