Noise wavetrains that bear a systematic phase relation (coherence) between adjacent traces. Most source-generated seismic noise (ground roll, shallow refractions, multiples, etc.) is coherent. The distinction between random and coherent noise is usually a matter of sampling (trace spacing), that is, very closely spaced geophones observe as coherent what phones more widely spaced (often >1–2 m) perceive as random. See Sheriff and Geldart (1995, 183–184).