In seismic investigations, the technique in which the signal-to-noise ratio is enhanced by summing the signals for a number of shots into one set of geophones or hydrophones at one offset. It is used extensively in land seismic-refraction surveys, using signal-enhancement seismographs which can sum up to 255 shots (e.g. hammer blows, weight-drops, etc.) to produce a good-quality seismic record, but is of limited value in marine work, where common-depth-point stacks are preferred.