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Showing posts with label Isostasy. Show all posts
Showing posts with label Isostasy. Show all posts

Thursday, October 25, 2012

Gravimetry

Gravity map of the Southern Ocean around the Antarctic continent
This gravity field was computed from sea-surface height measurements collected by the US Navy GEOSAT altimeter between March, 1985, and January, 1990. The high density GEOSAT Geodetic Mission data that lie south of 30 deg. S were declassified by the Navy in May of 1992 and contribute most of the fine-scale gravity information.
The Antarctic continent itself is shaded in blue depending on the thickness of the ice sheet (blue shades in steps of 1000 m); light blue is shelf ice; gray lines are the major ice devides; pink spots are parts of the continent which are not covered by ice; gray areas have no data.

Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of gravitational field or the properties of matter responsible for its creation are of interest. The term gravimetry or gravimetric is also used in chemistry to define a class of analytical procedures, called gravimetric analysis relying upon weighing a sample of material.


 See Also:
Atom interferometry: In light-pulse atom interferometers, atomic matter waves are split and recombined using pulses of laser light. The splitting occurs because when an atom interacts with the photons of a laser beam, it exchanges the momentum of a number of photons. The atom may thus continue on either of two spatially separate paths, the interferometer arms. When the paths are recombined, the probability that the atom is found depends upon the phase difference between them, which determines whether the matter waves will add or cancel. This phase is shifted by the atom’s coupling to electromagnetic fields, gravity, inertial forces, and other influences. By selecting the geometry of the interferometer, the atomic species, and its quantum state, one can maximize the wanted influence and minimize others. Advances in the control of the quantum state of atoms and photons have led to an extraordinary sensitivity and accuracy.




See:

Sunday, November 14, 2010

Gravimetry

For the chemical analysis technique, see Gravimetric analysis.


Gravity map of the Southern Ocean around the Antarctic continent
Author-Hannes Grobe, AWI

This gravity field was computed from sea-surface height measurements collected by the US Navy GEOSAT altimeter between March, 1985, and January, 1990. The high density GEOSAT Geodetic Mission data that lie south of 30 deg. S were declassified by the Navy in May of 1992 and contribute most of the fine-scale gravity information.

The Antarctic continent itself is shaded in blue depending on the thickness of the ice sheet (blue shades in steps of 1000 m); light blue is shelf ice; gray lines are the major ice devides; pink spots are parts of the continent which are not covered by ice; gray areas have no data.
Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of gravitational field or the properties of matter responsible for its creation are of interest. The term gravimetry or gravimetric is also used in chemistry to define a class of analytical procedures, called gravimetric analysis relying upon weighing a sample of material.

Contents

Units of measurement

Gravity is usually measured in units of acceleration. In the SI system of units, the standard unit of acceleration is 1 metre per second squared (abbreviated as m/s2). Other units include the gal (sometimes known as a galileo, in either case with symbol Gal), which equals 1 centimetre per second squared, and the g (gn), equal to 9.80665 m/s2. The value of the gn approximately equals the acceleration due to gravity at the Earth's surface (although the actual acceleration g varies fractionally from place to place).

How gravity is measured

An instrument used to measure gravity is known as a gravimeter, or gravitometer. Since general relativity regards the effects of gravity as indistinguishable from the effects of acceleration, gravimeters may be regarded as special purpose accelerometers. Many weighing scales may be regarded as simple gravimeters. In one common form, a spring is used to counteract the force of gravity pulling on an object. The change in length of the spring may be calibrated to the force required to balance the gravitational pull. The resulting measurement may be made in units of force (such as the newton), but is more commonly made in units of gals.

More sophisticated gravimeters are used when precise measurements are needed. When measuring the Earth's gravitational field, measurements are made to the precision of microgals to find density variations in the rocks making up the Earth. Several types of gravimeters exist for making these measurements, including some that are essentially refined versions of the spring scale described above. These measurements are used to define gravity anomalies.

Besides precision, also stability is an important property of a gravimeter, as it allows the monitoring of gravity changes. These changes can be the result of mass displacements inside the Earth, or of vertical movements of the Earth's crust on which measurements are being made: remember that gravity decreases 0.3 mGal for every metre of height. The study of gravity changes belongs to geodynamics.

The majority of modern gravimeters use specially-designed quartz zero-length springs to support the test mass. Zero length springs do not follow Hooke's Law, instead they have a force proportional to their length. The special property of these springs is that the natural resonant period of oscillation of the spring-mass system can be made very long - approaching a thousand seconds. This detunes the test mass from most local vibration and mechanical noise, increasing the sensitivity and utility of the gravimeter. The springs are quartz so that magnetic and electric fields do not affect measurements. The test mass is sealed in an air-tight container so that tiny changes of barometric pressure from blowing wind and other weather do not change the buoyancy of the test mass in air.

