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Nye data – nye muligheder?

Nye data – nye muligheder?. Esben Auken , Anders V. Christiansen, Nikolaj Foged and Kurt Sørensen. HydroGeophysics Group Department of Earth Sciences, University of Aarhus, Denmark www.hgg.au.dk. Indhold. Hvordan ser x-data ud? Modelanalyser – motivationen

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Nye data – nye muligheder?

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  1. Nye data – nye muligheder? Esben Auken, Anders V. Christiansen, Nikolaj Foged and Kurt Sørensen • HydroGeophysics Group • Department of Earth Sciences, University of Aarhus, Denmark • www.hgg.au.dk

  2. Indhold • Hvordan ser x-data ud? • Modelanalyser – motivationen • Problemerne med måling af vinkel – “forurening” af x-signalet • Inversion

  3. Theoretical z-response z-component data Model 100 Wm 10 m 30 Wm 20 m 80 Wm 70 m 10 Wm

  4. Model 100 Wm 10 m 30 Wm 20 m 80 Wm 70 m 10 Wm 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. The 3 Challenges for exploiting x-data • Signal to noise level • Altitude dependency • Natural background noise • “Contamination” of the x-data due to tilt of the Tx-frame • Timing of the instrumentation and measurement of the tilt

  10. Altitude Dependency x-data z-data Altitude: 1 m Altitude: 1 m

  11. Altitude Dependency x-data z-data Altitude: 1 m 18 m Altitude: 1 m 18 m

  12. Altitude Dependency x-data z-data Altitude: 1 m 18 m 29 m – operating altitude Altitude: 1 m 18 m 29 m

  13. The 3 Challenges for Exploiting x-data • 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 • “Contamination” of the x-data due to tilt of the Tx-frame • Timing of the instrumentation and measurement of the tilt

  14. The 3 Challenges for Exploiting x-data • 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 • “Contamination” of the x-data due to tilt of the Tx-frame • Timing of the instrumentation and measurement of the tilt

  15. x-component z-component Tilt – Normal Situation

  16. x-component z-contamination Positive Tilt of the Tx-frame • z-response adds signal to the x-response • The x-response caluclated as: Bxtotal = Bx + sin(Tilt) Bz

  17. ”Contaminated” x-response – Positive Tilt x-data Tilt: 0 deg

  18. ”Contaminated” x-response – Positive Tilt x-data 5 deg Tilt: 0 deg

  19. ”Contaminated” x-response – Positive Tilt x-data 10 deg 5 deg Tilt: 0 deg 9 usefull gates

  20. x-component z-contamination Negative Tilt of the Tx-frame • z-response subtracts from the x-response

  21. ”Contaminated” x-response – Negative Tilt x-data Tilt: 0 deg

  22. ”Contaminated” x-response – Negative Tilt x-data Tilt: 0 deg -5 deg

  23. ”Contaminated” x-response – Negative Tilt x-data Tilt: 0 deg -5 deg -10 deg 3 - 4 usefull gates

  24. The 3 Challenges for Exploiting x-data • 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 • “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 • Timing of the instrumentation and measurement of the tilt

  25. The 3 Challenges for Exploiting x-data • 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 • “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 • Timing of the instrumentation and measurement of the tilt

  26. Model x-data converted to apparent resistivity 100 Wm 10 m 30 Wm 20 m 80 Wm 70 m 10 Wm Front Gate in 7.8 µs Timing of the Front Gate Front Gate preventing the primary signal to saturate the receiver – opens for the signal just before the first time-gate

  27. Model 100 Wm 10 m 30 Wm 20 m 80 Wm 70 m 10 Wm Timing of the Front Gate 300 nSec shift corresponds to approx. 3 % shift of the first gate Front Gate preventing the primary signal to saturate the receiver – opens for the signal just before the first time-gate x-data converted to apparent resistivity Front Gate in 8.8 µs Front Gate in 7.8 µs

  28. The 3 Challenges for Exploiting x-data • 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 • “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 • Timing of the instrumentation and measurement of the tilt • The timing is accurate within 200 nanosec - OK! • Accurate measurement of the tilt while flying

  29. Inversion Methodology • LCI – soundings

  30. Inversion Methodology • LCI – soundings

  31. Inversion Methodology • LCI – soundings

  32. Inversion Methodology • LCI – soundings

  33. 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

  34. Data

  35. 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

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