On land the energy source is normally a small explosive charge detonated in a shallow drilled hole, but falling weight and vibrating plate sources are increasing in popularity. These have much less energy than a dynamite charge but addition of signals from repeated drops or vibrations improves the signal to noise ratio to compensate for this. The geophone cable is connected in sections so that a "roll-along" technique may be used in which the last recording section can be moved to the front, thus moving the spread along the line.