Airborne TEM On-Time Gate Sampling for Near-Surface Electrical Property Accuracy
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Solution Overview
Problem
Current airborne electromagnetic (EM) survey systems primarily rely on off-time measurements for data analysis, which limits the accuracy of electrical property calculations of near-surface formations, as they do not effectively utilize data collected during the on-time period.
Innovation Solution
A time-domain electromagnetic (TEM) system that generates a transient primary magnetic field during the on-time period and records magnetic-related data using multiple on-time gates sampling, allowing for more accurate calculation of electrical properties by capturing the current distribution patterns during the on-time period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If off-time measurements are used for data analysis, then the measurement process is simple, but the accuracy of electrical property calculations of near-surface formations is limited
Solution Approach 1:
The measurement process is segmented into multiple on-time gates (first on-time gate, second on-time gate, etc.) that sample the primary electromagnetic field at different time intervals during the on-time period. This segmentation allows capture of transient field characteristics at different depths, improving near-surface electrical property calculation accuracy without requiring complex additional hardware.
Solution Approach 2:
The system performs preliminary measurements of the primary electromagnetic field during the on-time period before the traditional off-time measurements. By capturing field data during the on-time period with multiple gates, the system prepares additional information that enhances the accuracy of near-surface electrical property calculations while maintaining the standard off-time measurement process.
2Loss of information
If traditional off-time measurements are used, then the data collection process is straightforward, but data relevant to near-surface electrical properties is not effectively utilized
Solution Approach 1:
The system continuously samples the primary electromagnetic field during the entire on-time period using multiple on-time gates, rather than only measuring during the off-time period. This continuous sampling during on-time captures transient field characteristics that are particularly sensitive to near-surface electrical properties, reducing information loss without significantly complicating the data collection process.
Solution Approach 2:
The measurement system dynamically adapts by implementing multiple sampling gates during the on-time period, allowing the measurement strategy to respond to the transient nature of the primary electromagnetic field. This dynamic approach captures time-varying field characteristics that provide enhanced information about near-surface electrical properties.
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
This approach enhances the accuracy of electrical property calculations by concentrating measurements on near-surface layers, providing more relevant data for near-surface electrical property estimation compared to traditional off-time measurements.
Implementation Method 1
an airborne transmitter 102 applies a time-varying current to a coil, which generates a primary time-varying magnetic field 104
Implementation Method 2
Primary time-varying magnetic field 104, when entering the ground 106, according to Faraday's Law, induces an electromotive force 108 (EMF, or potential) and an electric field 110 in the ground. The induced potential causes a current 112 to flow in the ground 106
Implementation Method 3
The secondary magnetic field 114 associated with these currents is sensed by a receiver 116 or, the time-variation of the magnetic field is sensed by a receiver 116
Data Source
AI summary
A device and method for calculating electrical properties of a surveyed underground formation. The method includes selecting a waveform having multiple current transition rates; placing a time-domain electromagnetic (TEM) system above the underground formation while generating with a transmitter a transient primary magnetic field during an on-time period and no magnetic field during a following off-time period, due to the waveform; and recording with a receiver magnetic related data generated by the earth as a result of the transient primary magnetic field. The receiver records the magnetic related data during the on-time period using plural on-time gates sampling.