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80-689: The WSC has a unique structure as it flows poleward off the western coast of Spitsbergen. It is easiest to discuss horizontal movements and vertical movements of the WSC, separately. The WSC begins its movement in the Norwegian Sea where it branches off the Norwegian Atlantic Current and arrives at Spitsbergen's western coast, where it is guided by the bathymetric profile of the ocean floor surrounding Svalbard . Specifically, it tends to follow along steep continental shelves. The current

160-492: A three-dimensional representation of whatever the light pulses reflect off, giving an accurate representation of the surface characteristics. A LiDAR system usually consists of a laser , scanner, and GPS receiver. Airplanes and helicopters are the most commonly used platforms for acquiring LIDAR data over broad areas. One application of LiDAR is bathymetric LiDAR, which uses water-penetrating green light to also measure seafloor and riverbed elevations. ALB generally operates in

240-461: A body of water , called saline water (see also soil salinity ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure , governs physical characteristics like

320-588: A complex mixture of many different elements from different sources (not all from dissolved salts) in different molecular forms. The chemical properties of some of these forms depend on temperature and pressure. Many of these forms are difficult to measure with high accuracy, and in any case complete chemical analysis is not practical when analyzing multiple samples. Different practical definitions of salinity result from different attempts to account for these problems, to different levels of precision, while still remaining reasonably easy to use. For practical reasons salinity

400-530: A contour target through both an active and passive system." What this means is that airborne laser bathymetry also uses light outside the visible spectrum to detect the curves in underwater landscape. LiDAR (light detection and ranging) is, according to the National Oceanic and Atmospheric Administration , "a remote sensing method that uses light in the form of a pulsed laser to measure distances". These light pulses, along with other data, generate

480-469: A fan-like swath of typically 90 to 170 degrees across. The tightly packed array of narrow individual beams provides very high angular resolution and accuracy. In general, a wide swath, which is depth dependent, allows a boat to map more seafloor in less time than a single-beam echosounder by making fewer passes. The beams update many times per second (typically 0.1–50 Hz depending on water depth), allowing faster boat speed while maintaining 100% coverage of

560-490: A few percent (%). Physical oceanographers working in the abyssal ocean , however, are often concerned with precision and intercomparability of measurements by different researchers, at different times, to almost five significant digits . A bottled seawater product known as IAPSO Standard Seawater is used by oceanographers to standardize their measurements with enough precision to meet this requirement. Measurement and definition difficulties arise because natural waters contain

640-490: A great visual interpretation of coastal environments. The other method of satellite imaging, multi-spectral (MS) imaging, tends to divide the EM spectrum into a small number of bands, unlike its partner hyper-spectral sensors which can capture a much larger number of spectral bands. MS sensing is used more in the mapping of the seabed due to its fewer spectral bands with relatively larger bandwidths. The larger bandwidths allow for

720-440: A larger spectral coverage, which is crucial in the visual detection of marine features and general spectral resolution of the images acquired. High-density airborne laser bathymetry (ALB) is a modern, highly technical, approach to the mapping the seafloor. First developed in the 1960s and 1970s, ALB is a "light detection and ranging (LiDAR) technique that uses visible, ultraviolet, and near infrared light to optically remote sense

800-456: A measured density. Marine waters are those of the ocean, another term for which is euhaline seas . The salinity of euhaline seas is 30 to 35 ‰. Brackish seas or waters have salinity in the range of 0.5 to 29 ‰ and metahaline seas from 36 to 40 ‰. These waters are all regarded as thalassic because their salinity is derived from the ocean and defined as homoiohaline if salinity does not vary much over time (essentially constant). The table on

880-399: A one depth at a time procedure which required very low speed for accuracy. Greater depths could be measured using weighted wires deployed and recovered by powered winches. The wires had less drag and were less affected by current, did not stretch as much, and were strong enough to support their own weight to considerable depths. The winches allowed faster deployment and recovery, necessary when

