GWR Instruments, Inc Published Papers - Research and Studies utilizing our Superconducting Gravimeter

Over three decades the Superconducting Gravimeter (SG) has been used by researchers to conduct studies in areas ranging from the earth's core to the sun and beyond. Below you will find a small sample of these papers and presentations.

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Paper Title	Authors	Abstract
Initial results with the new GWR iGrav™ Superconducting Gravity Meter	R.J. Warburton, H. Pillai, R.C. Reineman	Many geophysical studies presently using spring-type gravity meters could be significantly improved by replacing these instruments with superconducting gravimeters (SGs). The SGs are far superior with their extremely low drift rates and low noise. However, SGs would have to be much less expensive, portable and much simpler to use before they will be used in many existing and new applications. This year, GWR Instruments is introducing a new iGrav™ SG Meter that is designed to be portable, easy to use and much less expensive than the GWR Observatory SGs (OSG) that are used at most stations in the Global Geodynamics Project. Nonetheless, the iGrav™ SG Meter retains many of the characteristic of the Observatory SG. The iGrav™ has an ultra-low drift of less than 0.5 microGal/month and a virtually constant scale factor. In its cryogenic environment, the iGrav™ is totally insensitive to local changes in temperature, relative humidity, or pressure. With these properties, the iGrav™ provides a precise and continuous record of gravity variations that occur over periods of days, months,years, or even decades with a stability and precision that sets the highest industry standard. The iGrav™ is designed specifically for geophysical applications that require much higher stability and precision than provided by mechanical spring-type gravity meters, but can be set up easily and quickly without the need for an expensive platform, housing or infrastructure. In this paper, we discuss the new design features of the iGrav™; demonstrate both its simplicity and capabilities, and show first results that compare its performance to the Observatory SG.	Click to read entire paper (PDF - 637KB)
Yearly gravity variations of superconducting gravimeter (GWR C039) at Ny-Å lesund compared to GPS data and hydrological model	Omang, O. C.; Kierulf, H. P.	Gravity data from the superconducting gravimeter (GWR C039) at Ny-Å lesund, Svalbard, Norway, have been analyzed for long periodic variations. Prior to the analysis the gravity data was filtered and cleaned, by removing e.g. earthquakes and spikes. Any drift in the SCG data was removed using available absolute gravity measurements. Yearly variations in the gravity signal are visible after removal of short periodic tides, i.e. tides with period of approximately one month and shorter. The gravity station is co-located with 2 IGS-GPS stations. The GPS receivers are located within 5 m from the superconducting gravimeter. The variations in gravity data may be due to changes in the snow/water level. We investigated this effect by comparing to GPS data and global hydrological models. The effect of changes in the level of sediment deposits and glaciers are evaluated.	Click to read entire paper
Accurate determination of calibration factor for tidal gravity observation of a GWR-superconducting gravimeter	He-ping Sun, Xiao-dong Chen, Hou-tze Hsu and Yong Wang	It is recognized widely nowadays that the superconducting gravimeter (SG) is a kind of best relative gravimeter with high observing precision, good continuity and stability. However, it is necessary to calibrate the direct output (change in voltage) by using scale value (calibration factor) before getting the change of the real gravity field. Studies show that the accuracy of the scale value will influence the late analysis and explanation of the observations. By using absolute gravity measurements of a FG5 absolute gravimeter (AG) at Wuhan international tidal gravity fundamental station (two campaigns each for 3 days) and by using known tidal parameters at the same station, the calibration factors of the SG and their precision are studied in detail in this paper.	Click to read entire paper
