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90-414: Marine geophysics uses techniques largely employed on the continents, from fields including exploration geophysics and seismology , and methods unique to the ocean such as sonar . Most geophysical instruments are used from surface ships but some are towed near the seafloor or function autonomously, as with Autonomous Underwater Vehicles or AUVs. Objectives of marine geophysics include determination of

180-403: A thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water. The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation. Phase transitions involve the four fundamental states of matter : The boiling point of a substance

270-407: A body of fluid that is heated from underneath its container, conduction, and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy , while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On

360-489: A century to resolve. Since our global method of conflict resolution banks on warfare, we must be able to rely on specific practices to detect this unexploded ordnance, such as magnetic and electromagnetic surveys. By looking at differences in magnetic susceptibility and/or electrical conductivity in relation to the unexploded ordnance and the surrounding geology (soil, rock, etc.), we are able to detect and contain unexploded ordnance. Heat transfer Heat transfer

450-906: A computer model for the simulation of elastic waves in semi-infinite domains; and b) an optimization framework, through which the computed response is matched to the measured response by iteratively updating an initially assumed material distribution for the soil. Civil engineering can also use remote sensing information for topographical mapping, planning, and environmental impact assessment. Airborne electromagnetic surveys are also used to characterize soft sediments in planning and engineering roads, dams, and other structures. Magnetotellurics has proven useful for delineating groundwater reservoirs, mapping faults around areas where hazardous substances are stored (e.g. nuclear power stations and nuclear waste storage facilities), and earthquake precursor monitoring in areas with major structures such as hydro-electric dams subject to high levels of seismic activity. BS 5930

540-506: A conductive overburden). These are indirect inferential methods of detecting mineralization, as the commodity being sought is not directly conductive, or not sufficiently conductive to be measurable. EM surveys are also used in unexploded ordnance , archaeological, and geotechnical investigations. Regional EM surveys are conducted via airborne methods, using either fixed-wing aircraft or helicopter-borne EM rigs. Surface EM methods are based mostly on Transient EM methods using surface loops with

630-485: A height at their crest of two kilometers or more above the deep ocean basins, that extra mass was not related to an increase of gravity on the ridge of the magnitude that would be expected. The ridges are isostatically compensated, meaning the total mass below some reference depth in the mantle below the ridge is about the same everywhere. This requires a lower density mantle below the ridge crest and upper ridge flanks. Data from seismic studies revealed lower velocities under

720-430: A microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within

810-455: A narrow-angle i.e. coming from a source much smaller than its distance – can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation or a burning glass . For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F). The reachable temperature at

900-440: A phase transition. At standard atmospheric pressure and low temperatures , no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling , and is a very efficient heat transfer mechanism. At high bubble generation rates,

990-403: A result of a temperature difference. The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential , designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V). Joule is a unit to quantify energy , work, or the amount of heat. Heat transfer

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1080-447: A ridge to another. These are now known as transform faults , one of the three classes of plate boundaries. Echo sounding was used to map the deep trenches of the oceans and earthquake locations were noted to be located in and below the trenches. Data from marine seismic refraction experiments defined a thin ocean crust, approximately 6 to 8 kilometers in thickness, divided into three layers. Seismic reflection measurements made over

1170-405: A solid or between solid objects in thermal contact . Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact. The process of heat transfer from one place to another place without the movement of particles is called conduction, such as when placing a hand on a cold glass of water—heat is conducted from the warm skin to

1260-787: A surface receiver, or a downhole tool lowered into a borehole which transects a body of mineralization. These methods can map out sulphide bodies within the earth in three dimensions, and provide information to geologists to direct further exploratory drilling on known mineralization. Surface loop surveys are rarely used for regional exploration, however in some cases such surveys can be used with success (e.g.; SQUID surveys for nickel ore bodies). Electric-resistance methods such as induced polarization methods can be useful for directly detecting sulfide bodies, coal, and resistive rocks such as salt and carbonates. Seismic methods can also be used for mineral exploration, since they can provide high-resolution images of geologic structures hosting mineral deposits. It

1350-528: A survey ship. In more limited surveys magnetometers have been towed at a depth close to the seafloor or attached to deep submersibles .  Gravimeters using the zero-length spring technology are mounted in the most stable location on a ship; usually towards the center and low. They are specially designed to separate the acceleration of the ship from changes in the acceleration of Earth's gravity, or gravity anomalies , which are several thousand times less. In limited cases, gravity measurements have been made at

