1.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
2.
Terrain
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Terrain or relief is the vertical and horizontal dimension of the land surface. When relief is described underwater, the term bathymetry is used, the Latin Word Terra, is Earth. Terrain is used as a term in physical geography, referring to the lay of the land. This is usually expressed in terms of the elevation, slope, terrain affects surface water flow and distribution. Over a large area, it can affect weather and climate patterns, complex arrays of relief data are used as input parameters for hydrology transport models to allow prediction of river water quality. Understanding terrain also supports soil conservation, especially in agriculture, contour ploughing is an established practice enabling sustainable agriculture on sloping land, it is the practice of ploughing along lines of equal elevation instead of up and down a slope. Terrain is militarily critical because it determines the ability of armed forces to take and hold areas, an understanding of terrain is basic to both defensive and offensive strategy. Terrain is important in determining weather patterns, two areas geographically close to each other may differ radically in precipitation levels or timing because of elevation differences or a rain shadow effect. Precise knowledge of terrain is vital in aviation, especially for low-flying routes and maneuvers, terrain will also affect range and performance of radars and terrestrial radio navigation systems. Furthermore, a hilly or mountainous terrain can strongly impact the implementation of a new aerodrome, relief refers specifically to the quantitative measurement of vertical elevation change in a landscape. It is the difference between maximum and minimum elevations within an area, usually of limited extent. The relief of a landscape can change with the size of the area over which it is measured, making the definition of the scale over which it is measured very important. Because it is related to the slope of surfaces within the area of interest and to the gradient of any streams present, the relief of a landscape is a useful metric in the study of the Earths surface. Relief energy, which may be defined inter alia as the height range in a regular grid, is essentially an indication of the ruggedness or relative height of the terrain. Geomorphology is in part the study of the formation of terrain or topography. Terrain is formed by intersecting processes, Geological processes, Migration of tectonic plates, faulting and folding, volcanic eruptions, erosional processes, water and wind erosion, landslides. Tectonic processes such as orogenies cause land to be elevated, land surface parameters are quantitative measures of various morphometric properties of a surface. The most common examples are used to derive slope or aspect of a terrain or curvatures at each location and these measures can also be used to derive hydrological parameters that reflect flow/erosion processes
3.
National Centers for Environmental Information
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National Centers for Environmental Information, headquartered in Asheville, North Carolina, is the worlds largest active archive of environmental data. In 2015 it was established from the merger of the National Climatic Data Center, the National Geophysical Data Center, the current director is Thomas R. Karl, who was the director of NCDC before merger. The establishment of NCEI was rooted in the increase in the demand for environmental data. The transition is expected to finish beyond 2020, while at the meantime none of the existing products, NOAA Central Library Climate Prediction Center Environmental data rescue National Severe Storms Laboratory State of the Climate Storm Prediction Center National Centers for Environmental Information
4.
Seabed
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The seabed is the bottom of the ocean. Most of the oceans have a structure, created by common physical phenomena, mainly from tectonic movement. The mid-ocean ridge, as its name implies, is a rise through the middle of all the oceans. Typically a rift runs along the edge of this ridge, along tectonic plate edges there are typically oceanic trenches – deep valleys, created by the mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench. Hotspot volcanic island ridges are created by volcanic activity, erupting periodically, in areas with volcanic activity and in the oceanic trenches there are hydrothermal vents – releasing high pressure and extremely hot water and chemicals into the typically freezing water around it. Deep ocean water is divided into layers or zones, each with features of salinity, pressure, temperature and marine life. Lying along the top of the plain is the abyssal zone. The hadal zone – which includes the oceanic trenches, lies between 6, 000–11,000 metres and is the deepest oceanic zone, the acronym mbsf meaning meters below the seafloor is a convention used for depths below the seafloor. Benthos is the community of organisms which live on, in, or near the seabed and this community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths. The benthic zone is the region on, in and immediately above the seabed, including the sediment surface. Benthos generally live in relationship with the substrate bottom. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, each area of the seabed has typical features such as common soil composition, typical topography, salinity of water layers above it, marine life, magnetic direction of rocks, and sedimentation. Seabed topography is flat where sedimentation is heavy and covers the tectonic features, marine life is abundant in the deep sea, especially around hydrothermal vents. Large deep sea communities of life have been discovered around black and white smokers—vents emitting chemicals toxic to humans. This marine life receives its energy both from the temperature difference and from chemosynthesis by bacteria. Brine pools are another seabed feature, usually connected to cold seeps, the seabed has been explored by submersibles such as Alvin and, to some extent, scuba divers with special equipment. The process that adds new material to the ocean floor is seafloor spreading. In recent years satellite images show a very clear mapping of the seabed, some childrens play songs include elements such as Theres a hole at the bottom of the sea, or A sailor went to sea
5.
Topography
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Topography is the study of the shape and features of the surface of the Earth and other observable astronomical objects including planets, moons, and asteroids. The topography of an area could refer to the shapes and features themselves. This field of geoscience and planetary science is concerned with detail in general, including not only relief but also natural and artificial features. This meaning is common in the United States, where topographic maps with elevation contours have made topography synonymous with relief. The older sense of topography as the study of place still has currency in Europe, topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms. This is also known as geomorphometry, in modern usage, this involves generation of elevation data in digital form. It is often considered to include the representation of the landform on a map by a variety of techniques, including contour lines, hypsometric tints. The term topography originated in ancient Greece and continued in ancient Rome, the word comes from the Greek τόπος and -γραφία. In classical literature this refers to writing about a place or places, in Britain and in Europe in general, the word topography is still sometimes used in its original sense. Detailed military surveys in Britain were called Ordnance Surveys, and this term was used into the 20th century as generic for topographic surveys, the earliest scientific surveys in France were called the Cassini maps after the family who produced them over four generations. The term topographic surveys appears to be American in origin, the earliest detailed surveys in the United States were made by the “Topographical Bureau of the Army, ” formed during the War of 1812, which became the Corps of Topographical Engineers in 1838. In the 20th century, the term started to be used to describe surface description in other fields where mapping in a broader sense is used. An objective of topography is to determine the position of any feature or more generally any point in terms of both a horizontal coordinate system such as latitude, longitude, and altitude, identifying features, and recognizing typical landform patterns are also part of the field. There are a variety of approaches to studying topography, which method to use depend on the scale and size of the area under study, its accessibility, and the quality of existing surveys. Work on one of the first topographic maps was begun in France by Giovanni Domenico Cassini, in areas where there has been an extensive direct survey and mapping program, the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data. This data must often be cleaned to eliminate discrepancies between surveys, but it forms a valuable set of information for large-scale analysis. The original American topographic surveys involved not only recording of relief, remote sensing is a general term for geodata collection at a distance from the subject area. Besides their role in photogrammetry, aerial and satellite imagery can be used to identify and delineate terrain features, certainly they have become more and more a part of geovisualization, whether maps or GIS systems
6.
Greek language
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Greek is an independent branch of the Indo-European family of languages, native to Greece and other parts of the Eastern Mediterranean. It has the longest documented history of any living language, spanning 34 centuries of written records and its writing system has been the Greek alphabet for the major part of its history, other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic and many other writing systems. Together with the Latin texts and traditions of the Roman world, during antiquity, Greek was a widely spoken lingua franca in the Mediterranean world and many places beyond. It would eventually become the official parlance of the Byzantine Empire, the language is spoken by at least 13.2 million people today in Greece, Cyprus, Italy, Albania, Turkey, and the Greek diaspora. Greek roots are used to coin new words for other languages, Greek. Greek has been spoken in the Balkan peninsula since around the 3rd millennium BC, the earliest written evidence is a Linear B clay tablet found in Messenia that dates to between 1450 and 1350 BC, making Greek the worlds oldest recorded living language. Among the Indo-European languages, its date of earliest written attestation is matched only by the now extinct Anatolian languages, the Greek language is conventionally divided into the following periods, Proto-Greek, the unrecorded but assumed last ancestor of all known varieties of Greek. The unity of Proto-Greek would have ended as Hellenic migrants entered the Greek peninsula sometime in the Neolithic era or the Bronze Age, Mycenaean Greek, the language of the Mycenaean civilisation. It is recorded in the Linear B script on tablets dating from the 15th century BC onwards, Ancient Greek, in its various dialects, the language of the Archaic and Classical periods of the ancient Greek civilisation. It was widely known throughout the Roman Empire, after the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, Medieval Greek, also known as Byzantine Greek, the continuation of Koine Greek in Byzantine Greece, up to the demise of the Byzantine Empire in the 15th century. Much of the written Greek that was used as the language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine. Modern Greek, Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period and it is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it. In the modern era, the Greek language entered a state of diglossia, the historical unity and continuing identity between the various stages of the Greek language is often emphasised. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language and it is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English, Greek is spoken by about 13 million people, mainly in Greece, Albania and Cyprus, but also worldwide by the large Greek diaspora. Greek is the language of Greece, where it is spoken by almost the entire population
7.