Study of long-term gravity variations, based on data of the GGP co-operation	Martina Harnisch, Günter Harnisch	The study continues a paper with the same title, presented at the Earth Tides Symposium 2000 in Mizusawa. Now data series from 12 GGP stations could be included (BE, BO, CA, CB, MB, MC, MO, PO, ST, SU, VI, WE). The length of the data series varies between 4 and 18 years. From some stations hydrological data were available. In most cases, the drift of the gravimeters was low and nearly linear. No absolute gravity measurements were available to support the estimation of the instrumental drift. Again the annual wave and the Chandler wobble were separated by fitting two sinusoidal functions with periods of 365.25 and 432 days to the residual gravity. As to be expected, the results for the individual stations move closer together and become more reliable. The d-values of the Chandler wobble approach to 1.16. The correspondent values of the annual wobble are slightly smaller but demonstrate considerable variability. The phase lags of both phenomena are in the order of a few degrees.	Click to read entire paper
Measuring the transfer function of a superconducting gravimeter using step functions and sine waves	Michel Van Camp	This note presents a method to determine experimentally the transfer function (amplitude and phase responses) of a superconducting gravimeter by injecting known voltages into the control electronics of the system. Details are given on the analysis of the data by using the Tsoft software. Some parts of this manual summarize papers (see bibliography) as well as numerous personal communications with GWR.	Click to read entire paper
Connecting a Quanterra Data Logger Q330 on the GWR C021 Superconducting Gravimeter	Michel Van Camp, Joseph Steim, et al	Below 1.5 mHz the superconducting gravimeters (SGs; Figure 1) are competitive with the best spring gravimeters and seismometers and can achieve the lowest noise level at frequencies lower than 1.0 mHz (Van Camp 1999; Rosat et al. 2003; Widmer-Schnidrig 2003; Park et al. 2005). SGs can therefore make a significant contribution to the illumination of long-wavelength density heterogeneities in the Earth's mantle (Widmer-Schnidrig 2003). For reasons of price and complexity, the number of SGs is small compared to the number of sensors deployed in the Global Seismic Network (GSN). However, the potential of a sparse network of gravimeters for normal-mode research has been demonstrated by the International Deployment of Accelerometers (IDA) network (Agnew et al. 1986). Another point worth noting is the stability and accuracy ( 0.1% level) of the calibration factor of SGs (Francis et al. 1998) requested to validate Earth and ocean tide models using tidal gravity measurements (Baker and Bos 2003). This compares well with seismic networks, where results are barely better than 1%.	Click to read entire paper
Gravitational effects of atmospheric processes in SG gravity data	Bruno Meurers	Some typical case studies of short term (< 120 min) gravity residual variations are investigated by comparing the air pressure signal and the residual gravity in high temporal resolution. Most of these events are con¬nected with heavy rainfall and atmospheric processes characterized by high vertical convection activity. After almost perfect removal of even very short (< 20 min) pres¬sure pertur¬bations by applying a frequency inde¬pendent admittance factor, a typical behavior of the gravity residuals can be observed. A common feature is a sudden gravity decrease followed by a very slow return to the previous level. Two models of vertical mass trans¬port are used to explain the observations roughly.	Click to read entire paper
Intercomparison of IMGC Absolute and GWR SuperConducting Gravimeters	Baldi, P., Casula, G., et al	In May 1994 a first comparison campaign between a superconducting and the IMGC absolute gravimeter has been performed in Brasimone, near Bologna in Italy. The superconducting gravimeter was previously calibrated by means of a moving ring, the mass of which has been measured with the highest accuracy allowed by the actual technology. During the three days of observation with the absolute gravity meter, a maximum, a complete semidiurnal curve and a minimum of the tidal effect has been observed. These data have been used to compute the calibration factor of the superconducting gravity meter; it agrees in a rather satisfactory way with the results of the calibration with the moving mass.	Click to read entire paper
AGU 2007 Fall Meeting	Wilson, C R, Wu, H, et al	The gravimeter has a precision in the 10-nanogal range, and a nominal drift of a few microgals per year. Although the GWR instrument has been in production for about three decades, operations have been restricted previously to laboratory and vault environments. A ground water gravity signal has often been apparent, but complex hydrologic conditions have made quantitative interpretation difficult. By making the instrument transportable, one is able to choose sites where better-defined hydrologic problems can be investigated, and to consider tectonic, volcanic, and other applications. Technical advances have reduced the size of the helium Dewar and solved the helium replenishment requirement via a compact refrigeration