Concepts and procedures required for successful reduction of tensor magnetic gradiometer data obtained from an unexploded ordnance detection demonstration at Yuma Proving Grounds, Arizona

Abstract

Positions match the ideal 0.25-m grid ………………………………….. 24 corrections ……………………………………………………………… 25 Sensor positions are coincident with the virtual tetrahedron vertices …. 25 Assumptions Applied to the Spin-Calibration Data……………………………...25 The background field was stable and its tensor everywhere zero ……… 25 Deconvolving Bin Steps from Analog, and Matching Axes for Precision By Rotation ………………………………………………………………37 Sensor 1 is perfectly aligned with the virtual tetrahedron ………………26 The sensor temperatures did not vary ………………………………….. 26 Raw-Data Conversion……………………………………………………………26 Basic Data Forms ………………………………………………………. 26 Recording Method ……………………………………………………….26 Conversion Program …………………………………………………….27 27 Tracking…………………………………………………………………………. Removal of Intervening Data Records and Noisy Samples……………………...27 Bin Conversions………………………………………………………………….27 Application of Spin-Calibration Results for Converting Voltages to Fields……. 29 Axis Polynomial………………………………………………………… 29 Orthogonality Correction……………………………………………….. 30 Attitude Correction ……………………………………………………... 30 Temperature Corrections ………………………………………………..31 Differencing Magnetic Fields to Obtain Initial Gradients………………………. 31 Ten-Second Averaging of Gradients to Obtain Station Gradient Data…………..32 Thermal-Drift Correction………………………………………………………...33 Unknown Constant……………………………………………………… 34 In Lieu of Temperature-Dependent Spin-Cal Coefficients …………….. 34 Gradient Collocation……………………………………………………………..34 Converting Sensor-Pair Gradients to a Tensor………………………………….. 37

Magnetic tracking for TomoTherapy systems: Gradiometer based methods to filter eddy‐current magnetic fields

“…In practice, gradient measurement accuracy primarily depends on the baseline, balance between the sensors, sensor position and alignment, and individual sensor sensitivity. 16 Sensor sensitivity depends primarily on coil geometry; geometric and calibration methods are utilized to determine the sensitivity of each coil depending on the required precision. Magnetic calibration is typically the better choice since errors will be included in a similar way as in real use; however, the techniques are time consuming and relatively more difficult.…”

New Methods for Interpretation of Magnetic Gradient Tensor Data

“…been developed (Bracken and Brown, 2006). Wiegert et al (2007) describe a multiple tensor gradiometer system, comprising an array of eight triaxial low noise fluxgate magnetometers, that has a sensitivity of about 0.25 nT/m in hand-carried mobile operation.…”

Corrigendum to:New methods for interpretation of magnetic vector and gradient tensor data I: eigenvector analysis and the normalised source strength

“…Although the inherent sensitivity of fluxgate magnetometers is far inferior to that of superconducting devices, a practical fluxgate-based tensor gradiometer, capable of mapping anomalies greater than~10 nT/m in mobile operation, has been developed (Bracken and Brown, 2006). Wiegert et al (2007) describe a multiple tensor gradiometer system, comprising an array of eight triaxial low noise fluxgate magnetometers, that has a sensitivity of~0.25 nT/m in handcarried mobile operation.…”