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1
Vitushkin, L. F., E. P. Krivtsov, P. P. Krolitsky, V. V. Nalivaev, O. A. Orlov, and M. M. Haleev. "State primary special standard of acceleration unit in the field of gravimetry GET 190-2023: reproduction and transmission of the unit under the influence of geophysical factors." Izmeritel`naya Tekhnika, no. 1 (March 8, 2024): 4–11. http://dx.doi.org/10.32446/0368-1025it.2024-1-4-11.
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The relevance of research on the reproduction and transmission of the acceleration unit in gravimetry is determined by the development of measuring instruments for the absolute value of the acceleration of free fall and its changes. Qualitative and quantitative changes in the instrument base are due to the requirements of applied tasks solved using gravimetric data in such fields as geodesy, navigation, geodynamics, as well as the expansion of the field of practical application of absolute gravimeters. At the same time, in order to solve applied problems, along with accuracy requirements at a level close to the maximum achievable at the current level of technology development, maximum territorial coverage of measurement sites within the entire territory of the Russian Federation is often necessary. The accuracy of the results obtained with the help of measuring instruments is determined by the level of their metrological support, the main stages of which are the reproduction of the corresponding unit by the standard and its transfer to the measuring instrument. An analysis of possible sources of errors in gravimetric equipment has shown that when reproducing and transmitting the acceleration unit in gravimetry, it is necessary to take into account the influence of geophysical factors that manifest themselves as additional accelerations of a gravitational or inertial nature. The distribution of the gravitational field within a gravimetric point can manifest itself as an additional constant acceleration. Seismic processes and lunar and solar tides manifest themselves as variable accelerations. For various stages of metrological support of gravimetric devices, the mechanisms of the effects of such accelerations have been studied, as well as methods for accounting and reducing their influence using additional equipment have been developed. An additional gravimetric point with a cryogenic relative gravimeter and a broadband seismometer, as well as transported absolute ballistic and relative quartz gravimeters, were introduced into the State primary special standard of acceleration units in the field of gravimetry GET 190-2023.
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Wu, Xuejian, Zachary Pagel, Bola S. Malek, Timothy H. Nguyen, Fei Zi, Daniel S. Scheirer, and Holger Müller. "Gravity surveys using a mobile atom interferometer." Science Advances 5, no. 9 (September 2019): eaax0800. http://dx.doi.org/10.1126/sciadv.aax0800.
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Mobile gravimetry is important in metrology, navigation, geodesy, and geophysics. Atomic gravimeters could be among the most accurate mobile gravimeters but are currently constrained by being complex and fragile. Here, we demonstrate a mobile atomic gravimeter, measuring tidal gravity variations in the laboratory and surveying gravity in the field. The tidal gravity measurements achieve a sensitivity of 37 μGal/Hz (1 μGal = 10 nm/s2) and a long-term stability of better than 2 μGal, revealing ocean tidal loading effects and recording several distant earthquakes. We survey gravity in the Berkeley Hills with an uncertainty of around 0.04 mGal and determine the density of the subsurface rocks from the vertical gravity gradient. With simplicity and sensitivity, our instrument paves the way for bringing atomic gravimeters to field applications.
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NOVÁK, Adam, and Juraj JANÁK. "Estimating the thermal effect in gPhoneX observations." Contributions to Geophysics and Geodesy 52, no. 4 (December 12, 2022): 501–15. http://dx.doi.org/10.31577/congeo.2022.52.4.1.
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Stationary relative gravimeters are used in variety of applications, mainly due to their high sampling rate which is more suitable for study of certain geodynamic effects than absolute gravimeters. Study of weak signals is almost exclusively in the domain of superconducting gravimeters, as they possess the highest accuracy and stability of all types of relative gravimeters. Possible alternative to superconducting gravimeters are portable earth tide metal spring gravimeters. Zero-length spring gravimeters (e.g. LCR instruments) are usually considered to be the most accurate mechanical spring gravimeters. However, compared to superconducting instruments they remain too unstable for long-term gravity monitoring. Main reason supporting this statement is related to instrument's sensitivity to temperature changes and temperature induced tilts. Gravity observations from the gPhoneX #108 gravimeter stationed at Hurbanovo gravimetric observatory were tested in order to confirm the correlation between the observed gravity changes and ambient temperature changes and provide a solution for correcting the gPhone data for influence of the ambient temperature changes. Paper also aims to serve as a guide for other operators to estimate a parameters required for the calculation of ambient temperature correction.
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Greco, Filippo, Federica Riguzzi, and Giovanna Berrino. "Insights into Seismogenetic Areas in Central Italy from Combined Absolute Gravity and GNSS Measurements." Remote Sensing 13, no. 22 (November 18, 2021): 4649. http://dx.doi.org/10.3390/rs13224649.
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In this study we present and discuss gravity and ground deformation variations, at different time scales, observed in a wide mesh absolute gravity and GNSS network set up in central Italy. The network was installed in the area affected by the 2009 (L’Aquila; Mw 6.1) and 2016 (Amatrice-Norcia; Mw 6.0 and 6.5) seismic activity, in order to verify if gravity and ground deformation variations could be related to seismic effects. The new network includes 5 stations distributed between the Lazio, Umbria, and Abruzzo regions. From 2018 to 2020 three campaigns were carried out using the transportable Micro-g LaCoste FG5#238 and the portable Micro-g LaCoste A10#39 absolute gravimeters and completed with two simultaneous GNSS measurements. Topographic instruments, measurement and analysis techniques enabling accurate measurements in the positioning of the stations and to control their variations over time were applied. The high reliability and accuracy of the absolute gravity data gathered, after being corrected for known effects, showed a negative short-term (2018–2020) pattern throughout the area, up to −30 µGal. Since some stations of the new network coincided with benchmarks already measured in the past, an analysis of long-term gravity changes was carried out and a fair degree of stability was observed in two stations, while positive large variations, of approximately 70 and 157 µGal, were recorded in the other two stations in the time intervals 1954–2020 and 2005–2010, respectively. On the other hand, variations highlighted by GNSS height measurements were all below 3 cm. Here, the first long-lasting gravity measurements carried out with absolute gravimeters in a seismic area in Italy are presented, providing meaningful geophysical information. The obtained results, in terms of availability of a combined absolute gravity and GNSS network, definition of data acquisition and analysis procedures, as well as creation of a high quality data archive, lay the foundations for a multidisciplinary approach towards improving the knowledge of this seismogenetic area of Italy.
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Cooke, Anne-Karin, Cédric Champollion, and Nicolas Le Moigne. "First evaluation of an absolute quantum gravimeter (AQG#B01) for future field experiments." Geoscientific Instrumentation, Methods and Data Systems 10, no. 1 (March 24, 2021): 65–79. http://dx.doi.org/10.5194/gi-10-65-2021.
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Abstract. Quantum gravimeters are a promising new development allowing for continuous absolute gravity monitoring while remaining user-friendly and transportable. In this study, we present experiments carried out to assess the capacity of the AQG#B01 in view of future deployment as a field gravimeter for hydrogeophysical applications. The AQG#B01 is the field version follow-up of the AQG#A01 portable absolute quantum gravimeter developed by the French quantum sensor company Muquans. We assess the instrument's performance in terms of stability (absence of instrumental drift) and sensitivity in relation to other gravimeters. No significant instrumental drift was observed over several weeks of measurement. We discuss the observations concerning the accuracy of the AQG#B01 in comparison with a state-of-the-art absolute gravimeter (Micro-g-LaCoste, FG5#228). We report the repeatability to be better than 50 nm s−2. This study furthermore investigates whether changes in instrument tilt and external temperature and a combination of both, which are likely to occur during field campaigns, influence the measurement of gravitational attraction. We repeatedly tested external temperatures between 20 and 30 ∘C and did not find any significant effect. As an example of a geophysical signal, a 100 nm s−2 gravity change is detected with the AQG#B01 after a rainfall event at the Larzac geodetic observatory (southern France). The data agreed with the gravity changes measured with a superconducting relative gravimeter (GWR, iGrav#002) and the expected gravity change simulated as an infinite Bouguer slab approximation. We report 2 weeks of stable operation under semi-terrain conditions in a garage without temperature-control. We close with operational recommendations for potential users and discuss specific possible future field applications. While not claiming completeness, we nevertheless present the first characterization of a quantum gravimeter carried out by future users. Selected criteria for the assessment of its suitability in field applications have been investigated and are complemented with a discussion of further necessary experiments.
