1.
Sea ice
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Sea ice arises as seawater freezes. Because ice is less dense water, it floats on the oceans surface. Sea ice covers about 7% of the Earth’s surface and about 12% of the world’s oceans. Much of the sea ice is enclosed within the polar ice packs in the Earths polar regions, the Arctic ice pack of the Arctic Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean, depending on location, sea ice expanses may also incorporate icebergs. Sea ice does not simply grow and melt, during its lifespan, it is very dynamic. Due to the action of winds, currents, water temperature. Sea ice is classified according to whether or not it is able to drift, Sea ice can be classified according to whether or not it is attached to the shoreline. If attached, it is called landfast ice, or more often, alternatively, and unlike fast ice, drift ice occurs further offshore in very wide areas, and encompasses ice that is free to move with currents and winds. The physical boundary between fast ice and drift ice is the fast ice boundary, the drift ice zone may be further divided into a shear zone, a marginal ice zone and a central pack. Drift ice consists of floes, individual pieces of sea ice 20 metres or more across, the term pack ice is used either as a synonym to drift ice, or to designate drift ice zone in which the floes are densely packed. The overall sea ice cover is termed the ice canopy from the perspective of submarine navigation, another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are, new ice, nilas, young ice, first-year, new ice is a general term used for recently frozen sea water that does not yet make up solid ice. It may consist of ice, slush, or shuga. Other terms, such as ice and pancake ice, are used for ice crystal accumulations under the action of wind. Nilas designates a sea ice crust up to 10 centimetres in thickness and it bends without breaking around waves and swells. Nilas can be subdivided into dark nilas – up to 5 centimetres in thickness and very dark
2.
Stamukha
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A stamukha is a grounded accumulation of sea ice rubble that typically develops along the boundary between fast ice and the drifting pack ice, or becomes incorporated into the fast ice. Wind, currents and tides contribute to this phenomenon, stamukhi tend to occur in belts that are parallel to the shoreline, along coastal shoals, at water depths of about 20 m, but that can reach 50 m. They can build up to heights 10 metres or more above the waterline, although they remain pinned to the seabed, these features can be subject to small displacements, either due to thermal expansion or to the pressure exerted by the drifting pack ice onto the fast ice. Because stamukhi tend to be grounded, they may occur as isolated ice features in the open sea during the summer season. Since stamukhi extend downward into the seabed, they present a risk to submarine pipelines, seabed penetration by the ice can reach a depth of 5 metres
3.
Fast ice
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Fast ice is sea ice that is fastened to the coastline, to the sea floor along shoals or to grounded icebergs. Fast ice may either grow in place from the sea water or by freezing pieces of drifting ice to the shore or other anchor sites, unlike drift ice, fast ice does not move with currents and winds. The width of this ice zone is usually seasonal and depends on ice thickness, topography of the sea floor and it ranges from a few meters to several hundred kilometers. Seaward expansion is a function of a number of factors, notably water depth, shoreline protection, time of year, the topography of the fast ice varies from smooth and level to rugged. The ice foot refers to ice that has formed at the shoreline, further away from the coastline, the ice may become anchored to the sea bottom—it is then referred to as bottomfast ice. Fast ice can survive one or more melting seasons, in case it can be designated following the usual age-based categories. The fast ice boundary is the limit between fast ice and drift ice—in places, this boundary may coincide with a shear ridge, fast ice may be delimited or enclose pressure ridges which extend sufficiently downward so as to be grounded—these features are known as stamukhi. Anchor ice, also called bottom-fast ice Ice bridge Sea ice Stamukha
4.