system. With the ability to cool to 4 K, it is possible to maintain a full Dewar indefinitely. With support of NSF EAR Instrumentation and Facilities, we procured a GWR gravimeter and developed the system to be transportable, self contained within two enclosures, and accessible via cell-phone internet service. A bracket system allows the helium Dewar containing the gravity sensor to be locked to the frame and transported without disassembly. Initial application is to hydrologic investigations in karst and desert alluvial aquifers. The goal is to understand hydrologic signals at a level near one microgal, equivalent to the attraction of a 2cm layer of water. Instrument precision exceeds this, but the variety of sources in the atmosphere makes it difficult to identify hydrologic signals with greater precision. Companion weather and well observations are used to observe and interpret gravity variations in terms of infiltration and storage changes, and GRACE satellite gravity observations enable separation of regional and local influences.	Click to read entire paper

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Investigation of temporal gravity variations in SG-records	Bruno Meurers	Not all of the gravity signals commonly observed in records of superconducting gravimeters have a physically significant meaning. Instrumental noise or signal components generated by specific processing techniques can have a strong effect. This paper analyzes selected case studies from gravity data acquired during the first period of GGP and tries to give an answer to the question of which signals are significant. It is focused on small amplitude variations in the time domain, which are compared with those of conventional spring-type gravimeters. Coherent atmospheric gravity signals due to atmospheric processes associated with strong vertical convection could be observed by different sensors. The second part deals with temporal variations of main tidal parameters, which can be seen clearly in the tidal analysis results from SG data. Synthetic case studies show that they are not strongly influenced by the analysis procedure and therefore mainly reflect ocean loading processes.	Click to read entire paper
Potential of a superconducting long-period seismometer (pdf)	Richard J. Warburton	The Superconducting Gravimeter (SG) was invented and developed by John Goodkind and William Prothero at the University of California, San Diego (UCSD) during the mid-1960s. Their purpose was to build a gravimeter that achieved a precision of 1 µGal and a stability of 1µGal/year. The design was focused on long-term (years) stability and did not consider seismic applications. R. Warburton joined Goodkind's laboratory in 1971 as a postdoctoral candidate to complete development and to deploy SGs to field sites for making long-term gravity measurements. In response to a series of papers published by Warburton and Goodkind (1975 to 1978), German and Belgium scientists became interested in doing similar research in Europe. GWR Instruments was formed in 1979 to manufacture SGs for these groups. There are about 25 SGs operating worldwide and most are in the Global Geodynamics Project (GGP) network that was formed in 1991.	Click to read entire paper
Precise Gravity Time Series (pdf)	H. Wziontek, R. Falik, H. Wilmes, P. Wolf	This is a presentation given at the XXIV IUGG General Assembly in Perugia, Italy on July 2-3 2007 on precise gravity time series and instrumental properties from combination of superconducting and absolute gravity measurements	Click to read entire paper
Three Year Comparison Between a Superconducting Gravimeter and an Absolute Gravimeter	AMALVICT M, HINDERER J, et al	Two instruments operate in parallel since beginning 1997 in Strasbourg, France: a superconducting gravimeter(SG)(GWR C026) and an absolute gravimeter(AG)(Micro-g Sol. FG5-206). A first objective of this study is to check the stability in time over three years of the calibration factor which is directly obtained from least squares fitting the SG data to the absolute raw gravity measurements. Another important objective is to evaluate the capability of both types of instruments to retrieve long term changes in the Earth's gravity; in particular, we will focus on the signature of the polar motion and compare it to the theoretical prediction. Subsequently we will investigate the stability(or lack of stability) in gravity after correcting the previous s Fax: (33) 3 88 41 64 77; E-mail: mamalvict@eost.u-strasbg.fr ignals for the polar motion effect. (author abst.)	Click to read entire paper
