MGSTOOLS WORKSHOP July 9-10, 2005 MGSTOOLS Marine Gradiometer Software Workshop Dr. Richard Hansen PRJ, Inc. Presenter

MGSTOOLS WORKSHOP July 9-10, 2005 MGSTOOLS A tool for enhancing ability to discriminate between external signals and geology For use with longitudinal magnetic gradiometer systems Includes computation of power spectrum, sensor lag and ship’s heading effects

MGSTOOLS WORKSHOP July 9-10, 2005 MGSTOOLS Features (con’t) Provides ability to reconstruct total field data minimizing temporal variations and ship noise Provides tool for generation of synthetic data sets for testing parameters In conjunction with MagMap2000, provides graphical user interface for plotting raw and reconstucted data

MGSTOOLS WORKSHOP July 9-10, 2005 Geological Field Example

MGSTOOLS WORKSHOP July 9-10, 2005 External Field Example Solar wind, field line compression

MGSTOOLS WORKSHOP July 9-10, 2005 External Field Example Long term diurnal

MGSTOOLS WORKSHOP July 9-10, 2005 External Field Example Micropulsations

MGSTOOLS WORKSHOP July 9-10, 2005 External Field Example Magnetic Storm

MGSTOOLS WORKSHOP July 9-10, 2005 Superposition of geology and external fields Components cannot be distinguished with only one sensor On land, stationary base station is used (no geology)

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration Physical Arrangement

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration Show records at equal times, with geological source

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration Because sensors are in different positions, geology is shifted

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration External field anomaly has no appreciable shift

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration Difference: external field effects are gone, but geology is a directional gradient

MGSTOOLS WORKSHOP July 9-10, 2005 Gradiometer Configuration Need to reconstruct geology field from difference

MGSTOOLS WORKSHOP July 9-10, 2005 Reconstruction - General Look again at combination of geology and external field: equal spatial position For short-wavelength external field, shift is clear For long-wavelength external field, shift cannot be seen Reconstruction cannot distinguish at long wavelengths (compared to sensor separation)

MGSTOOLS WORKSHOP July 9-10, 2005 Reconstruction - General Look again at combination of geology and external field: equal spatial position

MGSTOOLS WORKSHOP July 9-10, 2005 Reconstruction - General For short-wavelength external field, shift is clear

MGSTOOLS WORKSHOP July 9-10, 2005 Reconstruction - General For long-wavelength external field, shift cannot be seen

MGSTOOLS WORKSHOP July 9-10, 2005 Reconstruction - General Reconstruction cannot distinguish at long wavelengths (compared to sensor separation)

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction – why it fails Trapezoid rule – show transfer function Short-wavelength errors (sensor noise, wave noise, …) unimportant because operator is small at short wavelengths. Long-wavelength errors are amplified: subheadings follow? Heading error (how do we show this? – We could show striping or swing curves) Leeway Vertical Offset

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Trapezoid rule transfer function

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Example Short-wavelength errors

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Example Long-wavelength errors

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Example Heading errors

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Example Leeway

MGSTOOLS WORKSHOP July 9-10, 2005 Naïve Reconstruction Example Vertical Offset

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm general strategy Roll off transfer function at long wavelengths Minimizes effects of long-wavelength errors Lose ability to discriminate external field at long wavelengths (e.g., diurnal) Need to adopt a rational strategy for designing roll-off Fit spectrum using a set of exponentials Identify components dominated by geology, external field, short-wavelength noise Use this to design operator

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Roll off transfer function at long wavelengths

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Minimizes effects of long-wavelength errors

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Lose ability to discriminate external field at long wavelengths (e.g., diurnal)

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Need to adopt a rational strategy for designing roll-off

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Fit spectrum using a set of exponentials

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Identify components dominated by geology, external field, short-wavelength noise

MGSTOOLS WORKSHOP July 9-10, 2005 MGS Tools Algorithm Use data to design operator