Spring gravimeters are, in practice, relative instruments which measure the difference in gravity between different locations. A relative instrument also requires calibration by comparing instrument readings taken at locations with known complete or absolute values of gravity. Absolute gravimeters provide such measurements by determining the gravitational acceleration of a test mass in vacuum. A test mass is allowed to fall freely inside a vacuum chamber and its position is measured with a laser interferometer and timed with an atomic clock. The laser wavelength is known to ±0.025 ppb and the clock is stable to ±0.03 ppb as well. Great care must be taken to minimize the effects of perturbing forces such as residual air resistance (even in vacuum) and magnetic forces. Such instruments are capable of an accuracy of a few parts per billion or 0.002 mGal and reference their measurement to atomic standards of length and time. Their primary use is for calibrating relative instruments, monitoring crustal deformation, and in geophysical studies requiring high accuracy and stability. However, absolute instruments are somewhat larger and significantly more expensive than relative spring gravimeters, and are thus relatively rare.

Gravimeters have been designed to mount in vehicles, including aircraft, ships and submarines. These special gravimeters isolate acceleration from the movement of the vehicle, and subtract it from measurements. The acceleration of the vehicles is often hundreds or thousands of times stronger than the changes being measured. A gravimeter (the Lunar Surface Gravimeter) was also deployed on the surface of the moon during the Apollo 17 mission, but did not work due to a design error. A second device (the Traverse Gravimeter Experiment) functioned as anticipated.

Microgravimetry

Microgravimetry is a rising and important branch developed on the foundation of classical gravimetry.

Microgravity investigations are carried out in order to solve various problems of engineering geology, mainly location of voids and their monitoring. Very detailed measurements of high accuracy can indicate voids of any origin, provided the size and depth are large enough to produce gravity effect stronger than is the level of confidence of relevant gravity signal.

History

The modern gravimeter was developed by Lucien LaCoste and Arnold Romberg in 1936.

They also invented most subsequent refinements, including the ship-mounted gravimeter, in 1965, temperature-resistant instruments for deep boreholes, and lightweight hand-carried instruments. Most of their designs remain in use (2005) with refinements in data collection and data processing.

See also

The Lunar Far Side: The Side Never Seen from Earth

                                                            Mass concentration (astronomy)

This figure shows the topography (top) and corresponding gravity (bottom) signal of Mare Smythii at the Moon. It nicely illustrates the term "mascon". Author Martin Pauer

While article is from Tuesday, June 22, 2010 9:00 PM it still amazes me how we see the moon in context of it's coloring.
Topography when seen in context of landscape, how we measure aspects of the gravitational field supply us with a more realistic interpretation of the globe as a accurate picture of how that sphere(isostatic equilibrium)  looks.


Image Credit: NASA/Goddard
Ten Cool Things Seen in the First Year of LRO

Tidal forces between the moon and the Earth have slowed the moon' rotation so that one side of the moon always faces toward our planet. Though sometimes improperly referred to as the "dark side of the moon," it should correctly be referred to as the "far side of the moon" since it receives just as much sunlight as the side that faces us. The dark side of the moon should refer to whatever hemisphere isn't lit at a given time. Though several spacecraft have imaged the far side of the moon since then, LRO is providing new details about the entire half of the moon that is obscured from Earth. The lunar far side is rougher and has many more craters than the near side, so quite a few of the most fascinating lunar features are located there, including one of the largest known impact craters in the solar system, the South Pole-Aitken Basin. The image highlighted here shows the moon's topography from LRO's LOLA instruments with the highest elevations up above 20,000 feet in red and the lowest areas down below -20,000 feet in blue.

Learn More About Far side of the Moon

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 Credit: NASA/Goddard/MIT/Brown

Figure 4: A lunar topographic map showing the Moon from the vantage point of the eastern limb. On the left side of the Moon seen in this view is part of the familiar part of the Moon observed from Earth (the eastern part of the nearside). In the middle left-most part of the globe is Mare Tranquillitatis (light blue) the site of the Apollo 11 landing, and above this an oval-appearing region (Mare Serenitatis; dark blue) the site of the Apollo 17 landing. Most of the dark blue areas are lunar maria, low lying regions composed of volcanic lava flows that formed after the heavily cratered lunar highlands (and are thus much less cratered). The topography is derived from over 2.4 billion shots made by the Lunar Orbiter Laser Altimeter (LOLA) instrument on board the NASA Lunar Reconnaissance Orbiter. The large near-circular basins show the effects of the early impacts on early planetary crusts in the inner solar system, including the Earth. 

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 Author and Image Credit: Mark A. Wieczorek
Radial gravitational anomaly at the surface of the Moon as determined from the gravity model LP150Q. The contribution due to the rotational flattening has been removed for clarity, and positive anomalies correspond to an increase in magnitude of the gravitational acceleration. Data are presented in two Lambert azimuthal equal area projections.
The major characteristic of the Moon's gravitational field is the presence of mascons, which are large positive gravity anomalies associated with some of the giant impact basins. These anomalies greatly influence the orbit of spacecraft about the Moon, and an accurate gravitational model is necessary in the planning of both manned and unmanned missions. They were initially discovered by the analysis of Lunar Orbiter tracking data,[2] since navigation tests prior to the Apollo program experienced positioning errors much larger than mission specifications.

