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Physical Geodesy
Physical geodesy is the study of the physical properties of Earth's gravity and its potential field (the geopotential), with a view to their application in geodesy. Measurement procedure Traditional geodetic instruments such as theodolites rely on the gravity field for orienting their vertical axis along the local plumb line or local vertical direction with the aid of a spirit level. After that, vertical angles (zenith angles or, alternatively, elevation angles) are obtained with respect to this local vertical, and horizontal angles in the plane of the local horizon, perpendicular to the vertical. Levelling instruments again are used to obtain geopotential differences between points on the Earth's surface. These can then be expressed as "height" differences by conversion to metric units. Units Gravity is commonly measured in units of m·s−2 (metres per second squared). This also can be expressed (multiplying by the gravitational constant G in order to change units) as newto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ocean Gravity Map
The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic Ocean),"Ocean." ''Merriam-Webster.com Dictionary'', Merriam-Webster, https://www.merriam-webster.com/dictionary/ocean . Accessed March 14, 2021. and are themselves mostly divided into s, s and subsequent bodies o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Joule
The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work done when a force of one newton displaces a body through a distance of one metre in the direction of that force. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889). Definition According to the International Bureau of Weights and Measures the joule is defined as "the work done when the point of application of 1 MKS unit of force ewtonmoves a distance of 1 metre in the direction of the force." In terms of SI base units and in terms of SI derived units with special names, the joule is defined as One joule is also equivalent to any of the following: * The work required to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bouguer Plate
In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly. Definition The Bouguer anomaly g_B defined as: g_B = g_ - \delta g_B + \delta g_T Here, * g_F is the free-air gravity anomaly. * \delta g_B is the ''Bouguer correction'' which allows for the gravitational attraction of rocks between the measurement point and sea level; * \delta g_T is a ''terrain correction'' which allows for deviations of the surface from an infinite horizontal plane The free-air anomaly g_F, in its turn, is related to the observed gravity g_ as follows: g_F = g_ - g_\lambda + \delta g_F where: * g_\lambda is the correction for latitude (because the Earth is not a perfect sphere; see normal gravity); * \delta g_F is the free-air correction. Reduction A Bouguer reduction is called ''simple'' (or ''incomplete'') if ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geophysics
Geophysics () is a subject of natural science concerned with the physical processes and Physical property, properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations across a wide range of scientific disciplines. The term ''geophysics'' classically refers to solid earth applications: Earth's figure of the Earth, shape; its gravitational, Earth's magnetic field, magnetic fields, and electromagnetic fields; its structure of the Earth, internal structure and Earth#Chemical composition, composition; its geodynamics, dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; geophysical fluid dynamics, fluid dynamics of the oceans and the atmosphere; atmospheric electricity, electricity and magnetism in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free-air Anomaly
In geophysics, the free-air gravity anomaly, often simply called the free-air anomaly, is the measured gravity anomaly after a free-air correction is applied to account for the elevation at which a measurement is made. It does so by adjusting these measurements of gravity to what would have been measured at a reference level, which is commonly taken as mean sea level or the geoid. Applications Studies of the subsurface structure and composition of the Earth's Crust (geology), crust and Mantle (geology), mantle employ surveys using Gravimetry, gravimeters to measure the departure of observed gravity from a theoretical gravity value to identify anomalies due to geologic features below the measurement locations. The computation of anomalies from observed measurements involves the application of corrections that define the resulting anomaly. The free-air anomaly can be used to test for Isostasy, isostatic equilibrium over broad regions. Survey methods The free-air correction adjus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Divergence Theorem
In vector calculus, the divergence theorem, also known as Gauss's theorem or Ostrogradsky's theorem, reprinted in is a theorem relating the '' flux'' of a vector field through a closed surface to the ''divergence'' of the field in the volume enclosed. More precisely, the divergence theorem states that the surface integral of a vector field over a closed surface, which is called the "flux" through the surface, is equal to the volume integral of the divergence over the region enclosed by the surface. Intuitively, it states that "the sum of all sources of the field in a region (with sinks regarded as negative sources) gives the net flux out of the region". The divergence theorem is an important result for the mathematics of physics and engineering, particularly in electrostatics and fluid dynamics. In these fields, it is usually applied in three dimensions. However, it generalizes to any number of dimensions. In one dimension, it is equivalent to the fundamental theorem of cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrogeodetic Leveling
