mgstools workshop july 9-10, 2005 mgstools marine gradiometer software workshop dr. richard hansen...

MGSTOOLS WORKSHOPJuly 9-10, 2005

MGSTOOLSMarine Gradiometer Software

Workshop

Dr. Richard Hansen

PRJ, Inc.

Presenter


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 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


Geological Field Example


External Field Example• Solar wind, field line compression


External Field Example• Long term diurnal


External Field Example

• Micropulsations


External Field Example

• Magnetic Storm


Superposition of geology and external fields

• Components cannot be distinguished with only one sensor

• On land, stationary base station is used (no geology)


Gradiometer Configuration

• Physical Arrangement



• Show records at equal times, with geological source



• Because sensors are in different positions, geology is shifted



• External field anomaly has no appreciable shift



• Difference: external field effects are gone, but geology is a directional gradient



• Need to reconstruct geology field from difference


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)



• 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)


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


Naïve Reconstruction

• Trapezoid rule transfer function



• Example Short-wavelength errors



• Example Long-wavelength errors



• Example Heading errors



• Example Leeway



• Example Vertical Offset


MGS Tools Algorithmgeneral 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


MGS Tools Algorithm

• Roll off transfer function at long wavelengths


MGS Tools Algorithm

• Minimizes effects of long-wavelength errors


MGS Tools Algorithm

• Lose ability to discriminate external field at long wavelengths (e.g., diurnal)


MGS Tools Algorithm

• Need to adopt a rational strategy for designing roll-off


MGS Tools Algorithm

• Fit spectrum using a set of exponentials


MGS Tools Algorithm

• Identify components dominated by geology, external field, short-wavelength noise


MGS Tools Algorithm

• Use data to design operator

mgstools workshop july 9-10, 2005 mgstools marine gradiometer software workshop dr. richard hansen...

Documents

geology field

external field effects

longwavelength errors

total field data

external signals

external fieldscomponents

shortwavelength noiseuse

wavelength errorslose