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Pettersen, Bjørn Ragnvald. "A historical review of gravimetric observations in Norway." History of Geo- and Space Sciences 7, no. 2 (October 27, 2016): 79–89. http://dx.doi.org/10.5194/hgss-7-79-2016.
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Abstract. The first gravity determinations in Norway were made by Edward Sabine in 1823 with a pendulum instrument by Henry Kater. Seventy years later a Sterneck pendulum was acquired by the Norwegian Commission for the International Arc Measurements. It improved the precision and eventually reduced the bias of the absolute calibration from 85 to 15 mGal. The last pendulum observations in Norway were made in 1955 with an instrument from Cambridge University. At a precision of ±1 mGal, the purpose was to calibrate a section of the gravity line from Rome, Italy, to Hammerfest, Norway. Relative spring gravimeters were introduced in Norway in 1946 and were used to densify and expand the national gravity network. These data were used to produce regional geoids for Norway and adjacent ocean areas. Improved instrument precision allowed them to connect Norwegian and foreign fundamental stations as well. Extensive geophysical prospecting was made, as in other countries. The introduction of absolute gravimeters based on free-fall methods, especially after 2004, improved the calibration by 3 orders of magnitude and immediately revealed the secular changes of the gravity field in Norway. This was later confirmed by satellite gravimetry, which provides homogeneous data sets for global and regional gravity models. The first-ever determinations of gravity at sea were made by pendulum observations onboard the Norwegian polar vessel Fram during frozen-in conditions in the Arctic Ocean in 1893–1896. Simultaneously, an indirect method was developed at the University of Oslo for deducing gravity at sea with a hypsometer. The precision of both methods was greatly superseded by relative spring gravimeters 50 years later. They were employed extensively both at sea and on land. When GPS allowed precise positioning, relative gravimeters were mounted in airplanes to cover large areas of ocean faster than before. Gravimetry is currently being applied to study geodynamical phenomena relevant to climate change. The viscoelastic postglacial land uplift of Fennoscandia has been detected by terrestrial gravity time series as well as by satellite gravimetry. Corrections for local effects of snow load, hydrology, and ocean loading at coastal stations have been improved. The elastic adjustment of present-day melting of glaciers at Svalbard and in mainland Norway has been detected. Gravimetry is extensively employed at offshore oil facilities to monitor the subsidence of the ocean floor during oil and gas extraction.
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Vu, Dinh Toan, Jérôme Verdun, José Cali, Marcia Maia, Charles Poitou, Jérôme Ammann, Clément Roussel, Jean-François D’Eu, and Marie-Édith Bouhier. "High-Resolution Gravity Measurements on Board an Autonomous Underwater Vehicle: Data Reduction and Accuracy Assessment." Remote Sensing 16, no. 3 (January 25, 2024): 461. http://dx.doi.org/10.3390/rs16030461.
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Gravity on Earth is of great interest in geodesy, geophysics, and natural resource exploration. Ship-based gravimeters are a widely used instrument for the collection of surface gravity field data in marine regions. However, due to the considerable distance from the sea surface to the seafloor, the spatial resolution of surface gravity data collected from ships is often insufficient to image the detail of seafloor geological structures and to explore offshore natural minerals. Therefore, the development of a mobile underwater gravimetry system is necessary. The GraviMob gravimeter, developed for a moving underwater platform by Geo-Ocean (UMR 6538 CNRS-Ifremer-UBO-UBS), GeF (UR4630, Cnam) and MAPPEM Geophysics, has been tested over the last few years. In this study, we report on the high-resolution gravity measurements from the GraviMob system mounted on an Autonomous Underwater Vehicle, which can measure at depths of up to several kilometres. The dedicated GraviMob underwater gravity measurements were conducted in the Mediterranean Sea in March 2016, with a total of 26 underwater measurement profiles. All these measurement profiles were processed and validated. In a first step, the GraviMob gravity measurements were corrected for temperature based on a linear relationship between temperature and gravity differences. Through repeated profiles, we acquired GraviMob gravity measurements with an estimated error varying from 0.8 to 2.6 mGal with standard deviation after applying the proposed temperature correction. In a second step, the shipborne gravity data were downward continued to the measurement depth to validate the GraviMob measurements. Comparisons between the corrected GraviMob gravity anomalies and downward continued surface shipborne gravity data revealed a standard deviation varying from 0.8 to 3.2 mGal and a mean bias value varying from −0.6 to 0.6 mGal. These results highlight the great potential of the GraviMob system in measuring underwater gravity.
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Genrich, J. F., and J. B. Minster. "Near‐real time reduction of shipboard gravity using Kalman‐filtered GPS measurements." GEOPHYSICS 56, no. 12 (December 1991): 1971–79. http://dx.doi.org/10.1190/1.1443008.
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We have developed a Kalman filter to estimate accurate Eötvös corrections and horizontal ship accelerations from Global Positioning System (GPS) fixes. High‐resolution shipboard gravity measurements are obtained with a newly designed, linear phase, Finite Impulse Response (FIR) low‐pass filter. Both filters are combined to yield accurate, near‐real time, Eötvös‐corrected underway gravity estimates. Error ranges that reflect uncertainty in navigation for these estimates are calculated from autocovariances of Kalman velocity estimates by means of variance propagation expressions for time‐invariant linear digital filters. Estimates of horizontal ship acceleration are combined with a simplified instrument impulse response model in an attempt to remove transient noise from the gravimeter output. We apply the technique to data collected by two shipboard gravimeters, a LaCoste & Romberg Model S Air‐Sea Gravity Meter and a Bell Aerospace BGM-3 Marine Gravity Meter System, operated side‐by‐side on the Scripps R/V Thomas Washington during Leg 1 of the Roundabout expedition. In the absence of significant horizontal accelerations due to course or speed changes, both instruments yield data with good repeatability, characterized by rms differences of less than 1 mGal. Horizontal accelerations generate transient signals that cannot be modeled at present to an accuracy of better than 5 mGal. Difficulties in removing these transients are primarily due to insufficient quantitative knowledge of the response of the instrument, including the gyro‐stabilized platform. This can be determined analytically or empirically.
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Dransfield, Mark. "Searchlights for gravity and magnetics." GEOPHYSICS 80, no. 1 (January 1, 2015): G27—G34. http://dx.doi.org/10.1190/geo2014-0256.1.
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The development of mental schemata is important in developing an understanding of physical phenomena and processes. Gravitational and magnetic fields are often visualized by geophysicists as equipotential surfaces (for gravity) and field lines (for magnetics). In these cases, the schemata treat the geology as the source of the field. In seismic and electromagnetic prospecting, one instead visualizes a field that is emitted by the instrument. Example schemata are traveling wavefronts (seismic) and smoke rings (electromagnetic induction in the dissipative limit). I carried this instrument-focused conceptualization over to potential field prospecting by a schema, which envisages the instrument as a probe, illuminating the earth in a manner analogous to a searchlight. Different potential-field instruments (potentiometers, gravimeters, magnetometers, and gradiometers) each have different beam characteristics and consequently illuminate the earth in different ways. This schema provides a new way of visualizing potential fields in prospecting with applications in instrument development, data acquisition and processing, and interpretation.
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Xie, Dongdong, Shuhua Yan, Lingxiao Zhu, Huankai Zhang, and Xu Zhang. "Review on Vibration Isolation Method for Atomic Interference Gravimeter." Journal of Physics: Conference Series 2125, no. 1 (November 1, 2021): 012022. http://dx.doi.org/10.1088/1742-6596/2125/1/012022.
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Abstract The cold atomic interference absolute gravimeter is an ultra-precision instrument for measuring absolute gravity acceleration. At present, the highest measurement accuracy can reach the order of micro gamma. It has important application value and research significance in many disciplines, such as geophysics, resource exploration and assisted navigation. Because of its ultra-high precision, the ultra-low frequency micro-vibration noise on the ground has become one of the important factors affecting its accuracy, and it is also the bottleneck of the further development of gravimeter. Firstly, based on the theoretical and experimental results, this paper analyzes the vibration isolation requirements of atomic interference gravimeter. Secondly, it summarizes the research progress of atomic interference gravimeter isolation system and introduces three main isolation methods: passive vibration isolation, active vibration isolation and vibration compensation. Finally, the future development direction of atomic interference gravimeter isolation technology is analyzed and prospected.