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960-431: A regular or irregular grid of points connected into a surface). Historically, selection of measurements was more common in hydrographic applications while DTM construction was used for engineering surveys, geology, flow modeling, etc. Since c.  2003 –2005, DTMs have become more accepted in hydrographic practice. Satellites are also used to measure bathymetry. Satellite radar maps deep-sea topography by detecting

1040-438: A series of lines and points at equal intervals, called depth contours or isobaths (a type of contour line ). 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. Salinity#Definitions Salinity ( / s ə ˈ l ɪ n ɪ t i / ) is the saltiness or amount of salt dissolved in

1120-464: A wide range of salinities is euryhaline . Salts are expensive to remove from water, and salt content is an important factor in water use, factoring into potability and suitability for irrigation . Increases in salinity have been observed in lakes and rivers in the United States, due to common road salt and other salt de-icers in runoff. The degree of salinity in oceans is a driver of

1200-456: Is a combination of continuous remote imaging and spectroscopy producing a single set of data. Two examples of this kind of sensing are AVIRIS ( airborne visible/infrared imaging spectrometer ) and HYPERION. The application of HS sensors in regards to the imaging of the seafloor is the detection and monitoring of chlorophyll, phytoplankton, salinity, water quality, dissolved organic materials, and suspended sediments. However, this does not provide

1280-533: Is a photon-counting lidar that uses the return time of laser light pulses from the Earth's surface to calculate altitude of the surface. ICESat-2 measurements can be combined with ship-based sonar data to fill in gaps and improve precision of maps of shallow water. Mapping of continental shelf seafloor topography using remotely sensed data has applied a variety of methods to visualise the bottom topography. Early methods included hachure maps, and were generally based on

1360-505: Is a powerful tool for mapping shallow clear waters on continental shelves, and airborne laser bathymetry, using reflected light pulses, is also very effective in those conditions, and hyperspectral and multispectral satellite sensors can provide a nearly constant stream of benthic environmental information. Remote sensing techniques have been used to develop new ways of visualizing dynamic benthic environments from general geomorphological features to biological coverage. A bathymetric chart

1440-429: Is a type of isarithmic map that depicts the submerged bathymetry 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 maps display elevation above ground ( topography ) and are complementary to bathymetric charts. Bathymeric charts showcase depth using

1520-600: Is not a concern) may also use a digital terrain model and artificial illumination techniques to illustrate the depths being portrayed. The global bathymetry is sometimes combined with topography data to yield a global relief model . Paleobathymetry is the study of past underwater depths. Synonyms include seafloor mapping , seabed mapping , seafloor imaging and seabed imaging . Bathymetric measurements are conducted with various methods, from depth sounding , sonar and lidar techniques, to buoys and satellite altimetry . Various methods have advantages and disadvantages and

1600-520: Is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. Salinity distribution contributes to shape the oceanic circulation. Limnologists and chemists often define salinity in terms of mass of salt per unit volume, expressed in units of mg/L or g/L. It is implied, although often not stated, that this value applies accurately only at some reference temperature because solution volume varies with temperature. Values presented in this way are typically accurate to

1680-607: Is quite narrow and strong, having a width of roughly 100 kilometers and a maximum speed of 35 cm/s. At about 80° North latitude the WSC splits into two different sections, the Svalbard branch and the Yermak Branch. The Svalbard Branch continues to follow the continental shelf northeastward, and eventually sinks to an intermediate depth and is cyclonically recirculated throughout the Arctic, eventually being pushed out through

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1760-651: Is referred to as brine . Salinity is an ecological factor of considerable importance, influencing the types of organisms that live in a body of water. As well, salinity influences the kinds of plants that will grow either in a water body, or on land fed by a water (or by a groundwater ). A plant adapted to saline conditions is called a halophyte . A halophyte which is tolerant to residual sodium carbonate salinity are called glasswort or saltwort or barilla plants. Organisms (mostly bacteria) that can live in very salty conditions are classified as extremophiles , or halophiles specifically. An organism that can withstand

