Depth contour
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A bathymetric chart is a type of
isarithmic map A contour line (also isoline, isopleth, isoquant or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensi ...
that depicts the submerged
bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), river floors, or lake floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of wate ...
and physiographic features of ocean and sea bottoms. Their primary purpose is to provide detailed depth contours of ocean topography as well as provide the size, shape and distribution of underwater features.
Topographic map In modern mapping, a topographic map or topographic sheet is a type of map characterized by large- scale detail and quantitative representation of relief features, usually using contour lines (connecting points of equal elevation), but histori ...
s display elevation above ground (
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...
) and are complementary to bathymetric charts. Bathymetric charts showcase depth using a series of lines and points at equal intervals, called depth contours or isobaths (a type of
contour line A contour line (also isoline, isopleth, isoquant or isarithm) of a Function of several real variables, function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a ...
). A closed shape with increasingly smaller shapes inside of it can indicate an ocean trench or a seamount, or underwater mountain, depending on whether the depths increase or decrease going inward. Bathymetric surveys and charts are associated with the science of
oceanography Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology. It is an Earth science, which covers a wide range of to ...
, particularly
marine geology Marine geology or geological oceanography is the study of the history and structure of the ocean floor. It involves geophysical, Geochemistry, geochemical, Sedimentology, sedimentological and paleontological investigations of the ocean floor and ...
, and underwater engineering or other specialized purposes. Bathymetric data used to produce charts can also be converted to bathymetric profiles which are vertical sections through a feature.


History


Ancient Egypt

The use of
bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), river floors, or lake floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of wate ...
and the development of bathymetric charts dates back around the 19th century BC to ancient
Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...
. Depictions on tomb walls such as the bas-relief carvings of Deir al-Bahri commissioned by Queen
Hatshepsut Hatshepsut ( ; BC) was the sixth pharaoh of the Eighteenth Dynasty of Ancient Egypt, Egypt, ruling first as regent, then as queen regnant from until (Low Chronology) and the Great Royal Wife of Pharaoh Thutmose II. She was Egypt's second c ...
in the
16th century BC The 16th century BC was a century that lasted from 1600 BC to 1501 BC. Events * 1700 BC – 1500 BC: Hurrian conquests. * 1601 BC: Sharma-Adad II became the King of Assyria. *c. 1600 BC: The creation of one of the oldest surviving astronomi ...
show ancient mariners using long slender poles as sounding poles to determine the depth of the
Nile River The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the longest river i ...
and into the Nile River Delta.


Ancient Greece

The first written account and mapped records of sounding did not occur until 1000 years after the Egyptians had begun sounding and mapping the Nile. The Greek historian
Herodotus Herodotus (; BC) was a Greek historian and geographer from the Greek city of Halicarnassus (now Bodrum, Turkey), under Persian control in the 5th century BC, and a later citizen of Thurii in modern Calabria, Italy. He wrote the '' Histori ...
writes of a sounding in 66 feet of water of the mouth of the Nile in the river delta. He writes of yellow mud being brought up similar to the same that was deposited with the yearly floods. These accounts show a heightened awareness of regional depths and seafloor characteristics among ancient mariners and demonstrate that discoveries in bathymetry and the use of bathymetric charts had progressed significantly.


Ancient Rome

The
New Testament The New Testament (NT) is the second division of the Christian biblical canon. It discusses the teachings and person of Jesus in Christianity, Jesus, as well as events relating to Christianity in the 1st century, first-century Christianit ...
recounts soundings being taken with the shipwreck of Paul on the island of
Malta Malta, officially the Republic of Malta, is an island country in Southern Europe located in the Mediterranean Sea, between Sicily and North Africa. It consists of an archipelago south of Italy, east of Tunisia, and north of Libya. The two ...
in the
Book of Acts The Acts of the Apostles (, ''Práxeis Apostólōn''; ) is the fifth book of the New Testament; it tells of the founding of the Christian Church and the spread of The gospel, its message to the Roman Empire. Acts and the Gospel of Luke make u ...
. Chapter 27, verses 27-44 recount the experience:
27 "...as we were driven up and down in Adria, about midnight the shipmen deemed that they drew near to some country;" 28 "And sounded, and found it twenty fathoms: and when they had gone a little further, they sounded again, and found it fifteen fathoms." 29 "Then fearing lest we should have fallen upon rocks, they cast four anchors out of the stern..." 39 "And when it was day, they knew not the land..." 40 "And when they had taken up the anchors, they committed themselves unto the sea . . . and made toward shore." 41 And falling into a place where two seas met, they ran the ship aground; and the forepart stuck fast, and remained unmoveable, but the hinder part was broken with the violence of the waves.
Verse 39 states that "they knew not the land" indicating that their knowledge of sea was obtained from the experiences of others as well as the memory of having been there before. Sailing directions called a periplus did exist by the First Century A.D. giving general coastal configurations. Commercially available charts of the depths of the sea and surrounding coast would not be available for almost another thousand years.


