162,629 research outputs found
Results from some calibration experiments conducted at Strasbourg Superconducting gravity station
No full textThe research deals with a calibration experiment performed in Strasbourg (France) superconducting gravity station by means of two FG5 AGs (#206 and #211) and some new generation spring meters (Scintrex Ltd. Autograv-CG3M and -CG5M and Microg-LaCoste gPhone). We discuss the results in terms of precision and accuracy of the SG calibration by means of different metrological approaches. Our main results turn out that spring gravimeters are not suitable to replace AG meters for SG calibration. Owing to the time variability of their sensitivity, the spring meters cannot be used as a stable reference for the SGs. On the contrary, the spring gravimeters could take advantage from measuring in well calibrated superconducting stations. In fact a monthly record session in a superconducting gravity observatory could provide a complete definition of the sensor's transfer function in the tidal band, both in phase and amplitude
Three years of monitoring using leveling and hybrid gravimetry applied to geothermal sites of Soultz-sous-Forêts and Rittershoffen, Rhine Graben, Fran
No full textHere we report on some case histories of geodetic and gravity surveys for monitoring of
geothermal sites. The monitoring of a geothermal reservoir by hybrid gravimetry combining
different types of instruments (permanent superconducting gravimeter, absolute ballistic
gravimeter and micro-gravimeters) is presented. A relative gravimetric network equipped with
levelling benchmarks was designed and surveyed at annual frequencies (2013, 2014, 2015 and
2016 for gravity measurements, 2014, 2015 and 2016 for the leveling). Repetition of high
precision relative gravity measurements on a network developed around a reference station,
which is regularly measured with both relative and absolute gravimeters, leads to the
knowledge of the time and space changes in surface gravity. The observed gravity changes
can be linked to the natural or anthropic activities of the reservoir. A feasibility study using
this methodology is applied to two geothermal sites of Soultz-sous-Forêts and Rittershoffen in
the Alsace region (France) in the Rhine graben (Hinderer et al. 2015)
On the Efficiency of Barometric Arrays to Improve the Corrections of Atmospheric Effects on Gravity Data
No full text[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
300-days of parallel gravity record with the gPhone-054 spring gravimeter and the GWR-C026 superconducting gravimeter in Strasbourg (France): a comparative study
No full textA wide set of geodynamical and hydrological phenomena, involving underground mass redistribution and/or change of the Earth’s figure, affects the gravity field, sometimes inducing “slow” and “small” temporal gravity changes, the detection of which relies on instruments with high sensitivity, long-term stability and a very low drift.
Here we report on the results of a comparative analysis carried out on more than ten months of co-located record collected with a new generation spring gravimeter, the gPhone-054, owned by the IGN of Madrid (Spain), and the GWR-C026 superconducting gravimeter (SG-C026) at the J9 gravity station in Strasbourg (France). The Microg-LaCoste gPhone is a portable Earth tide gravimeter equipped with a 0.1 μGal resolution feedback. The core sensor is the patented LaCoste & Romberg (LR) zero-length spring suspension system. The gPhone is essentially a LR, model G meter, but with significant upgrades: it has an improved thermal system (a double-oven) for increased temperature stability. Moreover the instrument should have a “true” vacuum seal making it almost insensitive to the buoyancy changes due to atmospheric pressure fluctuations.
We test the performances of the gPhone-054 in terms of resolution, accuracy, noise level and long-term stability (drift) with respect to the SG-C026. Our comparative analysis is performed in a wide spectral domain, ranging from the body tides to the seismic band. This study demonstrates that the SGs have better performances in the whole analyzed spectral band. Focusing on the gPhone-054 instrumental drift observed during this study, it still remains a critical point preventing the study of the long-term gravity changes. In fact the drift was large and even not linear, sometimes requiring a high degree (> 4) polynomial fitting to be reduced; the latter makes hard to distinguish real time gravity changes from the instrumental drift. We observed a drift rate evolution characterized by a decrease from 50 μGal/day to 15 μGal/day, after about 1 month of operation. Moreover we tried to improve the drift modeling by using frequent (about every 5 days) absolute gravity (AG) measurements collected within about forty days; the measurements have been carried out with FG5#211, but unfortunately during that time no significant gravity changes have been detected which would have helped us to discriminate short-term drift excursions from real gravity changes by superimposing the gPhone data onto the AG points
COMPARISON OF NOISE LEVELS OF THE NEWEST GENERATION OF RELATIVE GRAVIMETERS
No full textSince the beginning of the Global Geodynamics Project in 1997, the number of superconducting gravimeters (SGs) has increased to reach 25 operating sites today. Data from the network allows a comparison of the noise levels of the different contributing stations. Knowledge of the noise levels of each station is important in a number of studies that combine the data to determine global Earth parameters. We cite for example the stacking of the data to determine the period of the free core nutation and the Chandler wobble, and the use of the data in the search for elusive signals, like the gravity variations associated with the translational mode of the inner core. We use a standardized processing procedure to evaluate the combined instrument plus site noise in the long-period seismic band (0.3 mHz - 1 mHz) and in the sub-seismic frequency band (0.03 mHz – 0.3 mHz), based on computing residual power spectral densities (PSDs) over a quiet time period. The experience at Strasbourg (France) has shown improvements from the T005 full-size instrument to the C026 compact model in terms of noise and drift, while the most recent type Observatory SG OSG044 at Bad-Homburg (Germany) does not show any improvement with respect to the compact CD30. Besides the development of new models of SGs by GWR, a new generation of portable Earth tide meters was developed by Micro-g LaCoste. A 6-month inter-comparison performed at Strasbourg shows that the newest generation of portable Earth tide meter (gPhone-54) is 20 dB noisier than the SG C026 and that its instrumental drift cannot be modeled by a simple polynomial function, preventing the use of the gPhone for long-term gravity studies
Pok ta Pok: Raum – Gewalt – Subversion. Von der privilegierten Pforte zur Unterwelt zum world-wide field der global player
No full textKaltmeier O. Pok ta Pok: Raum – Gewalt – Subversion. Von der privilegierten Pforte zur Unterwelt zum world-wide field der global player. In: Hinderer M, Kastner J, eds. Pok ta Pok. Aneignung, Macht, Kunst. Wien: Turia + Kant; 2007: 53-75
Tilt effects on GWR superconducting gravimeters
No full textThe superconducting gravimeters (SGs) are the most sensitive and stable gravity sensors currently available. The low drift and high sensitivity of these instruments allow to investigate several geophysical phenomena inducing small- and long-period gravity changes. In order to study such topics, any kind of disturbance of instrumental origin has to be identified and possibly modelled. A critical point in gravity measurement is the alignment of the gravimeter to the local vertical. In fact a tilt of the instrument will lead to an apparent gravity change and can affect the instrumental drift. To avoid these drawbacks, SGs are provided with an "active tilt feedback system" (ATFS) designed to keep the meter aligned to the vertical. We analyse tilt and environmental parameters collected near Strasbourg, France, since 1997 to study the source of the tilt changes and check the capability of the ATFS to compensate them. We also present the outcomes of a calibration test applied to the ATFS output to convert the Tilt Power signals into angles. We find that most of the observed signal has a thermal origin dominated by a strong annual component of about 200 mu rad. Nevertheless, our analysis shows that even the tilt due to different geophysical phenomena, other than the thermal ones, can be detected. A clear tidal signal of about 0.05 mu rad is detectable thanks to the large data stacking (>11 years). We conclude that (i) the ATFS device compensates the tilt having a thermal origin or coming from any sources and (ii) no significant tilt changes alter the gravity signal, except for the high frequency (>1 mHz) perturbations
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