1440-451: A wide variety of mineral deposits, especially base metal sulphides via detection of conductivity anomalies which can be generated around sulphide bodies in the subsurface. EM surveys are also used in diamond exploration (where the kimberlite pipes tend to have lower resistance than enclosing rocks), graphite exploration, palaeochannel-hosted uranium deposits (which are associated with shallow aquifers, which often respond to EM surveys in

1530-405: Is a process function (or path function), as opposed to functions of state ; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process. Thermodynamic and mechanical heat transfer is calculated with the heat transfer coefficient ,

1620-417: Is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat ) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction , thermal convection , thermal radiation , and transfer of energy by phase changes . Engineers also consider the transfer of mass of differing chemical species (mass transfer in

1710-561: Is a measure that determines the relative strength of conduction and convection. R a = G r ⋅ P r = g Δ ρ L 3 μ α = g β Δ T L 3 ν α {\displaystyle \mathrm {Ra} =\mathrm {Gr} \cdot \mathrm {Pr} ={\frac {g\Delta \rho L^{3}}{\mu \alpha }}={\frac {g\beta \Delta TL^{3}}{\nu \alpha }}} where The Rayleigh number can be understood as

1800-402: Is a non-invasive technique, and is used within civil construction and engineering for a variety of uses, including detection of utilities (buried water, gas, sewerage, electrical and telecommunication cables), mapping of soft soils, overburden for geotechnical characterization, and other similar uses. The Spectral-Analysis-of-Surface-Waves (SASW) method is another non-invasive technique, which

1890-484: Is a thermal process that results in the phase transition of a substance from a solid to a liquid . The internal energy of a substance is increased, typically through heat or pressure, resulting in a rise of its temperature to the melting point , at which the ordering of ionic or molecular entities in the solid breaks down to a less ordered state and the solid liquefies. Molten substances generally have reduced viscosity with elevated temperature; an exception to this maxim

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1980-480: Is above 1,000–2,000. Radiative heat transfer is the transfer of energy via thermal radiation , i.e., electromagnetic waves . It occurs across vacuum or any transparent medium ( solid or fluid or gas ). Thermal radiation is emitted by all objects at temperatures above absolute zero , due to random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles ( protons and electrons ), their movement results in

2070-413: Is also common in the language of laymen and everyday life. The transport equations for thermal energy ( Fourier's law ), mechanical momentum ( Newton's law for fluids ), and mass transfer ( Fick's laws of diffusion ) are similar, and analogies among these three transport processes have been developed to facilitate the prediction of conversion from any one to the others. Thermal engineering concerns

2160-399: Is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction. Free, or natural, convection occurs when bulk fluid motions (streams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in

2250-927: Is an indirect method for assessing the likelihood of ore deposits or hydrocarbon accumulations. Methods devised for finding mineral or hydrocarbon deposits can also be used in other areas such as monitoring environmental impact, imaging subsurface archaeological sites, ground water investigations, subsurface salinity mapping, civil engineering site investigations , and interplanetary imaging. Magnetometric surveys can be useful in defining magnetic anomalies which represent ore (direct detection), or in some cases gangue minerals associated with ore deposits (indirect or inferential detection). The most direct method of detection of ore via magnetism involves detecting iron ore mineralization via mapping magnetic anomalies associated with banded iron formations which usually contain magnetite in some proportion. Skarn mineralization, which often contains magnetite, can also be detected though

2340-514: Is another widely used technique as it provides necessary high resolution information about rock and fluid properties in a vertical section, although they are limited in areal extent. This limitation in areal extent is the reason why seismic reflection techniques are so popular; they provide a method for interpolating and extrapolating well log information over a much larger area. Gravity and magnetics are also used, with considerable frequency, in oil and gas exploration. These can be used to determine

2430-400: Is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium . Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics . Heat convection occurs when

2520-412: Is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier ". Condensation occurs when a vapor is cooled and changes its phase to a liquid. During condensation, the latent heat of vaporization must be released. The amount of heat is the same as that absorbed during vaporization at the same fluid pressure. There are several types of condensation: Melting

2610-522: Is not just surface seismic surveys which are used, but also borehole seismic methods. All in all, the usage of seismic methods for mineral exploration is steadily increasing. Seismic reflection and refraction techniques are the most widely used geophysical technique in hydrocarbon exploration. They are used to map the subsurface distribution of stratigraphy and its structure which can be used to delineate potential hydrocarbon accumulations, both stratigraphic and structural deposits or "traps". Well logging

