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°  correction of voltage data y-tilt +/- 4° x-tilt +/- 8° Filtered

15. Altitude Processing 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 Laser reflections from tree tops Difference due to high y-tilt 5 min  3.5 line km

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

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

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

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 Trapezoid shaped average Average

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

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

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

36. Width? 360 m 540 m

37. 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

38. 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