Saturday, November 06, 2010

Colour of Gravity 3

Colour measurement

We know that colour is a psychophysical experience of an observer which changes from observer to observer and is therefore impossible to replicate absolutely. In order to quantify colour in meaningful terms we must be able to measure or represent the three attributes that together give a model of colour perception. i.e. light, object and the eye. All these attributes have been standardised by the CIE or Commission Internationale de l'Eclairage.

The colours of the clothes we wear and the textiles we use in our homes must be monitored to ensure that they are correct and consistent.

Colour measurement is therefore essential to put numbers to colour in order to remove physical samples and the interpretation of results.
See:Colour measuring equipment

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A New Culture?





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Colour Space and Colour Theory


So by having defined the "frame of reference," and by introducing "Colour of gravity" I thought it important and consistent with the science to reveal how dynamical any point within that reference can become expressive. The history in association also important.

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See Also:

Cymatics and the Heart Song

We might object that the heart makes heart sounds and jiggles water in the pericardial sac. Stuart Kauffman

The Colour of Gravity2
The Colour of Gravity1

Thursday, January 29, 2009

Formation of Gravity

Wegener proposed that the continents floated somewhat like icebergs in water. Wegener also noted that the continents move up and down to maintain equilibrium in a process called isostasy.Alfred Wegener


Just thought I would add this for consideration. Grace satellite does a wonderful job of discerning this feature? Amalgamating differing perspectives allows one to encapsulate a larger view on the reality of Earth. More then the sphere. More then, what Joseph Campbell describes:

The Power of Myth With Bill Moyers, by Joseph Campbell , Introduction that Bill Moyers writes,

"Campbell was no pessimist. He believed there is a "point of wisdom beyond the conflicts of illusion and truth by which lives can be put back together again." Finding it is the "prime question of the time." In his final years he was striving for a new synthesis of science and spirit. "The shift from a geocentric to a heliocentric world view," he wrote after the astronauts touched the moon, "seemed to have removed man from the center-and the center seemed so important...


While one can indeed approximate according to the spherical cow, in terms of events in the cosmos, I was being more specific when it comes to demonstrating a geometrical feature of the sphere in terms of the geometry of the Centroid. This feature is embedded in the validation of the sphere in regard to gravity?

Image: NASA/JPL-
Planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it. With its large body and internal heating from radioactive elements, a planet behaves like a fluid, and over long periods of time succumbs to the gravitational pull from its center of gravity. The only way to get all the mass as close to planet's center of gravity as possible is to form a sphere. The technical name for this process is "isostatic adjustment."

With much smaller bodies, such as the 20-kilometer asteroids we have seen in recent spacecraft images, the gravitational pull is too weak to overcome the asteroid's mechanical strength. As a result, these bodies do not form spheres. Rather they maintain irregular, fragmentary shapes.


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It was important to see how such planets form and given their "Mass and densities" which I thought to show how such a valuation could be seen in relation to the variance of gravity so it is understood.

Isostasy (Greek isos = "equal", stásis = "standstill") is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic heights can exist at the Earth's surface. When a certain area of lithosphere reaches the state of isostasy, it is said to be in isostatic equilibrium. Isostasy is not a process that upsets equilibrium, but rather one which restores it (a negative feedback). It is generally accepted that the earth is a dynamic system that responds to loads in many different ways, however isostasy provides an important 'view' of the processes that are actually happening. Nevertheless, certain areas (such as the Himalayas) are not in isostatic equilibrium, which has forced researchers to identify other reasons to explain their topographic heights (in the case of the Himalayas, by proposing that their elevation is being "propped-up" by the force of the impacting Indian plate).

In the simplest example, isostasy is the principle of buoyancy observed by Archimedes in his bath, where he saw that when an object was immersed, an amount of water equal in volume to that of the object was displaced. On a geological scale, isostasy can be observed where the Earth's strong lithosphere exerts stress on the weaker asthenosphere which, over geological time flows laterally such that the load of the lithosphere is accommodated by height adjustments.


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Such strength variances can be attributed to the height with which this measure is taken(time clocks and such) and such a validation in terms of Inverse Square Law goes to help to identify this strength and weakness, according to the nature of the mass and density of the planet.



As one of the fields which obey the general inverse square law, the gravity field can be put in the form shown below, showing that the acceleration of gravity, g, is an expression of the intensity of the gravity field.
See: Hyperphysics-Inverse Square Law-Gravity

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It is important then such a measure of the energy needed in which to overcome the pull of the earth, then was assigned it's energy value so such calculations are then validated in the escape velocity. There are other ways in which to measure spots in space when holding a bulk view of the reality in regards to gravity concentrations and it locations.

See: Hyperphysics-Gravity-Escape Velocity

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See Also:
  • Isostatic Adjustment is Why Planets are Round?
  • Concepts of the Fifth Dimension
  • Dealing With a 5D World