1840-466: Is sometimes referred to as chlorinity. Operationally, dissolved matter is defined as that which can pass through a very fine filter (historically a filter with a pore size of 0.45 μm, but later usually 0.2 μm). Salinity can be expressed in the form of a mass fraction , i.e. the mass of the dissolved material in a unit mass of solution. Seawater typically has a mass salinity of around 35 g/kg, although lower values are typical near coasts where rivers enter

1920-450: Is the process of creating an image that combines the geometric qualities with the characteristics of photographs. The result of this process is an orthoimage , a scale image which includes corrections made for feature displacement such as building tilt. These corrections are made through the use of a mathematical equation, information on sensor calibration, and the application of digital elevation models. An orthoimage can be created through

2000-727: Is the study of underwater depth of ocean floors ( seabed topography ), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography . The first recorded evidence of water depth measurements are from Ancient Egypt over 3000 years ago. Bathymetric charts (not to be confused with hydrographic charts ), are typically produced to support safety of surface or sub-surface navigation, and usually show seafloor relief or terrain as contour lines (called depth contours or isobaths ) and selected depths ( soundings ), and typically also provide surface navigational information. Bathymetric maps (a more general term where navigational safety

2080-470: Is usually related to the sum of masses of a subset of these dissolved chemical constituents (so-called solution salinity ), rather than to the unknown mass of salts that gave rise to this composition (an exception is when artificial seawater is created). For many purposes this sum can be limited to a set of eight major ions in natural waters, although for seawater at highest precision an additional seven minor ions are also included. The major ions dominate

2160-678: The East Greenland Current . The Yermak Branch moves northwesterly till about 81°N, and then it moves directly westward and eventually equatorward in the Return Atlantic Current. The Return Atlantic Current is directly east of the East Greenland Current. The high salinity and warm temperatures of the Return Atlantic Current compared to the cold temperatures and low salinities of the EGC contribute to

2240-529: The density and heat capacity of the water. A contour line of constant salinity is called an isohaline , or sometimes isohale . Salinity in rivers, lakes, and the ocean is conceptually simple, but technically challenging to define and measure precisely. Conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like sodium chloride , magnesium sulfate , potassium nitrate , and sodium bicarbonate which dissolve into ions. The concentration of dissolved chloride ions

2320-564: The hydrography is such that a possible cause of reduced circulation is the production of stratified oceans. In such cases, it is more difficult to subduct water through the thermohaline circulation. Not only is salinity a driver of ocean circulation, but changes in ocean circulation also affect salinity, particularly in the subpolar North Atlantic where from 1990 to 2010 increased contributions of Greenland meltwater were counteracted by increased northward transport of salty Atlantic waters. However, North Atlantic waters have become fresher since

2400-413: The world's ocean circulation , where density changes due to both salinity changes and temperature changes at the surface of the ocean produce changes in buoyancy, which cause the sinking and rising of water masses. Changes in the salinity of the oceans are thought to contribute to global changes in carbon dioxide as more saline waters are less soluble to carbon dioxide. In addition, during glacial periods,

2480-499: The 1960s. NOAA obtained an unclassified commercial version in the late 1970s and established protocols and standards. Data acquired with multibeam sonar have vastly increased understanding of the seafloor. The U.S. Landsat satellites of the 1970s and later the European Sentinel satellites, have provided new ways to find bathymetric information, which can be derived from satellite images. These methods include making use of

West Spitsbergen Current - Misplaced Pages Continue

2560-408: The 1980s. Titration with silver nitrate could be used to determine the concentration of halide ions (mainly chlorine and bromine ) to give a chlorinity . The chlorinity was then multiplied by a factor to account for all other constituents. The resulting 'Knudsen salinities' are expressed in units of parts per thousand (ppt or ‰ ). The use of electrical conductivity measurements to estimate

2640-600: The Atlantic Water core in the WSC is vertically upward then that would lead to warming of the Arctic Surface Water and the melting of more Arctic Sea Ice. Thus, this current topic is of high interest because an increase of heat flux out of the AW core will result in more Arctic Sea Ice melting. The second major topic being looked at is how this warming will affect methane gas release in the ocean seabed along

