Earth, Planets and Space

Journal: Earth, Planets and Space

Abbreviation

Earth Planets Space

Publisher

SpringerOpen

ISSN

1343-8832
1880-5981

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Publications 1 - 10 of 46

Introducing inter-site phase tensors to suppress galvanic distortion in the telluric method
Bakker, Jenneke; Kuvshinov, Alexey; Samrock, Friedemann; et al. (2015)
Earth, Planets and Space
A common problem when interpreting magnetotelluric (MT) data is that they often are distorted by shallow unresolvable local structures, an effect known as galvanic distortion. We present two transfer functions that are (almost) resistant to galvanic distortion. First, we introduce the electric phase tensor, which is derived from the electric tensor, where the electric tensor relates the horizontal electric fields at a field and base site. The electric phase tensor is only affected by galvanic distortion, if present, at the base site. Second, we introduce the quasi-electric phase tensor, which is derived from the quasi-electric tensor, where the quasi-electric tensor relates the electric field at a field site with the magnetic field at a base site. The quasi-electric tensor is not affected by galvanic distortion. Using a synthetic data-set, we show that the sensitivity of the MT phase tensor, the quasi-electric phase tensor, and the electric phase tensor is comparable for our model under consideration. Furthermore, we demonstrate that stable (quasi-) electric phase tensors can be recovered from a real data-set with the use of existing processing software. In addition, we provide a formalism to propagate the uncertainties from the estimated (quasi-) electric and impedance tensors to their respective phase tensors. The uncertainties of the (quasi-) electric phase tensors are of the same order of magnitude as the uncertainties of the MT phase tensor. From our study, we conclude that the (quasi-) electric phase tensors are an attractive complement to the standard MT responses.
GENESIS: co-location of geodetic techniques in space
Delva, Pacôme; Altamimi, Zuheir; Blazquez, Alejandro; et al. (2023)
Earth, Planets and Space
Improving and homogenizing time and space reference systems on Earth and, more specifically, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1 mm and a long-term stability of 0.1 mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, such as those located at tide gauges, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation, contributing to a better understanding of natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities, including the International Association of Geodesy (IAG), which has enunciated geodesy requirements for Earth sciences. Moreover, the United Nations Resolution 69/266 states that the full societal benefits in developing satellite missions for positioning and Remote Sensing of the Earth are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology. This paper has been written and supported by a large community of scientists from many countries and working in several different fields of science, ranging from geophysics and geodesy to time and frequency metrology, navigation and positioning. As it is explained throughout this paper, there is a very high scientific consensus that the GENESIS mission would deliver exemplary science and societal benefits across a multidisciplinary range of Navigation and Earth sciences applications, constituting a global infrastructure that is internationally agreed to be strongly desirable.
On the modelling of M2 tidal magnetic signatures: effects of physical approximations and numerical resolution
Velímský, Jakub; Grayver, Alexander; Kuvshinov, Alexey; et al. (2018)
Earth, Planets and Space
On the seismic response of instable rock slopes based on ambient vibration recordings
Kleinbrod, Ulrike; Burjánek, Jan; Fäh, Donat (2017)
Earth, Planets and Space
Rock slope failures can lead to huge human and economic loss depending on their size and exact location. Reasonable hazard mitigation requires thorough understanding of the underlying slope driving mechanisms and its rock mass properties. Measurements of seismic ambient vibrations could improve the characterization and detection of rock instabilities since there is a link between seismic response and internal structure of the unstable rock mass. An unstable slope near the village Gondo has been investigated. The unstable part shows strongly amplified ground motion with respect to the stable part of the rock slope. The amplification values reach maximum factors of 70. The seismic response on the instable part is highly directional and polarized. Re-measurements have been taken 1 year later showing exactly the same results as the original measurements. Neither the amplified frequencies nor the amplification values have changed. Therefore, ambient vibration measurements are repeatable and stay the same, if the rock mass has not undergone any significant change in structure or volume, respectively. Additionally, four new points have been measured during the re-measuring campaign in order to better map the border of the instability.