Precise observations of Gravity Changes with Superconducting Gravimeters in Kyoto (1988 - 1997) (Japanese Text)	Takemoto, Higashi Mukai, Fukuda, Tanaka	Precise observations of gravity changes with two GWR Superconducting Gravimeters (#008 and #009) has been carried out in the underground room at the Graduate School of Science, Kyoto University during the period from 1988 to 1997. Observational results, some of which are related to fluid core resonance and polar motion, are reported.	Click to read entire paper
Hydrological Influences on the Gravity Variations Recorded at Bad Homburg (ppt / doc)	Günter Harnisch, Martina Harnisch, et al	The gravimetric observatory in the cellar of the Bad Homburg castle was established more than 25 years ago. In 1999 the double-sphere superconducting gravimeter GWR CD030 was installed and has been recording up to the present. Three ground water gauges at distances of between 200 m and 3.5 km show a clear correlation between the variations in the ground water level and the recorded gravity data in the long-term (annual) range. The comparison with the observed gravity variations was based on the "corrected minute data" (repair code 02), stored in the GGP data-bank. A regression coefficient of about 50 nm s-2/m results from the amplitudes of the annual wave in the residual gravity (about 19 nm s-2) and that of the ground water variations at the Meiereiberg gauge (about 37 cm). - In the daily and weekly range the correlation is less clear. It seems that during late winter and spring strong precipitation events are clearly reflected in the ground water level while in autumn no precipitation influences are to be recognized.	Harnisch BHO 2006 (PPT - 3.56MB) Click to read entire paper (PDF - 205KB)
Continuous observation of periodic and non-periodic variations of the vertical component of gravity by a superconducting gravimeter	B. Meurers	Within the frame of the Global Geodynamics Project (GGP) this project contributes to the solution of geodynamical problems: Earth tides and Nearly diurnal free wobble (NDFW) Determination of tidal parameters (d -factor, phase) for the development of improved ocean loading models Determination of global d -factors of constituents near the NDFW resonance frequency Þ information about the structure of the earth's core Core Modes Search for coherent and global gravity signals (by stacking) of gravity oscillations in the outer core (undertones) translational oscillations of the inner core (Slichter-triplet) Air pressure and other meteorological hydrological effects Investigation of the direct and indirect (loading) effect of the atmosphere, effect of ground water level variations, precipitation, soil moisture Earth rotation and pole motion effects Gravity variations caused by tectonic processes Vertical crustal movement, deformation by active tectonics, postglacial deformation, sea level changes Free oscillations of the earth Observation of the spectrum of spheroidal oscillations excited by high magnitude earthquakes Interpretation of seasonal effects The GWR C025 Superconducting Gravimeter is operating since August 1995 in Vienna. Absolute gravity measurements will be performed regularly by using the Jilag-6 absolute gravimeter in order to calibrate the GWR C025 and to determine its instrumental drift. Cooperation with Central Institute of Meteorology and Geodynamics ( ZAMG, dept. of Geophysics), Vienna, which owns and maintains the GWR C025 gravimeter, and with the Federal Office of Surveying, Vienna, contributing by absolute gravity measurements (Dr. Ruess).	Click to read entire paper
Table Mountain Gravity Observatory Superconducting Gravity Data Download Site	VAN DAM, FRANCIS	In April of 1995, the National Oceanic and Atmospheric Administration (NOAA), as part of their Climate and Global Change Program, installed a GWR compact style superconducting gravimeter at their Table Mountain Gravity Observatory (TMGO) near Boulder, Colorado. The relative gravimeter, C024, is capable of detecting sub-microgal gravity variations. The instrument is very stable with a linear instrument drift of approximately 8 microgals/year. Data and information on the site are available on this web site. We will try to update the data monthly. NOAA participates in Global Geodynamics Project, a cooperative project between a number of international organizations, to pool superconducting data sets from around the world to investigate a number of geodynamic problems.	Click to read entire paper
High sampling rate data acquisition system for GWR superconducting gravimeter C021 (pdf)	Wilson, Clark R., Wu, Honqui, et al	In April of 1995, the National Oceanic and Atmospheric Administration (NOAA), as part of their Climate and Global Change Program, installed a GWR compact style superconducting gravimeter at their Table Mountain Gravity Observatory (TMGO) near Boulder, Colorado. The relative gravimeter, C024, is capable of detecting sub-microgal gravity variations. The instrument is very stable with a linear instrument drift of approximately 8 microgals/year. Data and information on the site are available on this web site. We will try to update the data monthly. NOAA participates in Global Geodynamics Project, a cooperative project between a number of international organizations, to pool superconducting data sets from around the world to investigate a number of geodynamic problems.	Click to read entire paper
