THE GRAVITY METER AS A GEODETIC INSTRUMENT

Geophysics ◽  
1950 ◽  
Vol 15 (1) ◽  
pp. 1-29 ◽  
Author(s):  
George Prior Woollard
Keyword(s):  
National Physical Laboratory ◽  
Base Stations ◽  
Absolute Gravity ◽  
Naval Research ◽  
Absolute Value ◽  
Office Of Naval Research ◽  
Physical Laboratory ◽  
The World ◽  
Before And After ◽  
The Absolute

A special Worden temperature compensated gravity meter having a range of 5,500 mgals, and a reading sensitivity of 0.1 mgal was used to tie together various primary gravity base stations around the world and to establish new stations. Air transport was used and in a 3 month period over 80,000 miles were flown. Thirty‐three pendulum stations were reoccupied involving a change in gravity of 3,800 mgals, and 125 gravity stations were established. The investigation demonstrated that this instrument could be used satisfactorily for long range geodetic work and the results appear to be the equal of good pendulum observations. Drift was corrected for on the basis of the drift rate established immediately before and after flights. Closures after correcting for drift averaged less than 0.4 mgals, and the closure for the world girdling loop was 0.33 mgals. The probable error based upon the gravity values at the reoccupied pendulum station was ±0.5 mgals. Reoccupation of the absolute gravity stations at the U. S. Bureau of Standards in Washington, D. C. and the National Physical Laboratory in Teddington, England, indicated an approximate 5 mgal error in these pendulum determinations. Indirect ties to the absolute gravity base in Potsdam, Germany, through the primary national gravity bases tied to it, indicated a 15 to 19 mgal error in the Potsdam absolute value. Most of the primary national gravity bases tied directly to Potsdam were found to agree among themselves to within 1 mgal, and the U. S. Bureau of Standards Absolute Base in Washington, D. C. to have a perfect connection within the limits of accuracy of the present measurements. This investigation was made under the auspices of the Office of Naval Research.

Comparison of the acceleration due to gravity at the National Physical Laboratory, Teddington, the Bureau International des Poids et Mesures, Sèvres, the Physikalisch-Technische Bundesanstalt, Brunswick, and the Geodetic Institute, Potsdam

1952 ◽  
Vol 213 (1114) ◽  
pp. 408-424 ◽  
Keyword(s):  
National Physical Laboratory ◽  
Absolute Value ◽  
Geodetic Institute ◽  
Physical Laboratory ◽  
The Absolute

The values of gravity at these stations have been compared by means of pendulum observations with Invar invariable pendulums. The observed differences of gravity from the National Physical Laboratory are: B. I. P. M. -256·73 ± 0·49 mgal P. T. B. + 68·68 ± 0·49 mgal Bad Harzburg - 15·68 ± 0·49 mgal The accuracy of the measurements is not so great as has been achieved once or twice previously with the same apparatus, mainly because the changes in the lengths of the pendulums were greater than usual. These differences have been combined with German pendulum observations and with gravimeter comparisons with the following results: Value of gravity at N. P. L. on the Potsdam system: 981196·29 ± 0·3 mgal. Differences between sites of absolute determinations of gravity: N. P. L. - B. I. P. M. +256·45 ± 0·3 mgal N. P. L. - P. T. B. - 68·98 ± 0·3 mgal P. T. B. - Potsdam - 8·95 ± 0·4 mgal ( g at Potsdam = 981274 mgal.) The effects of these results on gravity surveys based on Cambridge and on the absolute value of gravity are indicated.

Variations in rotation of the earth, results obtained with the dual-rate moon camera and photographic zenith tubes

1959 ◽  
Vol 11 ◽  
pp. 26-33
Author(s):  
Wm. Markowitz
Keyword(s):  
Seasonal Variation ◽  
Research Laboratory ◽  
Quartz Crystal ◽  
National Physical Laboratory ◽  
Naval Research ◽  
Love Number ◽  
The Earth ◽  
Physical Laboratory ◽  
Rotation Of The Earth ◽  
Irregular Variation

Comparison of photographic zenith tube (P.Z.T.) observations with time derived from quartz-crystal clocks during 1951 to 1955 and with cesium standards of frequency during 1955 to 1958 indicates that the seasonal variation is nearly the same from year to year. Lunar-tidal inequalities of semi-monthly and monthly periods with amplitudes of about 0S.001 each were found. A preliminary value of the Love number, k, is derived. Observations made since 1952 with the dual-rate moon position camera are used to derive ΔT = ET – UT. Comparison of the P.Z.T. observations and atomic standards at the National Physical Laboratory and the Naval Research Laboratory shows details of the irregular variation from 1955 to 1958.

scholarly journals On the determination of the absolute unit of resistance by alternating current methods

1912 ◽  
Vol 87 (597) ◽  
pp. 391-414 ◽  
Keyword(s):  
Lower Order ◽  
Alternating Current ◽  
National Physical Laboratory ◽  
Mutual Inductance ◽  
Electrical Circuits ◽  
Physical Laboratory ◽  
Absolute Measure ◽  
The Absolute ◽  
Set Up