Geodetic astronomy or astronomical geodesy (astro-geodesy) is the application of astronomical methods into geodetic networks and other technical projects of geodesy. Applications The most important applications are: * Establishment of geodetic datum systems (e.g. ED50) or at expeditions * apparent places of stars, and their proper motions * precise astronomical navigation * astro-geodetic geoid determination * modelling the rock densities of the topography and of geological layers in the subsurface * Monitoring of the Earth rotation and polar wandering * Contribution to the time system of physics and geosciences Measuring techniques Important measuring techniques are: * Latitude determination and longitude determination, by theodolites, tacheometers, astrolabes or zenith cameras * time and star positions by observation of star transits, e.g. by meridian circles (visual, photographic or CCD) * Azimuth determination ** for the exact orientation of geodetic netwo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Datum (geodesy)
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates. DatumsThe plural is not "data" in this case are crucial to any technology or technique based on spatial location, including geodesy, navigation, surveying, geographic information systems, remote sensing, and cartography. A horizontal datum is used to measure a horizontal position, across the Earth's surface, in latitude and longitude or another related coordinate system. A ''vertical datum'' is used to measure the elevation or depth relative to a standard origin, such as mean sea level (MSL). A three-dimensional datum enables the expression of both horizontal and vertical position components in a unified form. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Datum
In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built structures) and altitudes of satellite orbits and in aviation. In planetary science, vertical datums are also known as zero-elevation surface or zero-level reference. Commonly adopted criteria for a vertical datum include the following approaches: * Tides, based on sea level when specific conditions occur, such as NOAA's National Geodetic Survey-produced tidal datums; * Gravimetric, based on a geoid; or geometric, based on the same Earth ellipsoids that are used in computing a horizontal datum, such as NOAA's planned gravimetric and Global Navigation Satellite Systems (GNSS)-based Datum of 2022 set to be released that year by the National Geodetic Survey. In the United States, prominent vertical datums for professional uses include the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Sea Surface Topography
Ocean surface topography or sea surface topography, also called ocean dynamic topography, are highs and lows on the ocean surface, similar to the hills and valleys of Earth's land surface depicted on a topographic map. These variations are expressed in terms of average sea surface height (SSH) relative to Earth's geoid. The main purpose of measuring ocean surface topography is to understand the large-scale ocean circulation. Time variations Unaveraged or instantaneous sea surface height (SSH) is most obviously affected by the tidal forces of the Moon and by the seasonal cycle of the Sun acting on Earth. Over timescales longer than a year, the patterns in SSH can be influenced by ocean circulation. Typically, SSH anomalies resulting from these forces differ from the mean by less than ± at the global scale. Other influences include changing interannual patterns of temperature, salinity, waves, tides and winds. Ocean surface topography can be measured with high accuracy and pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Undulation Of The Geoid
The geoid ( ) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as might be approximated with very narrow hypothetical canals). According to Carl Friedrich Gauss, who first described it, it is the "mathematical figure of the Earth", a smooth but irregular surface whose shape results from the uneven distribution of mass within and on the surface of Earth. It can be known only through extensive gravitational measurements and calculations. Despite being an important concept for almost 200 years in the history of geodesy and geophysics, it has been defined to high precision only since advances in satellite geodesy in the late 20th century. The geoid is often expressed as a geoid undulation or geoidal height above a given reference ellipsoid, which is a slightly flattened sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, Indian peninsula by the Gulf of Mannar and the Palk Strait. It shares a maritime border with the Maldives in the southwest and India in the northwest. Sri Jayawardenepura Kotte is the legislative capital of Sri Lanka, while the largest city, Colombo, is the administrative and judicial capital which is the nation's political, financial and cultural centre. Kandy is the second-largest urban area and also the capital of the last native kingdom of Sri Lanka. The most spoken language Sinhala language, Sinhala, is spoken by the majority of the population (approximately 17 million). Tamil language, Tamil is also spoken by approximately five million people, making it the second most-spoken language in Sri Lanka. Sri Lanka has a population of appr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
