RECONNAISSANCE SURVEY USING AVERAGE HORIZONTAL GRADIENTS OF GRAVITY

Geophysics ◽  
1965 ◽  
Vol 30 (4) ◽  
pp. 661-664
Author(s):  
Stephen Thyssen‐Bornemisza
Keyword(s):  
Gravity Gradient ◽  
Gravity Gradients ◽  
The South ◽  
Horizontal Gradients ◽  
Experimental Profile ◽  
Reconnaissance Survey ◽  
Gradient Technique ◽  
Vertical Gradients ◽  
Reconnaissance Surveys

Some time ago, Romberg (1956/57) pointed out the advantage of reading horizontal gravity gradients rather than vertical gradients with the gravity meter. Several years later, in March, 1960, an experimental profile of gravity‐meter‐determined horizontal gradients was run for the author in the South Houston field by courtesy of Texas Instruments Incorporated. Since then, this gradient technique was repeatedly discussed but only very few results could be published (Thyssen‐Bornemisza et al., 1960, 1962a, 1962b). Stackler (1963) more recently pointed out again the value of the average gravity gradient for reconnaissance surveys predominantly in inaccessible areas.

Interval gravity‐gradient determination concepts

Geophysics ◽  
1984 ◽  
Vol 49 (6) ◽  
pp. 828-832 ◽  
Author(s):  
Dwain K. Butler
Keyword(s):  
Finite Difference ◽  
Gravity Data ◽  
Vertical Gradient ◽  
Gravity Gradient ◽  
Gravity Gradients ◽  
Tower Structure ◽  
Gravity Measurements ◽  
Vertical Gradients

Considerable attention has been directed recently to applications of gravity gradients, e.g., Hammer and Anzoleaga (1975), Stanley and Green (1976), Fajklewicz (1976), Butler (1979), Hammer (1979), Ager and Liard (1982), and Butler et al. (1982). Gravity‐gradient interpretive procedures are developed from properties of true or differential gradients, while gradients are determined in an interval or finite‐difference sense from field gravity data. The relations of the interval gravity gradients to the true or differential gravity gradients are examined in this paper. Figure 1 illustrates the concepts of finite‐difference procedures for gravity‐gradient determinations. In Figure 1a, a tower structure is illustrated schematically for determining vertical gradients. Gravity measurements are made at two or more elevations on the tower, and various finite‐difference or interval values of vertical gradient can be determined. For measurements at three elevations on the tower, for example, three interval gradient determinations are possible: [Formula: see text]; [Formula: see text]; [Formula: see text]; where [Formula: see text] and [Formula: see text] etc. For a positive downward z-;axis, these definitions for [Formula: see text] and [Formula: see text] will result in positive values for the vertical gradient. Relations of the interval gradients to each other and to the true or differential gradient are examined in this paper.

Reduction to the pole of the North American magnetic anomalies

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 218-225 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
W. E. S. Urquhart
Keyword(s):  
North America ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Gravity Gradient ◽  
Plate Boundaries ◽  
Gravity Gradients ◽  
The North ◽  
Vertical Gravity Gradient ◽  
Regional Tectonic ◽  
Vertical Gravity

Magnetic anomalies of North America are reduced to the pole using a generalized technique which takes into account the variations in the directions of the core field and the magnetization of the crust over North America. The reduced‐to‐the‐pole magnetic anomalies show good correlations with a number of regional tectonic features, such as the Mid‐Continental rift and the collision zones along plate boundaries, which are also apparent in the vertical gravity gradient map of North America. The magnetic anomalies do not, however, show consistent correlation with the vertical gravity gradients, suggesting that magnetic and gravity anomalies do not necessarily arise from common sources.

Double-diffusive interleaving due to horizontal gradients

1983 ◽  
Vol 137 ◽  
pp. 347-362 ◽  
Author(s):  
Judith Y. Holyer
Keyword(s):  
Stability Analysis ◽  
Small Region ◽  
Two Dimensional ◽  
Fully Nonlinear Equations ◽  
Salinity Stratification ◽  
Horizontal Gradients ◽  
Salinity Gradients ◽  
Horizontal Density Gradient ◽  
Double Diffusive ◽  
Vertical Gradients

In this paper we present a linear stability analysis for an unbounded, vertically stratified fluid which has compensating horizontal temperature and salinity gradients, so there is no horizontal density gradient. We obtain the most unstable perturbation for given linear horizontal and vertical gradients and calculate the growth rates, the vertical lengthscale of the intrusion and the slope of the intrusion to the horizontal. We show that the system is most unstable to two-dimensional disturbances and that, except for a small region in which the temperature stratification is unstable and the salinity stratification is stable, the most-unstable disturbance is non-oscillatory. We also obtain a solution to the fully nonlinear equations and calculate the fluxes of heat and salt. The nonlinear solution shows that alternating interfaces of salt-finger and diffusive interfaces will eventually appear on the intrusion when the vertical stratifications are both stable.

