Hydroacoustics

Summary

Hydroacoustics is the study and application of sound in water. Hydroacoustics, using sonar technology, is most commonly used for monitoring of underwater physical and biological characteristics.

Collecting Multibeam Sonar Data

Hydroacoustics can be used to detect the depth of a water body (bathymetry), as well as the presence or absence, abundance, distribution, size, and behavior of underwater plants[1] and animals. Hydroacoustic sensing involves "passive acoustics" (listening for sounds) or active acoustics making a sound and listening for the echo, hence the common name for the device, echo sounder or echosounder.

There are a number of different causes of noise from shipping. These can be subdivided into those caused by the propeller, those caused by machinery, and those caused by the movement of the hull through the water. The relative importance of these three different categories will depend, amongst other things, on the ship type[2] One of the main causes of hydro acoustic noise from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface's trailing edge that produces pressure fluctuations on the surface and unsteady oscillatory flow in the near wake. The relative motion between the surface and the ocean creates a turbulent boundary layer (TBL) that surrounds the surface. The noise is generated by the fluctuating velocity and pressure fields within this TBL.

Acoustical oceanographyEdit

 
A 38 kHz hydroacoustic tow fin used to conduct acoustic surveys by NOAA. Alaska, Southeast.

Acoustical oceanography is the use of underwater sound to study the sea, its boundaries and its contents.

HistoryEdit

Interest in developing echo ranging systems began in earnest following the sinking of the RMS Titanic in 1912. By sending a sound wave ahead of a ship, the theory went, a return echo bouncing off the submerged portion of an iceberg should give early warning of collisions. By directing the same type of beam downwards, the depth to the bottom of the ocean could be calculated.[3]

The first practical deep-ocean echo sounder was invented by Harvey C. Hayes, a U.S. Navy physicist. For the first time, it was possible to create a quasi-continuous profile of the ocean floor along the course of a ship. The first such profile was made by Hayes on board the U.S.S. Stewart, a Navy destroyer that sailed from Newport to Gibraltar between June 22 and 29, 1922. During that week, 900 deep-ocean soundings were made.[4]

Using a refined echo sounder, the German survey ship Meteor made several passes across the South Atlantic from the equator to Antarctica between 1925 and 1927, taking soundings every 5 to 20 miles. Their work created the first detailed map of the Mid-Atlantic Ridge. It showed that the Ridge was a rugged mountain range, and not the smooth plateau that some scientists had envisioned. Since that time, both naval and research vessels have operated echo sounders almost continuously while at sea.[5]

Important contributions to acoustical oceanography have been made by:

Equipment usedEdit

The earliest and most widespread use of sound and sonar technology to study the properties of the sea is the use of a rainbow echo sounder to measure water depth. Sounders were the devices used that mapped the many miles of the Santa Barbara Harbor ocean floor until 1993.

Fathometers measure the depth of the waters. It works by electronically sending sounds from ships, therefore also receiving the sound waves that bounces back from the bottom of the ocean. A paper chart moves through the fathometer and is calibrated to record the depth.

As technology advances, the development of high resolution sonars in the second half of the 20th century made it possible to not just detect underwater objects but to classify them and even image them. Electronic sensors are now attached to ROVs since nowadays, ships or robot submarines have Remotely Operated Vehicles (ROVs). There are cameras attached to these devices giving out accurate images. The oceanographers are able to get a clear and precise quality of pictures. The 'pictures' can also be sent from sonars by having sound reflected off ocean surroundings. Oftentimes sound waves reflect off animals, giving information which can be documented into deeper animal behaviour studies.[6][7][8]

ApplicationsEdit

Applications of acoustical oceanography include:

See alsoEdit

ReferencesEdit

  1. ^ "Archived copy". Archived from the original on 2012-02-19. Retrieved 2008-12-02.{{cite web}}: CS1 maint: archived copy as title (link)
  2. ^ reducing underwater noise pollution from large commercial vessels
  3. ^ Garrison, Tom. Essentials of Oceanography. 6th ed. Pacific Grove, CA: Brooks Cole, 2012. p.79.
  4. ^ Kunzig, Robert. Mapping the Deep: The Extraordinary Story of Ocean Science. New York: Norton 2000. p. 40-41.
  5. ^ Stewart, Robert. Introduction to Physical Oceanography, University Press of Florida, 2009 p. 28.
  6. ^ "Oceanography". Scholastic Teachers.
  7. ^ "Tools of the Oceanographer". marinebio.net.
  8. ^ "Technology used". noc.ac.uk. Archived from the original on 2015-01-21. Retrieved 2015-01-21.

Further readingEdit

  • Quality assurance of hydroacoustic surveys: the repeatability of fish-abundance and biomass estimates in lakes within and between hydroacoustic systems (free link to document)
  • Hydroacoustics as a tool for assessing fish biomass and size distribution associated with discrete shallow water estuarine habitats in Louisiana
  • Acoustic assessment of squid stocks
  • Summary of the use of hydroacoustics for quantifying the escapement of adult salmonids (Oncorhynchus and Salmo spp.) in rivers. Ransom, B.H., S.V. Johnston, and T.W. Steig. 1998. Presented at International Symposium and Workshop on Management and Ecology of River Fisheries, University of Hull, England, 30 March-3 April 1998
  • Multi-frequency acoustic assessment of fisheries and plankton resources. Torkelson,T.C., T.C. Austin, and P.H. Weibe. 1998. Presented at the 135th Meeting of the Acoustical Society of America and the 16th Meeting of the International Congress of Acoustics, Seattle, Washington.
  • Acoustics Unpacked A great reference for freshwater hydroacoustics for resource assessment
  • Inter-Calibration of Scientific Echosounders in the Great Lakes
  • Hydroacoustic Evaluation of Spawning Red Hind Aggregations Along the Coast of Puerto Rico in 2002 and 2003
  • Feasibility Assessment of Split-Beam Hydroacoustic Techniques for Monitoring Adult Shortnose Sturgeon in the Delaware River
  • Categorising Salmon Migration Behaviour Using Characteristics of Split-beam Acoustic Data
  • Evaluation of Methods to Estimate Lake Herring Spawner Abundance in Lake Superior
  • Estimating Sockeye Salmon Smolt Flux and Abundance with Side-Looking Sonar
  • Herring Research: Using Acoustics to Count Fish.
  • Hydroacoustic Applications in Lake, River and Marine environments for study of plankton, fish, vegetation, substrate or seabed classification, and bathymetry.
  • Hydroacoustics: Rivers (in: Salmonid Field Protocols Handbook: Chapter 4)
  • Hydroacoustics: Lakes and Reservoirs (in: Salmonid Field Protocols Handbook: Chapter 5)
  • PAMGUARD: An Open-Source Software Community Developing Marine Mammal Acoustic Detection and Localisation Software to Benefit the Marine Environment; https://web.archive.org/web/20070904035315/http://www.pamguard.org/home.shtml