Sea ice growth processes
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Sea ice is a complex composite composed primarily of pure ice in various states of crystallization along with air bubbles and included pockets of brine. Sea ice growth models for predicting the ice distribution and extent are also valuable for shipping concerns, an ice growth model can be combined with remote sensing measurements in an assimilation model as a means of generating more accurate ice charts. Several formation mechanisms of sea ice have been identified, at its earliest stages, sea ice consists of elongated, randomly oriented crystals. This is called frazil and mixed with water in the state is known as grease ice. If wave and wind conditions are calm, these crystals will consolidate at the surface and by pressure, begin to grow preferentially in the downward direction. Subsequent freezing will form ice with a more granular structure. One of the more interesting processes to occur within consolidated ice packs is changes in the saline content, as the ice freezes, most of the salt content gets rejected and forms highly saline brine inclusions between the crystals. With decreasing temperatures in the ice sheet, the size of the brine pockets decreases while the content goes up. Brine will also drain through vertical channels, particularly in the melt season. The net heat flux is a total over four components, Q ∗ = Q E + Q H + Q L W + Q S W which are latent, sensible, longwave and shortwave fluxes, respectively. For a description of the approximate parameterizations, see determining surface flux under sea ice thickness, the equation can be solved using a numerical root-finding algorithm such as bisection, the functional dependencies on surface temperature are given, with e being the equilibrium vapor pressure. While Cox and Weeks assume thermal equilibrium, Tonboe uses a more complex thermodynamic model based on solution of the heat equation. This would be appropriate when the ice is thick or the conditions are changing rapidly. The rate of ice growth can be calculated from heat flux by the equation, g = Q ∗ L ρ where L is the latent heat of fusion for water. The growth rate in turn determines the content of the newly frozen ice. g. F =0.120.12 +0.88 exp where g is in cm/s. Brine entrapped in sea ice will always be at or near freezing since any departure will either cause some of the water in the brine to freeze, thus, brine salinity is variable and can be determined based strictly on temperature—see freezing point depression. References and contain empirical formulas relating sea ice temperature to brine salinity, the relative brine volume, Vb, is defined as the fraction of brine relative to the total volume
5.
Theodolite
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A theodolite /θiːˈɒdəlaɪt/ is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are used mainly for surveying applications, and have adapted for specialized purposes such as meteorology. A modern theodolite consists of a telescope mounted within two perpendicular axes, the horizontal or trunnion axis and the zenith axis. A theodolite measures vertical angles as angles between the zenith, forwards or plunged—typically approximately 90 and 270 degrees, when the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc. A theodolite may be either transit or non-transit, in a transit theodolite, the telescope can be inverted in the vertical plane, whereas the rotation in the same plane is restricted to a semi-circle in a non-transit theodolite. Some types of transit theodolites do not allow the measurement of vertical angles, the builders level is sometimes mistaken for a transit theodolite, but it measures neither horizontal nor vertical angles. It uses a level to set a telescope level to define a line of sight along a horizontal plane. A theodolite is mounted on its head by means of a forced centering plate or tribrach containing four thumbscrews, or in modern theodolites. Before use, a theodolite must be placed vertically above the point to be measured using a plumb bob. The instrument is then set level using leveling footscrews and circular, both axes of a theodolite are equipped with graduated circles that can be read through magnifying lenses. The vertical circle which transits about the horizontal axis should read 90° when the axis is horizontal, or 270° when the instrument is in its second position. Half of the difference between the two positions is called the index error, the horizontal and vertical axes of a theodolite must be perpendicular, if not then a horizontal axis error exists. This can be tested by aligning the tubular spirit bubble parallel to a line between two footscrews and setting the bubble central, a horizontal axis error is present if the bubble runs off central when the tubular spirit bubble is reversed. To adjust, the operator removes 1/2 the amount the bubble has run off using the screw, then re-level, test. If not, then a collimation error exists, index error, horizontal axis error and collimation error are regularly determined by calibration and are removed by mechanical adjustment. Their existence is taken account in the choice of measurement procedure in order to eliminate their effect on the measurement results of the theodolite. The term diopter was used in old texts as a synonym for theodolite. This derives from an astronomical instrument called a dioptra
6.