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Sasagawa, Glenn S., Wayne Crawford, Ola Eiken, Scott Nooner, Torkjell Stenvold, and Mark A. Zumberge. "A new sea‐floor gravimeter." GEOPHYSICS 68, no. 2 (March 2003): 544–53. http://dx.doi.org/10.1190/1.1567223.
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A new reservoir management application uses precise time‐lapse gravity measurements on the sea floor to detect seawater infiltration in offshore natural gas fields during production. Reservoir models for the North Sea Troll field predict gravity changes as large as 0.060 mGal within a 3–5‐year period. We have constructed and deployed a new instrument—the ROVDOG (Remotely Operated Vehicle‐deployed Deep‐Ocean Gravimeter) system—for this application. Because the measurements must be relocated accurately (within 3 cm), we required a gravimeter which could be handled by an ROV and placed atop sea‐floor benchmarks. We have built an instrument based upon the Scintrex CG‐3M land gravimeter. Motorized gimbals level the gravimeter sensor within a watertight pressure case. Precision quartz pressure gauges provide depth information. A shipboard operator remotely controls the instrument and monitors the data. The system error budget considers both instrumental and field measurement uncertainties. The instrument prototype was deployed in the North Sea during June 1998; 75 observations were made at 32 stations. The standard deviation of repeated gravity measurements was 0.026 mGal; the standard deviation of pressure‐derived heights, for repeated measurements, was 1.4 cm. A refined instrument was deployed in August 2000 in a three‐sensor configuration. Multiple sensors improved the precision by averaging more samples without incurring additional survey time. A total of 159 measurements were made at 68 stations. The standard deviation of repeated measurements was 0.019 mGal; the standard deviation of pressure‐derived heights was 0.78 cm. A ROVDOG pressure case rated to 4500 m depth has also been constructed. This system was deployed with the Alvin manned submersible in November 2000 to a depth of 2700 m.
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Wang, Linhai, Shi Chen, Jiancang Zhuang, and Weimin Xu. "Simultaneous calibration of instrument scale factor and drift rate in network adjustment for continental-scale gravity survey campaign." Geophysical Journal International 228, no. 3 (October 14, 2021): 1541–55. http://dx.doi.org/10.1093/gji/ggab419.
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SUMMARY The scale factor of each relative gravimeter must be calibrated both before and after the fieldwork of a terrestrial gravity survey, to reduce uncertainties and ensure high precision. Conventionally, such calibration is a time-consuming process performed following well-established baselines. We propose a new Bayesian method to estimate the scale factor in a hybrid gravity network that includes several absolute gravity observation stations. In this approach, the scale factor is estimated as a hyperparameter using the Akaike Bayesian information criterion and using known absolute gravity stations in the network or/and calibrated instruments as constraints. Testing the sensitivity of the gravity values and the residuals of the gravity difference between two successive stations to the change of the scale factor demonstrates the robustness of this method. We also test the sensitivity of the estimated scale factor in the presence of Gaussian noise and the non-linear instrumental drift rate. Moreover, if the maximum absolute gravity interval is greater than 60 per cent of the range of gravity values in the network, or if the known scale factors of calibrated gravimeters are well calibrated, this approach can provide reasonable estimates of the daily drift rate and the unknown scale factors, where the latter has an error of <3 × 10−5. We apply this approach to real gravity campaign data from Yunnan in China and use a cross-validation method to compare estimated gravity values and corresponding gravity values obtained from absolute gravity observations at the same stations, to validate how the proposed method improves estimation accuracy of the gravity value at each station.
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Forbriger, Thomas, Walter Zürn, and Rudolf Widmer-Schnidrig. "Challenges and Perspectives for Lowering the Vertical-Component Long-Period Detection Level." Seismological Research Letters 92, no. 4 (March 24, 2021): 2498–512. http://dx.doi.org/10.1785/0220200399.
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Abstract For observations of vertical-component acceleration in the normal-mode band (0.3–10 mHz), the detection sensitivity for signals from the Earth’s body can be improved to levels below the Peterson low-noise model (PLNM). This is achieved by deterministic procedures that (at least partly) remove the accelerations originating from atmospheric mass fluctuations. The physical models used in such corrections are still too simple and fail at frequencies above 3 mHz. Anticipating improved atmospheric correction procedures, we explore the prospects of lowering the detection level. From recordings of excellent vertical-component sensors operated under exceptional site conditions at the Black Forest Observatory, we select time windows of very low background signal, for which all of the contributing broadband seismometers showed their best performance. Streckeisen seismometers of type STS-1, STS-2, and STS-6A, a Nanometrics Trillium T360, and the superconducting gravimeter (SG) SG056 manufactured by GWR Instruments take part in this comparison. Because of their low level of self-noise, the STS-1 and the SG056-G1 benefit the most from a correction with the best currently available improved Bouguer plate model for atmospherically induced signals at frequencies below 1 mHz. As far as we know, this is the first case in which the background level of a broadband seismometer could be lowered below the PLNM. At signal periods beyond the normal-mode band (investigated up to 12 hr), the gravimeters show the lowest level of self-noise, directly followed by the STS-6A. In the band from 0.3 to 10 mHz, the STS-1 has the lowest level of self-noise, which is at least 4 dB below the PLNM, directly followed by the T360 and the STS-6A. Sensors of lower self-noise than the currently manufactured STS-6A or T360 are needed before improved atmospheric correction procedures lead to a significantly lower vertical-component detection threshold.
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Ma, Jinxiu, An Li, Fangjun Qin, Wenbin Gong, and Hao Che. "ICEEMDAN/LOESS: An Improved Vibration-Signal Analysis Method for Marine Atomic Interferometric Gravimetry." Journal of Marine Science and Engineering 12, no. 2 (February 8, 2024): 302. http://dx.doi.org/10.3390/jmse12020302.
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The marine atomic interferometric gravimeter is a vital precision instrument for measuring marine geophysical information, which is widely used in mineral resources exploration, military applications, and missile launches. In practical measurements, vibration disturbance is an important factor that affects measurement accuracy. This paper proposes the combination of improved complete ensemble empirical mode decomposition with adaptive noise and locally weighted regression for vibration characterization of gravimeter vibration data. Firstly, the original signal is added into a pair of white noise for adaptive noise-complete ensemble empirical mode decomposition to obtain multiple intrinsic mode functions. The efficient IMF components and noise components are filtered out under the dual indicators of correlation coefficient and variance contribution ratio, and then the LOESS filtering method is used for noise reduction to obtain useful signal detail information; finally, the noise-containing components are reconstructed with the effective components after the noise-reduction process. The experimental results of both simulated and measured vibration signals show that the proposed method can effectively decompose the different high- and low-frequency bands contained in the vibration signal and remove the noise of the original signal.
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Ferguson, J. F., T. Chen, J. Brady, C. L. Aiken, and J. Seibert. "The 4D microgravity method for waterflood surveillance: Part II — Gravity measurements for the Prudhoe Bay reservoir, Alaska." GEOPHYSICS 72, no. 2 (March 2007): I33—I43. http://dx.doi.org/10.1190/1.2435473.
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Between 1994 and 2002, a series of experiments was conducted at Prudhoe Bay, Alaska, aimed at the development of an effective 4D (or time-lapse) gravity technique. Theoretical investigations had pointed out the potential for monitoring water injection in the [Formula: see text]-deep reservoir, but it was not clear that gravity measurements of sufficient accuracy could be made in the arctic environment. During the course of these experiments, new techniques and instrumentation were introduced and perfected for both gravity and position measurements. Gravity stations are located using high-precision global positioning system (GPS) techniques without permanent monuments. Robust methods for meter drift control have improved noise resistance in relative gravimeter surveys. Absolute gravity measurements with a field-portable instrument maintain absolute gravity levels among surveys. A 4D gravity-difference noise of [Formula: see text] standard deviation has been established at Prudhoe Bay for GPS-controlled relative gravimeter surveys. The lessons learned are now being applied to full-scale waterflood monitoring at Prudhoe Bay. The basic technique is applicable to microgravity surveys and 4D microgravity surveys for any purpose.
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Li, Hang, Jianqiao Xu, Xiaodong Chen, Heping Sun, Miaomiao Zhang, and Lingyun Zhang. "Extracting Long-Period Surface Waves and Free Oscillations Using Ambient Noise Recorded by Global Distributed Superconducting Gravimeters." Seismological Research Letters 91, no. 4 (May 27, 2020): 2234–46. http://dx.doi.org/10.1785/0220190166.
