THE DEVELOPMENT AND USE OF A HIGH‐PRECISION DOWNHOLE GRAVITY METER

Geophysics ◽  
1966 ◽  
Vol 31 (4) ◽  
pp. 764-772 ◽  
Author(s):  
Lynn G. Howell ◽  
K. O. Heintz ◽  
A. Barry
Keyword(s):  
High Precision ◽  
Acoustic Impedance ◽  
Gravity Measurement ◽  
Density Profiles ◽  
Density Measurements ◽  
Vibrating String ◽  
Gravity Interpretation

The vibrating string downhole gravity meter described has a precision of about .01 mgal in gravity measurement. With measurements of this precision, density of a 30‐ft section in the subsurface can be determined with an accuracy of [Formula: see text]. These density measurements are useful in gravity interpretation, in computing acoustic impedance for use in seismology, and in estimating porosities of formations. Examples of density profiles measured in boreholes are given.

scholarly journals Density structures inside the plasmasphere: Cluster observations

2004 ◽  
Vol 22 (7) ◽  
pp. 2577-2585 ◽  
Author(s):  
F. Darrouzet ◽  
P. M. E. Décréau ◽  
J. De Keyser ◽  
A. Masson ◽  
D. L. Gallagher ◽  
...  
Keyword(s):  
Density Gradient ◽  
Time Delays ◽  
Statistical Study ◽  
Outer Boundary ◽  
Normal Velocity ◽  
Density Profiles ◽  
Density Measurements ◽  
Image Satellite ◽  
Electron Density Profiles

Abstract. The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on 11 April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.

THE ANALYTIC BASIS OF GRAVITY INTERPRETATION

Geophysics ◽  
1942 ◽  
Vol 7 (2) ◽  
pp. 169-178 ◽  
Author(s):  
D. S. Hughes
Keyword(s):  
Analytic Continuation ◽  
High Precision ◽  
Continuation Method ◽  
Resolving Power ◽  
Surface Gravity ◽  
Gravity Interpretation ◽  
Very High ◽  
Gravity Profile

One method of gravity interpretation involves the use of analytic continuation processes. In this discussion the resolving power of this method is tested numerically. Using hypothetical structures comprising single and double blocks, a surface‐gravity profile is derived. Using these values as an “observed gravity” profile, the “continuation” method is applied to compute the gravity at intermediate depths. Comparing these computed values with the actual (directly computed) gravity profile at these depth‐planes, the resolving power of the continuation method is demonstrated. It is shown that a very high precision in the observed data is necessary for very accurate resolution of structures.

scholarly journals Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and detailed neutron-probe density measurements

2015 ◽  
Vol 9 (6) ◽  
pp. 6791-6828
Author(s):  
T. B. Overly ◽  
R. L. Hawley ◽  
V. Helm ◽  
E. M. Morris ◽  
R. N. Chaudhary
Keyword(s):  
Mesoscale Model ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Radar Altimeter ◽  
Density Profiles ◽  
Density Measurements ◽  
Fifth Generation ◽  
Neutron Probe ◽  
Airborne Sar

Abstract. We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and detailed neutron-probe (NP) density profiles. ASIRAS-NP accumulation rates are not statistically different (C.I. 95 %) from in situ EGIG accumulation measurements from 1985 to 2004. Below 3000 m elevation, ASIRAS-NP increases by 20 % for the period 1995 to 2004 compared to 1985 to 1994. Above 3000 m elevation, accumulation increases by 13 % for 1995–2004 compared to 1985–1994. Model snow accumulation results from the calibrated Fifth Generation Mesoscale Model modified for polar climates (Polar MM5) underestimate mean annual accumulation by 16 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modelled density profiles in place of detailed NP data. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the IceBridge campaign.

A Compound Recoil-Compensated Chamber Design for Free-Fall Absolute Gravimeters

2020 ◽  
Author(s):  
Yi Wen ◽  
Kang Wu ◽  
Meiying Guo ◽  
Lijun Wang
Keyword(s):  
High Precision ◽  
Free Fall ◽  
Test Mass ◽  
Precision Measurements ◽  
Gravity Measurement ◽  
Absolute Gravity ◽  
Systematic Bias ◽  
Chamber Design ◽  
Measurement Results ◽  
Gravity Measurements

Abstract The ballistic free-fall absolute gravimeters are most commonly-used instruments for high-precision absolute gravity measurements in many fields, such as scientific research, resource survey, geophysics and so on. The instrumental recoil vibrations generated by the release of the test mass can cause troublesome systematic bias, because these vibrations are highly reproducible from drop to drop with coherent phase. A compound counterbalanced design of chamber using both belt-driven mechanism and cam-driven structure is proposed in this paper. This structure is designed to achieve excellent recoil compensation as well as long freefall length for high precision measurements. Simulation results show that the recoil vibration amplitude of the compound recoil-compensated structure during the drop is about 1/4 of that with only belt-driven counterbalanced structure. This confirms the feasibility and superiority of the new design. And it is believed that the absolute gravimeter based on this newly proposed chamber design is expected to obtain more precise gravity measurement results in the future.

scholarly journals Design, optimization and calibration of an automated density gauge for firn and ice cores

2009 ◽  
Vol 55 (194) ◽  
pp. 1092-1100 ◽  
Author(s):  
Daniel J. Breton ◽  
Gordon S. Hamilton ◽  
C.T. Hess
Keyword(s):  
High Precision ◽  
Gamma Ray ◽  
Ice Cores ◽  
Mass Attenuation Coefficient ◽  
Pulse Mode ◽  
Average Throughput ◽  
Core Diameter ◽  
Counting System ◽  
Density Measurements ◽  
Ray Density

AbstractA gamma-ray density gauge can provide high-resolution and high-precision density measurements of firn and ice cores. This study describes the design, gamma-ray energy optimization and mass attenuation coefficient calibration of the Maine Automated Density Gauge Experiment (MADGE), a portable, field-operable gamma-ray density gauge used on overland traverses in East Antarctica. The MADGE instrument uses a 241Am gamma-ray source, a pulse-mode counting system and electronic core diameter calipers to collect high-precision (±0.004 g cm−3) density data from 3–8 cm diameter firn and ice cores. The data are collected at a 3.3 mm spatial resolution and an average throughput of 1.5 m h−1 for 5 cm diameter cores.

scholarly journals Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and neutron-probe density measurements

2016 ◽  
Vol 10 (4) ◽  
pp. 1679-1694 ◽  
Author(s):  
Thomas B. Overly ◽  
Robert L. Hawley ◽  
Veit Helm ◽  
Elizabeth M. Morris ◽  
Rohan N. Chaudhary
Keyword(s):  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Radar Altimeter ◽  
Density Profiles ◽  
Density Measurements ◽  
Neutron Probe

Abstract. We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and high resolution neutron-probe (NP) density profiles. ASIRAS-NP-derived accumulation rates are not statistically different (95 % confidence interval) from in situ EGIG accumulation measurements from 1985 to 2004. ASIRAS-NP-derived accumulation increases by 20 % below 3000 m elevation, and increases by 13 % above 3000 m elevation for the period 1995 to 2004 compared to 1985 to 1994. Three Regional Climate Models (PolarMM5, RACMO2.3, MAR) underestimate snow accumulation below 3000 m by 16–20 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modeled density profiles in place of NP densities. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates in the dry snow region. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the Operation IceBridge campaign.

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