Surface-wave energy that travels along or near the surface of the ground. It is usually characterized by relatively low velocity, low frequency, and high amplitude. Ground roll tends to mask desired reflection signals. Source and geophone patterns, frequency filtering, f-k filtering, and stacking are used to discriminate against it. It is usually a modified Rayleigh wave (q.v.), and ground roll is sometimes called pseudo-Rayleigh waves. See Figure R-3.