2700-421: Is often called "forced convection." In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means. Thermal radiation occurs through a vacuum or any transparent medium ( solid or fluid or gas ). It is the transfer of energy by means of photons or electromagnetic waves governed by the same laws. Heat transfer is the energy exchanged between materials (solid/liquid/gas) as

2790-399: Is the element sulfur , whose viscosity increases to a point due to polymerization and then decreases with higher temperatures in its molten state. Heat transfer can be modeled in various ways. The heat equation is an important partial differential equation that describes the distribution of heat (or temperature variation) in a given region over time. In some cases, exact solutions of

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2880-603: Is the standard used in the UK as a code of practice for site investigations. Ground penetrating radar can be used to map buried artifacts , such as graves, mortuaries, wreck sites, and other shallowly buried archaeological sites. Ground magnetometric surveys can be used for detecting buried ferrous metals, useful in surveying shipwrecks, modern battlefields strewn with metal debris, and even subtle disturbances such as large-scale ancient ruins. Sonar systems can be used to detect shipwrecks. Active sonar systems emit sound pulses into

2970-506: Is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid evaporates resulting in an abrupt change in vapor volume. In a closed system , saturation temperature and boiling point mean the same thing. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in

3060-457: Is the typical fluid velocity due to convection and T conv {\displaystyle T_{\text{conv}}} the order of its timescale. The conduction timescale, on the other hand, is of the order of T cond = L 2 / α {\displaystyle T_{\text{cond}}=L^{2}/\alpha } . Convection occurs when the Rayleigh number

3150-440: Is used in multibeam sonar or swath mapping that became more advanced toward the latter half of the 20th century. The thickness and type of sediments covering the ocean crust are estimated using the seismic reflection technique. This method was highly advanced by offshore oil exploration companies. The method employs a sound source at the ship with much lower frequencies than echo sounding, and an array of hydrophones towed by

3240-415: Is used to map the seafloor bottom texture to ranges from tens of meters to a kilometer or more depending on the device. When the sound or energy source is separated from the recording devices by distances of several kilometers or more, then refracted seismic waves are measured. Their travel time can be used to determine the internal structure of the ocean crust, and from the seismic velocities determined by

3330-493: Is widely used in practice to detect the shear wave velocity profile of the soil. The SASW method relies on the dispersive nature of Raleigh waves in layered media, i.e., the wave-velocity depends on the load's frequency. A material profile, based on the SASW method, is thus obtained according to: a) constructing an experimental dispersion curve, by performing field experiments, each time using a different loading frequency, and measuring

3420-517: The Stefan-Boltzmann equation can be exceeded when the objects exchanging thermal radiation or the distances separating them are comparable in scale or smaller than the dominant thermal wavelength . The study of these cases is called near-field radiative heat transfer . Radiation from the sun, or solar radiation, can be harvested for heat and power. Unlike conductive and convective forms of heat transfer, thermal radiation – arriving within

3510-420: The lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady-state system. That is, the method assumes that the temperature within

3600-422: The proportionality between the heat flux and the thermodynamic driving force for the flow of heat. Heat flux is a quantitative, vectorial representation of heat flow through a surface. In engineering contexts, the term heat is taken as synonymous with thermal energy. This usage has its origin in the historical interpretation of heat as a fluid ( caloric ) that can be transferred by various causes, and that

3690-446: The spectral signature of geochemically altered soils and vegetation. Specifically at sea, two methods are used: marine seismic reflection and electromagnetic seabed logging (SBL). Marine magnetotellurics (mMT), or marine Controlled Source Electro-Magnetics (mCSEM), can provide pseudo-direct detection of hydrocarbons by detecting resistivity changes over geological traps (signalled by seismic surveys). Ground penetrating radar

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3780-475: The U.S. GPS array or the Russian GLONASS for ship navigation. Geophysical instruments towed near the seafloor typically use acoustic transponder navigation sonar networks. The depth of the seafloor is measured using echo sounding , a sonar method developed during the 20th century and advanced during World War II . Common variations are based on the sonar beam width and number of sonar beams as

3870-433: The above techniques, have been developed and are currently used. However these are not as common due to cost-effectiveness, wide applicability, and/or uncertainty in the results produced. Exploration geophysics is also used to map the subsurface structure of a region, to elucidate the underlying structures, to recognize spatial distribution of rock units, and to detect structures such as faults, folds and intrusive rocks. This

