4 Geophysical Processing

1. Define Objectives: Survey Design • Data Acquisition • Quality Control • Removal of Cultural features, other noise, correction of positioning errors • Levelling & Micro-Levelling • Gridding • Primary Geophysical Processing • Secondary Geophysical Processing • Imaging & Compression • Modelling • Visualisation 4 Geophysical Processing

2. 1 Course Outline Pracs 4 7 2 3 5 6

3. 3.1 Airborne Surveys

4. Airborne Survey Pattern

5. Barometric vs Draped surveys

6. Flight Lines & Tie Lines 5m spacing along lines Flight lines 30 to 500m spacing Ties lines 3 OR 4 times flight line spacing

7. 3.2 Gravity Survey

8. 3.3 Processing Tasks • Quality Control • Flight Line Position Verification • Removal of Cultural Spikes • 3.4 Levelling & Micro-Levelling • 3.5 Gridding and stitching • Registration & Rectification • 3.6 Primary Geophysical Processing • Reduction to Pole (RTP) • First Vertical Derivative (1VD) • Automatic Gain Control (AGC) • Upward/downward continuation • Draping • Analytical Signal • Gravity (Bouger, Free Air…) • 3.7 Secondary Geophysical Processing • Euler Deconvolution • SPI • Wavelet Transforms • 3.8 Filtering • High Pass • Low Pass (Smoothing) • Directional including Sun Shading • 3.9 Visualisation & Compression • False Colour • Pseduocolour Imaging • Image Ratioing • Principal components

9. 3.4 Decorrugation filtering Flight line trend

10. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 3.5 Gridding data www.math.ucdavis.edu/~strohmer/ research/geo/geo.html

11. Gridding data

12. Gridding with trend information

13. Stitching

14. Stitch of many 1:100,000 sheets showing mis-matches at borders. Stitch mismatch

15. 3.6 Primary Geophysical Processing: Reduction to the Pole (RTP) -60º -90º (magnetic South Pole)

16. TMI: Total Magnetic Intensity TMI vs 1VD 1VD: 1st Vertical Derivative =dM/dZ At magnetic pole TMI TMI 1VD

17. TMI vs 1VD Greenland

18. Automatic Gain Control Filter (AGC) n = window size of filter

19. TMI TMI RTP AutomaticGainControl(AGC) TMI RTP 1VD TMI RTP 1VD AGC

20. Upward/Downward Continuation 200 m 1000 m gravity magnetics

21. Upward continuation of Arabian Shield & Peninsula 300m Upward continued to 10km

22. 3.7 Secondary Geophysical ProcessingAnalytic Signal The analytic signal A of a potential field F is A(x,y,z) = i dF/dx + j dF/dy + k dF/dz, where i,j,k are unit vectors in the x,y,z directions. The analytic signal amplitude (also called the envelope) is |A| = |[(dF/dx)2 + (dF/dy)2 + (dF/dz)2]1/2 | TMI Analytic Signal Amplitude of TMI Often used at low latitudes where RTP transforms are unstable, as it gives a maximum over the center of a symmetric body

23. 3.7 Secondary Geophysical Processing: Naudy, Euler & Phillips source parameter inversion

24. Euler Deconvolution window

25. Testing Euler Algorithm Depth 0m 500m Noddy Block Model Euler solutions, depth =100m N =1 Harris et al 1996

26. Comparison Unconformity Spatially averaged Euler Solutions Unconformity TMI

27. Vector Components of Gravity & Magnetic Fields Anomalous Component of Total Field X Component of Total Field Y Component of Total Field Z Component of Total Field Inclination -90º

28. Wavelet Transforms: Boschetti & Hornby (CSIRO) Upward continued profiles Horizontal derivative and wavelet transform gravity

29. USA Gravity Wavelet transform image of USA gravity image (Hornby et al 1998)

30. Plutons

31. Folds

32. 3.8 Visualisation • 120 million rods • Sensitive to grey scale contrast, not absolute levels • 6 to 7 million cones • Sensitive to absolute colour variation

35. Colour Display Gray Scale LUT Rainbow LUT Contours

36. 3.10 Filters and colouring • The human eye has wide dynamic range in colour (>10,000 levels) • It is highly sensitive to edges in gray scale (but with a low dynamic range ~32 levels) • Therefore: • if we want to see absolute intensity variations, use colour • if we want to see fine detail, use black and white (and use a high-pass filter)

37. Directional Filtering (High Pass Filter) Original Image Horizontal Edge Detection Vertical Edge Detection

38. Normal Colour Coded Topographic Image Sun Shading Simulated Sun Shading from 240/80 “Sun”

39. TMI TMI 1VD TMI 1VD NW Shade TMI 1VD AGC

40. Compression Typically can achieve 25:1 compression with minimal loss of information MrSID and ECW systems dominate (both wavelet based) Landsat Orthorectified (7-4-2) UTM Zone Mosaics compresses as MrSID Images http://zulu.ssc.nasa.gov/mrsid/mrsid.pl

41. 100 km 1 km Compression of Eire Raw: 986 Mb Compressed:21Mb ~47x compression c.f. http://www.ixoa.org/