Does anybody know what these guys are doing?

[Jamnanc]

I have several large off-road trucks in the field behind my house. They are running some sort of vibrator on the ground. There are small orange sensors placed every three hundred feet or so in all the adjacent fields. I'm guessing it has something to do with drilling for oil-natural gas.
They run a vibration at low frequency to high four times then pull forwand about a hundred feet and do it again. I know there is a natural gas pipeline near their present location.