Datum correction: A calculation of the time required for a seismic pulse to travel from the source to the datum plane and from the datum plane to the geophone. This value is subtracted from observed reflection times to give the arrival time as if sources and geophones had been located on the datum surface without any low or irregular velocities below the datum. Datum correction velocity: The velocity assumed beneath the datum surface, often the subweathering velocity.
Datuming is the arbitrary flattening and straightening of a particular reflection for use as a reference on a cross-section, i.e., using a paleo-datum; flattening thereby assuming that everything was horizontal at the time of the paleodatum. The result emphasizes differences between this and other reflections.