3960-414: The amount of heat entering a section is equal to amount of heat coming out, since the temperature change (a measure of heat energy) is zero. An example of steady state conduction is the heat flow through walls of a warm house on a cold day—inside the house is maintained at a high temperature and, outside, the temperature stays low, so the transfer of heat per unit time stays near a constant rate determined by

4050-410: The anomalies to the history of Earth's magnetic field reversals allowed the age of the seafloor to be estimated. This connection was interpreted as the spreading of the seafloor from the ridge crests. Linking spreading centers and transform faults to a common cause helped to develop the concept of plate tectonics. When the age of the ocean crust as determined by magnetic anomalies or drill hole samples

4140-411: The bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling , or DNB). At similar standard atmospheric pressure and high temperatures , the hydrodynamically quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low but rise slowly with temperature. Any contact between the fluid and

4230-446: The bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". The former process

4320-445: The cold glass, but if the hand is held a few inches from the glass, little conduction would occur since air is a poor conductor of heat. Steady-state conduction is an idealized model of conduction that happens when the temperature difference driving the conduction is constant so that after a time, the spatial distribution of temperatures in the conducting object does not change any further (see Fourier's law ). In steady state conduction,

4410-403: The combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming. The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid

4500-528: The convection is roughly g Δ ρ L 3 {\displaystyle g\Delta \rho L^{3}} , so the corresponding pressure is roughly g Δ ρ L {\displaystyle g\Delta \rho L} . In steady state , this is canceled by the shear stress due to viscosity, and therefore roughly equals μ V / L = μ / T conv {\displaystyle \mu V/L=\mu /T_{\text{conv}}} , where V

4590-467: The crust at the ridge crest spreading centers. This hypothesis was borne out in the late 20th century when investigations by deep submersibles discovered hydrothermal vents at spreading centers. Marine gravity profiles made across Mid-Ocean Ridges showed a lack of a gravity anomaly, the Free-air anomaly is small or near zero when averaged over a broad area. This suggested that although ridges reached

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4680-423: The deep sea sedimentary record. These have been interpreted as evidence of past global climate change events. Seismic reflection surveys made on polar continental selves have identified buried sedimentary features due to the advance and retreat of continental ice sheets. Swath sonar mapping has revealed the gouge tracks of ice sheets cut as they traversed polar continental shelves in the past. Heat flow measured in

4770-440: The depth and features of the seafloor, the seismic structure and earthquakes in the ocean basins, the mapping of gravity and magnetic anomalies over the basins and margins, the determination of heat flow through the seafloor, and electrical properties of the ocean crust and Earth's mantle . Modern marine geophysics, as with most oceanographic surveying with research ships, use Global Positioning System satellites, either

4860-492: The dysfunction or non-explosion of military explosives. Examples of these include, but are not limited to: bombs , flares , and grenades . It is important to be able to locate and contain unexploded ordnance to avoid injuries, and even possible death, to those who may come in contact with them. The issue of unexploded ordnance originated as a result of the Crimean War (1853-1856). Before this, most unexploded ordnance

4950-450: The emission of electromagnetic radiation which carries away energy. Radiation is typically only important in engineering applications for very hot objects, or for objects with a large temperature difference. When the objects and distances separating them are large in size and compared to the wavelength of thermal radiation, the rate of transfer of radiant energy is best described by the Stefan-Boltzmann equation . For an object in vacuum,

5040-492: The equation are available; in other cases the equation must be solved numerically using computational methods such as DEM-based models for thermal/reacting particulate systems (as critically reviewed by Peng et al. ). Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newton's law of cooling . System analysis by

5130-518: The equation is: ϕ q = ϵ σ T 4 . {\displaystyle \phi _{q}=\epsilon \sigma T^{4}.} For radiative transfer between two objects, the equation is as follows: ϕ q = ϵ σ F ( T a 4 − T b 4 ) , {\displaystyle \phi _{q}=\epsilon \sigma F(T_{a}^{4}-T_{b}^{4}),} where The blackbody limit established by

5220-448: The fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case, the fluid is forced to flow by using a pump, fan, or other mechanical means. Convective heat transfer , or simply, convection, is the transfer of heat from one place to another by

5310-427: The fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current. Convective cooling is sometimes described as Newton's law of cooling : The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings . However, by definition,

5400-405: The form of advection ), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object

