Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube-and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39 nm/s 2 and long-term stability of 0.5 nm/s 2 , short-term noise of 96 nm/s 2 / √ Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions. arXiv:1512.05660v1 [physics.atom-ph]
Superconducting gravimeters (SG) measure temporal changes of the Earth's gravity field with high accuracy and long term stability. Variations in local water storage components (snow, soil moisture, groundwater, surface water and water stored by vegetation) can have a significant influence on SG measurements and-from a geodetic perspective-add noise to the SG records. At the same time, this hydrological gravity signal can provide substantial information about the quantification of water balances. A 4D forward model with a spatially nested discretization domain was developed to investigate the local hydrological gravity effect on the SG records of the Geodetic Observatory Wettzell, Germany. The possible maximum gravity effect was investigated using hypothetical water storage changes based on physical boundary conditions. Generally, on flat terrain, a water mass change of one meter in the model domain causes a gravity change of 42 µGal. Simulation results show that topography increases this value to 52 µGal. Errors in the Digital Elevation Model can influence the results significantly. The radius of influence of local water storage variations is limited to 1000 m. Detailed hydrological measurements should be carried out in a radius of 50 to 100 m around the SG station. Groundwater, soil moisture and snow storage changes dominate the hydrological gravity effect at the SG Wettzell. Using observed time series for these variables in the 4D model and comparing the results to the measured gravity residuals show similarities in both seasonal and shorter-term dynamics. However, differences exist, e.g. the range comparison of the mean modeled (10 µGal) gravity signal and the measured (19 µGal) gravity signal, making additional hydrological measurements necessary in order to describe the full spatio-temporal variability of local water masses.
[1] Local water storage changes (WSC) are a key component of many hydrological issues, but their quantification is associated with a high level of uncertainty. High precision in situ gravity measurements are influenced by these WSC. This study evaluates the influence of local WSC (estimated using hydrological techniques) on gravity observations at the Geodetic Observatory Wettzell, Germany. WSC are comprehensively measured in all relevant storage components, namely groundwater, saprolite, soil, topsoil, and snow storage, and their gravity response is calculated. Total local WSC are derived, and uncertainties are assessed. With the exception of snow, all storage components have gravity responses of the same order of magnitude and are therefore relevant for gravity observations. The comparison of the total gravity response of local WSC to the gravity residuals obtained from a superconducting gravimeter shows similarities in both short-term and seasonal dynamics. A large proportion of the gravity residuals can be explained by local WSC. The results demonstrate the limitations of measuring total local WSC using hydrological methods and the potential use of in situ temporal gravity measurements for this purpose. Nevertheless, due to their integrative nature, gravity data must be interpreted with great care in hydrological studies.Citation: Creutzfeldt, B., A. Güntner, H. Thoss, B. Merz, and H. Wziontek (2010), Measuring the effect of local water storage changes on in situ gravity observations: Case study of the Geodetic Observatory Wettzell, Germany, Water Resour. Res., 46, W08531,
a b s t r a c tThe Newtonian attraction of the atmosphere is a major source of noise in precise gravimetric measurements. A major part of the effect is eliminated using local air pressure records and constant admittance factors. However, vertical mass shifts under constant surface pressure or distant pressure anomalies are not covered by this technique although they affect the gravimeter. In order to improve the atmospheric correction and to evaluate the horizontal components of attraction as well, the Newtonian attraction is computed based on the spatial density distribution derived from three-dimensional weather models.Operational models from the German Weather Service (DWD) of various scales were used, supplemented by a global data set from the European Centre of Medium Weather Forecast (ECMWF) for comparison. The low temporal resolution and the improper point-mass assumption in the near field are tackled by a cylindrical local model by computing the attraction analytically based on local air pressure records with high temporal resolution.It is shown that a height of at least 50 km and global coverage is required to meet a threshold of 1 nm/s 2 . Neglecting the upper atmosphere leads to an overestimation of the seasonal gravity signal. At distances greater than 10 • the time consuming three-dimensional computation can be replaced by a two-dimensional surface pressure approach without significant error.The results show differences up to 20 nm/s 2 as compared to the linear regression method. The threedimensional atmospheric correction significantly reduces noise in the time series, giving more insight into other signals such as hydrological effects or deformation processes.
S U M M A R YTemporal gravimeter observations, used in geodesy and geophysics to study the Earth's gravity field variations, are influenced by local water storage changes (WSC). At the Geodetic Observatory Wettzell (Germany), WSC in the snow pack, top soil, unsaturated saprolite and fractured aquifer are all important terms of the local water budget. In this study, lysimeter measurements are used for the first time to estimate the hydrological influence on temporal gravimeter observations. Lysimeter data are used to estimate WSC at the field scale in combination with complementary observations and a hydrological 1-D model. From these estimated WSC, we calculate the hydrological gravity response. The results are compared to other methods used in the past to correct temporal gravity observations for the local hydrological influence. Lysimeter measurements significantly improve the independent estimation of WSC and thus provide a better way of reducing the local hydrological effect from gravimeter measurements. We find that the gravity residuals are caused to a larger extent by local WSC than previously stated. At sites where temporal gravity observations are used to study geophysical processes beyond local hydrology, the installation of a lysimeter is recommended.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.