Hydrography
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The origins of hydrography lay in the making of charts to aid navigation, by individual mariners as they navigated into new waters. These were usually the property, even closely held secrets. National organizations, particularly navies, realized that the collection, systematization and distribution of this gave it great organizational. Thus were born dedicated national hydrographic organizations for the collection, organization, publication and distribution of hydrography incorporated into charts, prior to the establishment of the United Kingdom Hydrographic Office, Royal Navy captains were responsible for the provision of their own charts. In practice this meant that ships often sailed with inadequate information for safe navigation, and that when new areas were surveyed, the Admiralty appointed Alexander Dalrymple as Hydrographer in 1795, with a remit to gather and distribute charts to HM Ships. Within a year existing charts from the two centuries had been collated, and the first catalogue published. The first chart produced under the direction of the Admiralty, was a chart of Quiberon Bay in Brittany, under Captain Thomas Hurd the department received its first professional guidelines and the first catalogues were published and made available to the public and to other nations as well. In 1829, Rear-Admiral Sir Francis Beaufort, as Hydrographer, developed the eponymous Scale, and introduced the first official tide tables in 1833, the word hydrography comes from the Ancient Greek ὕδωρ, water and γράφω, to write. The science of oceanography is, in part, an outgrowth of classical hydrography, in many respects the data are interchangeable, but marine hydrographic data will be particularly directed toward marine navigation and safety of that navigation. Marine resource exploration and exploitation is a significant application of hydrography, hydrographical measurements include the tidal, current and wave information of physical oceanography. Bottom measurements also include collection of the nature of the bottom as it pertains to effective anchoring, unlike oceanography, hydrography will include shore features, natural and manmade, that aid in navigation. Hydrography, mostly for reasons of safety, adopted a number of conventions that have affected its portrayal of the data on nautical charts, the former are the mariners tools to avoid accident. The latter are best representations of the seabed, as in a topographic map, for scientific. Trends in hydrographic practice since c, 2003–2005 have led to a narrowing of this difference, with many more hydrographic offices maintaining best observed databases, and then making navigationally safe products as required. This has been coupled with a preference for multi-use surveys, so that the data collected for nautical charting purposes can also be used for bathymetric portrayal. For instance, if there is an area that can not be reached because it is surrounded by shallow water. The color filled areas that show different ranges of water are not the equivalent of contours on a topographic map since they are often drawn seaward of the actual shallowest depth portrayed. A bathymetric chart does show marine topology accurately, details covering the above limitations can be found in Part 1 of Bowditchs American Practical Navigator
8.
Contour line
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A contour line of a function of two variables is a curve along which the function has a constant value. It is a cross-section of the graph of the function f parallel to the x, y plane. In cartography, a contour line joins points of elevation above a given level. A contour map is a map illustrated with contour lines, for example a map, which thus shows valleys and hills. The contour interval of a map is the difference in elevation between successive contour lines. More generally, a line for a function of two variables is a curve connecting points where the function has the same particular value. The gradient of the function is always perpendicular to the contour lines, when the lines are close together the magnitude of the gradient is large, the variation is steep. A level set is a generalization of a line for functions of any number of variables. Contour lines are curved, straight or a mixture of lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these contours allows map readers to infer relative gradient of a parameter, in the latter case, the method of interpolation affects the reliability of individual isolines and their portrayal of slope, pits and peaks. Contour lines are given specific names beginning iso- according to the nature of the variable being mapped. Specific names are most common in meteorology, where multiple maps with different variables may be viewed simultaneously, the prefix iso- can be replaced with isallo- to specify a contour line connecting points where a variable changes at the same rate during a given time period. The words isoline and isarithm are general terms covering all types of contour line, an isogon is a contour line for a variable which measures direction. In meteorology and in geomagnetics, the term isogon has specific meanings which are described below, an isocline is a line joining points with equal slope. In population dynamics and in geomagnetics, the terms isocline and isoclinic line have specific meanings which are described below, equidistant is a line of equal distance from a given point, line, polyline. In geography, the word isopleth is used for lines that depict a variable which cannot be measured at a point. An example is population density, which can be calculated by dividing the population of a district by the surface area of that district. Each calculated value is presumed to be the value of the variable at the centre of the area, the idea of an isopleth map can be compared with that of a choropleth map
9.
Navigation
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Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another. The field of navigation includes four categories, land navigation, marine navigation, aeronautic navigation. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks, all navigational techniques involve locating the navigators position compared to known locations or patterns. Navigation, in a sense, can refer to any skill or study that involves the determination of position and direction. In this sense, navigation includes orienteering and pedestrian navigation, for information about different navigation strategies that people use, visit human navigation. In the European medieval period, navigation was considered part of the set of seven mechanical arts, early Pacific Polynesians used the motion of stars, weather, the position of certain wildlife species, or the size of waves to find the path from one island to another. Maritime navigation using scientific instruments such as the mariners astrolabe first occurred in the Mediterranean during the Middle Ages, the perfecting of this navigation instrument is attributed to Portuguese navigators during early Portuguese discoveries in the Age of Discovery. Open-seas navigation using the astrolabe and the compass started during the Age of Discovery in the 15th century, the Portuguese began systematically exploring the Atlantic coast of Africa from 1418, under the sponsorship of Prince Henry. In 1488 Bartolomeu Dias reached the Indian Ocean by this route, in 1492 the Spanish monarchs funded Christopher Columbuss expedition to sail west to reach the Indies by crossing the Atlantic, which resulted in the Discovery of America. In 1498, a Portuguese expedition commanded by Vasco da Gama reached India by sailing around Africa, soon, the Portuguese sailed further eastward, to the Spice Islands in 1512, landing in China one year later. The fleet of seven ships sailed from Sanlúcar de Barrameda in Southern Spain in 1519, crossed the Atlantic Ocean, some ships were lost, but the remaining fleet continued across the Pacific making a number of discoveries including Guam and the Philippines. By then, only two galleons were left from the original seven, the Victoria led by Elcano sailed across the Indian Ocean and north along the coast of Africa, to finally arrive in Spain in 1522, three years after its departure. The Trinidad sailed east from the Philippines, trying to find a path back to the Americas. He arrived in Acapulco on October 8,1565, the term stems from 1530s, from Latin navigationem, from navigatus, pp. of navigare to sail, sail over, go by sea, steer a ship, from navis ship and the root of agere to drive. Roughly, the latitude of a place on Earth is its angular distance north or south of the equator, latitude is usually expressed in degrees ranging from 0° at the Equator to 90° at the North and South poles. The height of Polaris in degrees above the horizon is the latitude of the observer, similar to latitude, the longitude of a place on Earth is the angular distance east or west of the prime meridian or Greenwich meridian. Longitude is usually expressed in degrees ranging from 0° at the Greenwich meridian to 180° east and west, sydney, for example, has a longitude of about 151° east. New York City has a longitude of 74° west, for most of history, mariners struggled to determine longitude
10.
Digital elevation model
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A digital elevation model is a digital model or 3D representation of a terrains surface — commonly for a planet, moon, or asteroid — created from terrain elevation data. There is no usage of the terms digital elevation model, digital terrain model. In most cases the term digital surface model represents the earths surface, in contrast to a DSM, the digital terrain model represents the bare ground surface without any objects like plants and buildings. DEM is often used as a term for DSMs and DTMs. Other definitions equalise the terms DEM and DTM, or define the DEM as a subset of the DTM, there are also definitions which equalise the terms DEM and DSM. On the Web definitions can be found which define DEM as a regularly spaced GRID, most of the data providers use the term DEM as a generic term for DSMs and DTMs. All datasets which are captured with satellites, airplanes or other flying platforms are originally DSMs and it is possible to compute a DTM from high resolution DSM datasets with complex algorithms. In the following the term DEM is used as a term for DSMs and DTMs. A DEM can be represented as a raster or as a vector-based triangular irregular network, the TIN DEM dataset is also referred to as a primary DEM, whereas the Raster DEM is referred to as a secondary DEM. The DEM could be acquired through techniques such as photogrammetry, lidar, IfSAR, land surveying, DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying. DEMs are used often in information systems, and are the most common basis for digitally produced relief maps. Mappers may prepare digital elevation models in a number of ways, the SPOT1 satellite provided the first usable elevation data for a sizeable portion of the planets landmass, using two-pass stereoscopic correlation. The HRS instrument on SPOT5 has acquired over 100 million square kilometers of stereo pairs, older methods of generating DEMs often involve interpolating digital contour maps that may have been produced by direct survey of the land surface. This method is used in mountain areas, where interferometry is not always satisfactory. Note that contour line data or any other sampled elevation datasets are not DEMs, a DEM implies that elevation is available continuously at each location in the study area. The quality of a DEM is a measure of how accurate elevation is at each pixel, the limitation with the GTOPO30 and SRTM datasets is that they cover continental landmasses only, and SRTM does not cover the polar regions and has mountain and desert no data areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface — quite often tree tops, so, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar. Submarine elevation data is generated using ship-mounted depth soundings, when land topography and bathymetry is combined, a truly Global Relief Model is obtained
11.
Ocean
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An ocean is a body of saline water that composes much of a planets hydrosphere. On Earth, an ocean is one of the major divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, the word sea is often used interchangeably with ocean in American English but, strictly speaking, a sea is a body of saline water partly or fully enclosed by land. The ocean contains 97% of Earths water, and oceanographers have stated that less than 5% of the World Ocean has been explored, the total volume is approximately 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the component of Earths hydrosphere, it is integral to all known life, forms part of the carbon cycle. The world ocean is the habitat of 230,000 known species, but because much of it is unexplored, the origin of Earths oceans remains unknown, oceans are thought to have formed in the Hadean period and may have been the impetus for the emergence of life. Extraterrestrial oceans may be composed of water or other elements and compounds, the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many planets and natural satellites, notably. The Solar Systems giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of water within a circumstellar habitable zone. Ocean planets are a type of planet with a surface completely covered with liquid. The concept of Ōkeanós has an Indo-European connection, Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases, though generally described as several separate oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This concept of a body of water with relatively free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, Oceans are fringed by smaller, adjoining bodies of water such as seas, gulfs, bays, bights, and straits. The Mid-Oceanic Ridge of the World are connected and form the Ocean Ridge, the continuous mountain range is 65,000 km long, and the total length of the oceanic ridge system is 80,000 km long
12.