5490-432: The generation, use, conversion, storage, and exchange of heat transfer. As such, heat transfer is involved in almost every sector of the economy. Heat transfer is classified into various mechanisms, such as thermal conduction , thermal convection , thermal radiation , and transfer of energy by phase changes . The fundamental modes of heat transfer are: By transferring matter, energy—including thermal energy—is moved by

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5580-441: The geometry and depth of covered geological structures including uplifts , subsiding basins , faults , folds , igneous intrusions , and salt diapirs due to their unique density and magnetic susceptibility signatures compared to the surrounding rocks; the latter is particularly useful for metallic ores. Remote sensing techniques, specifically hyperspectral imaging , have been used to detect hydrocarbon microseepages using

5670-417: The ground surface. These waves propagate through the soil, and due to the heterogeneous geological structure of the site under investigation, multiple reflections and refractions occur. The response of the site to the seismic vibrator is measured by sensors ( geophones ), also placed on the ground surface. Two key-components are required for the profiling based on full-waveform inversion. These components are: a)

5760-655: The insulation in the wall and the spatial distribution of temperature in the walls will be approximately constant over time. Transient conduction (see Heat equation ) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex, and analytic solutions of the heat equation are only valid for idealized model systems. Practical applications are generally investigated using numerical methods, approximation techniques, or empirical study. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands

5850-486: The method, an estimate can be made of the crustal rock type.  Recording devices include hydrophones at the ocean surface and also ocean bottom seismographs. Refraction experiments have detected anisotropy of seismic wave speed in the oceanic upper mantle. The usual method of measuring the Earth's magnetic field at the sea surface is by towing a total field proton precession magnetometer several hundred meters behind

5940-405: The movement of fluids , a process that is essentially the transfer of heat via mass transfer . The bulk motion of fluid enhances heat transfer in many physical situations, such as between a solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe

6030-494: The object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object. Climate models study the radiant heat transfer by using quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in

6120-475: The object is completely uniform, although its value may change over time. In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the object's boundary, known as the Biot number , is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into

6210-408: The ocean basins revealed that conductive heat flow decreased with the increased depth and crustal age of flanks of ocean ridges. On the ridge crest, however, conductive heat flow was found to be unexpectedly low for a location where active volcanism accompanies seafloor spreading. This anomaly was explained by the possible heat transfer by hydrothermal venting of seawater circulating in deep fissures in

6300-447: The ocean ridges found they are devoid of sediments at the crest, but covered by increasingly thicker sediment layers with increasing distance from the ridge crest. This observation implied that the ridge crests are younger than the ridge flanks. Magnetic surveys discovered linear magnetic anomalies that in many areas ran parallel to an ocean ridge crest and showed a mirror-image symmetrical pattern centered on ridge crests. Correlation of

6390-406: The ocean, rather than measuring the range or orientation of an object. Ground penetrating radar can be used to detect grave sites. This detection is of both legal and cultural importance, providing an opportunity for affected families to pursue justice through legal punishment of those responsible and to experience closure over the loss of a loved one. Unexploded ordnance (or UXO) refers to

6480-636: The ore minerals themselves would be non-magnetic. Similarly, magnetite, hematite, and often pyrrhotite are common minerals associated with hydrothermal alteration , which can be detected to provide an inference that some mineralizing hydrothermal event has affected the rocks. Gravity surveying can be used to detect dense bodies of rocks within host formations of less dense wall rocks. This can be used to directly detect Mississippi Valley Type ore deposits , IOCG ore deposits, iron ore deposits, skarn deposits, and salt diapirs which can form oil and gas traps. Electromagnetic (EM) surveys can be used to help detect

6570-467: The other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong. The Rayleigh number ( R a {\displaystyle \mathrm {Ra} } ) is the product of the Grashof ( G r {\displaystyle \mathrm {Gr} } ) and Prandtl ( P r {\displaystyle \mathrm {Pr} } ) numbers. It

6660-445: The physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons ; geothermal reservoirs; and groundwater reservoirs. It can also be used to detect the presence of unexploded ordnance . Exploration geophysics can be used to directly detect

6750-451: The physical transfer of a hot or cold object from one place to another. This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics . This can be described by the formula: ϕ q = v ρ c p Δ T {\displaystyle \phi _{q}=v\rho c_{p}\Delta T} where On

