Absolute gravity: A reconnaissance tool for studying vertical crustal motions

Niebauer, T. M.; Hoskins, J. K.; Faller, J. E.

doi:10.1029/jb091ib09p09145

Cited by 39 publications

(12 citation statements)

References 3 publications

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“…The beams are aligned with the local vertical with a horizontal mercury (or alcohol) reference. The accuracy of the alignment is better than 5", which is sufficient for an absolute measurement of 0.3 //Gal [1 galilei (Gal) = l cm/s 2 ). An error in the verticality of the beams, however, would appear as an anomalous horizontal gradient which was measured by exchanging the location of the dropping chambers.…”

Section: Sa/g^ \ (Ax/r)[b/^i] E [B/n \ { -B/fi | 2 ] [(P/p M )(L +?)]mentioning

confidence: 98%

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Galilean test for the fifth force

1987

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We have carried out a direct free-fall experiment to measure the differential acceleration between two different materials (copper and uranium) falling in the Earth's gravitational field. The differential acceleration was measured to be less than 5 parts in 10 10 of the normal gravitational acceleration. This null result puts new limits on the strength and range of the proposed fifth force.PACS numbers: 04.90.+e, 04.80,+z Our experiment is a modern-day counterpart to the experiment Galileo is alleged to have performed from the leaning tower of Pisa. We dropped two objects of differing composition (copper and depleted uranium) in a vacuum, and monitored their motion interferometrically in order to measure any differential acceleration. This experiment was designed to test for a possible fifth force coupled to hypercharge, as proposed by Fischbach et al. l to explain apparent anomalies in three different types of experiments. The proposed form of the anomalous hypercharge potential between two point masses iswhere / and X are the effective charge and range of the interaction, respectively, and B is the total baryon number. The magnitude of the charge would be about 10 ~1 9 of the elementary electron charge. The range may be as large as 10 4 m. The effect of this hypothesized fifth force would be to decrease the normal gravitational acceleration of a freely falling body. The anomalous acceleration would depend on the baryon-number-to-mass ratio which depends on the nuclear structure of the substance. Thus, two objects of differing composition would fall toward the Earth at different rates.The differential acceleration of two bodies toward the Earth is given by the following equation for ranges (X) smaller than the radius of the Earth (R):The parameter a is the anomaly in G which would arise from the hypothesized fifth force (GQ=GOO [\ +a]). B/ji is the ratio of the baryon number to the mass given in units of atomic hydrogen. Fischbach et al. presented Eq. (2) in their reanalysis of the Eotvos data, except that the density factor shown in brackets was not included. The ratio of the surface density to the mean density (p s /p m = 1/2) of the Earth is necessary because of the short range of the hyperphoton. The function £ expresses the interaction of the hypercharge force with the more dense inner layers of the Earth. £ can be computed with use of a linear radial density which overestimates the magnitude for ranges less than 2000 km. This model yields ^4X/R.r Dropping chambers were used from two of the absolute gravimeters recently developed in our laboratory. 2These gravimeters measure g by dropping an object in a vacuum. The vertical position of the dropped object is monitored interferometrically and its acceleration is then calculated. In this Galilean experiment, two dropping chambers are used. They are placed together over a single interferometer base in order to directly measure the differential acceleration of the objects. The apparatus and a block diagram of the optical measurement system is shown in Fi...

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Section: Sa/g^ \ (Ax/r)[b/^i] E [B/n \ { -B/fi | 2 ] [(P/p M )(L +?)]mentioning

confidence: 98%

“…2 These gravimeters measure g by dropping an object in a vacuum. The vertical position of the dropped object is monitored interferometrically and its acceleration is then calculated.…”

Section: Sa/g^ \ (Ax/r)[b/^i] E [B/n \ { -B/fi | 2 ] [(P/p M )(L +?)]mentioning

confidence: 99%

Galilean test for the fifth force

1987

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“…Since the development of lGal (1 lGal = 10 -8 m s -2 ) precision absolute gravimetry (AG) (NIEBAUER et al, 1986), collocated AG and GPS campaigns have become more frequent for a wide range of applications (HINDERER et al, 2003;FRANCIS et al, 2004;MÜ LLER et al, 2005;AMALVICT et al, 2006). This also applies when continuously monitoring the time-variable gravity field with superconducting gravimeters and the geodetic positions with GPS, VLBI or SLR at fixed observatories (CROSSLEY et al, 1999;ZERBINI et al, 2001ZERBINI et al, , 2002IHDE et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Variability of the Gravity-to-Height Ratio Due to Surface Loads

Linage

Hinderer

Boy

2009

Pure appl. geophys.

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We study the ratio between the gravity variation and vertical displacement on the surface of a self-gravitating earth model when a surface load is applied. We adopt a theoretical and numerical point of view, excluding any observations. First, we investigate the spectral behavior of the ratio of the harmonic components of the gravity variation and vertical displacement. Then, we model the gravity-to-height ratio for different surface loads (continental hydrology, atmospheric pressure, ocean tides) using outputs of global numerical models in order to relate the predicted spatial values to theoretical mean values deduced from the spectral domain. For locations inside loaded areas, the ratio is highly variable because of the Newtonian attraction of the local masses and depends on the size of the load. For the hydrological loading (soil moisture and snow), the mean ratio over the continents is -0.87 lGal mm -1 , but increases with decreasing size of the river basins. For the atmospheric loading, assuming an inverted-barometer response of the ocean, the ratio is positive, with larger values for high latitudes (0.49 lGal mm -1 )-particularly on the coasts-than for lower latitudes (0.30 lGal mm -1 ). The ratio, however, is much less variable outside the loaded areas: in desert areas such as the Sahara and Arabia, its mean value is -0.28 lGal mm -1 . For the ocean tidal loading, we find a mean ratio of -0.26 lGal mm -1 over the continents for the diurnal tidal waves. Both results are close to the theoretical mean value of -0.26 lGal mm -1 combining elastic and remote attraction contributions.

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“…Quite promising results have been reported with a series of new instruments constructed at the Joint Institute for Laboratory Astrophysics [Niebauer et al, 1986;Peter et al, 1989];…”

Section: Gravity Measuring Devicesmentioning

confidence: 97%