Depth sounding
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Depth sounding refers to the act of measuring depth. It is often referred to simply as sounding, data taken from soundings are used in bathymetry to make maps of the floor of a body of water, and were traditionally shown on nautical charts in fathoms and feet. The National Oceanic and Atmospheric Administration, the responsible for bathymetric data in the United States, still uses fathoms. In other countries, the International System of Units has become the standard for measuring depth, sounding derives from the Old English sund, meaning swimming, water, sea, it is not related to the word sound in the sense of noise or tones. Traditional terms for soundings are a source for common expressions in the English language, on the Mississippi River in the 1850s, the leadsmen also used old-fashioned words for some of the numbers, for example instead of two they would say twain. Thus when the depth was two fathoms, they would call by the mark twain, the American writer Mark Twain, a former river pilot, likely took his pen name from this cry. The term lives on in todays world in echo sounding, the technique of using sonar to measure depth, a sounding line or lead line is a length of thin rope with a plummet, generally of lead, at its end. Regardless of the composition of the plummet, it is still called a lead. Leads were swung, or cast, by a leadsman, usually standing in the chains of a ship, measuring the depth of water by lead and line dates back to ancient civilisation. Greek and Roman navigators are known to have used sounding leads, sounding by lead and line continued throughout the medieval and early modern periods. The Bible describes lead and line sounding in Acts, whilst the Bayeux Tapestry documents the use of a lead during King Harold’s landing in Normandy. Throughout this period, lead and line sounding operated alongside sounding poles, particularly when navigating in shallower waters and on rivers. At sea, in order to avoid repeatedly hauling in and measuring the wet line by stretching it out with ones arms, it became traditional to tie marks at intervals along the line. These marks were made of leather, calico, serge and other materials, the marks were at every second or third fathom, in a traditional order, at 2,3,5,7,10,13,15,17, and 20 fathoms. The leadsman called out the depth as he read it off the line, if the depth was at a mark he would call by the mark followed by the number, if the depth was between two marks, he would call by the deep followed by the estimated number. Soundings were also taken to establish position, a function then. Soundings of this type were taken using tallow coated leads with a wad of tallow in a concavity at the bottom of the plummet. The tallow would bring up part of the sediment and allow the ships officers to better estimate their position by providing information useful for pilotage
13.
Rope
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A rope is a group of yarns, plies, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting, as a result, they cannot be used for pushing or similar compressive applications. Rope is thicker and stronger than similarly constructed cord, line, string, fiber rope is made from fiber, whereas wire rope is made from wire. Rope may be constructed of any long, stringy, fibrous material, synthetic fibre ropes are significantly stronger than their natural fibre counterparts, but also possess certain disadvantages, including slipperiness. Common natural fibres for rope are manila hemp, hemp, feathers, linen, cotton, coir, jute, straw, synthetic fibres in use for rope-making include polypropylene, nylon, polyesters, polyethylene, Aramids and acrylics. Some ropes are constructed of mixtures of several fibres or use co-polymer fibres, wire rope is made of steel or other metal alloys. Ropes have been constructed of fibrous materials such as silk, wool, and hair. Rayon is a fibre used to make decorative rope. The twist of the strands in a twisted or braided rope serves not only to keep a rope together, without any twist in the rope, the shortest strand would always be supporting a much higher proportion of the total load. Rope is of paramount importance in fields as diverse as construction, seafaring, exploration, sports, theatre, and communications, to fasten rope, many types of knots have been invented for countless uses. Pulleys redirect the force to another direction, and can create mechanical advantage so that multiple strands of rope share a load. Winches and capstans are machines designed to pull ropes, such ropes normally use a kernmantle construction, as described below. Static ropes, used for example in caving, rappelling, and rescue applications, are designed for minimal stretch, the UIAA, in concert with the CEN, sets climbing-rope standards and oversees testing. Any rope bearing a GUIANA or CE certification tag is suitable for climbing, climbing ropes, however, do cut easily when under load. Keeping them away from sharp rock edges is imperative, rock climbing ropes come with either a designation for single, double or twin use. A single rope is the most common and it is intended to be used by itself, single ropes range in thickness from roughly 9mm to 11mm. Smaller ropes are lighter, but wear out faster, double ropes are thinner ropes, usually 9mm and under, and are intended for use as a pair. These ropes offer a margin or security against cutting, since it is unlikely that both ropes will be cut, but they complicate belaying and leading
14.
Sonar
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Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name sonar, passive sonar is essentially listening for the sound made by vessels, active sonar is emitting pulses of sounds, Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of targets in the water. Acoustic location in air was used before the introduction of radar, Sonar may also be used in air for robot navigation, and SODAR is used for atmospheric investigations. The term sonar is used for the equipment used to generate. The acoustic frequencies used in sonar systems vary from low to extremely high. The study of sound is known as underwater acoustics or hydroacoustics. In the 19th century a bell was used as an ancillary to lighthouses to provide warning of hazards. The use of sound to locate underwater in the same way as bats use sound for aerial navigation seems to have been prompted by the Titanic disaster of 1912. S. Revenue Cutter Miami on the Grand Banks off Newfoundland Canada, in that test, Fessenden demonstrated depth sounding, underwater communications and echo ranging. The so-called Fessenden oscillator, at ca.500 Hz frequency, was unable to determine the bearing of the due to the 3 metre wavelength. The ten Montreal-built British H class submarines launched in 1915 were equipped with a Fessenden oscillator, during World War I the need to detect submarines prompted more research into the use of sound. Although piezoelectric and magnetostrictive transducers later superseded the electrostatic transducers they used, lightweight sound-sensitive plastic film and fibre optics have been used for hydrophones, while Terfenol-D and PMN have been developed for projectors. By 1918, both France and Britain had built prototype active systems, the British tested their ASDIC on HMS Antrim in 1920, and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923, an anti-submarine school, HMS Osprey, and a training flotilla of four vessels were established on Portland in 1924. The US Sonar QB set arrived in 1931, by the outbreak of World War II, the Royal Navy had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine attack system. The effectiveness of early ASDIC was hamstrung by the use of the charge as an anti-submarine weapon. This required a vessel to pass over a submerged contact before dropping charges over the stern. The hunter was effectively firing blind, during which time a commander could take evasive action
15.
Lidar
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Lidar is a surveying method that measures distance to a target by illuminating that target with a laser light. The name lidar, sometimes considered an acronym of Light Detection And Ranging, was originally a portmanteau of light, the technology is also used for control and navigation for some autonomous cars. Lidar sometimes is called laser scanning and 3D scanning, with terrestrial, airborne and its first applications came in meteorology, where the National Center for Atmospheric Research used it to measure clouds. The general public aware of the accuracy and usefulness of lidar systems in 1971 during the Apollo 15 mission. Although some sources treat the word lidar as an acronym, the term originated as a portmanteau of light, the first published mention of lidar, in 1963, makes this clear, Eventually the laser may provide an extremely sensitive detector of particular wavelengths from distant objects. Meanwhile, it is being used to study the moon by lidar, the Oxford English Dictionary supports this etymology. Currently no consensus exists on capitalization, reflecting uncertainty about whether or not lidar is an acronym, various publications refer to lidar as LIDAR, LiDAR, LIDaR, or Lidar. Lidar uses ultraviolet, visible, or near infrared light to image objects and it can target a wide range of materials, including non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules. A narrow laser-beam can map physical features with high resolutions, for example. Lidar has been used extensively for research and meteorology. Lidar instruments fitted to aircraft and satellites carry out surveying and mapping – a recent example being the U. S. Geological Survey Experimental Advanced Airborne Research Lidar, NASA has identified lidar as a key technology for enabling autonomous precision safe landing of future robotic and crewed lunar-landing vehicles. Wavelengths vary to suit the target, from about 10 micrometers to the UV, typically light is reflected via backscattering, as opposed to pure reflection one might find with a mirror. Different types of scattering are used for different lidar applications, most commonly Rayleigh scattering, Mie scattering, Raman scattering, based on different kinds of backscattering, the lidar can be accordingly called Rayleigh Lidar, Mie Lidar, Raman Lidar, Na/Fe/K Fluorescence Lidar, and so on. Suitable combinations of wavelengths can allow for remote mapping of atmospheric contents by identifying wavelength-dependent changes in the intensity of the returned signal, in general there are two kinds of lidar detection schemes, incoherent or direct energy detection and coherent detection. In both coherent and incoherent lidar, there are two types of models, micropulse lidar systems and high energy systems. Micropulse systems utilizing intermittent bursts of energy have developed as a result of the amount of computer power available combined with advances in laser technology. They use considerably less energy in the laser, typically on the order of one microjoule, there are several major components to a lidar system, Laser — 600–1000 nm lasers are most common for non-scientific applications. They are inexpensive, but since they can be focused and easily absorbed by the eye, eye-safety is often a requirement for most applications
16.