6840-452: The presence of fluids within cracks and pores in rocks, the presence of magma , and mineral deposits like sulfides at the seafloor. Surveys can be done at either the sea surface or seafloor or in combination, using active current sources or natural Earth electrical currents, known as telluric currents . In special cases, measurements of natural gamma radiation from seafloor mineral deposits have been made using scintillometers towed near

6930-403: The ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system. The buoyancy force driving

7020-432: The ridges suggesting parts of the mantle below the crests are lower density rock melt. This is consistent with the theories of seafloor spreading and plate tectonics. Exploration geophysics Exploration geophysics is an applied branch of geophysics and economic geology , which uses physical methods at the surface of the Earth , such as seismic, gravitational, magnetic, electrical and electromagnetic, to measure

7110-405: The seafloor from deep submersibles. The geothermal gradient is measured using a 2-meter long temperature probe or with thermistors attached to sediment core barrels. Measured temperatures combined with the thermal conductivity of the sediment give a measure of the conductive heat flow through the seafloor. Electrical conductivity , or the converse resistivity, can be related to rock type,

7200-429: The seafloor. Echo sounding was used to refine the limits of the known mid-ocean ridges , and to discover new ones. Further sounding mapped linear seafloor fracture zones that are nearly orthogonal to the trends of the ridges.  Later, determining earthquake locations for the deep ocean discovered that quakes are restricted to the crests of the mid-ocean ridges and stretches of fracture zones that link one segment of

7290-421: The ship, that record echoes from the internal structure of the sediment cover and the crust below the sediment. In some cases, reflections from the internal structure of the ocean crust can be detected. Echo sounders that use lower frequencies near 3.5 kHz are used to detect both the seafloor and shallow structure below the seafloor.  Side-looking sonar , where the sonar beams are aimed just below horizontal,

7380-414: The soil. Full-waveform-inversion (FWI) methods are among the most recent techniques for geotechnical site characterization, and are still under continuous development. The method is fairly general, and is capable of imaging the arbitrarily heterogeneous compressional and shear wave velocity profiles of the soil. Elastic waves are used to probe the site under investigation, by placing seismic vibrators on

7470-404: The surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation "). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux , or CHF). The Leidenfrost Effect demonstrates how nucleate boiling slows heat transfer due to gas bubbles on the heater's surface. As mentioned, gas-phase thermal conductivity

7560-456: The surface wave-speed for each frequency; b) constructing a theoretical dispersion curve, by assuming a trial distribution for the material properties of a layered profile; c) varying the material properties of the layered profile, and repeating the previous step, until a match between the experimental dispersion curve, and the theoretical dispersion curve is attained. The SASW method renders a layered (one-dimensional) shear wave velocity profile for

7650-563: The target is limited by the temperature of the hot source of radiation. (T -law lets the reverse flow of radiation back to the source rise.) The (on its surface) somewhat 4000 K hot sun allows to reach coarsely 3000 K (or 3000 °C, which is about 3273 K) at a small probe in the focus spot of a big concave, concentrating mirror of the Mont-Louis Solar Furnace in France. Phase transition or phase change, takes place in

7740-419: The target style of mineralization by measuring its physical properties directly. For example, one may measure the density contrasts between the dense iron ore and the lighter silicate host rock, or one may measure the electrical conductivity contrast between conductive sulfide minerals and the resistive silicate host rock. The main techniques used are: Many other techniques, or methods of integration of

7830-415: The validity of Newton's law of cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients , and in some cases is strongly nonlinear. In these cases, Newton's law does not apply. In

7920-504: The water which then bounce off of objects and are returned to the sonar transducer. The sonar transducer is able to determine both the range and orientation of an underwater object by measuring the amount of time between the release of the sound pulse and its returned reception. Passive sonar systems are used to detect noises from marine objects or animals. This system does not emit sound pulses itself but instead focuses on sound detection from marine sources. This system simply 'listens' to

8010-409: Was compared to the ocean depth it was observed that depth and age are directly related in a seafloor depth age relationship . This relationship was explained by the cooling and contracting of an oceanic plate as it spreads away from a ridge crest. Seismic reflection data combined with deep-sea drilling at some locations have identified widespread unconformities and distinctive seismic reflectors in

8100-461: Was locally contained in smaller volumes, and was thus not a huge public issue. However, with the introduction of more widespread warfare, these quantities increased and were thus easy to lose track of and contain. According to Hooper & Hambric in their piece Unexploded Ordnance (UXO): The Problem , if we are unable to move away from war in the context of conflict resolution, this problem will only continue to get worse and will likely take more than

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