High sampling rate data acquisition system for GWR superconducting gravimeter C021	Van Camp, M	A data acquisition system is connected on the Gravity Signal output of the GWR Superconducting Gravimeter C021 installed in Membach (east of Belgium). The data acquisition system consists in a DCF-controlled card provided with an analog/digital converter. In order to study the Earth's free oscillations, the chosen sampling rate is 1 Hz. Analysis of an important earthquake and comparison with 3 others gravimeters are presented. This data acquisition system gives also an information on the phase shift induced by the filter of the Tide output. For that purpose, we perform an ETERNA tidal analysis on data from Gravity Signal output, which is compared with the results obtained with the Tide output.	Click to read entire paper

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Welcome to the Gravimetric Observatories Service	Hinderer, Gravimetric Observatory of Strasbourg	Gravimetric Observatory of Strasbourg is the French resort of permanent measures of temporal variations in Earth's gravity field. These data are obtained using the superconducting gravimeter GWR C026 and collected within the global network GGP (Global Geodynamics Project). The cryogenic gravimeter is in continuous operation since summer 1996 and replaced without interrupting another superconducting gravimeter (GWR T005) in operation from 1987 to 1996. The Observatory is also the main site since 1997 home portable absolute gravimeter FG5 # 206 from Micro-g Solutions whose EOST (School and Observatory of Earth Sciences) has responsibility at the national level and, as such, regular measurements of absolute gravity are performed in parallel with the cryogenic gravimeter but also off-site in France and abroad on issues of interest geodesic (vertical reference network of bases gravimetric calibration lines). Finally, since late 1999, the site also has a permanent station GPS (Global Positioning System) geodetic quality which is part of the French network and network RENAG RGP from IGN. A weather station is in operation since May 2005.	Click to read entire paper
Intercomparison of IMGC Absolute and GWR SuperConducting Gravimeters	Baldi, P, Casula, G, et al	In May 1994 a first comparison campaign between a superconducting and the IMGC absolute gravimeter has been performed in Brasimone, near Bologna in Italy. The superconducting gravimeter was previously calibrated by means of a moving ring, the mass of which has been measured with the highest accuracy allowed by the actual technology. During the three days of observation with the absolute gravity meter, a maximum, a complete semidiurnal curve and a minimum of the tidal effect has been observed. These data have been used to compute the calibration factor of the superconducting gravity meter; it agrees in a rather satisfactory way with the results of the calibration with the moving mass.	Click to read entire paper
GRAVITY CHANGES RELATED TO VERTICAL CRUSTAL MOTIONS (pdf)	H. Virtanen , J. Ahola	We present results on vertical crustal motion as seen in the gravity data of the superconducting gravimeter GWR T020 at Metsähovi station for years 1994 ?U 2002. We have associated temporal height variations with the loading effects of the atmosphere and of the nearby Baltic Sea at the distance of 15 km. The refined, tide-free gravity data have been corrected for local hydrological effects, such as groundwater level changes. Theoretical loading calculations using appropriate Green's functions are performed for both vertical motion and gravity and the modelled gravity is compared with a large amount of observational data. For Baltic Sea loading effects we have used data of the nearest tide gauge in Helsinki at the distance of 30 km as well as data of several tide gauges around the Baltic. The loading by atmosphere has been computed using a detailed surface pressure field from HIRLAM (High Resolution Limited Area Model) for North Europe. The gravity data are congruent with loading calculations. The loading effect of the Baltic Sea can exceed 10 mm and the deformation by atmosphere 25 mm. However, the effects partly oppose each other. The gravity station is co-located with a permanent GPS station. We show comparisons between variation in GPS height and in gravity observations for some shorter periods. We discuss the results of the loading calculations and achieved improvements in gravity residuals.	Click to read entire paper
