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MGSTOOLS Marine Gradiometer Software Workshop

MGSTOOLS Marine 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

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MGSTOOLS Marine Gradiometer Software Workshop

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

  2. 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

  3. 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

  4. Geological Field Example MGSTOOLS WORKSHOP July 9-10, 2005

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

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

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

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

  9. 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

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

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

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

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

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

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

  16. 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

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

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

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

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

  21. 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

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

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

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

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

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

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

  28. 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 MGSTOOLS WORKSHOP July 9-10, 2005

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

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

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

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

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

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

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

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