The seismic reflection technique profiles the earth by detection of returning elastic waves from boundaries in the subsurface across which there are contrasting physical properties. The principle material property contrasts that produce reflections are elastic constants and density. The elastic waves are produced by shot,
hammer, vibrator, weight drop, or some comparable method to put impulsive energy into the ground. In normal 2-D shooting, geophones are laid out at regular intervals in a line to measure the arrival of the wave train from a shot. Repeat records may be "stacked" in the field to obtain an enhanced composite record.
Reflected energy, as well as unwanted noise, is encoded as "information" within the wave train. Many strategies, both in the field and processing office, are applied to enhance the coherent reflective energy, and suppress both coherent and incoherent noise.