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Abstract Inversion of internal structure of the Earth using surface waves and free oscillations is a hot topic in seismological research nowadays. With the ambient noise data on seismically quiet days sourced from the gravity tidal observations of seven global distributed superconducting gravimeters (SGs) and the seismic observations for validation from three collocated STS-1 seismometers, long-period surface waves and background free oscillations are successfully extracted by the phase autocorrelation (PAC) method, respectively. Group-velocity dispersion curves at the frequency band of 2–7.5 mHz are extracted and compared with the theoretical values calculated with the preliminary reference Earth model. The comparison shows that the best observed values differ about ±2% from the corresponding theoretical results, and the extracted group velocities of the best SG are consistent with the result of the collocated STS-1 seismometer. The results indicate that reliable group-velocity dispersion curves can be measured with the ambient noise data from SGs. Furthermore, the fundamental frequency spherical free oscillations of 2–7 mHz are also clearly extracted using the same ambient noise data. The results in this study show that the SG, besides the seismometer, is proved to be another kind of instrument that can be used to observe long-period surface waves and free oscillations on seismically quiet days with a high degree of precision using the PAC method. It is worth mentioning that the PAC method is first and successfully introduced to analyze SG observations in our study.
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Imanishi, Y. "On the possible cause of long period instrumental noise (parasitic mode) of a superconducting gravimeter." Journal of Geodesy 78, no. 11-12 (March 30, 2005): 683–90. http://dx.doi.org/10.1007/s00190-005-0434-5.
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Ridgway, Jeff R., and Mark A. Zumberge. "Deep‐towed gravity surveys in the southern California Continental Borderland." GEOPHYSICS 67, no. 3 (May 2002): 777–87. http://dx.doi.org/10.1190/1.1484521.
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We surveyed two sites in the southern California continental borderland with a newly developed instrument, a towed deep ocean gravimeter—a gravity sensor that can be towed a few tens of meters above the sea floor. During its development phase, we used the instrument to survey two regions off the coast of southern California. The first was along two tracks in the San Diego Trough. The second was over a seamount‐like feature named Emery Knoll. Results of the trough survey reveal a basin with a geometry consistent with seismic data. We observed no significant density contrast across the San Diego Trough fault in the near‐surface sediments. The survey of Emery Knoll shed light on the question of the origin of this structure; modeling the knoll to determine its bulk density suggested a nearly uniform structure surrounded by sedimentary basins with a more massive central intrusive body. Derived densities of 2850 kg/m3 for the knoll and 3050 kg/m3 for the central intrusion assume that no deep unmodeled sources exist directly underneath the knoll. The gravity data favor a model of metamorphic basement rock uplifted and containing igneous intrusives.
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Onizawa, Shin’ya. "Apparent calibration shift of the Scintrex CG-5 gravimeter caused by reading-dependent scale factor and instrumental drift." Journal of Geodesy 93, no. 9 (March 11, 2019): 1335–45. http://dx.doi.org/10.1007/s00190-019-01247-9.
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Zumberge, Mark A., Jeff R. Ridgway, and John A. Hildebrand. "A towed marine gravity meter for near‐bottom surveys." GEOPHYSICS 62, no. 5 (September 1997): 1386–93. http://dx.doi.org/10.1190/1.1444243.
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Gravity is measured presently on the sea surface and on the sea floor. Surface gravity suffers from loss of resolution over the deep ocean because the perturbing source masses are far from the observer. Bottom measurements recover this resolution, but suffer from poor coverage because of the time needed for each measurement. We have constructed a gravimetry system that combines the rapid data collection capability of a moving platform with the high resolution gained by locating the observations near the bottom. This gravity sensor is tethered to a ship and towed just above the sea floor. The instrument consists of a LaCoste and Romberg shipboard gravity meter modified to fit inside a pressure case that is mounted on a platform designed for towing stability. We have tested it in a survey in the San Diego Trough, a 1000-m—deep sedimented valley in the Pacific Ocean in the California continental borderlands. Multiple gravity tracklines collected there at a depth of 935 m show a resolution of a few tenths of a mGal. The new instrument will be useful for surveys of features whose lateral extent is equal to or less than the ocean depth.
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Péquegnat, Catherine, Jonathan Schaeffer, Claudio Satriano, Helle Pedersen, Jérôme Touvier, Jean-Marie Saurel, Marie Calvet, et al. "RÉSIF-SI: A Distributed Information System for French Seismological Data." Seismological Research Letters 92, no. 3 (April 7, 2021): 1832–53. http://dx.doi.org/10.1785/0220200392.
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Abstract The Résif project, which started in 2008, aims at gathering under a common research infrastructure the French seismological, Global Navigation Satellite Systems and gravimeter permanent networks, as well as the mobile instrument pools. A central part of Résif is its seismological information system, Système d'Information de Résif (Résif-SI) (started in 2012), which is in charge of collecting, validating, archiving, and distributing seismological data and metadata from seven national centers. Résif-SI follows a distributed architecture, in which the six data collection and validation centers (A-nodes) send validated data and metadata to a national data center (Résif Data Center [Résif-DC]), which is the central point for data archiving and distribution. Résif-SI is based on international standard formats and protocols, and is fully integrated into European and international data exchange systems (European Integrated Data Archive, European Plate Observing System [EPOS], Incorporated Research Institutions for Seismology, International Federation of Digital Seismograph Networks). In this article, we present the organization of Résif-SI, the technical details of its implementation, and the catalog of services provided to the end users. The article is aimed both at seismologists, who want to discover and use Résif data, and at data center operators, who might be interested in the technical choices made in the implementation of Résif-SI. We believe that Résif-SI can be a model for other countries facing the problem of integrating different organizations into a centralized seismological information system.
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Mosher, Craig R. W., and Colin G. Farquharson. "Minimum-structure borehole gravity inversion for mineral exploration: A synthetic modeling study." GEOPHYSICS 78, no. 2 (March 1, 2013): G25—G39. http://dx.doi.org/10.1190/geo2012-0373.1.
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A borehole gravimeter for the diameters of holes typically used in mineral exploration has recently been developed. Investigating how the data from such instruments can contribute to the gravity interpretation procedures used in mineral exploration is therefore appropriate. Here, results are presented from a study in which synthetic data for 3D exploration-relevant earth models were inverted and the impact of borehole data assessed. The inversions were carried out using a minimum-structure procedure that is typical of those commonly used to invert surface gravity data. Examples involving data from a single borehole, from multiple boreholes, and combinations of borehole and surface data, are considered. Also, a range of options for the particulars of the inversion algorithm are investigated, including using a reference model and cell weights to incorporate along-borehole density information, and an [Formula: see text]-type measure of model structure. The selection of examples presented demonstrates what one can and cannot expect to determine about the density variation around and between boreholes when borehole gravity data are inverted using a minimum-structure approach. Specifically, the density variation along a borehole can be accurately determined, even without constraints in the inversion, but this capability decreases dramatically a few tens of meters from a borehole.
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Gettings, Paul, David S. Chapman, and Rick Allis. "Techniques, analysis, and noise in a Salt Lake Valley 4D gravity experiment." GEOPHYSICS 73, no. 6 (November 2008): WA71—WA82. http://dx.doi.org/10.1190/1.2996303.
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Repeated high-precision gravity measurements using an automated gravimeter and analysis of time series of [Formula: see text] samples allowed gravity measurements to be made with an accuracy of [Formula: see text] or better. Nonlinear instrument drift was removed using a new empirical staircase function built from multiple station loops. The new technique was developed between March 1999 and September 2000 in a pilot study conducted in the southern Salt Lake Valley along an east-west profile of eight stations from the Wasatch Mountains to the Jordan River. Gravity changes at eight profile stations were referenced to a set of five stations in the northern Salt Lake Valley, which showed residual signals of [Formula: see text] in amplitude, assuming a reference station near the Great Salt Lake to be stable. Referenced changes showed maximum amplitudes of [Formula: see text] through [Formula: see text] at profile stations, with minima in summer 1999, maxima in winter 1999–2000, and some decrease through summer 2000. Gravity signals were likely a composite of production-induced changes monitored by well-water levels, elevation changes, precipitation-induced vadose-zone changes, and local irrigation effects for which magnitudes were estimated quantitatively.