Relative precision of vertical and horizontal gravity gradients measured by gravimeter

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 99-101 ◽  
Author(s):  
Sigmund Hammer
Keyword(s):  
Survey Data ◽  
Hilbert Transform ◽  
Gravity Data ◽  
Gradient Methods ◽  
Vertical Gradient ◽  
Gravity Gradients ◽  
Relative Precision ◽  
The Hilbert Transform ◽  
Vertical Gradients ◽  
Vertical Gradient Of Gravity

Several recent publications advocate the use of the vertical gradient of gravity from gravimeter measurements at two elevations in a portable tower (Thyssen‐Bornemisza, 1976; Fajklewicz, 1976; Mortimer, 1977). Contrary opinions have also been expressed (Hammer and Anzoleaga, 1975; Stanley and Green, 1976; Thysen‐Bornemisza, 1977; Arzi, 1977). The disagreement revolves around the question of practically attainable precision of the vertical gradient tower method. Although it is possible to calculate both horizontal and vertical gradients from conventional gravity survey data by use of the Hilbert transform (Stanley and Green, 1976), it should be noted that highly precise gravity data are required. Also the need for connected elevation and location surveys, the major cost in gravity surveying, is not avoided. This is a significant advantage of the gradient methods. The purpose here is to present a brief consideration of the relative precision of the horizontal and vertical gradients, as measured in the field by special gravimeter observations.

scholarly journals Structure and Modification of the South Pacific Eastern Subtropical Mode Water

2009 ◽  
Vol 39 (7) ◽  
pp. 1700-1714 ◽  
Author(s):  
Kanako Sato ◽  
Toshio Suga
Keyword(s):  
Potential Vorticity ◽  
South Pacific ◽  
The South ◽  
Mode Water ◽  
Argo Data ◽  
Formation Region ◽  
Subtropical Mode Water ◽  
Vertical Changes ◽  
Salt Fingering ◽  
Vertical Gradients

Abstract Using all available temperature and salinity profiles obtained by Argo floats from July 2004 to June 2007, this study investigated the structure and modification of the South Pacific Eastern Subtropical Mode Water (SPESTMW). Based on the observed characteristics of the vertical minima of potential vorticity over the subtropical South Pacific, SPESTMW is defined as water with potential vorticity magnitude less than 2.5 × 10−10 m−1 s−1 and thickness exceeding 40 m. It is found between 35°–5°S and 160°–70°W and has a temperature of 13°–26°C, salinity greater than 34.0, and density of 24.5–25.8 kg m−3 at its core. This study confirmed that vertical changes in temperature and salinity tend to compensate for each other in terms of density changes, resulting in favorable salt fingering conditions, as previously reported. By analyzing many profiles of Argo data in spring immediately after the SPESTMW formation period, its temperature and salinity are vertically uniform in the formation region, but large vertical gradients of temperature and salinity are found downstream from that region, even in the SPESTMW core. Consequently, the low potential vorticity signature of SPESTMW spread much wider than its signature as a thermostad. The Argo data also captured the seasonal changes of the vertical gradients of temperature and salinity at the SPESTMW core; these gradients increased as the seasons progressed, even in the formation region. Therefore, SPESTMW is truly vertically uniform water (i.e., thermostad, halostad, and pycnostad simultaneously) only immediately after the formation period. Afterward, it is only pycnostad. This seasonal evolution is related to temperature and salinity diffusion due to salt fingering in a manner similar to the rapid modification of interannual anomalies as shown by previous research. The temperature and salinity near the SPESTMW core and lower region decreased soon after its formation.

The torsion balance as a tool for geophysical prospecting

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 527-534 ◽  
Author(s):  
Clive C. Speake ◽  
G. D. Hammond ◽  
C. Trenkel
Keyword(s):  
Mass Range ◽  
Torsion Balance ◽  
Gravity Gradient ◽  
Geophysical Prospecting ◽  
Balance Beam ◽  
Horizontal Gradients ◽  
Moving Platforms ◽  
Local Anomalies ◽  
Derivatives Of ◽  
Double Torsion

We discuss whether the torsion balance can again become a key tool for geophysical prospecting. We outline the acknowledged disadvantages of the Eötvös torsion balance and seek designs of a torsion balance beam that would enable the torsion balance to be used on moving platforms. A key result is that torsion balance beams designed to be insensitive to the curvature and horizontal gradients of the gravity field are insensitive to the angular motion of the platform about horizontal axes. We suggest that a double torsion balance using these balance beam designs could be used on moving platforms. We point out that second gradients of the gravitational field (third derivatives of the potential) can be determined with reasonable sensitivity with current technology. We describe double torsion balance schemes where the mass, range, and azimuth of localized mass anomalies could be estimated or where local anomalies could be rejected using information from the second gravity gradient.