2720-754: The Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) and the Laser Airborne Depth Sounder (LADS). SHOALS was first developed to help the United States Army Corps of Engineers (USACE) in bathymetric surveying by a company called Optech in the 1990s. SHOALS is done through the transmission of a laser, of wavelength between 530 and 532 nm, from a height of approximately 200 m at speed of 60 m/s on average. High resolution orthoimagery (HRO)

2800-592: The Svalbard Branch, the Atlantic Water core of the WSC continues to sink as it meets more and more freshwater on its eastern route. It sinks fairly quickly to a depth greater than 100 meters by the time it reaches the Barents Sea because in Northern Svalbard there is quite a lot of freshwater run-off from fjords which adds to a deeper, less dense Arctic Surface Water and thus a deeper WSC. By

2880-410: The WSC and thus the WSC begins to sink underneath the Arctic Surface Water. At this point the WSC is still relatively warm and very saline. Thus, this allows the Atlantic Water in the WSC to be completely isolated from the surface waters. After the current splits into the Svalbard Branch and the Yermak Branch, the general sinking process described above still continues in the Svalbard Branch. However, in

2960-470: The WSC has increased by almost 1 °C in recent years. It has also been well documented that the Atlantic Water core temperature decreases as you move cyclonically around the Arctic. Thus, this means that heat is being lost to the surrounding water. As the temperature of the water is increased, more heat will be lost to the surrounding water as the WSC tracts around the Arctic Ocean. If the heat flux out of

3040-492: The WSC splits off from the Norwegian Atlantic Current it begins to enter very cold atmospheric conditions. The cold atmosphere is able to cool the surface water, and in some instances this water cools so much that some of the WSC water actually sinks due to its density increase, all the while holding its salinity constant. This is one element of the formation of the Lower Arctic Intermediate Water. As

3120-521: The Yermak Branch the WSC is not able to penetrate deep inside the Arctic Ocean because the zone it enters has very strong tidal mixing. This allows the Atlantic Water to mix with the Polar Waters, creating more of a homogeneous mixture of relatively warm and moderately saline water. This extends down to about 300 meters which is recognized as the bottom depth of the Return Atlantic Current. For

3200-463: The angle of each individual beam. The resulting sounding measurements are then processed either manually, semi-automatically or automatically (in limited circumstances) to produce a map of the area. As of 2010 a number of different outputs are generated, including a sub-set of the original measurements that satisfy some conditions (e.g., most representative likely soundings, shallowest in a region, etc.) or integrated digital terrain models (DTM) (e.g.,

3280-454: The atmosphere or surrounding waters and thus warmer waters will be transported into the Arctic. This could have profound impacts on sea-ice melting. The temperature of the WSC is highly variable. It often depends on atmospheric conditions which are highly variable in their own right. In general, however, the warmest core temperature of the Atlantic Water in the WSC is around 2.75 °C near Svalbard to 2.25 °C near Franz Josef Land to 1.0 °C north of

West Spitsbergen Current - Misplaced Pages Continue

3360-535: The cartographer's personal interpretation of limited available data. Acoustic mapping methods developed from military sonar images produced a more vivid picture of the seafloor. Further development of sonar based technology have allowed more detail and greater resolution, and ground penetrating techniques provide information on what lies below the bottom surface. Airborne and satellite data acquisition have made further advances possible in visualisation of underwater surfaces: high-resolution aerial photography and orthoimagery

3440-483: The combination of a number of photos of the same target. The target is photographed from a number of different angles to allow for the perception of the true elevation and tilting of the object. This gives the viewer an accurate perception of the target area. High resolution orthoimagery is currently being used in the 'terrestrial mapping program', the aim of which is to 'produce high resolution topography data from Oregon to Mexico'. The orthoimagery will be used to provide

3520-417: The composition of seawater. They can also be determined by making direct density measurements. A sample of seawater from most locations with a chlorinity of 19.37 ppt will have a Knudsen salinity of 35.00 ppt, a PSS-78 practical salinity of about 35.0, and a TEOS-10 absolute salinity of about 35.2 g/kg. The electrical conductivity of this water at a temperature of 15 °C is 42.9 mS/cm. On