Towards probing Earth’s upper mantle with daily magnetic field variations: exploring a physics-based parametrization of the source
Zenhäusern, Géraldine; Kuvshinov, Alexey; Guzavina, Martina; et al. (2021)
Earth, Planets and Space
The electromagnetic (EM) field variations capable of probing the electrical conductivity of the upper mantle and mantle transition zone have a period range between a few hours and 1 day. At these periods, the dominant source of the EM signals is the ionospheric current system, which has a complex spatial and temporal structure. A concept of global-to-local (G2L) transfer functions can handle spatially complex source by relating global source expansion coefficients with locally measured magnetic (or/and electric) fields. When estimating the G2L transfer functions, the source is commonly expanded into spherical harmonics (SH). In this paper, we explore an alternative parametrization of the source based on a principal component analysis (PCA) of the Fourier transformed output from the physics-based Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). Specifically, we investigate whether magnetic fields computed in the realistic three-dimensional conductivity model of Earth excited by the PCA-based source agree better with observatory data than those computed in the same model but induced by the SH-based source. Using PCA to capture the source current compared to SH parametrization, we find that agreement with the observatory data is better during magnetically disturbed times and at shorter periods. Vice versa, it is poorer during magnetically quiet times and at longer periods.
Enormously large tippers observed in southwest China: can realistic 3-D EM modeling reproduce them?
Xu, Shan; Chen, Chaojian; Kruglyakov, Mikhail; et al. (2023)
Earth, Planets and Space
Vertical magnetic transfer functions (tippers) estimated at a global/continental net of geomagnetic observatories/sites can be used to image the electrical conductivity structure of the Earth’s crust and upper mantle (down to around 200 km). We estimated tippers at 54 geomagnetic observatories across China, aiming eventually to invert them in terms of subsurface three-dimensional (3-D) conductivity distribution. Strikingly, we obtained enormously large tippers at three inland observatories in southwest China. Large tippers are often observed at coastal/island observatories due to high conductivity contrasts between resistive bedrock and conductive seawater. However, tippers at those inland observatories appeared to be a few times larger than coastal/island tippers. As far as we know, such large tippers (reaching value 3) were never reported in any region worldwide. We perform electromagnetic simulations in 3-D conductivity models mimicking the geological setting and demonstrate that enormously large tippers are feasible and can be attributed to a current channeling effect.
Evaluation of candidate geomagnetic field models for IGRF-12
Thébault, Erwan; Finlay, Christopher C.; Alken, Patrick; et al. (2015)
Earth, Planets and Space
Background The 12th revision of the International Geomagnetic Reference Field (IGRF) was issued in December 2014 by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD (http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html). This revision comprises new spherical harmonic main field models for epochs 2010.0 (DGRF-2010) and 2015.0 (IGRF-2015) and predictive linear secular variation for the interval 2015.0-2020.0 (SV-2010-2015). Findings The models were derived from weighted averages of candidate models submitted by ten international teams. Teams were led by the British Geological Survey (UK), DTU Space (Denmark), ISTerre (France), IZMIRAN (Russia), NOAA/NGDC (USA), GFZ Potsdam (Germany), NASA/GSFC (USA), IPGP (France), LPG Nantes (France), and ETH Zurich (Switzerland). Each candidate model was carefully evaluated and compared to all other models and a mean model using well-defined statistical criteria in the spectral domain and maps in the physical space. These analyses were made to pinpoint both troublesome coefficients and the geographical regions where the candidate models most significantly differ. Some models showed clear deviation from other candidate models. However, a majority of the task force members appointed by IAGA thought that the differences were not sufficient to exclude models that were well documented and based on different techniques. Conclusions The task force thus voted for and applied an iterative robust estimation scheme in space. In this paper, we report on the evaluations of the candidate models and provide details of the algorithm that was used to derive the IGRF-12 product.
