Bathymetry is the study of the relief of the underwater part of water basins: both the world ocean and lakes, rivers, etc. Among specialists, this term can be used as a set of data on the depths of a water body , the result of a bathymetric survey . In other words, bathymetry is an underwater equivalent of topography or hypsometry. The name of the discipline is composed of the Greek words βαθύς (batus), “depth” and μέτρον (metron), “measure”. The data obtained as a result of bathymetric studies are mainly used to provide surface and underwater navigation , and also have a wide scientific application. The image of the underwater relief on bathymetric maps is in many respects similar to its image on ordinary topographic maps, but isobaths are used instead of isohyps - lines with the same depth relative to sea level. To increase the visibility of bathymetric maps, as in the case of their surface counterparts, the method of washing the relief, as well as digital models of relief, are widely used. Paleobatimetry is studying the underwater depths of previous eras.
Content
Data Acquisition
Sonar
The study of the relief of the depths of the sea began with the measurements of the depths with the help of the lot . In the old days, for this purpose, they used a strong twine with a cargo, which they hung overboard. Obviously, this method allowed to measure the depths only sequentially, one after another, and also required a considerable amount of time, not to mention the obtained measurement accuracy: the weight of the load and the speed of the vessel's motion affected the result, and the currents also contributed to the error.
Today, bathymetry operates data obtained using sonar lots (echo sounders, or sonars ), mounted in the bottom of the vessel; satellite data and lidars (infrared laser locators) are also actively used. The principle of operation of sonars is based on the calculation of the time between sending and receiving the reflected sound signal. The results of space imagery require the use of certain spectral channels and special processing to obtain depth data.
Since the 1930s, sonars with a narrow radiation pattern have been used to obtain bathymetric maps. Today, sonars with a radiation pattern equal to 90-170 degrees are used. The dense beam of radiation of such sonars provides high angular resolution, and therefore - measurement accuracy. A wide swath (depending on the depth of the underlying surface) allows a smaller number of entries, and an update rate of 0.1-50 Hz (also dependent on depth) allows the ship to move at a high speed without losing as a cover. On-board gyroscopes and spatial position sensors track the orientation of the vessel at the time of the survey and allow you to make corrections to roll , trim and yaw corrections to the measurement results, due to the dynamics of the water surface. GPS onboard sensors allow you to track the position of the vessel relative to the earth's surface and accurately link the results of the bathymetric survey.
The obtained results of depth measurements are processed automatically or in a semi-automated mode and, after processing, are usually presented as a digital elevation model ( as a set of points combined into a surface ).
Remote sensing data
As mentioned above, information obtained by remote sensing methods (space scanner and radar surveys of the oceans, etc.) is also actively used in bathymetry. According to the results of satellite radiometry, small changes in sea level are observed as a result of the gravitational uplift of submarine ridges, mountains, and other underwater objects. Since, on average, the sea level above the ridges and other elevations exceeds its level above the deep-water plains and valleys, on the basis of these measurements it is also possible to map the underwater relief.
Data Submission Problems
Bathymetry data is expressed in terms of coordinate systems , the height component of which is measured from the average level of tides. Some of the problems here are related to the fact that, for example, in the United States, deep-sea bathymetry data is based on a reference level associated with Mean Sea Level (MSL) , but most coastal areas are based on average minimum sea level ( Mean Lower Low Water, or MLLW ). In most countries, the minimum level of sea level associated with astronomical parameters Lowest Astronomical Tide (LAT) is taken as the zero level. Thus, depending on the tide mode for various territories, there are many levels of reference, which can lead to difficulties in organizing.
Bathymetry and related studies
Specialists in the field of bathymetry, along with studies of the underwater relief, also deal with the geology and geomorphology of the ocean floor, and the study of geodynamic activity ( underwater volcanoes and earthquakes). Thus, the acquisition and analysis of bathymetric data are essential in the study of the world's oceans, as well as in ensuring the safety of sea and river navigation.
See also
- Bathymetric survey
Links
- What is bathymetry? / NOAA (Eng.)
- Bathymetry and Global Relief / NGDC (English)
- Bathymetric Data Viewer / NGDC (English)
- Bathymetry / Geoscience Australia (eng.)
- bathymetry / Encyclopedia, National Geographic Society (English)