Bathymetry
Bathymetry is the scientific study of the depth and shape of underwater surfaces, such as those found on ocean and lake floors. It serves as the aquatic counterpart to topography, where land features are measured and mapped. Bathymetric maps are essential for various applications, most notably in creating nautical charts that ensure safe navigation for mariners by identifying underwater hazards. This field is a vital component of hydrography, which encompasses the study of water bodies' physical characteristics, including their depths, currents, and biological environments.
Historically, bathymetric techniques have evolved from simple methods like weighted ropes to advanced technologies such as echo sounding and multibeam sonar, which provide precise measurements and detailed maps of seafloor features. These modern methods allow scientists to gather comprehensive data about underwater landforms, including continental slopes and trenches, and to monitor changes over time due to environmental factors. The information gleaned from bathymetric studies plays a critical role in managing marine resources, assessing environmental impacts, and understanding oceanographic processes, contributing to both navigational safety and ecological research.
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Bathymetry
Bathymetry is the study of the depth of ocean or lake floors. Put another way, bathymetry can be viewed as the underwater equivalent of topography. Where topographic maps illustrate the shape and elevation of features on land, bathymetric maps show the shape and depth of features on the ocean or lake floors. These maps are created through bathymetric surveys, which use various scientific methods to measure the depth and map the underwater features of a given body of water. Bathymetry is a key component of the broader scientific field of hydrography. Bathymetric data has many practical uses. Most important, this data is used in the creation of nautical charts upon which mariners rely for safe travel on waterways. It also used in the study of biological oceanography and the effects of climate change.
Background
Bathymetry is an important element of a broader field of marine science known as hydrography. Hydrography is the study of the physical features of oceans, seas, lakes, and other bodies of water, as well as those of adjacent coastal areas. It is also concerned with predicting how these features will change over time. Hydrography has different uses depending upon the field in which it is applied. In oceanography, hydrography refers to the description and mapping of a body of water’s physical characteristics, including its salt content, temperature, and chemical composition. In geography and geology, hydrography is used to define water surfaces and the nature of water flow between different bodies of water. In nautical charting, hydrography serves as a means of identifying potentially dangerous underwater features such as rocks, shallow depths, and shipwrecks that must be avoided to ensure safe navigation.
Hydrographers conduct surveys in order to measure the depth and accurately map the underwater landscape of bodies of water. There are four major components of a hydrographic survey: positioning, water depth, features, and seafloor characteristics. Positioning is the precise location where a survey is conducted in regards to latitude and longitude. Water depth is a measurement of the depth of a body of water from the surface to the floor. Features include any underwater hazards that may interfere with safe navigation. Seafloor characteristics are a description of the type of bottom a body of water has, i.e., sand, mud, bedrock, or coral reef.
The data gathered during hydrographic surveys is ultimately used to produce or update nautical charts. Nautical charts are maps that illustrate the various features of a body of water. These charts are a critical tool for mariners who travel the world’s waterways. More specifically, hydrographic surveys and nautical charts help ensure safe navigation, aid in the environmental management of coastal areas, reveal changes to bathymetry and seafloor characteristics, and provide updated information that can lead to reduced insurance costs for commercial and private shipping companies, marinas, and port and harbor authorities.
Historically, the study of hydrography can be traced back as far as the Mediterranean cultures of the ancient Cretans and Phoenicians. In the United States, hydrographic study got its start when President Thomas Jefferson founded the Survey of the Coast in 1807. After publishing its first chart in 1835, the Survey of the Coast eventually evolved into the National Oceanic and Atmospheric Administration’s (NOAA) National Ocean Service.
Overview
Bathymetry is the study and mapping of sea or lake floors. The term refers to the measurement of the depth of water in oceans, seas, lakes, or other bodies of water. Bathymetry can also be described as a sort of submarine topography in that bathymetric maps illustrate the contours of a sea or lake floor in much the same way that topographic maps detail the shape and elevation of geographic features on land. Bathymetry and bathymetric data are crucial to the broader study of hydrography, offering key information about seafloors and their distinct features.
Scientists have been studying bathymetry since antiquity. Ancient researchers carried out bathymetric studies at sea by throwing a weighted rope overboard and noting how much rope it took to reach the seafloor. This method allowed for a rough measurement of the depth of a body of water in a specific location, but was frequently inaccurate. Currents often shifted the ropes and prevented them from traveling straight down to the seafloor. This method also meant that it would take a tremendous amount of time and effort to map out the entire seafloor. As a result, early attempts at bathymetry often amounted to little more than educated estimates.
Modern bathymetry is much more refined and reliable. Most bathymetric surveys are now conducted using a method known as echo sounding. Echo sounding is a form of sonar in which researches transmit sound waves into a body of water to measure its depth and map the seafloor. While standard echo sounding is generally effective, it does have some limitations. Because it is performed on board a ship, the movement of the vessel can lead to slightly inaccurate depth measurements. The presence of underwater lifeforms can also interfere with sound waves as they move through the water. Factors like temperature, salinity, and water pressure can also cause interference. In order to avoid these problems, many bathymetric surveys are conducted using multibeam echo sounders. Multibeam echo sounders emit sound pulses through numerous small beams. This approach makes it possible to achieve greater resolution and correct for movement of the vessel. Multibeam echo sounders and other advanced technologies allow for the most accurate and informative bathymetric surveys possible.
Through bathymetric surveys, scientists can learn a great deal about water depths and submarine landforms like continental slopes, seamounts, abyssal plains, and trenches. Studying these features is just as important a part of bathymetry as measuring water depth. The data yielded from bathymetric research is remarkably useful. Among other things, it can be used to help create or update nautical charts or manage commercial fisheries. It can also be used to aid environmental management tasks, determine maritime boundaries, assess the potential of alternative energy sources, learn more about ocean currents and coastal processes, and assess environmental considerations for marine geology resource management.
Bibliography
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“Bathymetry.” Ocean Tracks, 2020, oceantracks.org/library/oceanographic-factors/bathymetry. Accessed 3 Sept. 2020.
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“What Is Bathymetry?” National Ocean Service, 2020, oceanservice.noaa.gov/facts/bathymetry.html. Accessed 3 Sept. 2020.
“What Is Hydrography?” National Ocean Service, 2020, oceanservice.noaa.gov/facts/hydrography.html. Accessed 3 Sept. 2020.