Bathymetric chart
A bathymetric chart is a type of
Bathymetric surveys and charts are associated with the science of
History
Ancient Egypt
The use of
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 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.[4] 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 recounts soundings being taken with the shipwreck of Paul on the island of Malta in the Book of Acts. Chapter 27, verses 27-44[5] 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 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. 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 is the requirement for the hydrographic chart.
A
Joining a bathymetric chart and topographic map
In an ideal case, the joining of a bathymetric chart and topographic map of the same
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 of the science of hydrography. 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 charts and publications 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
Originally, bathymetry involved the measurement of ocean depth through depth sounding. Early techniques used pre-measured heavy rope or cable lowered over a ship's side.[6] This technique measures the depth only a singular point at a time, and is therefore inefficient. It is also subject to movements of the ship and currents moving the line out of true and therefore is not accurate.
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.[7] 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 informs the equipment of the distance to the seafloor. LIDAR/LADAR surveys are usually conducted by airborne systems.
Starting in the early 1930s, single-beam sounders were used to make bathymetry maps. Today,
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 over abyssal plains and trenches.[8]
In the
Occupations or careers related to bathymetry include the study of oceans and rocks and minerals on the ocean floor, and the study of underwater earthquakes or volcanoes. The taking and analysis of bathymetric measurements is one of the core areas of modern hydrography, and a fundamental component in ensuring the safe transport of goods worldwide.[6]
See also
- Hydrographic/nautical chart – Topographic map of a maritime area and adjacent coastal regions
- General Bathymetric Chart of the Oceans – Publicly available bathymetric chart of the world's oceans
- List of map projections
References
- ^ "Bathymetric map". Encyclopedia Britannica. Retrieved 2019-12-17.
- ^ "bathymetry". National Geographic Society. 2011-03-24. Retrieved 2019-12-17.
- ISSN 1755-1315.
- ^ "NOAA History - Tools of the Trade/Surveying and Mapping/Sounding Pole to Sea Beam". www.history.noaa.gov. Archived from the original on 2019-12-17. Retrieved 2019-12-17.
- ^ "Acts 27". www.churchofjesuschrist.org. Retrieved 2019-12-17.
- ^ a b Audrey, Furlong (November 7, 2018). "NGA Explains: What is hydrography?". National Geospatial-Intelligence Agency via YouTube.
- ISBN 978-0-8194-6235-0
- ISBN 0-13-262072-3
- ^ "Bathymetry and Global Relief". www.ngdc.noaa.gov. NOAA National Centers for Environmental Information. Retrieved 8 July 2022.
- ^ "Coastal Elevation Models". www.ngdc.noaa.gov. NOAA National Centers for Environmental Information. 15 September 2020. Retrieved 8 July 2022.
External links
- Bathymetric Data Viewer from NOAA's NCEI
- 3-D Bathymetric Chart Activity: An introduction to the Nautical Chart
- "The very earliest rendition of a bathymetric map of an oceanic basin. Matthew Fontaine Maury 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
- History of Bathymetry and Bathymetric Charts Archived 2019-12-17 at the Wayback Machine
- Web Based Bathymetry viewer for North America, Europe and Australia