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Nyeste erfaringer med processering af SkyTEM data

Nyeste erfaringer med processering af SkyTEM data. Esben Auken. GeoFysikSamarbejdet Geologisk Institut, Aarhus Universitet. Outline. What is in the database? Pitch and roll correction Data filtering Summary. Ensuring Best Possible Data Quality.

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Nyeste erfaringer med processering af SkyTEM data

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  1. Nyeste erfaringer med processering af SkyTEM data Esben Auken • GeoFysikSamarbejdet • Geologisk Institut, Aarhus Universitet

  2. Outline • What is in the database? • Pitch and roll correction • Data filtering • Summary

  3. Ensuring Best Possible Data Quality • Obtain maximum information about formation resistivities • 5% data reproducibility of SkyTEM data on Lyngby test site • 5% repeatability at each take off and landing • Accurate data processing (and inversion) – the basis!

  4. Data Basis • Data types measured by the system • GPS – 2 per sec. • Pitch and roll of transmitter frame – 1.5 per sec. • Laser altitude – 20 per sec. from two devices • Transmitter current – 1 per dataset • Single decays from 2 or more receiver channels – 40 -120 Mb per hour

  5. Outline • What is in the database? • Pitch and roll correction • Data filtering • Summery

  6. Data Processing • Voltage data and altitudes corrected with respect to the pitch and roll of the frame • Manual intervention is necessary for • Altitudes • Culling of distorted data caused by coupling to wires and fences • Data are not leveled (in the future - might be changed for very early times)

  7. Altitude and Tilt Correction • ”Normal” situation

  8. Altitude and Tilt Correction • ”Normal” situation

  9. Altitude and Tilt Correction • ”Normal” situation – modelled in the inversion

  10. Altitude and Tilt Correction • ”Field” situation

  11. Altitude and Tilt Correction • ”Field” situation

  12. Altitude and Tilt Correction • ”Field” situation

  13. Altitude and Tilt Correction • ”Normal” situation – modelled in the inversion

  14. Tilt data • 5 min  3.5 line km • Tilt of +/-10°  3% correction of voltage data y-tilt +/- 4° x-tilt +/- 8° Filtered

  15. Raw Laser 1 Raw Laser 2 Removed by filtering Final – tilt corrected and relocated Removal of laser reflection from tree tops Correction of altitudes for tilt – non perpendicular reflections from the ground Relocation of altitudes to center of Tx and Rx coils Difference due to high y-tilt Laser reflections from tree tops Altitude Processing 5 min  3.5 line km

  16. Outline • What is in the database? • Pitch and roll correction • Data filtering • Summery

  17. 5s ~ 65 m 30s ~ 400m Box average – Narrow/Wide • SkyTEM data example (Airborne TEM) gate 1 gate 2 gate 3 . . . . . . . gate n Raw SkyTEM data, 2 min ~ 1.5 Km

  18. Raw Average 30 s 5 s 2 min ~ 1.5 Km Box average – Narrow/Wide Raw Average

  19. Trapezoid shaped average • combines the best from the narrow and the wide box average • used for SkyTEM data Trapezoid shaped average Box shaped average

  20. Average Average Average Trapezoid shaped average

  21. Trapezoid average - Sounding view Box average, medium width Trapezoid average

  22. Trapezoid average - Sounding view Box average, medium width Trapezoid average High lateral resolution 4 gates culled Only 2 gates culled

  23. Trapezoid average • At each time gate data are median filtered • The standard deviation is calculated from the remaining stack

  24. Summary • Shallow part of model section/early time gates • maximum lateral resolution is obtain with a narrow data average • large data stack is not needed because of a high signal to noise ratio • Deep part of model section/late time gates • Wide data average suppress the background noise and increase penetration depth. • Wide data average does not reduce the lateral resolution • Trapezoid shaped average • maximum lateral resolution • maximum penetration depth

  25. Example - Sommersted

  26. Coupling in high resistive areas

  27. Width? 360 m 540 m

  28. Coming up in the future • New tools for removing data directly from the GIS map • Better automatic filters for detecting coupled data • Major revision when the new multi-moment SkyTEM system is introduced

  29. Summary • Quality of the data processing forms the basis for all subsequent use of the data • Pitch and roll is used to: • Calculate true altitudes • Perform first order correction for non-true z-receiver and transmitter • Coupled data are culled in the raw data - before inversion. How much to remove is dependent on the resistivity of the subsurface • Data average using trapezoid shaped filters and pruning

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