Probing 3-D electrical conductivity of the mantle using 6 years of Swarm, CryoSat-2 and observatory magnetic data and exploiting matrix Q-responses approach
Kuvshinov, Alexey; Grayver, Alexander; Tøffner-Clausen, Lars; et al. (2021)
Earth, Planets and Space
This study presents results of mapping three-dimensional (3-D) variations of the electrical conductivity in depths ranging from 400 to 1200 km using 6 years of magnetic data from the Swarm and CryoSat-2 satellites as well as from ground observatories. The approach involves the 3-D inversion of matrix Q-responses (transfer functions) that relate spherical harmonic coefficients of external (inducing) and internal (induced) origin of the magnetic potential. Transfer functions were estimated from geomagnetic field variations at periods ranging from 2 to 40 days. We study the effect of different combinations of input data sets on the transfer functions. We also present a new global 1-D conductivity profile based on a joint analysis of satellite tidal signals and global magnetospheric Q-responses.
Influence of composition-dependent thermal conductivity on the long-term evolution of primordial reservoirs in Earth's lower mantle
Li, Yang; Deschamps, Frédéric; Shi, Zhidong; et al. (2022)
Earth, Planets and Space
The influence of composition-dependent thermal conductivity and heterogeneous internal heating of primordial dense material on the long-term evolution of primordial reservoirs in the lower mantle of the Earth is investigated utilizing thermochemical mantle convection simulations in a 2-D spherical annulus geometry. Our results show that a reduction in the thermal conductivity of primordial dense material due to iron enrichment does not substantially alter mantle dynamics nor the long-term stability of the reservoirs of this dense material. If the primordial dense material is also enriched in heat-producing elements, the average altitude of these reservoirs slightly increases as the thermal conductivity is reduced, therefore, covering smaller core-mantle boundary areas. Our study indicates that the composition-dependent thermal conductivity of primordial material plays a second order role in the long-term evolution of Earth's mantle.
Optimal antenna locations of the VLBI Global Observing System for the estimation of Earth orientation parameters
Schartner, Matthias; Böhm, Johannes; Nothnagel, Axel (2020)
Earth, Planets and Space
To support monitoring subtle effects in the Earth system such as a mean sea level rise of 3 mm/year, a next-generation VLBI system, the VLBI Global Observing System (VGOS), has been developed and a new VGOS station network is being built. However, the geometry of the current VGOS network and its planned extension suffer from a lack of stations in the southern hemisphere. In this investigation, we identify optimal locations for additional VGOS radio telescopes with a new method based on bulk observing schedule generation and subsequent large-scale Monte-Carlo simulations. The location of the additional station is varied over 477 possible locations, homogeneously distributed over land areas on the globe. For each antenna location, several schedules have been generated and simulated to minimize the effects of scheduling and the randomness of simulations. Thereby, it is possible to judge, in which regions an additional VGOS station would have the biggest impact on the precision of the estimated geodetic parameters, in our case assessed by the repeatabilities of the estimated Earth orientation parameters (EOPs). To generate highly optimized schedules and to remove effects due to non-optimized scheduling, a total of 93 thousand schedules were iteratively generated, investigating over 300 billion scans and 2.4 trillion observations. Each schedule was further simulated 1000 times, leading to over 5 trillion simulated and analyzed observations. Although the optimum location of a future VLBI station depends on the EOP of interest and the geometry of the existing network, it is shown that the more the VGOS network grows, the more the lack of southern stations becomes prominent. The best location for an additional VGOS station for most EOP components and especially in the case of future VGOS networks would be the southern part of South America. It is further shown that the location of the additional antenna highly determines the expectable precision of the EOP estimates. For a 6-station network, the location of an additional seventh antenna can improve the precision of the EOP by a factor of 2.4 to 3.8. For an 18-station network, the location of an additional 19th station still improves the repeatability by a factor of 1.6. It is also found that adding a station at some locations will not improve the precision at all.

Publications 1 - 10 of 46

Journal: Earth, Planets and Space

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