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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