Data Acquisition and Processing of a Distributed 3D Induced Polarisation Imaging system

Transcription

1 Data Acquisition and Processing of a Distributed 3D Induced Polarisation Imaging system J Bernard, IRIS Instruments, France IP Workshop W3: IP processing and QC - from amps in the ground to an Inversion input

2 Traditional IP field work: 2D lines, all electrodes are connected to the receiver GOOD FOR SHALLOW / MEDIUM DEPTHS: - 2D surveys - rather short spacing, regular grid - flat areas Innovative IP field work: 3D distributed system many small receivers, no cable between receivers GOOD FOR DEEP EXPLORATION: - 3D surveys - flexible spacing, no grid - rough topography areas

3 DEEP IP SURVEY ACQUIRING 3D DATA WITH A DISTRIBUTED RESISTIVITY / IP SYSTEM: NO CABLES BETWEEN THE RECEIVERS The V units (receivers) keep same position for many positions of the transmitting electrodes: => a lot of acquisition time is saved => high resolution made possible for 3D surveys

4 ACQUIRING 3D DATA WITH THE FULL WAVER DISTRIBUTED RESISTIVITY / IP SYSTEM Main specifications of the distributed IP system: - two channel receivers (V-FullWaver) records signal all time long (full waveform) - they have GPS for position, time and synchronization - a receiver can be used for remote reference (signal enhancement) - a transmitter unit (I-FullWaver) records the current all time long (full waveform) - at the end of the day, the data are transferred into a PC, for further the signal processing and edition of the data

5 I & V FULL WAVER RESISTIVITY / IP UNITS I Full Waver unit, for current recording V Full Waver unit, for primary voltage and chargeability recording (2 channels) note: the V-FullWaver features 2 channels for measuring, for instance, two perpendicular components of the electric field, whichever the direction of the lines of current

6 I & V FULL WAVER RESISTIVITY / IP UNITS Main specifications: CONTINUOUS ACQUISITION at 10 ms period (100 Hz), Time Domain waveform: ON+, OFF, ON-, OFF INTERNAL MEMORY: hundreds of hours of time series acquisition USB STICK for DATA TRANSFER: 1 key pressing for downloading the data REAL TIME DISPLAY OF IP SIGNAL during acquisition for checking the data quality

7 Test of the FULL WAVER 3D IP SYSTEM in Shandong Province, May 2014 VIP transmitter, for transmitting the current Max power: 10 kw Max voltage: V Max current: 20 A Current regulated I Full Waver unit, for recording the current:

8 Test of the FULL WAVER 3D IP SYSTEM in Shandong Province, May units of V Full Waver for recording the signal (Resistivity & IP chargeability) current samples, every 10ms GPS synchronisedtime 1 unit of I Full Waver for recording the current: current samples, each 10ms GPS synchronised time

9 Test of the FULL WAVER 3D IP SYSTEM in Shandong Province, May 2014 V Full Waver unit: 2 channel receiver, for 2 perpendicular components of the Electric field M1 M2 Channel 1 Channel 2 = VM1N = VM2N N Digging a hole for setting up a non polarisable electrode V Full Waver unit

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26 Test of the FULL WAVER 3D IP SYSTEM in South America, 2015 FullWaver system used in the field: 9 V-FullWavers (MN = 50m), 1 I-FullWaver, 1 VIP 4000 transmitter 12 current injections (A fixed at infinity, B moving) Pole-Dipole array Area: 300m x 400m, rough topography (+/- 100m)

27 Test of the FULL WAVER 3D IP SYSTEM Top view of the electrode locations I current electrode (pole-dipole) V potential electrode M1 M2 N V Full Waver unit

28 Test of the FULL WAVER 3D IP SYSTEM 100 m TOPOGRAPHY IMAGE

29 Test of the FULL WAVER 3D IP SYSTEM RESISTIVITY DATA POINTS

30 Test of the FULL WAVER 3D IP SYSTEM RESISTIVITY < 200 ohm.m

31 Test of the FULL WAVER 3D IP SYSTEM IP CHARGEABITILITY DATA POINTS

32 Test of the FULL WAVER 3D IP SYSTEM IP CHARGEABITILITY 5 to 30 mv/v + data points

33 FULL-WAVE VIEWER Software Full-Wave-Viewer PC software: Current data transfer: file-name.iab (x, y, z, t, i) Full-Wave-Viewer PC software: Signal data transfer: file-name.vmn (x, y, z, t, v1, v2) Full-Wave-Viewer PC software: => Merge iab & vmn files: file-name.srw (x, y, z, t, i, v1, v2) Plot raw data (current, voltage) on PC screen Reject spikes & eliminate high noise periods Export to PROSYS software for quality control Export to Interpretation software data are transferred from FullWaver units to PC by SD card or USB cable, at the end of the day

34 FULL-WAVE VIEWER Software ma current file (AB)1 current file (AB)2 current file (AB)3 mv signal file signal file signal file (MN)1 (MN)6 (MN)11 time, ms => one current file for each position of the (AB) transmitting electrodes: here, 3 transmissions (AB)1 to (AB)3 => one signal file for all the (MN) receiving dipoles, all together: here 11 dipoles (MN)1 to (MN)11 The FULL-WAVE VIEWER software can automatically combine current and signal raw data periods of time (thanks to the GPS time stamping) for getting the 3 x 11 = 33 sets of readings (Iab, Vmn)

