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Information about Bathymetry

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Present day Earth bathymetry (and altimetry). Data from the National Geophysical Data Center's TerrainBase Digital Terrain Model.


Bathymetry is the underwater equivalent to altimetry. The name comes from Greek βαθυς, deep, and μετρον, measure. In other words, bathymetry is the study of underwater depth, of the third dimension of lake or ocean floors. A bathymetric map or chart usually shows floor relief or terrain as contour lines, and may additionally provide surface navigational information.

Introduction

Originally, bathymetry referred to the measurement of ocean depth. Early techniques used pre-measured heavy rope or cable lowered over a ship's side. The greatest limitation of this technique is that it measures the depth only a single point at a time, and so is inefficient. It is also subject to movements of the ship and currents moving the line out of true and therefore is inaccurate.

The data used to make bathymetric maps today typically comes from an echosounder (sonar) mounted beneath or over the side of a boat, "pinging" a beam of sound downward at the seafloor or from remote sensing LIDAR or LADAR systems [1]. The amount of time it takes for the sound or light to travel through the water, bounce off the seafloor, and return to the sounder tells the equipment how far down the seafloor is. LIDAR/LADAR surveys are usually conducted by airborne systems.

Years ago, the occasional pings of a single-beam sounder might be averaged to make a map. Today, a multibeam echosounder may be used, featuring dozens of very narrow adjacent beams arranged in a fan-like swath of perhaps 90 to 180 degrees across. The tightly packed array of narrow individual beams provides very high angular resolution and accuracy. In general, the wide swath, which is depth dependent, allows a boat to map more seafloor in less time by making fewer passes. The beams update many times per second (typically 1-40 Hz depending on water depth), allowing faster boat speed while maintaining 100% coverage of the seafloor. Attitude sensors correct for the boat's roll, pitch and yaw on the ocean surface, and a gyrocompass provides accurate heading information to correct for vessel yaw. The Global Positioning System specifies where the boat is. Sound velocity profiles (speed of sound in water) of the water column correct for refraction or "ray-bending" of the sound waves owing to non-uniform water column characteristics such as temperature, conductivity, and pressure. A computer system processes all the data, correcting for all of the above factors as well as for the angle of each individual beam. In the end, a map is semi-automatically generated from this massive trove of data. Satellites are also used to measure bathymetry. Satellite radar maps deep-sea topography by detecting the subtle variations in sea level caused by the gravitational pull of undersea mountains, ridges, and other masses. On average, sea level is higher over mountains and ridges than abyssal plains and trenches[2].

Most surveys of navigable waterways in the United States are performed or commissioned by the United States Army Corps of Engineers, for inland waterways, and the National Oceanic and Atmospheric Administration for oceans. Coastal bathymetry data is available from the National Geodetic Data Center [3]. Bathymetry data is often referenced to tidal vertical datums of MSL or MLW.[4]

Some occupations or careers related to bathymetry is the study of oceans and rocks and minerals on the ocean floor. Also the study of underwater earthquakes or volcanology can apply. People who work with different types of terrains may also study the ocean floor, since it is such a unique area of the earth. Submarines and ships study the depths of the oceans, using sonars, and so people who work on those ships work with that area of expertise, as well.

See also

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The seafloor topography near the Puerto Rico Trench

References

1. ^ Olsen, R. C. (2007), Remote Sensing from Air and Space, SPIE, ISBN 9780819462350
2. ^ Thurman, H. V. (1997), Introductory Oceanography, New Jersey, USA: Prentice Hall College, ISBN 0132620723
3. ^ [1]
4. ^ [2]

External links

altimeter is an active instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.
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Terrain, or relief, is the third or vertical dimension of land surface. When relief is described underwater, the term bathymetry is used. Topography has recently become an additional synonym, though in many parts of the world it retains its original more general
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contour map (topographic map) uses contour lines (often just called a "contour") to join points of equal elevation (height) and thus show valleys and hills, and the steepness of slopes.
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Earth's oceans
(World Ocean)
  • Arctic Ocean
  • Atlantic Ocean
  • Indian Ocean
  • Pacific Ocean
  • Southern Ocean
An ocean (from Ωκεανός, Okeanos
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rope (IPA: /rəʊp/) is a length of fibers, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength (i.e.
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SONAR (SOund NAvigation and R anging) — or sonar — is a technique that uses sound propagation under water (primarily) to navigate, communicate or to detect other vessels. There are two kinds of sonar — active and passive.
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LIDAR (Light Detection and Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses.
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Multibeam or "Swathe" or "Swath" echosounders originated in the late 1950's, developed by the US Navy and General Instruments in the 1970's to map large swaths of the ocean floor to assist with underwater navigation of its submarine force.
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Angular resolution describes the resolving power of any image forming device such as an optical or radio telescope, a microscope, a camera, or an eye.

Definition of terms

Resolving power
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Hz or hz may mean:
  • Herero language (ISO 639 alpha-2, hz)
  • Hertz, unit of frequency
HZ, in all capitals, can stand for:
  • Hazard
  • Herpes Zoster
  • Horizons, a computer game

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For the dynamics of flight, see Flight dynamics.


Rockwell Collins Flight Dynamics is a subdivision of the aerospace giant Rockwell Collins. They manufacture and develop heads-up displays for civilian applications.
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Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
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Motto
"In God We Trust"   (since 1956)
"E Pluribus Unum"   ("From Many, One"; Latin, traditional)
Anthem
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United States Army Corps of Engineers, or USACE, is a federal agency made up of some 34,600 civilian and 650 military men and women. The Corps's mission is to provide military and civil works engineering services to the United States, including:

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National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere.
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This article describes a concept from surveying and geodesy. Datum is also the last known position of a submarine in ASW, the singular form of data, and a city in ancient Macedonia, probably on the site of the modern Kavala.

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Terrain, or relief, is the third or vertical dimension of land surface. When relief is described underwater, the term bathymetry is used. Topography has recently become an additional synonym, though in many parts of the world it retains its original more general
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