Puerto Rico Trench
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The Puerto Rico Trench is located on the boundary between the Caribbean Sea and the Atlantic Ocean. Scientific studies have concluded that an earthquake occurring along this zone could generate a significant tsunami. The island of Puerto Rico which lies immediately to the south of the fault zone, the Puerto Rico Trench is located at a boundary between two plates that pass each other along a transform boundary with only a small component of subduction. The Caribbean Plate is moving to the east while the North American Plate is moving to the west and this subduction zone explains the presence of active volcanoes over the southeastern part of the Caribbean Sea. Volcanic activity is frequent along the island arc southeast from Puerto Rico to the coast of South America. Puerto Rico, the United States Virgin Islands, British Virgin Islands, the Puerto Rico Trench is capable of producing earthquakes greater than magnitude 8.0. Knowledge of the earthquake and tsunami risks has not been widespread among the public of the islands located near the trench. Since 1988, the Puerto Rican Seismic Society has been trying to use the Puerto Rican media to inform people about an earthquake that could result in a catastrophic tragedy. Following the 2004 tsunami that affected more than forty countries in the Indian Ocean, local governments have begun emergency planning. In the case of Puerto Rico and the U. S. Virgin Islands and it is increasing its seismic investigations and developing tsunami warning systems. On 11 October 1918, the western coast of the island was hit by an earthquake which caused a tsunami. The 1918 earthquake was caused by an old left-lateral strike-slip fault near the Mona Passage, in 1953, Santo Domingo, Dominican Republic, was affected by the Santo Domingo earthquake. The actual subduction zone has not ruptured in over 200 years, Puerto Rico has always been an area of concern to earthquake experts because, apart from the 1918 episode, there are frequent tremors in and around the island, indicating activity. A1981 tremor was felt across the island, while another in 1985 was felt in the towns of Cayey, the January 13,2014 M6.4 earthquake north of Puerto Rico occurred as a result of oblique-thrust faulting. The location, depth and mechanism of the earthquake are consistent with the event occurring on this subduction zone interface
17.
Multibeam echosounder
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A multibeam echosounder is a type of sonar that is used to map the seabed. Like other sonar systems, multibeam systems emit sound waves in a fan shape beneath a ships hull, the amount of time it takes for the sound waves to bounce off the seabed and return to a receiver is used to determine water depth. Unlike other sonars, multibeam systems use beamforming to extract information from the returning soundwaves. Multibeam sonar sounding systems, also known as swathe or swath, SASS was tested aboard the USS Compass Island. The final array system, composed of one degree beams with a swath width of approximately 1.15 times water depth, was then installed on the USNS Bowditch, USNS Dutton. The first commercial multibeam is now known as the SeaBeam Classic and was put in service in May 1977 on the Australian survey vessel HMAS Cook and this system produced up to 16 beams across a 45-degree arc. The term SeaBeam Classic was coined after the manufacturer developed newer systems such as the SeaBeam 2000, the second SeaBeam Classic installation was on the French Research Vessel Jean Charcot. The SB Classic arrays on the Charcot were damaged in a grounding, although it seems that the original SeaBeam Classic installation was not used much, the others were widely used, and subsequent installations were made on many vessels. SeaBeam Classic systems were installed on the US academic research vessels USNS Thomas Washington, the USNS Robert D. Conrad. Multibeam echosounders are commonly used for geological and oceanographic research. In 1989, Atlas Electronics installed a second-generation deep-sea multibeam called Hydrosweep DS on the German research vessel Meteor, the Hydrosweep DS produced up to 59 beams across a 90-degree swath, which was a vast improvement and was inherently ice-strengthened. As the cost of components has decreased, the number of systems sold. Smaller, portable systems can be operated on a launch or tender vessel unlike the older systems that required considerable time. Some multibeam echosounders such as the Teledyne Odom ES3 also incorporate a motion sensor at the face of the acoustic transducer, multibeam echosounders like this are allowing many smaller hydrographic survey companies to move from traditional single beam echosounders to swath systems. Multibeam data includes bathymetry, acoustic backscatter, and water column data, gas plumes now commonly identified in midwater multibeam data are termed flares. A multibeam echosounder is a device used by hydrographic surveyors to determine the depth of water. From this narrow beam a two way travel time of the pulse is then established utilizing a bottom detection algorithm. If the speed of sound in water is known for the water column profile, the depth and position of the return signal can be determined from the receive angle
18.
Swathe
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The mower with a scythe moves along the mowing-edge with the uncut grass to the right and the cut grass laid in a neat row to the left, on the previously mown land. The swathe width depends on the length, the nature of the crop. Mowing may be done by a team of mowers, usually starting at the edges of a meadow then proceeding clockwise leaving a series of staggered swathes and finishing in the middle. The mower swings the scythe steadily in long, left handed arcs ending in front of the mower, the mower takes a small step forward and repeats the motion, proceeding with a steady rhythm, stopping at frequent intervals to hone the blade. The correct technique has an action on the grass, cutting a narrow strip, leaving a uniform stubble on the ground. The scythe has generally replaced by machinery such as the swather pictured. For example, the strip of the Earth’s surface from which data are collected by a moving vehicle such as a satellite. The longitudinal extent of the swath is defined by the motion of the vehicle with respect to the surface, note that swath width is also cited in the context of sonar specifications. It is measured and represented in metres or kilometres
19.
Angular resolution
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In scientific analysis, in general, the term resolution is used to describe the precision with which any instrument measures and records any variable in the specimen or sample under study. The imaging systems resolution can be limited either by aberration or by diffraction causing blurring of the image and these two phenomena have different origins and are unrelated. Aberrations can be explained by geometrical optics and can in principle be solved by increasing the optical quality —, on the other hand, diffraction comes from the wave nature of light and is determined by the finite aperture of the optical elements. The lens circular aperture is analogous to a version of the single-slit experiment. The interplay between diffraction and aberration can be characterised by the point spread function, the narrower the aperture of a lens the more likely the PSF is dominated by diffraction. If the distance is greater, the two points are well resolved and if it is smaller, they are regarded as not resolved, Rayleigh defended this criteria on sources of equal strength. Considering diffraction through an aperture, this translates into, θ =1.220 λ D where θ is the angular resolution, λ is the wavelength of light. The factor 1.220 is derived from a calculation of the position of the first dark circular ring surrounding the central Airy disc of the diffraction pattern and this number is more precisely 1.21966989. The first zero of the order-one Bessel function of the first kind J1 divided by π, the formal Rayleigh criterion is close to the empirical resolution limit found earlier by the English astronomer W. R. Dawes who tested human observers on close binary stars of equal brightness. The result, θ =4. 3% dip, modern image processing techniques including deconvolution of the point spread function allow resolution of binaries with even less angular separation. The angular resolution may be converted into a resolution, Δℓ. For a microscope, that distance is close to the length f of the objective. For this case, the Rayleigh criterion reads, Δ ℓ =1.220 f λ D. This is the size, in the plane, of smallest object that the lens can resolve. The size is proportional to wavelength, λ, and thus, for example and this result is related to the Fourier properties of a lens.220 f λ D =1.22 λ ⋅. Since this is the radius of the Airy disk, the resolution is better estimated by the diameter,2.44 λ ⋅ Point-like sources separated by a smaller than the angular resolution cannot be resolved. A single optical telescope may have a resolution less than one arcsecond. The angular resolution R of a telescope can usually be approximated by R = λ D where λ is the wavelength of the observed radiation, the Resulting R is in radians
20.
Hertz
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The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
21.
Flight dynamics
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Flight dynamics is the study of the performance, stability, and control of vehicles flying through the air or in outer space. It is concerned with how forces acting on the vehicle influence its speed, in fixed-wing aircraft, the changing orientation of the vehicle with respect to the local air flow is represented by two critical parameters, angle of attack and angle of sideslip. These angles describe the direction of airspeed, important because they are the principal source of modulations in the aerodynamic forces. Spacecraft flight dynamics involve three forces, propulsive, gravitational, and lift and drag, because aerodynamic forces involved with spacecraft flight are very small, this leaves gravity as the dominant force. These angles are the product of the equations of motion. For all flight vehicles, these two sets of dynamics, rotational and translational, operate simultaneously and in a fashion to evolve the vehicles state trajectory. This section focuses on fixed-wing aircraft, flight dynamics is the science of air-vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the center of mass, known as roll, pitch and yaw. Aircraft engineers develop control systems for a vehicles orientation about its center of mass, for example, a pitching moment is a vertical force applied at a distance forward or aft from the center of gravity of the aircraft, causing the aircraft to pitch up or down. Roll, pitch and yaw refer, in context, to rotations about the respective axes starting from a defined equilibrium state. The equilibrium roll angle is known as wings level or zero bank angle, a fixed-wing aircraft increases or decreases the lift generated by the wings when it pitches nose up or down by increasing or decreasing the angle of attack. The roll angle is known as bank angle on a fixed-wing aircraft. The forces acting on spacecraft are of three types, propulsive force, gravitational force exerted by the Earth and other celestial bodies, the vehicles attitude must be taken into account because of its effect on the aerodynamic and propulsive forces. There are other reasons, unrelated to flight dynamics, for controlling the attitude in non-powered flight. Also, most of a flight time is usually unpowered
22.
Global Positioning System
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The Global Positioning System is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. The GPS system operates independently of any telephonic or internet reception, the GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, however, the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War. The U. S. Department of Defense developed the system and it became fully operational in 1995. Roger L. Easton of the Naval Research Laboratory, Ivan A, getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes, in 2000, the U. S. Congress authorized the modernization effort, GPS III. In addition to GPS, other systems are in use or under development, mainly because of a denial of access. The Russian Global Navigation Satellite System was developed contemporaneously with GPS, GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within two meters. There are also the European Union Galileo positioning system and Chinas BeiDou Navigation Satellite System, special and general relativity predict that the clocks on the GPS satellites would be seen by the Earths observers to run 38 microseconds faster per day than the clocks on the Earth. The GPS calculated positions would quickly drift into error, accumulating to 10 kilometers per day, the relativistic time effect of the GPS clocks running faster than the clocks on earth was corrected for in the design of GPS. The Soviet Union launched the first man-made satellite, Sputnik 1, two American physicists, William Guier and George Weiffenbach, at Johns Hopkinss Applied Physics Laboratory, decided to monitor Sputniks radio transmissions. Within hours they realized that, because of the Doppler effect, the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the users location and this led them and APL to develop the TRANSIT system. In 1959, ARPA also played a role in TRANSIT, the first satellite navigation system, TRANSIT, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour, in 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based OMEGA navigation system, based on comparison of signal transmission from pairs of stations. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy, during the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded and it is also the reason for the ultra secrecy at that time
23.