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Brozena, John M., and Mary F. Peters. "An airborne gravity study of eastern North Carolina." GEOPHYSICS 53, no. 2 (February 1988): 245–53. http://dx.doi.org/10.1190/1.1442459.
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The Naval Research Laboratory (NRL) has developed a prototype airborne gravity measurement system. The core of the system is a LaCoste and Romberg air‐sea gravity meter mounted on a three‐axis stable platform. Corrections to the gravimeter data for altitude and variations in altitude are determined from a combination of highly precise radar and pressure altimeters. The original prototype system was designed for use over oceanic areas. We recently incorporated the pressure measurement to extend use of the airborne system to terrestrial regions where occasional radar altitudes over points of known topographic height can be obtained. The radar heights are used to relate the pressure altitudes to absolute altitudes and to determine the slopes of the isobaric surfaces. Vertical accelerations due to horizontal velocity over a curved, rotating earth (the Eötvös correction) and precise two‐dimensional positions are determined from a Texas Instrument P-code global positioning system. The updated system was tested over eastern North Carolina and the Outer Banks, an area that is difficult to survey by conventional means. Over one‐third of the region consists of low lying swampy terrain and another one‐third is the shallow water of the Pamlico and Albemarle Sounds. Neither the land method nor the shipboard gravity surveying method is well suited for these types of areas. Flying at an altitude of 600 m at 375 km/hr, we were able to cover an area over [Formula: see text] with a nominal track spacing of 9 km by 9 km in less than 18 hours of flying time. A comparison by the Defense Mapping Agency showed a 2.8 mGal rms and a −0.2 mGal mean difference between ground truth data and the airborne data at grid points when both data sets were interpolated to a common 9 km grid.
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Claudino Mendes, Hérick, Joel Medeiros Bezerra, and Vinícius José Correia Arlindo. "Diagnóstico do Gerenciamento de Resíduos Sólidos por Meio da Análise SWOT ao Município de Tabuleiro do Norte – CE." Revista Brasileira de Geografia Física 15, no. 1 (March 23, 2022): 092. http://dx.doi.org/10.26848/rbgf.v15.1.p092-108.
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A produção de resíduos é uma característica da humanidade, que devido ao grande volume gerado, tem-se promovido um cenário de limitação da capacidade de assimilação do meio ambiente, desencadeando cenários de crise e problemas ambientais. Assim, os responsáveis pela gestão dos resíduos devem obedecer a orientações adequadas para erradicar esses problemas aos seres humanos e ao ambiente. Visto então, a necessidade de verificar as tomadas de decisões frente à gestão ordenada, este trabalho objetivou efetuar o diagnóstico do atual cenário do gerenciamento de resíduos sólidos urbanos (RSU) em Tabuleiro do Norte – CE. Para isso, adotou-se o modelo descritivo e exploratório juntamente com a análise da matriz FOFA como metodologia. Diante dos dados obtidos, verificaram-se resultados positivos para alguns critérios estabelecidos, como a aplicação da coleta seletiva e a inserção dos catadores, porém houve grandes oportunidades que podem e devem ser alcançadas, como a promoção da educação ambiental, buscando assim aprimorar questões relacionadas com o gerenciamento descentralizado e assim cumprir com políticas públicas estaduais e federais. Para tanto, o município deve, em caráter urgente, realizar a sua gravimetria para suprir necessidades básicas do gerenciamento dos RSU, além de encontrar outras formas de descarte e tratamento, como o aproveitamento energético.Palavras-chave: Tomada de decisão. Análise FOFA. Gerenciamento de Resíduos. Planejamento. Instrumento.Diagnosis of solid waste management through SWOT analysis to the municipality of Tabuleiro do Norte - CEA B S T R A C TThe production of waste is a characteristic of humanity, which, due to the large volume generated, has promoted a scenario of limited capacity to assimilate the environment, triggering scenarios of crisis and environmental problems. Thus, those responsible for waste management must comply with adequate guidelines to eradicate these problems for humans and the environment. Seen then, the need to verify decision-making against orderly management, this work aimed to diagnose the current scenario of urban solid waste (USW) management in Tabuleiro do Norte - CE. For this, the descriptive and exploratory model was adopted along with the SWOT matrix analysis as a methodology. Based on the data obtained, there were positive results for some established criteria, such as the application of selective collection and the inclusion of collectors, but there were great opportunities that can and should be achieved, such as the promotion of environmental education, thus seeking to improve related issues with decentralized management and thus comply with state and federal public policies. Therefore, the municipality must, as a matter of urgency, carry out its gravimetry to meet the basic needs of MSW management, in addition to finding other forms of disposal and treatment, such as energy use.Keywords: Decision-making. SWOT Analysis. Waste Management. Planning. Instrument..
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Schilling, Manuel, Étienne Wodey, Ludger Timmen, Dorothee Tell, Klaus H. Zipfel, Dennis Schlippert, Christian Schubert, Ernst M. Rasel, and Jürgen Müller. "Gravity field modelling for the Hannover 10 m atom interferometer." Journal of Geodesy 94, no. 12 (November 27, 2020). http://dx.doi.org/10.1007/s00190-020-01451-y.
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AbstractAbsolute gravimeters are used in geodesy, geophysics and physics for a wide spectrum of applications. Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes. Users of absolute gravimeters participate in comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. However, since no measurement standard of higher-order accuracy currently exists, users of absolute gravimeters participate in key comparisons led by the International Committee for Weights and Measures. These comparisons provide the reference values of highest accuracy compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large-scale atom interferometers paves the way for a new measurement standard in absolute gravimetry used as a reference with a potential stability up to $$1\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 1 nm / s 2 at 1 s integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10-m-long interaction zone. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument’s uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We therefore established a control network for relative gravimeters and repeatedly measured its connections during the construction of the atom interferometer. We additionally developed a 3D model of the host building to investigate the self-attraction effect and studied the impact of mass changes due to groundwater hydrology on the gravity field around the reference instrument. The gravitational effect from the building 3D model is in excellent agreement with the latest gravimetric measurement campaign which opens the possibility to transfer gravity values with an uncertainty below the $${10}\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 10 nm / s 2 level.
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Дробышев, М. Н., Д. В. Абрамов, С. Г. Бычков, В. Н. Конешов, М. И. Герман, О. А. Храпенко, С. В. Горожанцев, С. А. Красилов, А. С. Бебнев, and А. В. Овчаренко. "An experiment on the study of synchronous continental microseisms in northern Eurasia using a combination of gravimetric and seismic observations." Геология и геофизика Юга России, no. 2 (June 28, 2019). http://dx.doi.org/10.23671/vnc.2019.2.31979.