35 FULL-WAVE VIEWER Software Basic Data Processing, Quality Control: ANALOG FILTERING at 10 Hz, STACKING samples taken every 10 ms SP LINEAR DRIFT COMPENSATION SYNCHRONISATION BY PPS GIVEN BY GPS SPIKE and SP JUMPS removal SYNCHRONISATION BY FRONT DETECTION given the TIME ON duration (usually 2s) or : STACKING, then SYNCHRONISATION RE-SYNCHRONISATION by front checking at each new pulse (TIME ON) AUTOMATIC DETERMINATION OF THE PULSE DURATION MANUAL SELECTION OF PERIODS OF TIME where the chargeability will be computed (for instance after discarding noisy periods) After any processing: computation of resistivity and IP chargeability

36 FULL-WAVE VIEWER Software Three modes of operation: 1/ PROCESSING ONE FILE on its full acquisition time, according to the options taken (synchronisation, spike filtering, ) or, 2/ PROCESSING SEVERAL (ALL?) THE FILES in their full acquisition time, thanks to a «BATCH» mode, to save time at the end of the day or, 3/ PROCESSING ONE FILE MANUALLY by selecting the period of time where to compute the average. Selection with the mouse of the PC

37 FULL-WAVE VIEWER Software frequency domain processing: Remark: as the analog filtering is the same on the I-FullWaver and on the V-FullWaver, the transfer function V/I in the frequency domain is independant of this filter. In the Time domain, a correction of the filter can be applied if desired. FFT amplitude (mv) Fourier Frequency Analysis of the time series Frequency (Hz)

38 FULL-WAVE VIEWER Software signal record stacked IP curve signal FFT signal time series plotting & processing

39 FULL-WAVE VIEWER Software current record signal record

40 FULL-WAVE VIEWER Software Process: - automatic synchronization - averaging Filtering: - cancel SP jumps -cancel spikes Redefinition of IP windows: equally spaced or logarithmic,

41 FULL-WAVE VIEWER Software Mouse-selection of a (noise free) period of time where the resistivity and IP will be re-computed

42 FULL-WAVE VIEWER Software Automatic determination of the pulse duration (usually 2 s)

43 FULL-WAVE VIEWER Software Automatic resynchronisation process on V and I samples for an accurate determination of the starting time of the IP decay curve

44 FULL-WAVE VIEWER Software 1.55 mv voltage raw data samples Effect of stacking: 4 periods of 8s = 1/2mn record stacked IP decay curve voltage stacked data

45 FULL-WAVE VIEWER Software 1.55 mv voltage raw data samples Effect of stacking: 8 periods of 8s = 1mn record stacked IP decay curve voltage stacked data

46 FULL-WAVE VIEWER Software 1.55 mv voltage raw data samples Effect of stacking: 16 periods of 8s = 2mn record stacked IP decay curve voltage stacked data

47 1.55 mv FULL-WAVE VIEWER Software voltage raw data samples Effect of stacking: 32 periods of 8s = 4mn record stacked IP decay curve voltage stacked data

48 FULL-WAVE VIEWER Software spike re-processing Removal of a spike appearing during a record stacked IP decay curve stacked IP decay curve raw data with a spike stacking after removal of the spike

49 FULL-WAVE VIEWER Software Low amplitude signal with STANDARD PROCESS difficult to detect the wavefront

50 FULL-WAVE VIEWER Software Low amplitude signal with STACKING + FRONT DETECTION PROCESS Good synchronization and good signal quality (Vmn = 60 microv)

51 FULL-WAVE VIEWER Software Export data (raw, processed or averaged) for other processing or interpretation)

52 FULL-WAVER Raw Data Binary Format Description 1/ Heading Structure - electrode coordinates, channel number, - PPS, GMT offset, - input voltage range, overload indicator, - acquisition starting time, - number of samples acquired (every 10 ms) 2/ Data Structure - Raw data sample in mv (floating value, 4 bytes) - File organised by page of 512 bytes note: a «C» code is available to recover the raw data from this binary format and use them in other processing software

53 FULL-WAVER: a MATLAB script for reading raw data (binary) files data in clear time voltage ms mv MATLAB software IRIS script

54 FULL-WAVER: visualisation of raw data with MATLAB easy plotting

55 FULL-WAVER: Fast Fourier Transform MATLAB easy processing

56 Benefits of FULL-WAVER IP SYSTEM Benefits of distributed Resistivity / IP systems: - saving acquisition time - increasing the data quality by post processing of raw data and using remote reference techniques - increasing the target resolution by getting information from many transmitter positions - making realistic and efficient 3D surveys GEOMETRY FREEDOM ARRAYS FULL WAVEFORM RECORDING QUALITY CONTROL FOR POST PROCESSING by signal to noise improvement

57 CONCLUSIONS FULL WAVER SYSTEM: 3D Resistivity and IP system for deep targets => GEOMETRY FREEDOM ARRAYS, easy set up, adaptation to real field local conditions => FULL WAVEFORM RECORDING, raw data storage, GPS synchronisation QUALITY CONTROL FOR POST PROCESSING, by signal /noise improvement, possible remote reference BEST RESOLUTION IN THE INVERSION with multi-directional possible current positions