1. Introductory .—Recently at the National Physical Laboratory we have constructed a standard of mutual inductance of novel type, whose value has been accurately calculated from the dimensions. This inductance has formed the basis for the determination of the unit of resistance in absolute measure by two different methods, in both of which alternating current is employed. Although there is no doubt that the accuracy attainable by these methods could be increased by greater elaboration of the apparatus used, the results already obtained seem to be of sufficient interest to warrant publication. It should be mentioned that the accuracy here aimed at was of a considerably lower order than that contemplated in the determination of the ohm by the Lorenz apparatus which is at present being carried out in the laboratory. For the experiments here described, no apparatus was specially constructed, but use was made of instruments which had already been designed and set up for the measurement of inductance and capacity. I shall first give a brief description of the standard inductance and then pass on to the methods and results. 2. Standard Mutual Inductance .—The design of the mutual inductance has already been described. The electrical circuits have the form and arrange­ment shown in section in fig. 1.

scholarly journals The significance of determination of the absolute value of gravity in geodesy

Tehnika ◽  
2021 ◽  
Vol 76 (1) ◽  
pp. 17-24
Author(s):  
Sofija Naod
Keyword(s):  
Theoretical Basis ◽  
Absolute Gravity ◽  
Reference Systems ◽  
Global Knowledge ◽  
Earth’S Gravity Field ◽  
Absolute Value ◽  
Reference Networks ◽  
The Absolute ◽  
Gravimetric System

The gravity is used to solve geodesy's primary tasks, such as determining geoid and defining the height and gravimetric reference networks of different scales, from national to global. Knowledge of gravity is of great importance for both metrology and geodetic metrology. In addition to the historical overview of absolute gravimeters, this paper presents the theoretical basis of the most commonly used method for determining the absolute value of gravity. The principle of operation of the absolute gravimeter FG5 and the importance of international comparison of absolute gravimeters are briefly presented. An overview of the gravimetric reference systems is given, emphasizing the establishment of the International Reference Gravimetric System. The previous works concerning the absolute determination of acceleration due to Earth's gravity field in Serbia are presented. Finally, the importance of determining the absolute value of gravity from the geodetic and metrological perspective is pointed out. Both national and international significance of determining absolute gravity in defining gravimetric reference systems and the importance of absolute gravity in monitoring global phenomena are emphasized.

AN ABSOLUTE MEASUREMENT OF THE ACCELERATION DUE TO GRAVITY AT OTTAWA

1960 ◽  
Vol 38 (6) ◽  
pp. 824-852 ◽  
Author(s):  
H. Preston-Thomas ◽  
L. G. Turnbull ◽  
E. Green ◽  
T. M. Dauphinee ◽  
S. N. Kalra
Keyword(s):  
Stainless Steel ◽  
Discrete Time ◽  
Absolute Measurement ◽  
Absolute Gravity ◽  
Time Intervals ◽  
Absolute Value ◽  
Gravity Station ◽  
A Value ◽  
The Absolute

An apparatus for determining the absolute value of gravity by measuring the distances through which a rule falls in discrete time intervals is described. From the data associated with 64 drops with two non-magnetic stainless steel rules in vacuum, a value of g at the absolute gravity station at Ottawa of 980.6132 cm sec−2 with a possible error of ± 0.0015 cm sec−2 has been obtained. This value is 13.7 ± 2.0 milligal less than the Potsdam value at that position.

scholarly journals On the force between two coaxial single layer helices carrying current

1936 ◽  
Vol 154 (881) ◽  
pp. 1-3
Keyword(s):  
Electric Current ◽  
Single Layer ◽  
Absolute Measurement ◽  
National Physical Laboratory ◽  
General Description ◽  
Physical Laboratory ◽  
The Absolute

The following is an abstract of a paper bearing the above title which is being printed in the Collected Researches of the National Physical Laboratory , vol. 24. The detailed calculations are very long and of interest to only a few persons. The result, however, is of importance to all interested in the absolute measurement of an electric current; it seemed desirable therefore to put it on record, to give a general description of the method employed with its limitations, and to indicate where full particulars may be found.

Gravity changes before and after the 2015 Mw7.8 Nepal earthquake

2020 ◽  
Author(s):  
Weimin Xu ◽  
Shi Chen ◽  
Hongyan Lu
Keyword(s):  
Source Region ◽  
Absolute Gravity ◽  
Nepal Earthquake ◽  
Source Regions ◽  
Gravity Changes ◽  
Seismogenic Source ◽  
Before And After ◽  
Gravity Measurements ◽  
The Absolute ◽  
Regional Gravity