New Developments in Gravity Applications and Instruments		Gravity meters are commonly used to map spatial changes in the earth's gravity, achieving resolution of parts per billion on microgravity surveys. The application of gravity surveys to monitor change and recent improvements in gravity instrumentation will be summarized. The use of gravity to track the progress of a water flood in Prudhoe Bay, Alaska, provides a 4D Gravity case history. The surface gravity change caused by the injection of water into the gas cap is measured annually and compared to the expected change calculated from the reservoir model. 4D Gravity provides an effective ``early warning system' for injection and sequestration projects. A recent borehole gravity survey in Hanford, Washington, demonstrates the ability to measure bulk densities using a borehole gravimeter. The applications include geotechnical studies at waste disposal sites, bridges and structures, locating and monitoring thief zones in reservoirs, and grade control in iron mines. A new borehole gravity meter will be introduced during 2008 that can be used in smaller, inclined boreholes. Earth tides and other long period movements of the earth can be recorded by suitably configured gravity meters. The ground shaking in Luxembourg before and after the January 13, 2007, earthquake in Japan was recorded on a long period seismometer, a superconducting gravity meter and a new portable gPhone gravity meter. The match between the seismometer data and the gPhone data during the earthquake is excellent. The relatively inexpensive portable gPhone gravity meter provides the means to record earth movements along active fault zones and other critical locations. gPhone data recorded in Denver, Colorado on August 15, 2007, indicates F40pre-shock and post-shock ground motion as well as the 8.0 earthquake in Peru.	Click to read entire paper
Comment on "Incessant excitation of the Earth's free oscillations"	Yuichi Imanishi	The report of Nawa et al. (1998) that incessant excitation of the Earth's free oscillations was discovered in the low frequency spectra of the superconducting gravimeter at the Syowa station in Antarctica is reexamined. The mean spectra for Syowa are compared with those for Matsushiro, another superconducting gravimeter station in an extremely calm circumstance, hence showing a much lower noise level than Syowa. Although the spectra for Syowa have many peaks below 3 mHz corresponding to those present in the time-frequency diagram of Nawa et al., no similar peaks are found in the spectra for Matsushiro. This result suggests that the peaks below 3 mHz in the Syowa spectra are not real signals of the Earth's free oscillations.	Click to read entire paper
Gravity Monitoring Equipment	Australian National University, Research School Of Earth Sciences (RSES)	RSES operates a Superconducting Gravimeter at Mt Stromlo Observatory, continuously monitoring small changes in gravity caused by tidal, environmental and seismic effects.	Click to read entire paper
Taking the superconducting gravimeter to the field for hydrologic and other investigations	Wilson, C. R.; Wu, H, et al	We have adapted the GWR superconducting gravity meter to a transportable configuration for field studies in support of hydrologic and other investigations. The gravimeter has a precision in the 10-nanogal range, and a nominal drift of a few microgals per year. Although the GWR instrument has been in production for about three decades, operations have been restricted previously to laboratory and vault environments. A ground water gravity signal has often been apparent, but complex hydrologic conditions have made quantitative interpretation difficult. By making the instrument transportable, one is able to choose sites where better-defined hydrologic problems can be investigated, and to consider tectonic, volcanic, and other applications. Technical advances have reduced the size of the helium Dewar and solved the helium replenishment requirement via a compact refrigeration system. With the ability to cool to 4 K, it is possible to maintain a full Dewar indefinitely. With support of NSF EAR Instrumentation and Facilities, we procured a GWR gravimeter and developed the system to be transportable, self contained within two enclosures, and accessible via cell-phone internet service. A bracket system allows the helium Dewar containing the gravity sensor to be locked to the frame and transported without disassembly. Initial application is to hydrologic investigations in karst and desert alluvial aquifers. The goal is to understand hydrologic signals at a level near one microgal, equivalent to the attraction of a 2cm layer of water. Instrument precision exceeds this, but the variety of sources in the atmosphere makes it difficult to identify hydrologic signals with greater precision. Companion weather and well observations are used to observe and interpret gravity variations in terms of infiltration and storage changes, and GRACE satellite gravity observations enable separation of regional and local influences.	Click to read entire paper