United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
24.
United States Army Corps of Engineers
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The United States Army Corps of Engineers, also sometimes shortened to CoE is a U. S. Although generally associated with dams, canals and flood protection in the United States, the Corps of Engineers provides outdoor recreation opportunities to the public, and provides 24% of U. S. hydropower capacity. The corps mission is to Deliver vital public and military engineering services, partnering in peace and war to strengthen our Nations security, energize the economy and their most visible missions include, Planning, designing, building, and operating locks and dams. Other civil engineering projects include flood control, beach nourishment, design and construction of flood protection systems through various federal mandates. Design and construction management of military facilities for the Army, Air Force, Army Reserve and Air Force Reserve and other Defense and Federal agencies. The history of United States Army Corps of Engineers can be traced back to 16 June 1775, colonel Richard Gridley became General George Washingtons first chief engineer, however, it was not until 1779 that Congress created a separate Corps of Engineers. One of its first tasks was to build fortifications near Boston at Bunker Hill, the first Corps of Engineers was mostly composed of French subjects who had been hired by General Washington from the service of Louis XVI. that the said Corps. Shall be stationed at West Point in the State of New York, until 1866, the superintendent of the United States Military Academy was always an officer of engineer. During the first half of the 19th century, West Point was the major and, for a while, the General Survey Act of 1824 authorized the use of Army engineers to survey road and canal routes. Separately authorized on 4 July 1838, the U. S and it was merged with the Corps of Engineers on 31 March 1863, at which point the Corps of Engineers also assumed the Lakes Survey District mission for the Great Lakes. In 1841, Congress created the Lake Survey, the survey, based in Detroit, Mich. was charged with conducting a hydrographical survey of the Northern and Northwestern Lakes and preparing and publishing nautical charts and other navigation aids. The Lake Survey published its first charts in 1852, in the mid-19th century, Corps of Engineers officers ran Lighthouse Districts in tandem with U. S. Naval officers. The Army Corps of Engineers played a significant role in the American Civil War, many of the men who would serve in the top leadership in this institution were West Point graduates who rose to military fame and power during the Civil War. Some of these men were Union Generals George McClellan, Henry Halleck, George Meade, and Confederate generals Robert E. Lee, Joseph Johnston, the versatility of officers in the Army Corps of Engineers contributed to the success of numerous missions throughout the Civil War. They were responsible for building pontoon and railroad bridges, forts and batteries, the destruction of supply lines. The Army Corps of Engineers served as a function in making the war effort logistically feasible. This method of building trenches was known as the zigzag pattern, from the beginning, many politicians wanted the Corps of Engineers to contribute to both military construction and works of a civil nature. During World War II the mission grew to more than 27,000 military, included were aircraft, tank assembly, and ammunition plants, camps for 5.3 million soldiers, depots, ports, and hospitals, as well as the Manhattan Project, and the Pentagon
25.
National Oceanic and Atmospheric Administration
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The National Oceanic and Atmospheric Administration is an American scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. NOAA warns of dangerous weather, charts seas, guides the use and protection of ocean and coastal resources, and conducts research to improve understanding and stewardship of the environment. In addition to its employees, over 11,000 as of 2015, NOAA research. NOAA plays several roles in society, the benefits of which extend beyond the U. S. economy and into the larger global community. NOAA supplies information to its customers and partners pertaining to the state of the oceans and this is clearly manifest in the production of weather warnings and forecasts through the National Weather Service, but NOAAs information products extend to climate, ecosystems, and commerce as well. A Provider of Environmental Stewardship Services, NOAA is also the steward of U. S. coastal and marine environments. A Leader in Applied Scientific Research, the five fundamental activities are, Monitoring and observing Earth systems with instruments and data collection networks. Understanding and describing Earth systems through research and analysis of that data, assessing and predicting the changes of these systems over time. Engaging, advising, and informing the public and partner organizations with important information, managing resources for the betterment of society, economy and environment. NOAA formed a conglomeration of several existing agencies that were among the oldest in the federal government, NOAA was established within the Department of Commerce via the Reorganization Plan No.4 of 1970. In 2007 NOAA celebrated 200 years of service with its ties to the United States Coast, the NOAA Commissioned Officer Corps is a uniformed service of men and women who operate NOAA ships and aircraft, and serve in scientific and administrative posts. And in addition more than a dozen staff offices, including the Office of the Federal Coordinator for Meteorology, the NOAA Central Library and this is done through a collection of national and regional centers,13 river forecast centers, and more than 120 local weather forecast offices. They are charged with issuing weather and river forecasts, advisories, watches and they issue more than 734,000 weather and 850,000 river forecasts, and more than 45,000 severe weather warnings annually. NOAA data is relevant to the issues of global warming. The NWS operates NEXRAD, a network of Doppler weather radars which can detect precipitation. Many of their products are broadcast on NOAA Weather Radio, a network of transmitters that broadcasts weather forecasts, severe weather statements, watches. The National Ocean Service focuses on ensuring that ocean and coastal areas are safe, healthy, in 1960 TIROS-1, NOAAs first owned and operated geostationary satellite was launched. Since 1966 NESDIS has managed polar orbiting satellites and since 1974 it has operated geosynchronous satellites, in 1979 NOAAs first polar-orbiting environmental satellite was launched
26.
Geodetic datum
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A geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth. An approximate definition of sea level is the datum WGS84, other datums are defined for other areas or at other times, ED50 was defined in 1950 over Europe and differs from WGS84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there. Datums are used in geodesy, navigation, and surveying by cartographers, each starts with an ellipsoid, and then defines latitude, longitude and altitude coordinates. One or more locations on the Earths surface are chosen as anchor base-points, the difference in co-ordinates between datums is commonly referred to as datum shift. The datum shift between two particular datums can vary from one place to another within one country or region, the North Pole, South Pole and Equator will be in different positions on different datums, so True North will be slightly different. Different datums use different interpolations for the shape and size of the Earth. Because the Earth is an ellipsoid, localised datums can give a more accurate representation of the area of coverage than WGS84. OSGB36, for example, is an approximation to the geoid covering the British Isles than the global WGS84 ellipsoid. However, as the benefits of a global system outweigh the greater accuracy, horizontal datums are used for describing a point on the Earths surface, in latitude and longitude or another coordinate system. Vertical datums measure elevations or depths, in surveying and geodesy, a datum is a reference system or an approximation of the Earths surface against which positional measurements are made for computing locations. Horizontal datums are used for describing a point on the Earths surface, vertical datums are used to measure elevations or underwater depths. The horizontal datum is the used to measure positions on the Earth. A specific point on the Earth can have different coordinates. There are hundreds of local horizontal datums around the world, usually referenced to some convenient local reference point, contemporary datums, based on increasingly accurate measurements of the shape of the Earth, are intended to cover larger areas. The WGS84 datum, which is almost identical to the NAD83 datum used in North America, a vertical datum is used as a reference point for elevations of surfaces and features on the Earth including terrain, bathymetry, water levels, and man-made structures. Vertical datums are either, tidal, based on sea levels, gravimetric, based on a geoid, or geodetic, for the purpose of measuring the height of objects on land, the usual datum used is mean sea level. This is a datum which is described as the arithmetic mean of the hourly water elevation taken over a specific 19 years cycle
27.
STL (file format)
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STL is a file format native to the stereolithography CAD software created by 3D Systems. STL has several after-the-fact backronyms such as Standard Triangle Language and Standard Tessellation Language and this file format is supported by many other software packages, it is widely used for rapid prototyping, 3D printing and computer-aided manufacturing. STL files describe only the surface geometry of an object without any representation of color. The STL format specifies both ASCII and binary representations, binary files are more common, since they are more compact. An STL file describes a raw unstructured triangulated surface by the unit normal, STL coordinates must be positive numbers, there is no scale information, and the units are arbitrary. An ASCII STL file begins with the line solid name where name is an optional string. g, the file concludes with endsolid name The structure of the format suggests that other possibilities exist. In practice, however, all facets are simple triangles, white space may be used anywhere in the file except within numbers or words. The spaces between facet and normal and between outer and loop are required, because ASCII STL files can become very large, a binary version of STL exists. A binary STL file has an 80-character header, following the header is a 4-byte unsigned integer indicating the number of triangular facets in the file. Following that is data describing each triangle in turn, the file simply ends after the last triangle. Each triangle is described by twelve 32-bit floating-point numbers, three for the normal and then three for the X/Y/Z coordinate of each vertex – just as with the ASCII version of STL. After these follows a 2-byte unsigned integer that is the byte count – in the standard format. Floating-point numbers are represented as IEEE floating-point numbers and are assumed to be little-endian, the Materialise Magics software uses the 80-byte header at the top of the file to represent the overall color of the entire part. If color is used, then somewhere in the header should be the ASCII string COLOR= followed by four bytes representing red, green, blue and this is the color of the entire object, unless overridden at each facet. Magics also recognizes a material description, a detailed surface characteristic. Material settings are preferred over color, there is also no way to have facets be selectively transparent because there is no per-facet alpha value – although in the context of current rapid prototyping machinery, this is not important. In both ASCII and binary versions of STL, the facet normal should be a vector pointing outwards from the solid object. In most software this may be set to, and the software will automatically calculate a normal based on the order of the triangle vertices using the right-hand rule
28.