3600-529: The continental margins in West Spitsbergen. There exists these gas hydrate stability zones where a small fluctuation in temperature could dissociate these hydrates and release methane gas bubbles that rise to the surface and are released into the atmosphere. Bathymetry Bathymetry ( / b ə ˈ θ ɪ m ə t r i / ; from Ancient Greek βαθύς ( bathús )  'deep' and μέτρον ( métron )  'measure')

3680-407: The current continues to move northward and reaches the continental shelf of western Svalbard it begins to encounter sea-ice. The sea-ice melts due to the warmth of the WSC, and thus a surface layer of very freshwater begins to exist. Winds mix the freshwater and the warm salty water of the WSC mix, creating some Arctic Surface Water. This Arctic Surface Water is now less dense than the Atlantic Water in

3760-400: The depth of the Svalbard Branch of the WSC. It is important to note that if the WSC encounters a significant amount of ice along the continental shelves of Spitsbergen, then the WSC advancing poleward will sink much faster, due to a greater amount of freshwater melt from the increased sea-ice. The ability to sink faster means more of the heat content of the WSC will be preserved and not lost to

3840-405: The depths measured were of several kilometers. Wire drag surveys continued to be used until the 1990s due to reliability and accuracy. This procedure involved towing a cable by two boats, supported by floats and weighted to keep a constant depth The wire would snag on obstacles shallower than the cable depth. This was very useful for finding navigational hazards which could be missed by soundings, but

3920-431: The different depths to which different frequencies of light penetrate the water. When water is clear and the seafloor is sufficiently reflective, depth can be estimated by measuring the amount of reflectance observed by a satellite and then modeling how far the light should penetrate in the known conditions. The Advanced Topographic Laser Altimeter System (ATLAS) on NASA's Ice, Cloud, and land Elevation Satellite 2 (ICESat-2)

4000-564: The existence of the East Greenland Polar Front a result of the strong gradient in both salinity and temperature. There is a current that splits off from the Yermak Branch and flows towards the Northeast at a higher latitude. This current is not well understood in the literature, and thus more information is needed. It is believed this current loops back into the Svalbard Branch further along in its track eastward. After

4080-491: The form of silicic acid , which usually appears as a neutral molecule in the pH range of most natural waters, may also be included for some purposes (e.g., when salinity/density relationships are being investigated). The term 'salinity' is, for oceanographers, usually associated with one of a set of specific measurement techniques. As the dominant techniques evolve, so do different descriptions of salinity. Salinities were largely measured using titration -based techniques before

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4160-445: The form of a pulse of non-visible light being emitted from a low-flying aircraft and a receiver recording two reflections from the water. The first of which originates from the surface of the water, and the second from the seabed. This method has been used in a number of studies to map segments of the seafloor of various coastal areas. There are various LIDAR bathymetry systems that are commercially accessible. Two of these systems are

4240-411: The global scale, it is extremely likely that human-caused climate change has contributed to observed surface and subsurface salinity changes since the 1950s, and projections of surface salinity changes throughout the 21st century indicate that fresh ocean regions will continue to get fresher and salty regions will continue to get saltier. Salinity is serving as a tracer of different masses. Surface water

4320-421: The inorganic composition of most (but by no means all) natural waters. Exceptions include some pit lakes and waters from some hydrothermal springs . The concentrations of dissolved gases like oxygen and nitrogen are not usually included in descriptions of salinity. However, carbon dioxide gas, which when dissolved is partially converted into carbonates and bicarbonates , is often included. Silicon in

4400-412: The ionic content of seawater led to the development of the scale called the practical salinity scale 1978 (PSS-78). Salinities measured using PSS-78 do not have units. The suffix psu or PSU (denoting practical salinity unit ) is sometimes added to PSS-78 measurement values. The addition of PSU as a unit after the value is "formally incorrect and strongly discouraged". In 2010 a new standard for

4480-411: The locality and tidal regime. 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. Another form of mapping

