Four in a Row is an expanded view of yesterday's photo (and also the photo I processed in the soon to be released Topaz Clarity).
On the crews I worked on in libya, Tunisia and Oman we had six vibs (seismic vibrators). Typically, one was in camp for maintenance, one was on the line as a spare and the other four were in service. In South Africa, depending on the client, sometimes we'd only have five.
Patterns were usually similar though some clients liked to get more experimental. Here the four vibs were running in echelon. They'd take a sweep, lift the pad, move forward a few meters, drop the pads and sweep again, over and over. By adding all these sweeps together the echoes back to the geophones were added on top of each other to produce a louder signal. Sometimes the pattern meant that the distance between swweps was always the same and sometimes the pattern was such that there's be a longer drive between stations to the next start position.
Just as the geophones were arrayed in a pattern, so was the vib pattern. The net effect was to assume that the energy was being put into the ground at the center of the vib array and being detected at the center of the geophone array.
Given all these approximations, and then my hatchet job of static corrections to eliminate the variations in the surface terrain and the 10 cm shortening of the pegs I mentioned in this post would not have been noticeable, except we were being paid to place the peg within 1 cm. I always found it curious that we'd accurately position the peg and then the geophone arrays and source arrays were all approximated, and neither were centered on the peg.
With these tires the lead driver would figure out the count of treads on the tires that would pass his door frame for the distance he'd have to travel. The other drivers would line something up on their vib with the lead vib to keep their station in the echelon and an observer would check to make sure they weren't drifting off pattern.
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