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Исследованы непериодические повышения интенсивности микросейсмического шума. На протяжении четырех месяцев осуществлялись синхронные геофизические наблюдения гравиметрами ScintrexCG5 Autograv в Обнинске, Мурманске, Екатеринбурге и Красноярске. При проведении измерений были зарегистрированы множественные случаи синхронного повышения интенсивности микросейсмических шумов, как в пунктах гравиметрических наблюдений, так ив ряде сейсмометрических пунктов северовосточной части Евразии. Продолжительность зарегистрированного аномального повышения микровибраций составляет от нескольких часов до нескольких суток. Высокочувствительные гравиметры регистрируют не только гравитационное поле и его вариации, связанные с приливными изменения силы тяжести и другими неприливными и метеорологическими явлениями, но и высокочастотные вариации, связанные в первую очередь с воздействием процессов инерциального характера. Гравиметры и сейсмографы обладают различными характеристиками, однако, высокочастотное воздействие, от общего источника регистрируется обоими приборами, с той лишь разницей, что в гравиметре оно считается помехой и характеризуется среднеквадратичным отклонением (СКО). СКО гравиметрических данных, и СКО, посчитанное по рядам измерений сейсмометров, обнаруживают высокое сходство. Сопоставление с микросейсмическими шумами позволяет говорить об инерциальной, а не о гравиметрической природе зарегистрированных гравиметрами аномалий. Результаты исследования корреляционных связей сигналов объясняются крупными локальными вариациями микросейсм и метеорологических характеристик, их влиянием на тонкую структуру геофизических сигналов, регистрируемых гравиметрами. Кратковременные полугодовые наблюдения обнаружили особенности геофизических процессов на обширной территории Евразии. Дальнейшие исследования позволят выявить тонкую структуру взаимных влияний геофизических процессов по данным наблюдений чувствительными гравиметрами и сейсмометрами. Учет этого явления необходим при планировании и выполнении высокоточных гравиметрических съемок и долговременных гравиметрических наблюдений. Nonperiodic intensity increase of microseismic noise was researched. During four months, synchronous geophysical observations were carried out using Scintrex CG5 Autograv gravimeters in Obninsk, Murmansk, Yekaterinburg and Krasnoyarsk. During the measurements, multiple cases of synchronous intensity increase of microseismic noise were recorded, both at the gravimetric observation points and at a number of seismometric points in northeastern Eurasia. The duration of the registered anomalous increase in microvibrations ranges from several hours to several days. Highly sensitive gravimeters register not only the gravitational field and its variations associated with tidal changes of gravity and other nontidal and meteorological phenomena, but also highfrequency variations associated primarily with the effects of inertial processes. Gravimeters and seismographs have different characteristics, however, both instruments record highfrequency effects from a common source, with the only difference that in the gravimeter it is considered interference and is characterized by standard deviation (RMS). RMS of gravimetric data, and RMS, calculated by series of seismometers measurements, show high similarity. Comparison with microseismic noise suggests an inertial rather than a gravimetric nature of anomalies recorded by gravimeters. The results of the signals correlation study are explained by large local variations of microseisms and meteorological characteristics, their influence on the fine structure of geophysical signals recorded by gravimeters. Shortterm semiannual observations revealed features of geophysical processes in the vast territory of Eurasia. Further studies will reveal the fine structure of the mutual influences of geophysical processes according to observation data by sensitive gravimeters and seismometers. Consideration of this phenomenon is necessary when planning, performing highprecision gravimetric surveys, and longterm gravimetric observations
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Riccardi, U., S. Carlino, T. Pivetta, J. Hinderer, S. Rosat, and G. Ricciardi. "Continuous Gravity Observations at Mt. Somma-Vesuvius with a gPhoneX Gravimeter: In-Depth Instrumental Response Characterization and Tidal Model." Pure and Applied Geophysics, June 24, 2023. http://dx.doi.org/10.1007/s00024-023-03313-y.
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AbstractWe report on the results of about 9 months of gravimetric recordings acquired at Mt. Somma-Vesuvius (SV) volcano (Southern Italy) with the new generation relative gravimeter gPhoneX#116 (gPh#116), which is a gravimeter specifically designed for continuous gravity recording. We also present the outcomes of an intercomparison experiment of the gPhone#116 conducted at the J9 gravity observatory in Strasbourg (France). In this intercomparison, we were able to check the scale factor of the meter with a high degree of precision by means of an intercomparison with 2 superconducting gravimeters (SGs) and a FG5-type absolute ballistic gravimeter. Multiple calibration approaches allowed us to validate the manufacturer's original calibration constants to a level of 1% accuracy and 0.1% precision. Moreover, we carried out a comparative study of the noise level of the gPh#116 with respect to the SGs and other spring meters routinely used in both prospecting and time-lapse gravimetry. It turns out that gPh#116 exhibits lower levels at hourly time-scales than other compared spring gravimeters (Graviton, gPhone#054, Scintrex-CG5). It was also possible to carry out a detailed study of the instrumental drift, a crucial topic for reliable monitoring of the long-term gravity variations in active volcanic areas. In fact, a challenge in time-lapse gravimetry is the proper separation of the instrumental variations from real gravity changes eventually attributable to recharge or drainage processes of magma or fluids in the feeding systems of active volcanoes. A negative finding coming out from the intercomparison is that, even when applying the tilt correction, the gravimetric residuals obtained with the gPh#116 are an order of magnitude larger and quite inconsistent with those obtained with co-located superconducting gravimeters. We guess this problem could be overcome by installing the gravimeter on an auto-levelling platform. From the analysis of the gravity records, a reliable tidal gravity model was derived, which we believe will help to improve the accuracy of volcano monitoring, as it will allow appropriate correction of tidal effects for both relative and absolute gravity measurements acquired in the area. Two further interesting elements arose from our study: (1) a peculiar cavity effect of the SV underground laboratory that seems to influence the tilt change; (2) the small residual gravity signals are time correlated with the rainfall peaks and are compatible with gravity decreases induced by increases in soil moisture above the gravimeter.
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Huang, Xing, Xinning Hu, Chunyan Cui, Hao Wang, Zili Zhang, Feifei Niu, Yuan Zhang, and Qiuliang Wang. "Numerical simulation of AC losses in superconducting gravimeter." Superconductor Science and Technology, August 8, 2022. http://dx.doi.org/10.1088/1361-6668/ac87da.
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Abstract The annual drift of μGal level is an important indicator of superconducting gravimeters, which helps geophysicists to clarify the weak geophysical signals. In this paper, a finite element simulation model of the superconducting gravimeter sensor is developed based on the H formulation for evaluating the contribution of the excitation AC losses and the AC losses under operating conditions to the superconducting gravimeter’s drift. The model combines the H formulation and the heat transfer module of COMSOL Multiphysics software to calculate the AC losses of the superconducting gravimeter’s test mass and obtain the distribution images of the test mass’s temperature due to the AC losses-induced heating. The overall temperature rise of the test mass is obtained by assuming that it heats up uniformly and thus combines the temperature dependence factor (10 μGal/mK) of the superconducting gravimeter to derive the instrument drift induced by AC losses. Then, the long-term drift due to excitation losses can reach 0.847 μGal/year, while the operating losses can be 0.45 μGal/year or even less, according to the simulation. In addition, this paper discusses the effects of the parameters (index number, critical electric field and critical current density) in the E-J power law introduced by the H formulation on the AC loss evaluation. It is concluded that the AC losses are sensitive to the critical current density, and increasing the test mass’s critical current density helps enhance the stability of the superconducting gravimeter.
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要佳敏, 庄伟, 冯金扬, 王启宇, 赵阳, 王少凯, 吴书清, and 李天初. "A vibration correction method based on element searching applied in atomic-interferometry absolute gravimeter." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20220037.
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Absolute gravimeter has played an important role in geophysics, metrology, geological exploration, etc. It is an instrument applying laser interferometry or atom interferometry for the measurement of gravitational acceleration g (approximately 9.8 m/s2). To achieve a high accuracy, vibration correction method is often employed to reduce the influence of the vibration of the reference object (a retro-reflector or a mirror) on the measurement results of absolute gravimeters. Specifically, in an atomic-interferometry absolute gravimeter, the phase noise caused by the vibration of the reference mirror, namely the vibration phase, can be calculated from the output signal of a sensor placed below or next to the mirror, either a seismometer or an accelerometer. Considering this vibration phase, the fringe signal of the atomic interferometer as a function of the phase shift set by the control system of the gravimeter can be corrected to approach an ideal sinusoidal curve, with the fitting residual to be decreased. Currently, the parameters in the algorithm of most vibration correction methods applied in atomic-interferometry absolute gravimeters are set to be constant. As a result, the performance of these methods may be limited when the practical transfer function between the real vibration of the reference mirror and the signal of the sensor has a variation due to the change of measurement environments. In this paper, based on a simplified model of the practical transfer function previously proposed in an algorithm used in laser-interferometry absolute gravimeter, a new vibration correction method for atomic-interferometry absolute gravimeter is presented. Firstly, a detailed description of its principle is introduced. With a searching algorithm, the time delay and the proportional element in the simplified model can be obtained from the fringe signal of the atomic interferometer and the output of the vibration sensor. In this way, the parameters used to calculate the vibration phase can be adjusted to approach their true values in different environments, causing the fitting residual of the corrected fringe to be decreased as much as possible. Then the measurement results of the homemade NIM-AGRb-1 atomic-interferometry absolute gravimeters applying this method is analyzed. It is indicated that, with the vibration correction algorithm, the standard deviation of the fitting residual of the measured fringe signal can be decreased by 58% at the best level in a quiet environment. In the future, the performance of this vibration correction algorithm will be further evaluated in other atomic-interferometry absolute gravimeters during their measurements in hostile environments.
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Wang Kai-Nan, Xu Han, Zhou Yin, Xu Yun-Peng, Song Wei, Tang Hong-Zhi, Wang Qiao-Wei, et al. "Research on rapid surveying of the absolute gravity field based on the vehicle-mounted atomic gravimeter." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20220267.