4560-409: The measured conductivity at 5 °C might only be in the range of 50–80 μS/cm. Direct density measurements are also used to estimate salinities, particularly in highly saline lakes . Sometimes density at a specific temperature is used as a proxy for salinity. At other times an empirical salinity/density relationship developed for a particular body of water is used to estimate the salinity of samples from

4640-474: The measurement of ocean depth through depth sounding . Early techniques used pre-measured heavy rope or cable lowered over a ship's side. 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

4720-503: The minimum volume transport occurred in August (~5 sverdrups). One big issue in deriving these mass volume transports is the fact that in some areas of the WSC there exist counter-currents, which make it difficult to gauge how much volume is actually being transported. Current research on the WSC focuses in on two areas: heat content and methane gas release. It has been well documented that the Atlantic Water core temperature associated with

4800-573: The natural system more than any physical driver. Marine topographies include coastal and oceanic landforms ranging from coastal estuaries and shorelines to continental shelves and coral reefs . Further out in the open ocean, they include underwater and deep sea features such as ocean rises and seamounts . The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes , oceanic trenches , submarine canyons , oceanic plateaus and abyssal plains . Originally, bathymetry involved

4880-473: The new Siberian Islands. Salinity in this warm core is often greater than 34.95 psu . Ocean temperature values for the beginning of the WSC are typically between 6 and 8 °C with salinities between 35.1 and 35.3 psu. Water mass transport in the WSC at around 78.83° North varies strongly on an annual time scale. Fahbrach et al. showed that the maximum volume transport (~20 sverdrups ) occurred in February and

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4960-422: The ocean. Rivers and lakes can have a wide range of salinities, from less than 0.01 g/kg to a few g/kg, although there are many places where higher salinities are found. The Dead Sea has a salinity of more than 200 g/kg. Precipitation typically has a TDS of 20 mg/kg or less. Whatever pore size is used in the definition, the resulting salinity value of a given sample of natural water will not vary by more than

5040-454: The ocean. These shapes are obvious along coastlines, but they occur also in significant ways underwater. The effectiveness of marine habitats is partially defined by these shapes, including the way they interact with and shape ocean currents , and the way sunlight diminishes when these landforms occupy increasing depths. Tidal networks depend on the balance between sedimentary processes and hydrodynamics however, anthropogenic influences can impact

5120-491: The order of 1%. Limnologists also use electrical conductivity , or "reference conductivity", as a proxy for salinity. This measurement may be corrected for temperature effects, and is usually expressed in units of μS/cm . A river or lake water with a salinity of around 70 mg/L will typically have a specific conductivity at 25 °C of between 80 and 130 μS/cm. The actual ratio depends on the ions present. The actual conductivity usually changes by about 2% per degree Celsius, so

5200-401: The photographic data for these regions. The earliest known depth measurements were made about 1800 BCE by Egyptians by probing with a pole. Later a weighted line was used, with depths marked off at intervals. This process was known as sounding. Both these methods were limited by being spot depths, taken at a point, and could easily miss significant variations in the immediate vicinity. Accuracy

5280-598: The properties of seawater called the thermodynamic equation of seawater 2010 ( TEOS-10 ) was introduced, advocating absolute salinity as a replacement for practical salinity, and conservative temperature as a replacement for potential temperature . This standard includes a new scale called the reference composition salinity scale . Absolute salinities on this scale are expressed as a mass fraction, in grams per kilogram of solution. Salinities on this scale are determined by combining electrical conductivity measurements with other information that can account for regional changes in

5360-417: The research of the world's oceans. The development of multibeam systems made it possible to obtain depth information across the width of the sonar swath, to higher resolutions, and with precise position and attitude data for the transducers, made it possible to get multiple high resolution soundings from a single pass. The US Naval Oceanographic Office developed a classified version of multibeam technology in

5440-650: The right, modified from Por (1972), follows the "Venice system" (1959). In contrast to homoiohaline environments are certain poikilohaline environments (which may also be thalassic ) in which the salinity variation is biologically significant. Poikilohaline water salinities may range anywhere from 0.5 to greater than 300 ‰. The important characteristic is that these waters tend to vary in salinity over some biologically meaningful range seasonally or on some other roughly comparable time scale. Put simply, these are bodies of water with quite variable salinity. Highly saline water, from which salts crystallize (or are about to),

