Depth sounding in the context of "Bathymetry"

A fathom is a unit of length in the imperial and U.S. customary systems equal to 6 feet (1.8288 m), used especially for measuring the depth of water. The fathom is neither an international standard (SI) unit, nor an internationally accepted non-SI unit. Historically, it was the maritime measure of depth in the English-speaking world but, apart from within the US, charts now use metres.

There are two yards (6 feet) in an imperial fathom. Originally the span of a man's outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around 5–5+1⁄2 feet (1.5–1.7 m).

St. Paul (Aleut: Tanax̂ Amix̂ or Sanpuulax̂, Russian: Сент-Пол, romanized: Sent-Pol) is a city in the Aleutians West Census Area, Alaska, United States. It is the main settlement of Saint Paul Island in the Pribilofs, a small island group in the Bering Sea. The population was 413 at the 2020 census, down from 479 in 2010. Saint Paul Island is known as a birdwatching haven.

The three closest islands to Saint Paul Island are Otter Island to the southwest, Saint George slightly to the south, and Walrus Island to the east.

A multibeam echosounder (MBES) is a type of sonar that is used to map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time it takes for the sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth. Unlike other sonars and echo sounders, MBES uses beamforming to extract directional information from the returning soundwaves, producing a swathe of depth soundings from a single ping.

The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. One of the longest seamount chains on Earth, it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The chain's formation is best explained by movement of the Pacific Plate over the Louisville hotspot, although others have suggested that it formed by leakage of magma from the shallow mantle up through the Eltanin fracture zone, which it follows closely for some of its course.

Depth-sounding data first revealed existence consistent with a seamount chain in 1972, although some of the seamounts had been described as a ridge in 1964 linked to the Eltanin fracture zone system, hence the name.