Post on 11-Dec-2015
transcript
Nye data – nye muligheder?
Esben Auken, Anders V. Christiansen, Nikolaj Foged and Kurt Sørensen
HydroGeophysics GroupDepartment of Earth Sciences, University of Aarhus, Denmarkwww.hgg.au.dk
Indhold Hvordan ser x-data ud?
Modelanalyser – motivationen
Problemerne med måling af vinkel – “forurening” af x-signalet
Inversion
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
)]
1e-10
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
)]
1e-10
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
Theoretical z-response
100 m 10 m
30 m 20 m
80 m 70 m
10 m
Model z-component data
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
)]
1e-10
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
Theoretical z- and x-response
Late time x ∞ t-3
Late time z ∞ t-2.5
x-component signal level is 5 – 8 times smaller than z-component
x- and z-component
100 m 10 m
30 m 20 m
80 m 70 m
10 m
Model
Model Sensitivity Analysis – model 2 White: z-component alone
Grey: x- and z-component
Black: x- and z-component, x with 60 kHz low-pass filter
Model Sensitivity Analysis – model 1 White: z-component alone
Grey: x- and z-component
Black: x- and z-component, x with 60 kHz low-pass filter
Model Sensitivity Analysis – model 3 White: z-component alone
Grey: x- and z-component
Black: x- and z-component, x with 60 kHz low-pass filter
Location of first gate – 11 or 18 micros? White: z-component alone
Grey: x- and z-component
Black: x- and z-component, x with 60 kHz low-pass filter
The 3 Challenges for exploiting x-data1. Signal to noise level
• Altitude dependency• Natural background noise
2. “Contamination” of the x-data due to tilt of the Tx-frame
3. Timing of the instrumentation and measurement of the tilt
Altitude Dependency
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02z-data x-data
Altitude: 1 m
Altitude: 1 m
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02
Altitude Dependencyz-data x-data
Altitude: 1 m 18 m
Altitude: 1 m 18 m
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02
Time [s]1e-06 1e-05 1e-04 1e-03 1e-02
dB
/dt
[V/(
m^2
*s)]
1e-09
1e-08
1e-07
1e-06
1e-05
1e-04
1e-03
1e-02
Altitude Dependencyz-data x-data
Altitude: 1 m 18 m
29 m – operating altitude
Altitude: 1 m 18 m 29 m
The 3 Challenges for Exploiting x-data1. Signal to noise level
• x-signal is 5 – 8 times smaller than z-signal• x-signal decreases faster with altitude compared to the z-
signal• x-noise is 5 – 10 times larger than z-noise
2. “Contamination” of the x-data due to tilt of the Tx-frame
3. Timing of the instrumentation and measurement of the tilt
The 3 Challenges for Exploiting x-data1. Signal to noise level
• x-signal is 5 – 8 times smaller than z-signal• x-signal decreases faster with altitude compared to the z-
signal• x-noise is 5 – 10 times larger than z-noise
2. “Contamination” of the x-data due to tilt of the Tx-frame
3. Timing of the instrumentation and measurement of the tilt
z-component
x-component
Ground
Tx-frame
z-Rx
Ground
x-Rx
Tilt – Normal Situation
Positive Tilt of the Tx-frame
z-response adds signal to the x-response
The x-response caluclated as: Bxtotal = Bx + sin(Tilt) Bz
z-contamination
x-component
GroundGround
GroundGround
”Contaminated” x-response – Positive Tilt
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05x-data
Tilt: 0 deg
GroundGround
”Contaminated” x-response – Positive Tilt
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05x-data
5 deg
Tilt: 0 deg
GroundGround
”Contaminated” x-response – Positive Tilt
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05x-data
10 deg 5 deg
Tilt: 0 deg
9 usefull gates
Negative Tilt of the Tx-frame
z-response subtracts from the x-response
z-contamination
GroundGround
x-component
GroundGround
”Contaminated” x-response – Negative Tilt
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05x-data
Tilt: 0 deg
GroundGround
”Contaminated” x-response – Negative Tilt
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05x-data
Tilt: 0 deg -5 deg
GroundGround
Time [s]1e-06 1e-05 1e-04 1e-03
1.0e-11
1.0e-10
1.0e-09
1.0e-08
1.0e-07
1.0e-06
1.0e-05
”Contaminated” x-response – Negative Tilt
x-data
Tilt: 0 deg -5 deg -10 deg
3 - 4 usefull gates
The 3 Challenges for Exploiting x-data1. Signal to noise level