Changes in Gravity	Heikki Virtanen	The superconducting gravimeter GWR T020 at Metsähovi observes temporal variations in gravity, smaller than 10-12g. The main goal is the maintenance of the equipment, continuous data acquisition and good quality. The data of gravimeter have been transmitted to the GGP (Global Geodynamic Project), respectively data from other global stations (20) are available. Due to high precision, the data has been applied all-round to investigations at Metsähovi. Main topics are Earth tides, local hydrological effects on gravity (rain, snow and groundwater) and loading effects. The atmosphere and Baltic Sea level cause gravity changes and vertical motion. The gravity data is compared to results of gravity satellites (CHAMP and GRACE). The gravimeter has been used as a long-periodic seismometer to study free oscillations of the Earth after major earthquakes.	Click to read entire paper
International tidal gravity reference values at Wuhan station	Houze Xu, Heping Sun, et al	The international tidal gravity reference values at Wuhan station are determined accurately based on the comprehensive analysis of the tidal gravity observations obtained from 8 instruments. By comparing these with those in the tidal models given by Dehant (1997) while considering simultaneously (i) the global satellite altimeters tidal data, and (ii) the Schwiderski global tidal data and the local ones along the coast of China, it is found that the average discrepancy of the amplitude factors and of the phase differences for four main waves are given as 5.2% and 3.6% and as 0.16° and 0.08° respectively. They are improved evidently compared to those determined in early stage, indicating the important procedures in improving the Wuhan international tidal gravity reference values when including the long-series observations obtained with a superconducting gravimeter, and when considering the influence of the ocean loading and of the nearly daily free wobble of the Earth's core.	Click to read entire paper
Indication of the uplift of the Ardenne in long-term gravity variations in Membach (Belgium)	Olivier Francis; Michel Van Camp, et al	We report on the results of 7 yr of collocated gravity observations made with an FG5 absolute (AG) gravimeter and a GWR C-Series superconducting gravimeter (SG) located at the Membach Geophysical Station in eastern Belgium. The SG gravity residuals track changes in gravity periodically observed by the AG, at the microgal level. Further, in the SG residual signal we distinguish a quasi-seasonal term that can be mostly explained by variations in local water storage effects. In the AG time-series we observe a small trend in the gravity of -0.6 ± 0.1 Gal yr-1 perhaps indicating that the Membach Station is being displaced upwards by about 3.0 mm yr-1. An uplift of the region is confirmed by Global Positioning System (GPS) measurements performed 3 km away. We are able to explain the features in the gravity time-series in terms of water storage variability, post-glacial rebound and tectonic activity.	Click to read entire paper

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Comparison of Different Approaches to Combine Superconducting and Absolute Gravity Measurements	H. Wziontek, R. Falk, H. Wilmes, P. Wolf	The combination of concurrent sets of superconducting and absolute gravity measurements allow to determine a verified gravity time series and an entire control of both contributing instruments. A method is proposed to derive the scale factor and zero drift function of the superconducting gravimeter and a reliable survey of the instrumental stability of absolute meters with high precision and without the demand of gravity reductions. In this way it is possible to separate between geophysical signals and instrumental effects in gravity time series. Results for SG stations Bad Homburg, Wettzell and Medicina are presented and compared with classical combination approaches based on reduced mean values over a certain epoch.	Click to read entire paper