<p>Based on the absolute gravity measurements of 4 gravimetric stations (Shigatse, Zhongba, Lhasa and Naqu) in southern Tibet surveyed from 2010 to 2013, we modeled the source region as a disk of 580 km in diameter by Hypocentroid model, shown that the gravity increase at these stations may be related to mass changes in the source region of the 2015 Mw7.8 Nepal earthquake. We analyzed the characteristics of gravity variations from the repeated regional gravity network, which including the 4 absolute gravimetric stations and 13 relative gravimetric stations from 2010 to 2019, to study the characteristics of gravity changes before and after the earthquake.</p><p>We firstly estimated the reliability of the absolute gravity measurements by the errors of each station, and considered the effect of vertical displacement, denudation of surface mass, GIA correction and the secular and background gravity changes. Secondly we employed the Bayesian adjustment method for the relative gravimetric network data analysis, which was more robust and adaptive for solving problems caused by irregular nonlinear drift of different gravimeters, and then carried out error analysis for the repeated relative gravity measurements. Furthermore, we took the Shigatse station as example, which covered absolute and relative measurements and was most close to the Hypocenter of the inversion Hypocentroid model, the hydrologic effects of the Shigatse station was modeled exactly, and the results shown that the secular and background gravity changes were much smaller than the observed gravity changes. Lastly we studied the characteristics of gravity changes before and after the earthquake through the Hypocentroid model, we found the coincident gravity increase both in absolute and repeated regional gravity results before the earthquake, and gravity decreased after the earthquake, which suggested that the pre-earthquake gravity increase may be caused by strain and mass (fluid) transfer in broad seismogenic source regions of the earthquake. Moreover, the study indicated that high-precision ground gravity measurements (absolute and relative) may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes.</p><p> </p><p><strong>Acknowledgment: </strong>This research is supported by National Key R&D Program of China (Grant No.2018YFC1503806 and No.2017YFC1500503) and National Natural Science Foundation of China (Grant No.U1939205 and No.41774090).</p>

scholarly journals Improving Reproducibility in Research: The Role of Measurement Science

2019 ◽  
Vol 124 ◽  
Author(s):  
Robert J. Hanisch ◽  
Ian S. Gilmore ◽  
Anne L. Plant
Keyword(s):  
Bosnia And Herzegovina ◽  
Life Sciences ◽  
National Physical Laboratory ◽  
Physical Laboratory ◽  
Funding Agencies ◽  
Measurement Science ◽  
The World ◽  
Research Findings ◽  
Good Measurement

We present here a summary of a workshop held 1-3 May 2018 at the National Physical Laboratory, Teddington, UK in which the focus was how the national metrology institutes of the world might help to address challenges in reproducibility of research. The workshop brought together experts from the measurement and wider research communities (Physical-, Data- and Life-sciences, Engineering, and Geology) to understand the issues and to explore how good measurement practice and principles can foster confidence in research findings [1, 2, 3], including how we can tackle the challenge posed by increasing data volumes in both industry and research. The workshop involved 63 participants from metrology laboratories (38), academia (16), industry (5), funding agencies (2), and publishers (2). The participants came from UK, US, Korea, France, Germany, Australia, Bosnia and Herzegovina, Canada, Turkey, and Singapore.

Microstructural properties of major white matter tracts in constant exotropia before and after strabismus surgery

2021 ◽  
pp. bjophthalmol-2020-317948
Author(s):  
Yanming Wang ◽  
Xiaoxiao Wang ◽  
Hongmei Shi ◽  
Lin Xia ◽  
Jiong Dong ◽  
...  
Keyword(s):  
White Matter ◽  
Diffusion Tensor ◽  
Mean Diffusivity ◽  
Strabismus Surgery ◽  
Microstructural Properties ◽  
Imaging Data ◽  
Absolute Value ◽  
Microstructural Alterations ◽  
Before And After ◽  
The Absolute

AimsThe purpose of this study was to explore the microstructural properties of the major white matter (WM) tracts in constant exotropia (XT) before and after strabismus surgery, and further investigate the association between microstructural alterations and the ocular dominance (OD).MethodsWe collected diffusion tensor imaging data of patients with XT before (n=19) and after (n=15) strabismus surgery and 20 healthy controls and evaluated OD and stereopsis. The probabilistic streamline tractography of the 24 major WM tracts was reconstructed by using the automated fibre quantification package. Fractional anisotropy and mean diffusivity (MD) along each tract were estimated, and their differences between the groups were examined. Furthermore, we evaluated the relationship between OD and the absolute value of altered microstructural parameters.ResultsWhile all postoperative XT patients restored normal stereopsis, most of their OD remained aberrant (9 out of 11). Compared with that of preoperation, the MD of postoperative patients decreased significantly along left anterior thalamic radiation (ATR), left arcuate fasciculus (AF), left corticospinal tract (CST), left cingulum cingulate (CGC) and left inferior fronto-occipital fasciculus. Moreover, OD was negatively correlated with the absolute value of MD changes in left ATR, left AF, left CST and left CGC.ConclusionMicrostructural alterations after surgery in the visuospatial network tracts may contribute to the stereopsis restoration. Additionally, the results of the correlation analysis may signify that the balanced binocular input may be more conducive for the restoration and improvement of binocular visual function, including stereopsis. Thus, restoring normal ocular balance after surgical correction may be necessary to achieve more substantial improvements.

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