• x-signal is 5 – 8 times smaller than z-signal• x-signal decreases faster with altitude compared to the z-signal• x-noise is 5 – 10 times larger than z-noise
2. “Contamination” of the x-data due to tilt of the Tx-frame• The tilt of the frame adds or subtracts signal form the x-
response• Addition of signal is preferred from subtraction of signal • Tilt must treated as an inversion parameter - it can not be
measured with the desired accuracy• Does (probably) not need a priori information for the tilt
3. Timing of the instrumentation and measurement of the tilt
The 3 Challenges for Exploiting x-data1. Signal to noise level
• x-signal is 5 – 8 times smaller than z-signal• x-signal decreases faster with altitude compared to the z-signal• x-noise is 5 – 10 times larger than z-noise
2. “Contamination” of the x-data due to tilt of the Tx-frame• The tilt of the frame adds or subtracts signal form the x-
response• Addition of signal is preferred from subtraction of signal • Tilt must treated as an inversion parameter - it can not be
measured with the desired accuracy• Does (probably) not need a priori information for the tilt
3. Timing of the instrumentation and measurement of the tilt
Timing of the Front Gate
Time [s]1e-06 1e-05 1e-04 1e-03
100.0
1000.0x-data converted to apparent resistivity
Front Gate in 7.8 µs
Front Gate preventing the primary signal to saturate the receiver – opens for the signal just before the first time-gate
Coil Front Gate Receiver
100 m 10 m
30 m 20 m
80 m 70 m
10 m
Model
Time [s]1e-06 1e-05 1e-04 1e-03
100.0
1000.0
Timing of the Front Gate
Front Gate in 8.8 µs
300 nSec shift corresponds to approx. 3 % shift of the first gate
x-data converted to apparent resistivity
Front Gate in 7.8 µs
Coil Front Gate Receiver
100 m 10 m
30 m 20 m
80 m 70 m
10 m
Model
Front Gate preventing the primary signal to saturate the receiver – opens for the signal just before the first time-gate
The 3 Challenges for Exploiting x-data1. Signal to noise level
• x-signal is 5 – 8 times smaller than z-signal• x-signal decreases faster with altitude compared to the z-signal• x-noise is 5 – 10 times larger than z-noise
2. “Contamination” of the x-data due to tilt of the Tx-frame• The tilt of the frame adds or subtracts signal form the x-response• Addition of signal is preferred from subtraction of signal • Tilt must treated as an inversion parameter as it can not be
measured with the desired accuracy• Does probably not need a priori information from the device
3. Timing of the instrumentation and measurement of the tilt• The timing is accurate within 200 nanosec - OK!• Accurate measurement of the tilt while flying
Inversion Methodology LCI – soundings
Profile
TE M soundings - m odelsz z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . z
Inversion Methodology LCI – soundings
Profile
x x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
TE M soundings - m odelsz z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . z
Inversion Methodology LCI – soundings
Profile
TE M soundings - m odels
x
z
x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . z
Inversion Methodology LCI – soundings
n
n+1
n
n+1
n
n+1
d n d
n+1
d n d
n+1
Profile
TEM soundings - m odels
x
z
x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . z
n+2
n+2
n+2
d n+2
d n+2
x-m odel z-m odel x-m odel
Inversion Methodology Damped least squares scheme, modeling of system
transfer function• Low pass filters, front gate, turn-on and turn-off exponential
ramps• Flight altitude and tilt are constrained parameters
The model is parameterized or smooth 1D
n
n+1
n
n+1
n
n+1
d n d
n+1
d n d
n+1
Profile
TEM soundings - m odels
x
z
x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . z
n+2
n+2
n+2
d n+2
d n+2
x-m odel z-m odel x-m odel
Data
Diskussion og konklusion x-data tilfører information om den overfladenære geologi
Ved to-moment-system kompenserer x-data for, at første gate er i 16 microsek.
Ved ét-moment-system (første gate i 10 microsek.) tilfører x-data opløslighed i betragetligt omfang.
x-signalet kan anvendes, hvis ikke modstanden er for høj • Kræver at flyvehøjden er omkring 30 m (eller lavere)• Kræver nøjagtig måling af vinkel og kalibrering af
instrumenterne
Giver ikke ekstra arbejde i felten, men giver ekstra processerings- og tolkningsarbejde
Stadigvæk på forskningsstadiet