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