A comparative analysis between an absolute gravimeter (FG5-206) and a superconducting gravimeter ( GWR CO26) in Strasbourg: new results on calibration and long-term gravity changes	M. Amalvict, J. Hinderer, et al	This paper is devoted to a comparative analysis of gravity changes as observed both by an absolute gravimeter (AG-FG5 model 206) and a superconducting gravimeter (SG-GWR model C026) operating in parallel in Strasbourg in 1997-1998. Two main objectives will be sought: on the one hand, we want to establish the calibration capability of AG/SG parallel registrations, especially with respect to stability in time, duration requirement and precision; on the other hand, the absolute gravity values will be superimposed on the superconducting gravimeter observations in order to estimate long-term gravity changes and to attempt to separate true physical effects from the instrumental drift contribution of the cryogenic meter.	Click to read entire paper
Two Years of Continuous Measurements of Tidal and Nontidal Variations of Gravity in Boulder, Colorado	Tonie M. van Dam, Olivier Francis	We report here on the results of an analysis of 2 years of data from NOAA's superconducting gravimeter located at the Table Mountain Gravity Observatory in Boulder, Colorado. Observed tidal parameters, corrected for ocean loading effects, are compared with theoretical tidal parameters predicted for a non-hydrostatic inelastic Earth model and demonstrate excellent agreement. Tidal residuals, corrected for polar motion and a linear instrument drift are highly correlated with gravity changes measured by two absolute gravimeters over he same time period. The admittance to local pressure is found to be -0.356 mGal / mbar. However, this admittance factor is found to be seasonally and frequency dependent. Correlations between rainfall events and gravity changes are observed. Attempts to model these gravity changes as exponential functions of time were unsuccessful.	Click to read entire paper
Development of the European Combined Geodetic Network in Austria	Diethard Ruess	Austria takes part in the European Combined Geodetic Network - Project with three different stations: Graz, Trafelberg and Pfänder. One of them - Graz (= IGS) - is the oldest station and therefore it has got a very long time series for the position and the combination of GPS and laser instruments, whereas Trafelberg, a very new station, combines geodetic, gravimetric and seismic measurement devices. The presentation will concentrate on the present state of the three stations in Austria.	Click to read entire paper
Tidal Gravity Variation Data in Antarctica by JARE	Shibuya, K., Ogawa, F	Tidal gravity variations using LaCoste-Romberg gravimeter were observed at Syowa and Asuka Stations. The data were processed according to the data format of ICET (International Centre for Earth Tides, Brussels) and sent to it. The users should send a request to ICET for a copy of the data. Measurement using a superconducting gravimeter (GWR model TT70#016) was done at Syowa Station from 1993 through 2002. The data were sent to the GGP (Global Geodynamics Project) data center and the users should send a request to ICET for a copy of the data. The ICET moved from Belgium to French Polynesia on 2008	Click to read entire paper
Gravity monitoring project in Mizunami, central Japan - Subsurface structure under the observation station	Toshiyuki Tanaka, Harumi Aoki	Tono Research Institute of Earthquake Science (TRIES) showed the plan to introduce an absolute gravimeter (FG5 made by Micro-g Inc.) in the Syomasama lot of the MIzunami Underground research laboratory (MIU) project in the 2003 fiscal year (Tanaka et al., 2002). Though we do not recur to the significance, purpose, and background, the scheme of introducing a superconducting gravimeter instead of an absolute gravimeter has emerged by recent announcement of a new superconducting gravimeter (Field SG made by GWR Inc.). The Field SG realizes low-drift less than 1 microGal/month and no refilling of liquid helium, although the Dewar size is 10L (30kg in weight). Even if either gravimeter will be introduced, it is important to investigate subsurface structure just under and around the observation point in the Syomasama lot. In this report, we clarify the subsurface structure above basement rock by combining microgravity survey executed by this study and existing data (boring and reflection surveys).	Click to read entire paper
Precise Observation of Gravity Changes with Superconducting Gravimeters in Kyoto(1988-1997)	TAKEMOTO SHUZO, HIGASHI TOSHIHIRO, et al	Precise observation of gravity changes with two GWR Superconducting Gravimeters(#008 and #009) has been carried out in the underground room at the Graduate School of Science, Kyoto University during the period from 1988 to 1997. Observational results, some of which are related to fluid core resonance and polar motion, are reported. (author abst.)	Click to read entire paper

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