Differential GPS
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DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the GPS satellite systems and the known fixed positions. These stations broadcast the difference between the measured satellite pseudoranges and actual pseudoranges, and receiver stations may correct their pseudoranges by the same amount, the digital correction signal is typically broadcast locally over ground-based transmitters of shorter range. The term refers to a technique of augmentation. The United States Coast Guard and Canadian Coast Guard each run such systems in the U. S. the USCGs DGPS system has been named NDGPS and is now jointly administered by the Coast Guard and the U. S. Department of Transportation’s Federal Highway Administration. It consists of broadcast sites located throughout the inland and coastal portions of the United States including Alaska, Hawaii, a similar system that transmits corrections from orbiting satellites instead of ground-based transmitters is called a Wide-Area DGPS or Satellite Based Augmentation System. When GPS was first being put into service, the US military was concerned about the possibility of enemy forces using the globally available GPS signals to guide their own weapon systems. Originally, the government thought the coarse acquisition signal would only give about 100 meter accuracy, but with improved receiver designs and this technique, known as Selective Availability, or SA for short, seriously degraded the usefulness of the GPS signal for non-military users. This presented a problem for users who relied upon ground-based radio navigation systems such as LORAN, VOR. The advent of a global satellite system could provide greatly improved accuracy. The accuracy inherent in the S/A signal was too poor to make this realistic. Through the early to mid 1980s, a number of developed a solution to the SA problem. This suggested that broadcasting this offset to local GPS receivers could eliminate the effects of SA, resulting in closer to GPSs theoretical performance. Additionally, another source of errors in a GPS fix is due to transmission delays in the ionosphere. This offered an improvement to about 5 meters accuracy, more than enough for most civilian needs, the US Coast Guard was one of the more aggressive proponents of the DGPS system, experimenting with the system on an ever-wider basis through the late 1980s and early 1990s. These signals are broadcast on marine longwave frequencies, which could be received on existing radiotelephones, almost all major GPS vendors offered units with DGPS inputs, not only for the USCG signals, but also aviation units on either VHF or commercial AM radio bands. Plans were put into place to expand the system across the US, the quality of the DGPS corrections generally fell with distance, and large transmitters capable of covering large areas tend to cluster near cities. This meant that lower-population areas, notably in the midwest and Alaska, in addition the system provides single or dual coverage to a majority of the inland portion of United States. Instead, the FAA started studying broadcasting the signals across the entire hemisphere from communications satellites in geostationary orbit and this led to the Wide Area Augmentation System and similar systems, although these are generally not referred to as DGPS, or alternatively, wide-area DGPS
7.
Scuba diving
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Scuba diving is a mode of underwater diving in which the scuba diver uses a self-contained underwater breathing apparatus which is completely independent of surface supply, to breathe underwater. They may include additional cylinders for decompression gas or emergency breathing gas, closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open circuit, therefore, scuba divers engaged in armed forces covert operations may be referred to as frogmen, combat divers or attack swimmers. A scuba diver primarily moves underwater by using fins attached to the feet, scuba divers are trained in the procedures and skills appropriate to their level of certification by instructors affiliated to the diver certification organisations which issue these certifications. A minimum level of fitness and health is required by most training organisations, the closed-circuit rebreathers were first developed for escape and rescue purposes, and were modified for military use, due to their stealth advantages, as they produce very few bubbles. The first commercially successful closed-circuit scuba was designed and built by English diving engineer, Henry Fleuss in 1878, while working for Siebe Gorman in London. Sir Robert Davis, head of Siebe Gorman, improved the oxygen rebreather in 1910 with his invention of the Davis Submerged Escape Apparatus, rebreathers have been increasingly used by civilians for recreation, especially since the end of the Cold War. This reduced the risk of attack by Communist Bloc forces. After that, the armed forces had less reason to requisition civilian rebreather patents. The single hose two stage scuba regulators trace their origins to Australia, where Ted Eldred developed the first example of type of regulator. This was developed because patents protected the Aqualungs twin hose design, the single hose regulator separates the demand valve from the cylinder, giving the diver air at the ambient pressure at the mouth, rather than ambient pressure at the cylinder valve. The term SCUBA originally referred to United States combat frogmens oxygen rebreathers, SCUBA was originally an acronym, but is now generally used as a common noun or adjective, scuba. It has become acceptable to refer to equipment or scuba apparatus—examples of the linguistic RAS syndrome. Scuba diving may be performed for a number of reasons, both personal and professional, recreational diving is done purely for enjoyment and has a number of technical disciplines to increase interest underwater, such as cave diving, wreck diving, ice diving and deep diving. Divers may be employed professionally to perform tasks underwater, some of these tasks are suitable for scuba. There are divers who work, full or part-time, in the diving community as instructors, assistant instructors, divemasters. Other specialist areas of diving include military diving, with a long history of military frogmen in various roles. Their roles include direct combat, infiltration behind enemy lines, placing mines or using a manned torpedo, in some cases diver rescue teams may also be part of a fire department, paramedical service or lifeguard unit, and may be classed as public service diving
8.