5520-616: The same role for ocean waterways. Coastal bathymetry data is available from NOAA's National Geophysical Data Center (NGDC), which is now merged into National Centers for Environmental Information . Bathymetric data is usually referenced to tidal vertical datums . For deep-water bathymetry, this is typically Mean Sea Level (MSL), but most data used for nautical charting is referenced to Mean Lower Low Water (MLLW) in American surveys, and Lowest Astronomical Tide (LAT) in other countries. Many other datums are used in practice, depending on

5600-442: The sea floor started by using sound waves , contoured into isobaths and early bathymetric charts of shelf topography. These provided the first insight into seafloor morphology, though mistakes were made due to horizontal positional accuracy and imprecise depths. Sidescan sonar was developed in the 1950s to 1970s and could be used to create an image of the bottom, but the technology lacked the capacity for direct depth measurement across

5680-462: The seafloor is through the use of satellites. The satellites are equipped with hyper-spectral and multi-spectral sensors which are used to provide constant streams of images of coastal areas providing a more feasible method of visualising the bottom of the seabed. The data-sets produced by hyper-spectral (HS) sensors tend to range between 100 and 200 spectral bands of approximately 5–10 nm bandwidths. Hyper-spectral sensing, or imaging spectroscopy,

5760-449: The seafloor. Attitude sensors allow for the correction of the boat's roll and pitch on the ocean surface, and a gyrocompass provides accurate heading information to correct for vessel yaw . (Most modern MBES systems use an integrated motion-sensor and position system that measures yaw as well as the other dynamics and position.) A boat-mounted Global Positioning System (GPS) (or other Global Navigation Satellite System (GNSS)) positions

5840-594: The side of a boat, "pinging" a beam of sound downward at the seafloor or from remote sensing LIDAR or LADAR systems. 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, multibeam echosounders (MBES) are typically used, which use hundreds of very narrow adjacent beams (typically 256) arranged in

5920-401: The soundings with respect to the surface of the earth. Sound speed profiles (speed of sound in water as a function of depth) 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

6000-402: The specific method used depends upon the scale of the area under study, financial means, desired measurement accuracy, and additional variables. Despite modern computer-based research, the ocean seabed in many locations is less measured than the topography of Mars . Seabed topography (ocean topography or marine topography) refers to the shape of the land ( topography ) when it interfaces with

6080-565: 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. In the United States the United States Army Corps of Engineers performs or commissions most surveys of navigable inland waterways, while the National Oceanic and Atmospheric Administration (NOAA) performs

6160-527: The time this water recirculates to the Beaufort Gyre , the Atlantic core of the WSC is 400 to 500 meters deep. Unlike the Yermak Branch and the Return Atlantic Current, the Svalbard Branch is able to retain a strong Atlantic Water chemical signal whereas the Yermak Branch and the Return Atlantic Current carry a very weak Atlantic Water signal. The Atlantic Water core temperature is a direct reflection of

6240-423: The width of the scan. In 1957, Marie Tharp , working with Bruce Charles Heezen , created the first three-dimensional physiographic map of the world's ocean basins. Tharp's discovery was made at the perfect time. It was one of many discoveries that took place near the same time as the invention of the computer . Computers, with their ability to compute large quantities of data, have made research much easier, include

6320-460: Was also affected by water movement–current could swing the weight from the vertical and both depth and position would be affected. This was a laborious and time-consuming process and was strongly affected by weather and sea conditions. There were significant improvements with the voyage of HMS Challenger in the 1870s, when similar systems using wires and a winch were used for measuring much greater depths than previously possible, but this remained

6400-414: Was limited to relatively shallow depths. Single-beam echo sounders were used from the 1920s-1930s to measure the distance of the seafloor directly below a vessel at relatively close intervals along the line of travel. By running roughly parallel lines, data points could be collected at better resolution, but this method still left gaps between the data points, particularly between the lines. The mapping of

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