Data Acquisition Step By Step Procedure
- Prepare equipment presented in hardware section (see Table 1). Don’t forget to prepare field notes and a laptop computer with acquisition
software installed. It is highly recommended you run a mock acquisition in the office by connecting those parts illustrated in the Hardware
section. Only a short portion of the cable to connect a few geophones will be enough. The triggering sensor (i.e., hammer switch) can be
attached to a small carpenter hammer which can be gently tapped against office floor when testing. Try to record and save a few files
(records) on the computer. At this stage, you can test vertical stacking (i.e., stack limit > 1) if stacking is planned during the actual survey.
You can simulate in your mind the entire field operation procedure that may include initial layout, test, and moving source and receivers for
the production survey.
- Arriving at the survey site, walk along the potential survey line. Choose the transect along as flat a surface as possible with the least amount
of surface objects (e.g., buildings, roads, ditches, etc.). Mark start and end points of the line below which the final 2-D shear-velocity (Vs)
map is to be obtained. The exact end point may change at the end of the actual survey. The beginning point is where X = 0 (see Figure 2 in
- Pull out tape measure and start laying it out from the location (Xa) a certain distance ahead of X = 0 to account for half the receiver spread
(plus the source offset, X1, in case of a push-mode survey); i.e., Xa = -(Nch/2-1)dx (-X1 if push mode) where Nch=number of channels and
dx=receiver spacing (see Figure 2 in Product section).
- Start placing stake flags, preferably, every dx distance along the tape measure until the end of the tape measure is reached. Mark station
numbers every, say, five stations (e.g., 1005, 1010, 1015, etc.). This step will be repeated if the survey continues over the end of the tape
measure. Often, distances are used for surface coordinate, instead of station numbers, and in this case tape measure by itself (with
occasional markings on the ground by using a spray paint) can be enough to guide the coordinate.
- Lay out receivers (land streamer) so that the (Nch/2)-th channel can be placed at X = 0 (see Figure 2 in Product section).
- Bring seismic source (with hammer switch attached) to the appropriate place for the first record (i.e., X1 ahead of the first channel if push-
mode survey, or X1 after the last channel if pull-mode survey).
- Connect seismic cable and trigger (hammer switch) cable to seismograph. Power on seismograph.
- Connect laptop computer to seismograph and run acquisition software.
- Setup acquisition software (refer to “Acquisition Software Setup”).
- Execute 1-2 test impacts with seismic source to make sure everything is running properly. Before starting acquisition these test files should
be deleted (or named differently) and the beginning file name reset (e.g., return to 1001.dat).
- Start production survey. Avoid “false triggering” when moving source by avoiding unnecessary abrupt contact with other objects. The false
trigger will record (and save, if auto-save is on) ambient noise. The false triggering has to be monitored by periodically checking file name
(number) to be saved. Note in your field notes each time saving a record or whenever an “unusual” event occurs.