Geometrics Atom Manuel utilisateur
02/06/2019, Rev. 1.6
Passive and Active Seismic Surveys
using Atom and SeisImager
Quick Start
02/06/2019, Rev. 1.6
Contents
1. Introduction................................................................................................................................................... 1
2. Typical survey configuration for microtremor array measurements (MAM)........................................... 3
3. Typical survey configuration for multi-channel analysis of surface waves (MASW) .............................. 7
4. General operation of Atom ........................................................................................................................... 8
5. LED Colors on Atom ..................................................................................................................................... 9
6. Start and stop recording............................................................................................................................. 10
7. Battery status ............................................................................................................................................. 12
8. Confirm or set up the Atom’s acquisition parameters via Wi-Fi............................................................. 13
9. Use Wi-Fi to turn off all Atom units.......................................................................................................... 17
10. Battery charging ....................................................................................................................................... 18
11. Data format ............................................................................................................................................... 19
12. Data download .......................................................................................................................................... 20
13. Delete data directory and format SD card.............................................................................................. 28
14. Export waveform data as SEG2 or ASCII file using SPACPlus in SeisImager ................................... 29
15. Basic passive data processing using SPACPlus in SeisImager. ............................................................ 34
16. Basic active data processing using SPACPlus and Pickwin in SeisImager.......................................... 42
17. Combine passive and active surface wave data...................................................................................... 53
18. Huddle test................................................................................................................................................ 60
19. Data example ............................................................................................................................................ 63
Appendix A : Confirm or set up the acquisition parameters using SPACPlus........................................... 65
Appendix B : Data download using SPACPlus ............................................................................................. 67
Appendix C : Data download using SPACPlus via USB .............................................................................. 69
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1. Introduction
This manual summarizes data acquisition and processing of seismic survey. It particularly focuses on 1D
passive and active surface wave methods using 10 ~ 12 Atom acquisition units (AUs) for average S-wave
(shear wave or secondary wave) velocity to a depth of 30 m (AVS30). See “SeisImager/SWTM Manual”,
“SeisImager/SWTM Manual Addendum (H/V)” and “SeisImager/SW-ProTM Manual” for the detailed analysis of
dispersion curves and/or H/V curves.
Figure 1.1 summarizes software suite and modules will be mentioned in this manual and outline of data
processing. Two software suites, Geometrics Atom Downloader and SeisImager will be used to download
waveform data from Atom and to process the data. Geometrics Atom Downloader downloads waveform data
from Atom AUs via Wi-Fi and save it raw data files (.mtn). SPACPlus reads the raw data, edits and pre-process
raw data and save it as SEG2 files. It also calculates an 1D dispersion curve from ambient noise data. Pickwin
takes over pre-processed data and applies 2D or 3D dispersion curves. Pickwin also directory reads the raw
data file (.mtn). WaveEq applies various inversions to 1D to 3D dispersion curves and provides 1D to 3D S-
wave velocity model. The SPACPlus also downloads data from Atom AUs and set up acquisition parameters
via Wi-Fi or USB.
Although the manual mainly describes data acquisition and processing for 1D passive and active surface wave
methods, Atom can be used for other seismic surveys such as refraction and reflection. SPACPlus cuts out
and saves shot records as SEG2 files and Pickwin and Plotrefa take over these data and applies refraction or
general seismic processing.
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Atom
Geometrics
Atom Downloader
Geometrics
Atom Downloader
Figure 1.1 Software suite and modules described in the manual and outline of processing.
SPACPlus
Pickwin
WaveEq
Raw data file
(.mtn)
Data file (.sg2)
2D/3D surface wave processing
Editing, pre-processing and
1D surface wave processing
Dispersion curve analysis
Download data via Wi-Fi.
Download data via Wi-Fi or USB.