Bathymetric chart
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A bathymetric chart is the submerged equivalent of an above-water topographic map. Bathymetric charts are designed to present accurate, measurable description and visual presentation of the submerged terrain, in an ideal case, the joining of a bathymetric chart and topographic map of the same scale and projection of the same geographic area would be seamless. The only difference would be that the values begin increasing after crossing the zero at the sea level datum. Thus the topographic maps mountains have the greatest values while the charts greatest depths have the greatest values. Simply put, the chart is intended to show the land if overlying waters were removed in exactly the same manner as the topographic map. A bathymetric chart differs from a chart in that accurate presentation of the underwater features is the goal while safe navigation is the requirement for the hydrographic chart. A hydrographic chart will obscure the actual features to present a simplified version to aid mariners in avoiding underwater hazards, Bathymetric surveys are a subset of the science of hydrography. That chart product is more accurately termed a navigation or hydrographic chart with a bias toward the presentation of essential safety information. Bathymetric surveys and charts are more closely tied to the science of oceanography, particularly marine geology, Bathymetric charts can also be converted to bathymetric profiles. Matthew Fontaine Maury published this map in 1853 in his book Explanations and Sailing Directions to Accompany the Wind, general Bathymetric Chart of the Oceans
29.
Depth gauge
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A depth gauge is a pressure gauge that displays the equivalent depth in water. It is a piece of diving equipment often used by SCUBA divers, most modern diving depth gauges have an electronic mechanism and digital display. Older types used a mechanism and analogue display. A diver uses a gauge with decompression tables and a watch to avoid decompression sickness. A common alternative to the gauge, watch and decompression tables is a dive computer. A depth gauge and an oxygen analyser/oxygen sensor can be used to measure the pressure of oxygen of the breathing gas. Digital depth gauges commonly also include a timer showing the interval of time that the diver has been submerged, some show the divers rate of ascent and descent, which can be is useful for avoiding barotrauma. Articles on depth gauges hosted by the Rubicon Foundation
30.
General Bathymetric Chart of the Oceans
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The General Bathymetric Chart of the Oceans is a publicly available bathymetric chart of the worlds oceans. The project was conceived with the aim of preparing a series of charts showing the general shape of the seafloor. Over the years it has become a reference map of the bathymetry of the oceans for scientists. GEBCO operates under the joint auspices of the International Hydrographic Organization, and the Intergovernmental Oceanographic Commission of UNESCO. Its work is done by an group of experts in seafloor mapping who develop a range of bathymetric data sets. Although originally GEBCO published paper contour charts, today it has moved into the digital age, gEBCO_2014 Grid — an update to the previously released GEBCO_08 Grid. GEBCO One Minute Grid — a global grid at one arc-minute intervals, the grids are available to download from the British Oceanographic Data Centre in the form of netCDF files, along with free software for displaying and accessing data in ASCII and netCDF. The grids can be used with the Generic Mapping Tools system and it is available to be downloaded from the International Hydrographic Organization. The GEBCO world map — a global, coloured, paper map of the bathymetry of the world’s oceans based upon the GEBCO One Minute Grid, the map is available to be downloaded in the form of jpeg file. The GEBCO chart series was initiated in 1903 by an group of geographers and oceanographers. At that time there was an explosion of interest in the study of the natural world, the first hundred years of the project were described in the book The History of GEBCO 1903-2003 published by GITC in 2003. Nowadays GEBCO’s role has become important, due to the increased interest in the oceans for scientific research. Since 1903, five editions of paper, bathymetric contour charts covering the whole world have been produced. GEBCO is now maintained in form as the GEBCO Digital Atlas. The Nippon Foundation of Japan has provided funding for GEBCO to train a new generation of scientists, the 12-month course, leading to a Postgraduate Certificate in Ocean Bathymetry, has been held at the University of New Hampshire, USA, since 2004. 60 GEBCO scholars from 31 different countries have completed the course and are supporting GEBCO programs, official website GEBCO Digital Atlas GEBCOs gridded data sets GEBCO world map The Academy Of Positioning Marine And Bathymetry - is an independent, no-profit, no-governmental. It provides a forum for all involved in activities related to the disciplines of marine positioning
31.
Hydrographic survey
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Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities. Hydrography is collected under rules which vary depending on the acceptance authority, traditionally conducted by ships with a sounding line or echo sounding, surveys are increasingly conducted with the aid of aircraft and sophisticated electronic sensor systems in shallow waters. Hydrographic offices evolved from naval heritage and are found within national naval structures. The IHO publishes Standards and Specifications followed by its Member States as well as Memoranda of Understanding, increasingly those charts are provided and used in electronic form unders IHO standards. Governmental entities below the national level conduct or contract for hydrographic surveys for waters within their jurisdictions with both internal and contract assets, in the United States, there is coordination with the National Hydrography Dataset in survey collection and publication. State environmental organizations publish hydrographic data relating to their mission, commercial entities also conduct large-scale hydrographic and geophysical surveying, particularly in the dredging, marine construction, oil exploration, and drilling industries. Specialized companies exist that haveboth the equipment and expertise to contract with both commercial and governmental entities to perform such surveys, companies, universities, and investment groups will often fund hydrographic surveys of public waterways prior to developing areas adjacent those waterways. Survey firms are also contracted to survey in support of design, private surveys are also conducted before dredging operations and after these operations are completed. Crowdsourcing also is entering hydrographic surveying, with such as OpenSeaMap, TeamSurv. Apart from obvious cost savings, this gives a continuous survey of an area. Although sometimes accurate to 0.1 -0. 2m, this approach cannot substitute for a systematic survey. Nevertheless, the results are more than adequate for many requirements where high resolution. The history of hydrographic surveying dates almost as far back as that of sailing, in either case, the depths measured had to be read manually and recorded, as did the position of each measurement with regard to mapped reference points as determined by three-point sextant fixes. Single-beam echosounders and fathometers began to service in the 1930s which used sonar to measure the depth beneath a vessel. However, it shared the weakness of earlier methods by lacking depth information for areas in between the strips of sea bottom the vessel sounded, in 1904, wire-drag surveys were introduced into hydrography, and the U. S. Coast and Geodetic Surveys Nicholas H. Heck played a prominent role in developing and perfecting the technique between 1906 and 1916, in the wire-drag method, a wire attached to two ships or boats and set at a certain depth by a system of weights and buoys was dragged between two points. If the wire encountered an obstruction, it would become taut, the location of the V revealed the position of submerged rocks, wrecks, and other obstructions, while the depth at which the wire was set showed the depth at which the obstruction was encountered. This method revolutionized hydrographic surveying, as it allowed a quicker, less laborious, prior to the advent of sidescan sonar, wire-drag surveying was the only method for searching large areas for obstructions and lost vessels and aircraft
32.
Ocean surface topography
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The ocean surface has highs and lows, similar to the hills and valleys of Earths land surface depicted on a topographic map. These variations, called ocean surface topography, also dynamic topography, are mapped using measurements of sea surface height relative to Earths geoid. Earths geoid is a surface of equal gravitational potential energy. Topography is the arrangement of natural and artificial features of an area, Ocean surface topography is specifically the distance between the height of the ocean surface from the geoid. Ocean surface topography is caused by waves, tides, currents. The main purpose to measure ocean surface topography is to understand the large-scale circulation of the ocean, the height variations of ocean surface topography can be as much as two meters and are influenced by ocean circulation, ocean temperature, and salinity. Ocean surface topography is used to map ocean currents, which move around the oceans hills, a clockwise sense of rotation is found around hills in the northern hemisphere and valleys in the southern hemisphere. This is because of the Coriolis effect, conversely, a counterclockwise sense of rotation is found around valleys in the northern hemisphere and hills in the southern hemisphere. Ocean surface topography is used to understand how the ocean moves heat around the globe, a critical component of Earths climate. The satellites then measure the distance between their orbit altitude and the surface of the water, due to the differing depths of the ocean, an approximation is made. This is called the Arbitrary Reference Surface, Arbitrary Reference Surface is an estimated surface that is calculated to factor in the shape of the Earth. The general shape of the earth is spherical, but flattened out at the North and South Pole and this approximated surface is called the reference ellipsoid. This enables data to be taken due to the uniform surface level. The satellite’s altitude then has to be calculated with respect to the reference ellipsoid and it is calculated using the orbital parameters of the satellite and various positioning instruments. The sea surface height is then the difference between the altitude relative to the reference ellipsoid and the altimeter range. The satellite sends microwave pulses to the ocean surface, the travel time of the pulses ascending to the oceans surface and back provides data of the sea surface height. In the image below you can see the measurement system using by the satellite Jason-1, the collection of the data is useful for the long-term information about the ocean and its currents. According to NASA science this data can also be used to understanding of weather, climate, navigation, fisheries management
33.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
34.
