Adaptation of sonar techniques for exploring the sediments and crust of the Earth beneath the ocean

Abstract

The ‘continuous seismic profiler’ is an instrument system for studying the structure of sediments and rock beneath the sea floor by the seismic reflection method. Pulses of sound reflected at near-normal incidence are automatically timed and correlated by the recording method used in echo sounding. The sound source is chosen to give a repeatable pulse having a broad spectrum rich in low frequencies. One sound source called the ‘sparker’ has been developed into a unit with a power supply delivering 25,000 joules. A second source called the ‘boomer’ generates a sound pulse by means of the repulsive force induced between a flat spiral coil and a contiguous plate of aluminium when a large pulse of current passes through the coil. The latest ‘boomer’ is designed to accept 13,000 joules of electrical energy. Recordings of good quality can be made in 3000 fathoms of water from a ship proceeding at 6 knots and echoes have been recorded well over one second after the initial bottom reflection.These sound sources and recording techniques have also been applied to studying layered structures in the sediments by the refraction method and by studying reflection of sound from these layers as a function of angle of incidence.