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2. Typical survey configuration for microtremor array measurements (MAM)
1) In microtremor array measurements (MAM), the array size (or maximum separation of receivers) must be
larger than the depth of investigation. For example, the array size must be bigger than approximately 30 m in
the investigation for an AVS30 investigation. SeisImager allows four set types of array configurations as well
as a custom option. Figures 2.1 through 2.5 illustrate the various set configurations. Note that “Array size” in
the Figures is the definition used for processing in SeisImager and not the same as the maximum receiver
separation. See SeisImager/SW manual for more details. As in Figure 1, the black line represents the order
of the Atom’s ID and the green inverted triangles represent each Atom.
Start
End
Figure 2.2 Map view of MAM survey equilateral triangle spread configurations with 7 (Triangle 7)
and 4 geophones (Triangle 4).
Figure 2.1 Map view of MAM survey equilateral triangle spread configuration with 10 geophones
(Triangle 10).
Start
End
Start
End
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Start
Figure 2.4 Map view of MAM survey circle spread configurations with 8 outer geophones on one circle
and one center geophone (Single circle 9) and 18 geophones in two circles and one center geophone
(Double circle 37).
Start
End
End
Figure 2.5 MAM survey linear spread configuration using all channels, one per geophone.
Start
End
Figure 2.3 Map view of MAM survey L-shape spread configurations with 11 (L11), 9 (L9), and 7
(L7) geophones. An angle between two edges does not need to be 90 degrees.
End
Start
Start
End
Start
End
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2) A typical example of an L-shape array for an AVS30 survey using Atom units is shown below. For the sake
of simplicity, deploy the Atoms in numerical order of ID. In this example, the Atom ID’s are 10006 to 100050.
25 ~ 75 m
25 ~ 75 m
100011
100006
100014
100015
100027
100031
100036
100038
100039
100049
100050
Deploy Atom units in numerical order
Figure 2.6 L-shaped array (L11) using 11 Atom AUs.
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During processing, waveform traces are shown and processed in the numerical order of each Atom unit’s ID.
3) Data acquisition
For an S-wave velocity investigation, such as an AVS30, record between 15 to 30 minutes of ambient noise
per survey. This will be sufficient for surveys with penetration depth of 30 to 100 meters. As arrays become
larger, increase the recording time. Standard recording time for different size arrays is summarized in Table
2.1. Note that the standard time is just a rough indication and is dependent on site conditions. For surveys
larger than 100 meters in urban areas, it is better to acquire the data at night.
Table 2.1 Array size and standard recording time
Array size or investigation
depth (m)
Recording time
(min.)
Remark
< 30
> 15
NA
30 ~ 100
> 30
NA
100 ~ 500
> 45
In urban areas, survey at night
500 <
> 60
In urban areas, survey at night
Traces are shown and
processed in numerical order
of Atom
Figure 2.7 Example of data obtained from Atom units.
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3. Typical survey configuration for multi-channel analysis of surface waves (MASW)
In multi-channel analysis of surface waves (MASW), the array size (spread length or maximum separation of
receivers) must be larger than the double of investigation depth. For example, the array size must be bigger
than approximately 20 m in the investigation depth of 10 m. Figures 3.1 illustrates the typical configurations.
Figure 3.1 Typical source-receiver geometry for multi-channel analysis of surface waves
(MASW).
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4. General operation of Atom
The atom generally has two modes of operation. The first is the recording mode without Wi-Fi and the second
mode is downloading with Wi-Fi.
Table 4.1 Recording mode and downloading mode
Mode
Wi-Fi
Wi-Fi LED
Operation
Recording
Off
No blinking or blink once
Recording data
Downloading
On
Blink twice
Downloading data
Set up acquisition parameters
Figure 4.1 describes the behavior of Atom when turned on.
Figure 4.1 Recording mode and downloading mode for Atom
Found an access point “atom0000”?
Received search command from
“Geometrics Atom Downloader”?
Downloading mode
Recording mode
Turn on
No
Yes
No
Yes
Table des matières