Early modern period

Up to this point, bathymetric charts were rare as mariners continued to rely on heavy ropes and
lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
weights to take depth readings and chart the open ocean. Minor advances in the surveying and depth charting of the oceans occurred in the 200 years since Columbus sailed to the
Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...
. In 1647, Robert Dudley published the atlas, ' Dell'Arcano del Mare' (Secrets of the Sea). His work far outpaced anything that had been published previously with maps and charts constructed in the Mercator projection as well as containing some of the first charts to show printed depths on the North American Atlantic Seaboard. His publication provided the groundwork for future mariners and inventors to continue to develop new and inventive ways to produce high quality charts and surveys of the world's lakes and oceans.


Comparison with hydrographic chart

A bathymetric chart differs from a hydrographic chart in that accurate presentation of the underwater features is the goal, while safe
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
is the requirement for the hydrographic chart. A hydrographic chart will obscure the actual features to present a simplified version to help mariners avoid underwater hazards.


Joining a bathymetric chart and topographic map

In an ideal case, the joining of a bathymetric chart and topographic map of the same scale and
projection Projection or projections may refer to: Physics * Projection (physics), the action/process of light, heat, or sound reflecting from a surface to another in a different direction * The display of images by a projector Optics, graphics, and carto ...
of the same geographic area would be seamless. The only difference would be that the values begin increasing after crossing the zero at the designated
sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...
datum Data ( , ) are a collection of discrete or continuous value (semiotics), values that convey information, describing the quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols t ...
. Thus the topographic map's
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...
s have the greatest values while the bathymetric chart's greatest depths have the greatest values. Simply put, the bathymetric chart is intended to show the land if overlying waters were removed in exactly the same manner as the topographic map.


Within hydrography

Bathymetric surveys are a
subset In mathematics, a Set (mathematics), set ''A'' is a subset of a set ''B'' if all Element (mathematics), elements of ''A'' are also elements of ''B''; ''B'' is then a superset of ''A''. It is possible for ''A'' and ''B'' to be equal; if they a ...
of the science of
hydrography Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary ...
. They differ slightly from the surveys required to create the product of hydrography in its more limited application and as conducted by the national and international agencies tasked with producing
chart A chart (sometimes known as a graph) is a graphics, graphical representation for data visualization, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart". A chart can repres ...
s and
publication To publish is to make content available to the general public.Berne Convention, articl ...
s for safe navigation. That chart product is more accurately termed a navigation or hydrographic chart with a strong bias toward the presentation of essential safety information.


Bathymetric surveys


See also

* * *


References


External links


Bathymetric Data Viewer from NOAA's NCEI

3-D Bathymetric Chart Activity: An introduction to the Nautical Chart


Matthew Fontaine Maury Matthew Fontaine Maury (January 14, 1806February 1, 1873) was an American oceanographer and naval officer, serving the United States and then joining the Confederacy during the American Civil War. He was nicknamed "Pathfinder of the Seas" and ...
published this map in 1853 in his book "Explanations and Sailing Directions to Accompany the Wind and Current Charts ...." NOAA Photo Library.
General Bathymetric Chart of the Oceans (GEBCO)USGS Bathymetric Surveys

Web Based Bathymetry viewer for North America, Europe and Australia
{{Authority control Thematic maps Hydrography Physical geography Scientific visualization