Nyeste erfaringer med processering

af SkyTEM data

Esben Auken

GeoFysikSamarbejdetGeologisk Institut, Aarhus Universitet

Outline What is in the database?

Pitch and roll correction

Data filtering

Summary

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!

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

Outline What is in the database?

Pitch and roll correction

Data filtering

Summery

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)

Altitude and Tilt Correction ”Normal” situation

Tx

R x

G round

1

lTx

R x

G round

1

l

Altitude and Tilt Correction ”Normal” situation

Tx

R x

G round

1

Tx A lt

l

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

Tx

R x

G round

1

Tx A lt R x A lt

l

Altitude and Tilt Correction ”Field” situation

G round

2

Altitude and Tilt Correction ”Field” situation

G round

2

Tx A lt

l

Altitude and Tilt Correction ”Field” situation

G round

2

Tx A lt

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

G round

2

Tx A lt R x A lt

R xl cos

Tilt data 5 min 3.5 line km

Tilt of +/-10° correction of voltage data

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Tilt [D

eg

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s]

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-8.0

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Tilt [D

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Tilt [D

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y-tilt +/- 4°x-tilt +/- 8°Filtered

Altitude Processing

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Altitu

de

[m]

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Altitu

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Altitu

de

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Raw Laser 1Raw Laser 2Removed by filteringFinal – 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

Outline What is in the database?

Pitch and roll correction

Data filtering

Summery

Time14:29:5014:29:4014:29:3014:29:2014:29:1014:29:0014:28:5014:28:4014:28:3014:28:2014:28:1014:28:00

Log

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o U

nit

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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

Box average – Narrow/Wide

Time14:29:5014:29:4014:29:3014:29:2014:29:1014:29:0014:28:5014:28:4014:28:3014:28:2014:28:1014:28:00

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Raw

Time14:29:5014:29:4014:29:3014:29:2014:29:1014:29:0014:28:5014:28:4014:28:3014:28:2014:28:1014:28:00

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Raw

Time14:29:5014:29:4014:29:3014:29:2014:29:1014:29:0014:28:5014:28:4014:28:3014:28:2014:28:1014:28:00

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Average

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Average

30 s

5 s

2 min ~ 1.5 Km

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Trapezoid shaped average combines the best from the narrow and the wide box

average

used for SkyTEM data

Trapezoid shaped average

Box shaped average

Time14:29:5014:29:4014:29:3014:29:2014:29:1014:29:0014:28:5014:28:4014:28:3014:28:2014:28:1014:28:00

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Average

Trapezoid shaped average

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Average

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Average

Trapezoid average - Sounding view

Trapezoid averageBox average, medium width

Trapezoid average - Sounding view

Trapezoid average

Box average, medium width

4 gates culled

Only 2 gates culled

High lateral resolution

Trapezoid average At each time gate data are median filtered

The standard deviation is calculated from the remaining stack

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

Example - Sommersted

Coupling in high resistive areas

Width?

360 m

540 m

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

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