Physical oceanography
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Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters. Physical oceanography is one of several sub-domains into which oceanography is divided, others include biological, chemical and geological oceanography. Physical oceanography may be subdivided into descriptive and dynamical physical oceanography, descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precise as possible. Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and these are part of the large field of Geophysical Fluid Dynamics that is shared together with meteorology. The fundamental role of the oceans in shaping Earth is acknowledged by ecologists, geologists, meteorologists, climatologists, an Earth without oceans would truly be unrecognizable. Roughly 97% of the water is in its oceans. The tremendous heat capacity of the oceans moderates the planets climate, the oceans influence extends even to the composition of volcanic rocks through seafloor metamorphism, as well as to that of volcanic gases and magmas created at subduction zones. Though this apparent discrepancy is great, for land and sea, the respective extremes such as mountains and trenches are rare. Because the vast majority of the oceans volume is deep water. The same percentage falls in a salinity range between 34–35 ppt, there is still quite a bit of variation, however. Surface temperatures can range from below freezing near the poles to 35 °C in restricted tropical seas, in terms of temperature, the oceans layers are highly latitude-dependent, the thermocline is pronounced in the tropics, but nonexistent in polar waters. The halocline usually lies near the surface, where evaporation raises salinity in the tropics and these variations of salinity and temperature with depth change the density of the seawater, creating the pycnocline. Energy for the ocean circulation comes from solar radiation and gravitational energy from the sun, perhaps three quarters of this heat is carried in the atmosphere, the rest is carried in the ocean. The atmosphere is heated from below, which leads to convection, by contrast the ocean is heated from above, which tends to suppress convection. Instead ocean deep water is formed in regions where cold salty waters sink in fairly restricted areas. This is the beginning of the thermohaline circulation, oceanic currents are largely driven by the surface wind stress, hence the large-scale atmospheric circulation is important to understanding the ocean circulation. The Hadley circulation leads to Easterly winds in the tropics and Westerlies in mid-latitudes and this leads to slow equatorward flow throughout most of a subtropical ocean basin. The return flow occurs in an intense, narrow, poleward western boundary current, like the atmosphere, the ocean is far wider than it is deep, and hence horizontal motion is in general much faster than vertical motion
35.
Wind wave
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In fluid dynamics, wind waves, or wind-generated waves, are surface waves that occur on the free surface of bodies of water. They result from the wind blowing over an area of fluid surface, Waves in the oceans can travel thousands of miles before reaching land. Wind waves on Earth range in size from small ripples, to waves over 100 ft high, when directly generated and affected by local winds, a wind wave system is called a wind sea. After the wind ceases to blow, wind waves are called swells, more generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time. They have been generated elsewhere or some time ago, wind waves in the ocean are called ocean surface waves. Wind waves have an amount of randomness, subsequent waves differ in height, duration. The key statistics of wind waves in evolving sea states can be predicted with wind wave models, although waves are usually considered in the water seas of Earth, the hydrocarbon seas of Titan may also have wind-driven waves. The great majority of large breakers seen at a result from distant winds. Water depth All of these work together to determine the size of wind waves. Further exposure to that wind could only cause a dissipation of energy due to the breaking of wave tops. Waves in an area typically have a range of heights. For weather reporting and for analysis of wind wave statistics. This figure represents an average height of the highest one-third of the waves in a time period. The significant wave height is also the value a trained observer would estimate from visual observation of a sea state, given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for a particular day or storm. Wave formation on a flat water surface by wind is started by a random distribution of normal pressure of turbulent wind flow over the water. This pressure fluctuation produces normal and tangential stresses in the surface water and it is assumed that, The water is originally at rest. There is a distribution of normal pressure to the water surface from the turbulent wind. Correlations between air and water motions are neglected, the second mechanism involves wind shear forces on the water surface
36.
Airy wave theory
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In fluid dynamics, Airy wave theory gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer. The theory assumes that the layer has a uniform mean depth. This theory was first published, in form, by George Biddell Airy in the 19th century. Further, several second-order nonlinear properties of gravity waves, and their propagation. Airy wave theory is also a good approximation for tsunami waves in the ocean and this linear theory is often used to get a quick and rough estimate of wave characteristics and their effects. This approximation is accurate for small ratios of the height to water depth. Airy wave theory uses a potential approach to describe the motion of gravity waves on a fluid surface. This is due to the fact that for the part of the fluid motion. Airy wave theory is used in ocean engineering and coastal engineering. Diffraction is one of the effects which can be described with Airy wave theory. Further, by using the WKBJ approximation, wave shoaling and refraction can be predicted, earlier attempts to describe surface gravity waves using potential flow were made by, among others, Laplace, Poisson, Cauchy and Kelland. But Airy was the first to publish the correct derivation and formulation in 1841, soon after, in 1847, the linear theory of Airy was extended by Stokes for non-linear wave motion – known as Stokes wave theory – correct up to third order in the wave steepness. Even before Airys linear theory, Gerstner derived a nonlinear wave theory in 1802. Airy wave theory is a theory for the propagation of waves on the surface of a potential flow. The waves propagate along the surface with the phase speed cp. The angular wavenumber k and frequency ω are not independent parameters, surface gravity waves on a fluid are dispersive waves – exhibiting frequency dispersion – meaning that each wavenumber has its own frequency and phase speed. Note that in engineering the wave height H – the difference in elevation between crest and trough – is often used, H =2 a and a =12 H, underneath the surface, there is a fluid motion associated with the free surface motion. While the surface shows a propagating wave, the fluid particles are in an orbital motion
37.
Ballantine scale
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The Ballantine scale is a biologically defined scale for measuring the degree of exposure level of wave action on a rocky shore. The species present in the littoral zone therefore indicate the degree of the shores exposure, an abbreviated summary of the scale is given below. The scale runs from 1) an extremely exposed shore, to 8) an extremely sheltered shore, the littoral zone generally is the zone between low and high tides. The supra-littoral is above the barnacle line, the eulittoral zone is dominated by barnacles and limpets with a coralline belt in the very low littoral along with other Rhodophyta and Alaria in the upper sublittoral. Exposed shores show a Verrucaria belt mainly above the tide, with Porphyra. The mid shore is dominated by barnacles, limpets and some Fucus, Himanthalia and some Rhodophyta such as Mastocarpus and Corallina are found in the low littorral with Himanthalia, Alaria and Laminaria digitata dominant in the upper sublittoral. Semi-exposed shores show a Verrucaria belt just above high tide with clear Pelvetia in the upper-littoral, limpets, barnacles and short Fucus vesiculosus midshore. Laminaria and Saccorhiza polyschides and small algae common in the sublittoral, sheltered shores show a narrow Verrucaria zone at high water and a full sequence of fucoids, Pelvetia, Fucus spiralis, Fucus vesiculosus, Fucus serratus, Ascophyllum nodosum. Laminaria digitata is dominant the upper sublittoral, very sheltered shores show a very narrow zone of Verrucaria, the dominance of the littoral by a full sequence of the fucoids and Ascophyllum covering the rocks. Laminaria saccharina, Halidrys, Chondrus and or Furcellaria, a Biologically-defined Exposure Scale for the Comparative Description of Rocky Shores
38.
Modulational instability
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The phenomenon was first discovered − and modelled − for periodic surface gravity waves on deep water by T. Brooke Benjamin and Jim E. Feir, in 1967. Therefore, it is known as the Benjamin−Feir instability. It is a mechanism for the generation of rogue waves. Modulation instability only happens under certain circumstances, the most important condition is anomalous group velocity dispersion, whereby pulses with shorter wavelengths travel with higher group velocity than pulses with longer wavelength. The instability is strongly dependent on the frequency of the perturbation, at certain frequencies, a perturbation will have little effect, whilst at other frequencies, a perturbation will grow exponentially. The overall gain spectrum can be derived analytically, as is shown below, random perturbations will generally contain a broad range of frequency components, and so will cause the generation of spectral sidebands which reflect the underlying gain spectrum. The tendency of a signal to grow makes modulation instability a form of amplification. By tuning an input signal to a peak of the gain spectrum, the imaginary unit i satisfies i 2 = −1. The model includes group velocity dispersion described by the parameter β2, a periodic waveform of constant power P is assumed. The beginning of instability can be investigated by perturbing this solution as A = e i γ P z, the complex conjugate of ε is denoted as ε ∗. Instability can now be discovered by searching for solutions of the equation which grow exponentially. The nonlinear Schrödinger equation is constructed by removing the carrier wave of the light being modelled, therefore, ω m and k m dont represent absolute frequencies and wavenumbers, but the difference between these and those of the initial beam of light. It can be shown that the function is valid, provided c 2 = c 1 ∗. Therefore, instability will occur when β22 ω m 2 +2 γ P β2 <0 and this condition describes the requirement for anomalous dispersion. The gain spectrum can be described by defining a gain parameter as g ≡2 | ℑ |, the growth rate is maximum for ω2 = − γ P / β2. Modulation instability of optical fields has been observed in systems, namely. Modulation instability occurs owing to inherent optical nonlinearity of the due to photoreaction-induced changes in the refractive index. Ostrovsky, L. A. Modulation instability, The beginning
39.
