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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
Time
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Tilt [D
eg
ree
s]
10.0
8.0
6.0
4.0
2.0
0.0
-2.0
-4.0
-6.0
-8.0
Time
10
:16
:30
10
:16
:20
10
:16
:10
10
:16
:00
10
:15
:50
10
:15
:40
10
:15
:30
10
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:20
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:15
:10
10
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:00
10
:14
:50
10
:14
:40
10
:14
:30
10
:14
:20
10
:14
:10
10
:14
:00
10
:13
:50
10
:13
:40
10
:13
:30
10
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:20
10
:13
:10
10
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:00
10
:12
:50
10
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:40
10
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10
:12
:20
10
:12
:10
10
:12
:00
10
:11
:50
10
:11
:40
Tilt [D
eg
ree
s]
10.0
8.0
6.0
4.0
2.0
0.0
-2.0
-4.0
-6.0
-8.0
Time
10
:16
:30
10
:16
:20
10
:16
:10
10
:16
:00
10
:15
:50
10
:15
:40
10
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:30
10
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:20
10
:15
:10
10
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:00
10
:14
:50
10
:14
:40
10
:14
:30
10
:14
:20
10
:14
:10
10
:14
:00
10
:13
:50
10
:13
:40
10
:13
:30
10
:13
:20
10
:13
:10
10
:13
:00
10
:12
:50
10
:12
:40
10
:12
:30
10
:12
:20
10
:12
:10
10
:12
:00
10
:11
:50
10
:11
:40
Tilt [D
eg
ree
s]
10.0
8.0
6.0
4.0
2.0
0.0
-2.0
-4.0
-6.0
-8.0
y-tilt +/- 4°x-tilt +/- 8°Filtered
Altitude Processing
Time
10
:16
:30
10
:16
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10
:16
:10
10
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:00
10
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10
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10
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10
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:00
10
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10
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10
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10
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10
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:10
10
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10
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10
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10
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:00
10
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10
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:40
Altitu
de
[m]
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
Time
10
:16
:30
10
:16
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10
:16
:10
10
:16
:00
10
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:50
10
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10
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:00
10
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10
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10
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10
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:10
10
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10
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:40
Altitu
de
[m]
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
Time
10
:16
:30
10
:16
:20
10
:16
:10
10
:16
:00
10
:15
:50
10
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10
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10
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10
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:00
10
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:50
10
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10
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10
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10
:14
:10
10
:14
:00
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10
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:10
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:00
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10
:12
:20
10
:12
:10
10
:12
:00
10
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:50
10
:11
:40
Altitu
de
[m]
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
Time
10
:16
:30
10
:16
:20
10
:16
:10
10
:16
:00
10
:15
:50
10
:15
:40
10
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10
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:10
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:00
10
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10
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10
:14
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10
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:10
10
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:00
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10
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:00
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10
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10
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:00
10
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10
:11
:40
Altitu
de
[m]
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
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
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
Average
30 s
5 s
2 min ~ 1.5 Km
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
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
Average
Trapezoid 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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Log
- N
o U
nit
1e+00
1e+01
1e+02
1e+03
1e+04
1e+05
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
Recommended