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The information of Earth's gravity field is an important basic information necessarily for geodesy, geophysics, geodynamics and other disciplines, and the mapping of gravity field is an effective mean to obtain the gravity field information. Compared with the surveying of gravity field based on satellite, ship, and airplane, vehicle-mounted gravity mapping has advantages of strong flexibility, high spatial resolution and high accuracy. A short baseline or a small-scale gravity field mapping can be realized based on the combination of relative gravimeters and the high-precision absolute gravity reference point. However, this method is not suitable for the situation of a long baseline or a large-scale gravity field surveying due to the drift of relative gravimeter. In this paper, a vehicle-mounted system for rapid surveying of the absolute gravity field is built up based on a miniaturized atomic gravimeter. The inner precision of the instrument is evaluated to 0.123 mGal, and the outer precision is 0.112 mGal in a field test which contains 12 points for 3 km distance. Furthermore, with this system, the absolute gravity data have been obatined within 2 minutes for adjusting and 5 minutes for measuring in downtown for each measured point. A rapid surveying of absolute gravity field for 19 points has been carried out and the route covers 24 km. The inner precision of the instrument is evaluated to 0.162 mGal, and the outer precision is 0.169 mGal. Finally, the free-air gravity anomalies obtained by the measured data of atomic gravimeter and the fitting results of satellite gravity model have been analyzed, and it is found that the trends of changing are basically consistent. This paper provides a new proposal for the rapid surveying of the absolute gravity field.
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Karkowska, Kamila. "Analysis of earthquakes recordings of tidal gravimeters in the period range of 10-1000 s." Acta Geodynamica et Geomaterialia, December 21, 2021, 79–92. http://dx.doi.org/10.13168/agg.2021.0043.
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The physical properties of tidal gravimetric instruments allow recording, not only tidal effects, but also waves generated by earthquakes. Three gravimetric stations with determined transfer functions and co-located seismic stations from the observatories in Western and Central Europe were selected for analysis. The observatories are equipped with almost all types of sensors available on the market, which allow for thorough analysis of earthquake recordings in the period range of 10–1000 s. In total, over 10,000 traces of worldwide earthquakes were investigated. The saturation levels of gravimeters as well as a correlation between the gravimetric and seismometric signals of an earthquake were carefully analysed. A simple processing scheme of gravimetric signal of earthquakes was adopted thanks to the probabilistic power spectral density analysis of continuous recordings. The detail analysis of transfer function of gravimeters allowed to define a period range when a sensitivity coefficient (calibration factor) and a time lag value only can be used to properly describe the properties of instruments. What’s more, it has been shown based on the calculated group-velocity dispersion curves of fundamental mode of Rayleigh waves, that the Earth’s mantle structure can be determined for greater depths from the recording of tidal gravimeters than from typical broad-band seismometers.
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P. Baldi, G. Casula, S. Focardi, and F. Palmonari. "Tidal analysis of data recorded by a superconducting gravimeter." Annals of Geophysics 38, no. 2 (May 18, 1995). http://dx.doi.org/10.4401/ag-4116.
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A superconducting gravimeter was used to monitor the tidal signal for a period of five months. The instrument was placed in a site (Brasimone station, Italy) chat-acterized by a low noise level, and was calibrated with a precision of 0.2%. Then tidal analysis on hourly data was performed and the results presented in this paper; amplitudes, gravimetric factors, phase differences for the main tidal waves, M2, S2, N2, 01, Pl, K1, QI, were calculated together with barometric pressure admittance and long term instrumental drift.
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Mou, Zonglei, Xiao Han, Ruo Hu, Zhenfei Li, and Chunhui Liu. "The influence of the selection of zero-crossing starting point on measurement accuracy of the absolute gravimeter." AIP Advances 13, no. 6 (June 1, 2023). http://dx.doi.org/10.1063/5.0151822.
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The absolute gravimeter is an important precision instrument for obtaining gravity acceleration in fields such as geophysics, resource survey, and national defense construction. It is greatly affected by its self-vibration during operation. If the self-vibration frequency exceeds the range of the sensor, it will not be effectively processed by the method of vibration compensation. To solve this problem, the effect of instrument self-vibration on the accuracy of gravity is analyzed through simulation and actual measurement data. Based on the calculation of the simulation data, the functional relationship between the self-vibration frequency of the instrument and the zero-crossing starting point is obtained. The Starting Point Mathematical Model is established to accurately calculate the zero-crossing starting point. Then, the zero-crossing starting point calculated by the model is taken as the time reference of the zero crossing for the least square fitting. The split and platform absolute gravity measurement systems are built, respectively, to test the measured data. The test results reveal that, compared with the traditional method using the initial falling time as the zero-crossing starting point, the proposed method can reduce the gravity deviation by 50 μGal and improve the accuracy by an average of 35.35% under split-type working conditions. Under platform-type working conditions, it can decrease the gravity deviation by 3 mGal and improve the accuracy by an average of 53.78%. The method proposed can reduce the fixed phase vibration interference caused by the instrument self-vibration and provide a reference for improving the measurement accuracy of the instrument under different working conditions.
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Scherneck, Hans-Georg, Marcin Rajner, and Andreas Engfeldt. "Superconducting gravimeter and seismometer shedding light on FG5’s offsets, trends and noise: what observations at Onsala Space Observatory can tell us." Journal of Geodesy 94, no. 9 (August 8, 2020). http://dx.doi.org/10.1007/s00190-020-01409-0.
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AbstractTen-year worth of absolute gravity (AG) campaigns at Onsala Space Observatory (OSO), Sweden, are simultaneously reduced using synchronous data from a superconducting gravimeter (SG). In this multi-campaign adjustment, the a priori models commonly applied for each setup in AG-alone experiments are sidestepped in favour of SG records and a model to estimate its drift. We obtain a residual (hourly samples) at the 5 nm/s$$^2$$ 2 RMS level, reducing the SG data with a range of ancillary data for the site’s exposure to ocean and atmospheric loading, and hydrology effects. The target quantity in AG projects in the Baltic Shield area is the secular change of gravity dominated by glacial isostatic adjustment with land uplift as its major part. Investigating into the details of the associated processes using AG requires a long-term stable reference, which is the aim of international comparison campaigns of FG5 instruments. Two of these have been campaigning at OSO since 2009 when the SG had been installed. In the simultaneous inversion of all sixteen campaigns, we identify weaknesses of AG observations, like varying systematic offsets over time, excess microseismic sensitivity, trends in the AG data and side effects on the SG’s scale factor when campaigns are evaluated one by one. The simultaneous adjustment afforded us an SG scale factor very near the result from a campaign with a prototype quantum gravimeter. Whence, we propose that single-campaign results may be biased and conjectures into their variation, let alone its causes misleading. The OSO site appears to present manageable problems as far as environmental influences are concerned. Our findings advocate the use of AG instruments and procedures that are more long-term stable (reference realization), more short-term stable too (setup drifts), less service craving and more resilient to microseismic noise.
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Pfaffenzeller, Nikolas, and Roland Pail. "Small Satellite Formations and Constellations for Observing Sub-Daily Mass Changes in the Earth System." Geophysical Journal International, March 24, 2023. http://dx.doi.org/10.1093/gji/ggad132.
Full textAbstract:
Summary Satellite gravity missions so far are medium size satellites consisting of one or a pair of satellites flying in near-polar or sun-synchronous orbital planes. Due to the limited observation geometry and the related space-time sampling, high-frequency non-tidal mass variation signals from atmosphere and ocean cannot be observed and cause temporal aliasing. For current single-pair satellite gravimetry missions as GRACE and GRACE Follow-On (GRACE-FO) temporal aliasing is the limiting factor and represents the major error source in the gravity field time series. Adding a second inclined satellite pair to a GRACE-like polar pair (Bender constellation) currently is the most promising solution to increase the spatio-temporal resolution and to significantly reduce the temporal aliasing error. This shall be implemented with the MAGIC mission in future. With the ongoing developments in miniaturization of satellites and gravity-relevant instruments (accelerometers and inter-satellite ranging), in future constellations of multiple small satellite pairs may solve this problem even beyond the capabilities of a Bender constellation. Therefore, in this study the capabilities of such constellations flying in specific formations are investigated in order to enable a retrieval of the temporal gravity field on short time scales. We assess the performance of up to 18 satellite pairs. The satellite configurations cover satellite pairs in polar and inclined orbits flying in pair-wise or pearl-string formation with varying mean anomalies and right ascensions of the ascending node (RAAN). As future potential miniaturized instruments optomechanical accelerometers with similar performance as those flying on GRACE-FO are a candidate, while for the inter-satellite ranging instrument still some technological development is required. Therefore, in this study a microwave ranging system equivalent to the GRACE and GRACE-FO instruments performance is taken as baseline assuming that such instruments can be miniaturized in future as well. In numerical closed-loop simulations, up to nine different satellite configurations with up to 18 satellite pairs are evaluated based on the retrieval of the non-tidal temporal gravity field on a monthly basis. From the simulation results it is concluded that the best performing satellite constellation of 18 polar satellite pairs already is outperformed by a typical Bender-like constellation of 1 polar and 1 inclined pair. In general, we identify that increasing the number of satellite pairs leads to an improved gravity field retrieval, either at low spherical harmonic degree and order (d/o) by the shift in RAAN or at high d/o by the shift in mean anomaly. By a two-step simulation approach, co-estimating also (sub-) daily gravity fields for selected configurations with a large number of satellite pairs distributed equally over the globe, it is possible to retrieve stand-alone gravity fields at 24, 12 and 6 hour temporal resolution. Ultimately it is concluded that a network of miniaturized satellites with instrument performances similar to GRACE-FO and flying in a well-defined constellation has the potential to observe (sub-) daily mass variations and therefore could drastically reduce the problem of temporal aliasing due to high frequency mass variations in the Earth system.