The space-wise approach for cold-atom interferometry geodetic data analysis: the MOCASS study

2020 ◽  
Author(s):  
Federica Migliaccio ◽  
Mirko Reguzzoni ◽  
Khulan Batsukh
Keyword(s):  
Data Analysis ◽  
Hydrological Cycle ◽  
Cold Atom ◽  
Atom Interferometer ◽  
Geodetic Data ◽  
Gravity Models ◽  
Relative Mass ◽  
Gravity Gradient ◽  
Gravity Gradients ◽  
The Earth

<p>In recent years, an innovative mission concept has been proposed for gravity measurements with the aim of continuously monitoring the Earth gravity and its changes. The concept is based on a satellite-borne interferometer exploiting ultra-cold atom technology. Among other studies, a team of researchers from Italian universities and research institutions proposed and carried out the MOCASS project, to investigate the performance of a cold atom interferometer flying on a low Earth orbiter and its impact on the modeling of different geophysical phenomena.</p><p>In this study, the basic idea was that of a GOCE follow-on mission, with a unique spacecraft carrying an instrument capable of measuring functionals of the Earth gravitational potential. The geodetic data analysis of the gravity gradient data attainable by such a mission was carried out following the space-wise approach developed at Politecnico di Milano. The mathematical model for the processing of the MOCASS data was formulated, including the filtering strategy applied to take into account the cold atom interferometer transfer function. Numerical simulations were performed, with different configurations of the satellite orbit and pointing mode of the interferometer; data were simulated for two cases: (i) a single-arm gradiometer observing T<sub>xx</sub> or T<sub>yy</sub> or T<sub>zz </sub>gradients; (ii) a double-arm gradiometer observing T<sub>xx </sub>and T<sub>zz </sub>gradients or T<sub>yy </sub>and T<sub>zz</sub> gradients. The results of the simulations will be illustrated, showing the applicability of the proposed concept and the neat improvement in modeling the static gravity field with respect to GOCE.</p><p>Moreover, a new study called MOCAST+ has been lately started proposing an enhanced cold atom interferometer which can deliver not only gravity gradients but also time measurements. The study will investigate whether this could give the possibility of improving the estimation of gravity models even at low harmonic degrees, with inherent advantages in the modeling of mass transport and its global variations: this will represent fundamental information, e.g. in the study of variations in the hydrological cycle and relative mass exchange between atmosphere, oceans, cryosphere and solid Earth.</p>

GRAVITY GRADIENTS AND THE INTERPRETATION OF THE TRUNCATED PLATE

Geophysics ◽  
1976 ◽  
Vol 41 (6) ◽  
pp. 1370-1376 ◽  
Author(s):  
John M. Stanley ◽  
Ronald Green
Keyword(s):  
Hilbert Transform ◽  
Theoretical Data ◽  
Vertical Gradient ◽  
Density Contrast ◽  
Horizontal Gradient ◽  
Gravity Gradients ◽  
Gravity Method ◽  
Commercially Important ◽  
Dip Angle ◽  
Vertical Gradients

The truncated plate and geologic contact are commercially important structures which can be located by the gravity method. The interpretation can be improved if both the horizontal and vertical gradients are known. Vertical gradients are difficult to measure precisely, but with modern gravimeters the horizontal gradient can be measured conveniently and accurately. This paper shows how the vertical gradient can be obtained from the horizontal gradient by the use of a Hilbert transform. A procedure is then presented which easily enables the position, dip angle, depth, thickness, and density contrast of a postulated plate to be precisely and unambiguously derived from a plot of the horizontal gradient against the vertical gradient at each point measured. The procedure is demonstrated using theoretical data.

THE AVERAGE HORIZONTAL GRAVITY GRADIENT

Geophysics ◽  
1962 ◽  
Vol 27 (5) ◽  
pp. 714-715
Author(s):  
Stephen Thyssen‐Bornemisza ◽  
W. F. Stackler
Keyword(s):  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Theoretical Discussion ◽  
Gravity Gradients ◽  
Geophysical Exploration

The authors reported experiments of making measurements with the gravity meter at close spacings (Geophysics, 1956, 1958; Journal ASPG, 1960, 1962) for the purpose of obtaining gravity gradients and micro‐gravimetric maps. Since the average horizontal gradient seems to be of some interest for geophysical exploration, a brief theoretical discussion is presented.

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