Boussinesq approximation (water waves)
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In fluid dynamics, the Boussinesq approximation for water waves is an approximation valid for weakly non-linear and fairly long waves. The approximation is named after Joseph Boussinesq, who first derived them in response to the observation by John Scott Russell of the wave of translation, the 1872 paper of Boussinesq introduces the equations now known as the Boussinesq equations. The Boussinesq approximation for water waves takes into account the structure of the horizontal and vertical flow velocity. This results in partial differential equations, called Boussinesq-type equations. In coastal engineering, Boussinesq-type equations are used in computer models for the simulation of water waves in shallow seas. While the Boussinesq approximation is applicable to fairly long waves – that is and this is useful because the waves propagate in the horizontal plane and have a different behaviour in the vertical direction. Often, as in Boussinesqs case, the interest is primarily in the wave propagation and this elimination of the vertical coordinate was first done by Joseph Boussinesq in 1871, to construct an approximate solution for the solitary wave. Subsequently, in 1872, Boussinesq derived the equations known nowadays as the Boussinesq equations, thereafter, the Boussinesq approximation is applied to the remaining flow equations, in order to eliminate the dependence on the vertical coordinate. As a result, the partial differential equations are in terms of functions of the horizontal coordinates. As an example, consider potential flow over a bed in the plane, with x the horizontal. The bed is located at z = −h, where h is the water depth. Invoking Laplaces equation for φ, as valid for incompressible flow, gives, φ = + = and this series may subsequently be truncated to a finite number of terms. Now the Boussinesq approximation for the velocity potential φ, as given above, is applied in these boundary conditions, further, in the resulting equations only the linear and quadratic terms with respect to η and ub are retained. The cubic and higher terms are assumed to be negligible. This set of equations has been derived for a horizontal bed. When the right-hand sides of the equations are set to zero. From the terms between brackets, the importance of nonlinearity of the equation can be expressed in terms of the Ursell number, for the case of infinitesimal wave amplitude, the terminology is linear frequency dispersion. The frequency dispersion characteristics of a Boussinesq-type of equation can be used to determine the range of wave lengths, for which it is a valid approximation
40.
Breaking wave
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At this point, simple physical models that describe wave dynamics often become invalid, particularly those that assume linear behaviour. The most generally familiar sort of breaking wave is the breaking of surface waves on a coastline. Wave breaking generally occurs where the amplitude reaches the point that the crest of the wave actually overturns—though the types of breaking water waves are discussed in more detail below. Certain other effects in fluid dynamics have also been termed breaking waves, wave breaking also occurs in plasmas, when the particle velocities exceed the waves phase speed. Breaking of water surface waves may occur anywhere that the amplitude is sufficient, however, it is particularly common on beaches because wave heights are amplified in the region of shallower water. See also waves and shallow water, there are four basic types of breaking water waves. They are spilling, plunging, collapsing, and surging, when the ocean floor has a gradual slope, the wave will steepen until the crest becomes unstable, resulting in turbulent whitewater spilling down the face of the wave. This continues as the approaches the shore, and the waves energy is slowly dissipated in the whitewater. Because of this, spilling waves break for a time than other waves. Onshore wind conditions make spillers more likely, a plunging wave occurs when the ocean floor is steep or has sudden depth changes, such as from a reef or sandbar. A plunging wave breaks with more energy than a significantly larger spilling wave, the wave can trap and compress the air under the lip, which creates the crashing sound associated with waves. With large waves, this crash can be felt by beachgoers on land, offshore wind conditions can make plungers more likely. This is the tube that is so highly sought after by surfers, the surfer tries to stay near or under the crashing lip, often trying to stay as deep in the tube as possible while still being able to shoot forward and exit the barrel before it closes. A plunging wave that is parallel to the beach can break along its length at once, rendering it unrideable. Surfers refer to waves as closed out. Collapsing waves are a cross between plunging and surging, in which the crest never fully breaks, yet the bottom face of the wave gets steeper and collapses, surging breakers originate from long period, low steepness waves and/or steep beach profiles. The outcome is the movement of the base of the wave up the swash slope. The front face and crest of the wave remain relatively smooth with little foam or bubbles, resulting in a very narrow surf zone, or no breaking waves at all
41.
Clapotis
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The resulting clapotic wave does not travel horizontally, but has a fixed pattern of nodes and antinodes. These waves promote erosion at the toe of the wall, the term was coined in 1877 by French mathematician and physicist Joseph Valentin Boussinesq who called these waves ‘le clapotis’ meaning ‘’the lapping. The standing waves alternately rise and fall in a mirror image pattern, as energy is converted to potential energy. This may also occur at sea between two different wave trains of near equal wavelength moving in opposite directions, but with unequal amplitudes, in partial clapotis the wave envelope contains some vertical motion at the nodes. When a wave strikes a wall at an oblique angle. In this situation, the individual crests formed at the intersection of the incident and this wave motion, when combined with the resultant vortices, can erode material from the seabed and transport it along the wall, undermining the structure until it fails. Clapotic waves on the sea surface also radiate infrasonic microbaroms into the atmosphere, clapotis has been called the bane and the pleasure of Sea kayaking. Rogue wave Boussinesq, J. Théorie des ondes liquides périodiques, mémoires présentés par divers savants à lAcadémie des Sciences. Boussinesq, J. Essai sur la théorie des eaux courantes, mémoires présentés par divers savants à lAcadémie des Sciences. Clapotis and Wave Reflection, With an Application to Vertical Breakwater Design, clapotis Wave Action – via YouTube
42.
Cnoidal wave
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In fluid dynamics, a cnoidal wave is a nonlinear and exact periodic wave solution of the Korteweg–de Vries equation. These solutions are in terms of the Jacobi elliptic function cn and they are used to describe surface gravity waves of fairly long wavelength, as compared to the water depth. The cnoidal wave solutions were derived by Korteweg and de Vries, in their 1895 paper in which they also propose their dispersive long-wave equation, in the limit of infinite wavelength, the cnoidal wave becomes a solitary wave. The Benjamin–Bona–Mahony equation has improved short-wavelength behaviour, as compared to the Korteweg–de Vries equation, cnoidal wave solutions can appear in other applications than surface gravity waves as well, for instance to describe ion acoustic waves in plasma physics. The KdV equation is a wave equation, including both frequency dispersion and amplitude dispersion effects. Shallow water equations — are also nonlinear and do have amplitude dispersion, Boussinesq equations — have the same range of validity as the KdV equation, but allow for wave propagation in arbitrary directions, so not only forward-propagating waves. The drawback is that the Boussinesq equations are more difficult to solve than the KdV equation. Airy wave theory — has full frequency dispersion, so valid for arbitrary depth and wavelength, however, for long waves the Boussinesq approach—as also applied in the KdV equation—is often preferred. This is because in shallow water the Stokes perturbation series needs many terms before convergence towards the solution, due to the peaked crests, while the KdV or Boussinesq models give good approximations for these long nonlinear waves. The KdV equation can be derived from the Boussinesq equations, further improvements in short-wave performance can be obtained by starting to derive a one-way wave equation from a modern improved Boussinesq model, valid for even shorter wavelengths. The cnoidal wave solutions of the KdV equation were presented by Korteweg and de Vries in their 1895 paper, solitary wave solutions for nonlinear and dispersive long waves had been found earlier by Boussinesq in 1872, and Rayleigh in 1876. The search for these solutions was triggered by the observations of this solitary wave by Russell, cnoidal wave solutions of the KdV equation are stable with respect to small perturbations. Further cn is one of the Jacobi elliptic functions and K is the elliptic integral of the first kind. The latter, m, determines the shape of the cnoidal wave, for m equal to zero the cnoidal wave becomes a cosine function, while for values close to one the cnoidal wave gets peaked crests and flat troughs. For values of m less than 0.95, the function can be approximated with trigonometric functions. An important dimensionless parameter for nonlinear long waves is the Ursell parameter, for small values of U, say U <5, a linear theory can be used, and at higher values nonlinear theories have to be used, like cnoidal wave theory. The demarcation zone between—third or fifth order—Stokes and cnoidal wave theories is in the range 10–25 of the Ursell parameter. Based on the analysis of the nonlinear problem of surface gravity waves within potential flow theory
43.
Cross sea
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In surface navigation, a cross sea is a sea state with two wave systems traveling at oblique angles. This may occur when waves from one weather system continue despite a shift in wind. Waves generated by the new wind run at an angle to the old, creating a shifting, two weather systems that are far from each other may create a cross sea when the waves from the systems meet, usually at a place far from either weather system. Until the older waves have dissipated, they create a sea hazard among the most perilous and this sea state is fairly common and a larger percentage of ship accidents were found to have occurred in this state. A cross swell is generated when the systems are longer period swell
44.
Dispersion (water waves)
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In fluid dynamics, dispersion of water waves generally refers to frequency dispersion, which means that waves of different wavelengths travel at different phase speeds. Water waves, in context, are waves propagating on the water surface, with gravity. As a result, water with a surface is generally considered to be a dispersive medium. For a certain depth, surface gravity waves – i. e. waves occurring at the air–water interface. On the other hand, for a wavelength, gravity waves in deeper water have a larger phase speed than in shallower water. In contrast with the behavior of gravity waves, capillary waves propagate faster for shorter wavelengths, besides frequency dispersion, water waves also exhibit amplitude dispersion. This is an effect, by which waves of larger amplitude have a different phase speed from small-amplitude waves. This section is about frequency dispersion for waves on a fluid layer forced by gravity, for surface tension effects on frequency dispersion, see surface tension effects in Airy wave theory and capillary wave. The simplest propagating wave of unchanging form is a sine wave. Characteristic phases of a wave are, the upward zero-crossing at θ =0, the wave crest at θ = ½ π, the downward zero-crossing at θ = π. A certain phase repeats itself after an integer m multiple of 2π, the dispersion relation has two solutions, ω = +Ω and ω = −Ω, corresponding to waves travelling in the positive or negative x–direction. The dispersion relation will in general depend on other parameters in addition to the wavenumber k. For gravity waves, according to theory, these are the acceleration by gravity g. The dispersion relation for these waves is, an equation with tanh denoting the hyperbolic tangent function. An initial wave phase θ = θ0 propagates as a function of space and its subsequent position is given by, x = λ T t + λ2 π θ0 = ω k t + θ0 k. This shows that the moves with the velocity, c p = λ T = ω k = Ω k. A sinusoidal wave, of small amplitude and with a constant wavelength, propagates with the phase velocity. While the phase velocity is a vector and has an associated direction, according to linear theory for waves forced by gravity, the phase speed depends on the wavelength and the water depth