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Bramanto, B., K. Breili, C. Gerlach, V. Ophaug, and J. G. O. Gjevestad. "Reducing hydrological disturbances in absolute gravity observations by combining global hydrological models with a regional runoff model." Geophysical Journal International, February 10, 2022. http://dx.doi.org/10.1093/gji/ggac054.
Full textAbstract:
Summary Since the beginning of the 1990s, absolute gravity has been observed at several locations in Norway with FG5-type instruments to investigate the temporal gravity changes due to Glacial Isostatic Adjustment (GIA). Previous work suggests that some of the estimated secular gravity trends may be affected by remaining unmodeled geophysical effects, such as the effect of local hydrology. In this work, we compute hydrological gravity effects from global hydrological models for the far zone and a combination of regional run-off models and modeling of residual hydrological effects for the near zone. The method developed in this paper is first tested at the geodetic observatory in Wettzell, Germany, where both high-resolution superconducting gravimeter data as well as a regional hydrological model are available. Next, the method is transferred to two Norwegian gravity sites (NMBU and TRYC), with long time series of frequent absolute gravity observations using FG5-226. At these sites, we investigate the impact of the hydrological gravity correction on data variability as well as estimated secular gravity trends. We find that the data variability is reduced by up to 40 per cent when applying the modeled hydrological gravity effect at TRYC. The reduction is less at NMBU where the amplitude of the hydrological signal and in consequence also the signal-to-noise ratio are smaller. We also note that it is challenging to determine the near zone residual hydrological effects without carefully taking into account the hydrogeological setting of the area for modeling such effects. When utilizing the long corrected absolute gravity series to determine the gravity trends, we find that the estimated trends are not significantly different from the uncorrected observations. However, the uncertainty of the estimated trends is reduced significantly for a limited corrected gravity series. We further suggest repeatability analysis of the absolute gravimeter. From the long time series at NMBU we find a significant step coinciding with hardware replacement. We find that the fit between observed and modeled secular trends improves when introducing the step. Further analysis of gravity rates at other stations is needed to verify the existence of a real instrumental offset.
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Yan, Yihao, Vitali Müller, Gerhard Heinzel, and Min Zhong. "Revisiting the light time correction in gravimetric missions like GRACE and GRACE follow-on." Journal of Geodesy 95, no. 5 (April 7, 2021). http://dx.doi.org/10.1007/s00190-021-01498-5.
Full textAbstract:
AbstractThe gravity field maps of the satellite gravimetry missions Gravity Recovery and Climate Experiment (GRACE ) and GRACE Follow-On are derived by means of precise orbit determination. The key observation is the biased inter-satellite range, which is measured primarily by a K-Band Ranging system (KBR) in GRACE and GRACE Follow-On. The GRACE Follow-On satellites are additionally equipped with a Laser Ranging Interferometer (LRI), which provides measurements with lower noise compared to the KBR. The biased range of KBR and LRI needs to be converted for gravity field recovery into an instantaneous range, i.e. the biased Euclidean distance between the satellites’ center-of-mass at the same time. One contributor to the difference between measured and instantaneous range arises due to the nonzero travel time of electro-magnetic waves between the spacecraft. We revisit the calculation of the light time correction (LTC) from first principles considering general relativistic effects and state-of-the-art models of Earth’s potential field. The novel analytical expressions for the LTC of KBR and LRI can circumvent numerical limitations of the classical approach. The dependency of the LTC on geopotential models and on the parameterization is studied, and afterwards the results are compared against the LTC provided in the official datasets of GRACE and GRACE Follow-On. It is shown that the new approach has a significantly lower noise, well below the instrument noise of current instruments, especially relevant for the LRI, and even if used with kinematic orbit products. This allows calculating the LTC accurate enough even for the next generation of gravimetric missions.
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Kvas, A., E. Boergens, H. Dobslaw, A. Eicker, T. Mayer-Guerr, and A. Güntner. "Evaluating long-term water storage trends in small catchments and aquifers from a joint inversion of 20 years of GRACE/GRACE-FO mission data." Geophysical Journal International, December 5, 2023. http://dx.doi.org/10.1093/gji/ggad468.
Full textAbstract:
Summary More than twenty years of measurement data of the gravity missions GRACE (Gravity Recovery And Climate Experiment) and GRACE-FO (GRACE-Follow-On) allow detailed investigations of long-term trends in continental terrestrial water storage (TWS). However, the spatial resolution of conventional GRACE/GRACE-FO data products is limited to a few hundred kilometers which restrains from investigating hydrological trends at smaller spatial scales. In this study GRACE and GRACE-FO data have been used to calculate TWS trends with maximized spatial resolution. Conventionally, GRACE/GRACE-FO is presented as a series of either unconstrained gravity fields post-processed with spatial low pass filters or constrained inversions commonly known as Mascon products. This paper demonstrates that both approaches to suppress spatially correlated noise are mathematically equivalent. Moreover, we demonstrate that readily inverting all available sensor data from GRACE/GRACE-FO for a single TWS trend map, together with annual variations and a mean gravity field, provides additional spatial detail not accessible from the standard products. The variable trade-off between spatial and temporal resolution as a unique feature of satellite gravimetry allows for gravity products that are tailored towards specific geophysical applications. We show additional signal content in terms of long-term water storage trends for four dedicated examples (Lake Victoria, North-West India, Bugachany Reservoir, and High Plains Aquifer) for which external information from other remote sensing instruments corroborates the enhanced spatial resolution of the new mean-field trend (MFT) product.
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Papp, Gábor, Dániel István Csáki, and Judit Benedek. "Newtonian (moving mass) calibration of tilt and gravity meters and the investigation of some factors influencing its accuracy." Journal of Geodesy 96, no. 12 (December 2022). http://dx.doi.org/10.1007/s00190-022-01676-z.
Full textAbstract:
AbstractThe idea of moving mass calibration (MMC) of relative gravity meters dates back to the seventies of the last century. Probably the MMC apparatus built in the underground Mátyáshegy Gravity and Geodynamics Laboratory Budapest has been used most extensively and several spring type instruments (LaCoste and Romberg and Scintrex) have been investigated and calibrated by it. Its test mass is a cylindrical ring having a weight of 3 tons. Its main advantage is simplicity in terms of metrology. The same principle and technology can be used to test compact tilt sensors having nanoradian resolution capability. Up to now rigorous testing methods below microradian range were not available in practice. The analysis of the so-called off-axis variation of the gravitational vector generated by the vertical movement of the cylindrical ring mass of the Mátyáshegy MMC device, however, showed that a sufficiently accurate reference signal having (15 ± 0.02) nrad peak-to-peak amplitude can be provided for calibration. It is just in the range of tilt induced by earth tide effect, which is a “standard” signal component in the time series recorded in observatory environment. In the first part of the paper, a discussion of the proposed methodology of tilt meter calibration is given. Then the analysis of the effect of volumetric discretization of the cylindrical ring on the accuracy of calibration is provided. Finally, possible material inhomogeneities of the ring mass and their gravitational effects are investigated by forward simulations and inversion. For this purpose the results of 300 gravimeter calibration experiments, analysed and published earlier, were utilized.