Thermistor
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A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor, thermistors are widely used as inrush current limiter, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements. Thermistors are of two fundamental types, With NTC, resistance decreases as temperature rises to protect against inrush overvoltage conditions. Commonly installed in parallel as a current sink, with PTC, resistance increases as temperature rises to protect against overcurrent conditions. Commonly installed in series as a resettable fuse, thermistors differ from resistance temperature detectors in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. If k is positive, the resistance increases with increasing temperature, if k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient thermistor. Resistors that are not thermistors are designed to have a k as close to 0 as possible, instead of the temperature coefficient k, sometimes the temperature coefficient of resistance α T is used. It is defined as α T =1 R d R d T and this α T coefficient should not be confused with the a parameter below. In practice, the linear approximation works only over a temperature range. For accurate temperature measurements, the curve of the device must be described in more detail. The Steinhart–Hart equation is a widely used third-order approximation,1 T = a + b ln + c 3 where a, b and c are called the Steinhart–Hart parameters, T is the absolute temperature and R is the resistance. As an example, typical values for a thermistor with a resistance of 3 kΩ at room temperature are, a =1.40 ×10 −3 b =2.37 ×10 −4 c =9. Solving for R yields, R = R0 e − B or, alternatively and this can be solved for the temperature, T = B ln The B-parameter equation can also be written as ln R = B / T + ln r ∞. This can be used to convert the function of resistance vs. temperature of a thermistor into a function of ln R vs.1 / T. The average slope of this function will yield an estimate of the value of the B parameter. Many NTC thermistors are made from a disc, rod, plate. They work because raising the temperature of a semiconductor increases the number of charge carriers - it promotes them into the conduction band. The more charge carriers that are available, the current a material can conduct
9.
Electromagnetic induction
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Electromagnetic or magnetic induction is the production of an electromotive force across an electrical conductor due to its dynamic interaction with a magnetic field. Michael Faraday is generally credited with the discovery of induction in 1831, Lenzs law describes the direction of the induced field. Faradays law was later generalized to become the Maxwell-Faraday equation, one of the four Maxwells equations in James Clerk Maxwells theory of electromagnetism, electromagnetic induction has found many applications in technology, including electrical components such as inductors and transformers, and devices such as electric motors and generators. Electromagnetic induction was first discovered by Michael Faraday, who made his discovery public in 1831 and it was discovered independently by Joseph Henry in 1832. In Faradays first experimental demonstration, he wrapped two wires around opposite sides of a ring or torus. He plugged one wire into a galvanometer, and watched it as he connected the wire to a battery. He saw a transient current, which he called a wave of electricity and this induction was due to the change in magnetic flux that occurred when the battery was connected and disconnected. Within two months, Faraday found several other manifestations of electromagnetic induction, Faraday explained electromagnetic induction using a concept he called lines of force. However, scientists at the time widely rejected his theoretical ideas, an exception was James Clerk Maxwell, who used Faradays ideas as the basis of his quantitative electromagnetic theory. Heavisides version is the form recognized today in the group of known as Maxwells equations. In 1834 Heinrich Lenz formulated the law named after him to describe the flux through the circuit, Lenzs law gives the direction of the induced EMF and current resulting from electromagnetic induction. Faradays law of induction makes use of the magnetic flux ΦB through a region of space enclosed by a wire loop. The magnetic flux is defined by an integral, Φ B = ∫ Σ B ⋅ d A. The dot product B·dA corresponds to an amount of magnetic flux. In more visual terms, the flux through the wire loop is proportional to the number of magnetic flux lines that pass through the loop. When the flux through the changes, Faradays law of induction says that the wire loop acquires an electromotive force. The direction of the force is given by Lenzs law which states that an induced current will flow in the direction that will oppose the change which produced it. This is due to the sign in the previous equation
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