Airborne Composite EM System for Depth and Precision
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Solution Overview
Problem
Current geophysical exploration systems are limited in depth penetration, as frequency-domain EM systems can only map near-surface conductivity up to 150 m, and existing systems for measuring natural EM fields have inaccuracies and are cumbersome and expensive when trying to combine data from controlled and natural EM fields.
Innovation Solution
A composite EM system that simultaneously records controlled and natural EM fields using a combination of frequency-domain EM and audio-magnetotelluric systems, integrated with a position and orientation system, allowing for airborne surveys with reduced noise and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency-domain EM systems are used to map near-surface conductivity, then measurement precision for shallow depths is improved, but depth penetration is limited to 150 m
Solution Approach 1:
The patent combines frequency-domain EM systems and audio-magnetotelluric systems into a single airborne composite system. This merging allows the system to simultaneously measure both controlled-source EM fields (for shallow high-resolution mapping) and natural EM fields (for deep exploration), thereby resolving the contradiction between shallow measurement precision and deep penetration capability.
Solution Approach 2:
The airborne composite EM system is designed with multi-functionality to perform both frequency-domain EM surveys and audio-magnetotelluric surveys using a single platform. This universal system can operate at different frequency ranges (400 Hz to 150 kHz for FDEM and 10 Hz to 500 Hz for AMT), enabling it to address both shallow and deep subsurface exploration requirements without requiring separate dedicated systems.
2Length of stationary object
If natural EM fields are used to extend depth of exploration, then depth penetration is improved, but measurement precision is reduced due to extreme variability and require stationary receivers
Solution Approach 1:
By merging natural EM field measurements with controlled-source EM field measurements in a single airborne system, the patent can use the stable, controllable controlled-source fields to provide reference data and improve measurement precision, while simultaneously using the natural fields to extend depth penetration capability.
Solution Approach 2:
The system uses controlled-source EM measurements as a feedback reference to calibrate and correct natural EM field measurements. The controlled-source data provides a known signal pattern that can be used to characterize the instrument response and environmental conditions, thereby improving the precision of natural field-based conductivity estimates.
3Productivity
If airborne systems are used to tow FDEM systems, then productivity is improved, but device complexity increases due to cumbersome and expensive ground-based systems
Solution Approach 1:
The patent merges both FDEM and AMT systems into a single integrated airborne platform, eliminating the need for separate ground-based systems for each measurement type. This consolidation reduces overall device complexity while maintaining the productivity benefits of airborne surveying, as one aircraft can perform both shallow and deep exploration measurements without requiring multiple ground stations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables deeper exploration by combining data from controlled and natural EM fields, providing improved vertical and spatial resolution of conductivity estimates, and reducing the need for cumbersome and expensive ground-based systems.
Implementation Method 1
A schematic airborne EM survey system generally includes, as illustrated in FIG. 1, a transmitter for generating a primary electromagnetic field that is directed toward the earth. When primary EM field enters the ground, it induces eddy currents inside the earth. These eddy currents generate a secondary electromagnetic field or ground response.
Implementation Method 2
The energy source for natural EM fields in the 10 Hz to 20 kHz audio-magnetotelluric (AMT) range is mainly worldwide thunderstorm activity. The usable range of AMT signals for a moving platform is between about 10 Hz and 500 Hz.
Implementation Method 3
a position and orientation (POS) system attached to the housing and configured to calculate an orientation and a position of the AMT system and housing relative to the earth
Data Source
AI summary
A composite electromagnetic (EM) system and method for measuring naturally occurring magnetic fields and controlled magnetic fields. The composite EM system includes a housing, an audio-magnetotelluric (AMT) system attached to the housing and measuring natural magnetic fields generated by earth, a frequency-domain EM (FDEM) system attached to the housing and measuring controlled magnetic fields generated by a controlled source, and a position and orientation (POS) system attached to the housing and configured to calculate an orientation and a position of the AMT system and housing relative to the earth. The housing is configured to be attached to an aircraft for being airborne while measuring the natural magnetic fields and the controlled magnetic fields.