Magnetic Gradient Tensor Detection Using Rotational Invariants
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Solution Overview
Problem
Current magnetic surveys face challenges in accurately locating and characterizing magnetic targets due to orientation errors, noise sensitivity, and ambiguity in gradient tensor measurements, particularly in detecting weak anomalies amidst strong geomagnetic fields, leading to unreliable and noisy results.
Innovation Solution
The method involves obtaining multiple magnetic gradient tensor measurements at varying orientations between a sensor and a magnetized body during relative movement, using rotational invariants calculated from eigenvalues to determine characteristics such as range, direction, and magnetic moment, thereby eliminating spurious solutions and averaging out noise for more robust estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If vector magnetometers are used to measure three components of the field, then more information is obtainable, but the measurement precision deteriorates due to large orientation errors
Solution Approach 1:
The patent extracts only the necessary information (rotational invariants) from the gradient tensor measurements that are independent of orientation errors. By calculating invariants from eigenvalues rather than directly using vector components, the method obtains sufficient information about the magnetic body while eliminating the harmful effect of orientation inaccuracies.
Solution Approach 2:
The patent converts the harmful effect of orientation errors into a benefit by using rotational invariants. These invariants are specifically designed to be independent of the sensor's orientation, so the orientation errors that would normally corrupt vector measurements actually help identify and eliminate spurious solutions, leaving only the correct solution.
2Measurement precision
If point-by-point analysis of gradient tensor eigenvectors is used, then dipole location can be determined, but the reliability deteriorates due to noise sensitivity
Solution Approach 1:
The patent merges multiple gradient tensor measurements taken at different positions along the profile into a single coherent solution. By combining information from all measurements and using the fact that rotational invariants are independent of orientation, the method produces a more reliable and noise-resistant determination of dipole location and moment vector.
Solution Approach 2:
The patent uses continuous measurements along the profile rather than isolated point-by-point analysis. This continuous approach allows the method to maintain solution reliability even in the presence of noise, as the rotational invariants provide consistent information throughout the measurement profile.
3Ease of manufacture
If TMI sensors are used for magnetic surveys, then the equipment cost is reduced, but the measurement precision deteriorates due to asymmetric anomalies and low resolution
Solution Approach 1:
The patent replaces the need for expensive gradient tensor sensors with a simpler TMI sensor by using a different measurement and analysis approach. By measuring TMI at multiple orientations and calculating rotational invariants, the method achieves precision comparable to gradient tensor measurements while using less complex, lower-cost equipment.
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 provides a unique and precise solution for locating and characterizing magnetized bodies by reducing noise and orientation errors, enhancing the accuracy and reliability of magnetic target detection even in challenging environments.
Implementation Method 1
magnetic gradient tensor sensor for obtaining a magnetic gradient tensor of a magnetic field
Data Source
AI summary
Locating and characterising a magnetised body involves moving a magnetic gradient tensor sensor relative to the magnetised body along a profile, or allowing the magnetised body to move along a profile past the sensor. Magnetic gradient tensor measurements are obtained at points along the profile. A rotational invariant calculated from the eigenvalues of the magnetic gradient tensor measurements is then used to locate and/or characterize the body. The rotational invariant can be the scaled moment of a point dipole representation of the magnetised body, or one third of the square root of the scaled moment. The rotational invariant is modelled and sufficient measurements obtained to over-determine parameters of the model. A system of linear equations resulting from a model of the gradient tensor elements is then solved using the determined values of parameters.