INFOMAR Sub-bottom Profile

A Sub-bottom profile aims to identify and characterise layers of sediment or rock under the seabed. These systems also can be helpful in locating hard objects buried beneath the seabed shallow sediment layers. In sub-bottom profiling, a sound source directs a pulse toward the seabed. Parts of this sound pulse reflect off of the seabed, while other parts penetrate the seabed. The portions of the sound pulse that penetrate the seabed are both reflected and refracted as they pass into different layers of sediment. Sub-bottom profile data can be collected by 2 systems a Pinger, a Chirp system or a Sparker system. The Pinger/Chirp systems operate in a similar way to the SBES but at lower frequencies. A pinger system transmits a single frequency (~4 kHz) while the chirp system transmits a sweep of frequencies (e.g. 2-7 kHz) in a single pulse. The sound penetrates the seabed and reflects off boundaries where there are changes in the sediment properties (e.g. mud-sand transitions). The depth of penetration into the subsurface is dependent on the type of sediment. The Sparker system is used sub-seabed investigations where deeper penetration is required or coarse/ compacted sediments dominate. Operating at lower frequencies (500 – 2000 Hz) the unit is towed behind the vessel, transmitting a more powerful pulse of sound into the seabed.