Zabranova E.,Charles University |
Matyska C.,Charles University |
Hanyk L.,Charles University |
Palinkas V.,Research Institute of Geodesy
Geophysical Research Letters | Year: 2012
Surface acceleration caused by the radial modes depends only on the M rr component of the centroid moment tensor and on its depth assuming the isotropic component to be negligible. The 0S 0-mode amplitude enables one to obtain a relatively narrow interval of M rr values, whereas 1S0-mode amplitude is more sensitive to centroid depth. We have used these facts to analyze the 2010 Maule (Chile) M w = 8.8 and 2011 Tohoku (Japan) M w = 9.1 earthquakes using PREM. Superconducting gravimeter data available within the framework of the Global Geodynamic Project reveal that the Mrr components of these earthquakes should be in the interval 0.95- 1.15 × 10 22 Nm (Maule) and 1.50-1.75 × 10 22 Nm (Tohoku), respectively. Re-evaluation of the modal quality factors Q is needed to obtain constraints on Mrr self-consistently. The joint analysis of gravity data from both events yields Q = 5500 ± 140 for the 0S0 mode and Q = 2000 ± 80 for the 1S0 mode. We were not able to determine the quality factor of the 2S 0 mode with an accuracy sufficient to allow meaningful constraints (Q = 1120 ± 270). Citation: Zábranová, E., C. Matyska, L. Hanyk, and V. Pálinkáš (2012), Constraints on the centroid moment tensors of the 2010 Maule and 2011 Tohoku earthquakes from radial modes, Geophys. Res. Lett., 39, L18302. © 2012. American Geophysical Union.
Novak P.,University of West Bohemia |
Novak P.,Research Institute of Geodesy
Surveys in Geophysics | Year: 2010
During the General Assembly of the European Geosciences Union in April 2008, the new Earth Gravitational Model 2008 (EGM08) was released with fully-normalized coefficients in the spherical harmonic expansion of the Earth's gravitational potential complete to degree and order 2159 (for selected degrees up to 2190). EGM08 was derived through combination of a satellite-based geopotential model and 5 arcmin mean ground gravity data. Spherical harmonic coefficients of the global height function, that describes the surface of the solid Earth with the same angular resolution as EGM08, became available at the same time. This global topographical model can be used for estimation of selected constituents of EGM08, namely the gravitational potentials of the Earth's atmosphere, ocean water (fluid masses below the geoid) and topographical masses (solid masses above the geoid), which can be evaluated numerically through spherical harmonic expansions. The spectral properties of the respective potential coefficients are studied in terms of power spectra and their relation to the EGM08 potential coefficients is analyzed by using correlation coefficients. The power spectra of the topographical and sea water potentials exceed the power of the EGM08 potential over substantial parts of the considered spectrum indicating large effects of global isostasy. The correlation analysis reveals significant correlations of all three potentials with the EGM08 potential. The potential constituents (namely their functionals such as directional derivatives) can be used for a step known in geodesy and geophysics as the gravity field reduction or stripping. Removing from EGM08 known constituents will help to analyze the internal structure of the Earth (geophysics) as well as to derive the Earth's gravitational field harmonic outside the geoid (geodesy). © Springer Science+Business Media B.V. 2009.
Nesvadba O.,Land Survey Office |
Holota P.,Research Institute of Geodesy
International Association of Geodesy Symposia | Year: 2016
The technology progress today makes it possible to treat most of the problems of physical geodesy by means of numerical arrangements hardly imaginable earlier. Nevertheless, considering an evaluation of spheroidal (spherical and ellipsoidal) harmonic functions in our typical tasks, we still observe a huge performance gap between our demands and capabilities of common CPUs. Methods used for calculating associated Legendre functions aremostly recursive and thus sequential. Therefore, it is challenging, but feasible, to arrange the processing of Legendre functions in a way that reduces memory utilisation and admits massive parallelism. Following this aim, we developed a streaming-parallel algorithm for computing oblate spheroidal harmonic functions and their derivatives. The algorithm is free of assumptions concerning the function arguments, maximal degree/order or number of computation points and can be utilised on any data type, like a vector or scalar float, double or even integer numbers. Besides, it solves floating-point issues in the numerical treatment of Legendre functions.We demonstrate its Open Computing Language (OpenCL) implementation on a general-purpose graphics processing unit (GPGPU), which is ideal for its inexpensive computational power of some TFlops. Added performance benchmarks lead to the conclusion that our implementation on a single GPGPU device substantially outperforms recent multi-core CPUs, free of any precision penalty. Furthermore, thanks to the OpenCL standard, we can benefit from an excellent portability and scalability over heterogeneous parallel platforms. Let us note finally, that the topic presented is a matter of importance in many other application fields, not only in physical geodesy. © Springer International Publishing Switzerland 2015.
Palinkas V.,Research Institute of Geodesy |
Liard J.,Natural Resources Canada |
Jiang Z.,International Bureau of Weights and Measures BIPM
Metrologia | Year: 2012
FG5 absolute gravimeters are the most accurate gravimeters available at present and have significant influence on the realization of a gravity reference through international comparisons of absolute gravimeters. The latter comparisons are the only way to maintain the traceability of absolute gravimetry to the International System of Units (SI). Sources of systematic error such as the self-attraction effect (SAE) have to be taken into account when determining accurate values of the acceleration due to gravity, as needed, for example, for the watt balance project or the International Gravity Reference System. In this paper the SAE for two types of FG5 gravimeter is estimated using two independent methods. The resulting SAEs are 1.2(0.2)Gal and 1.7(0.2)Gal for FG5 with fibre and bulk interferometer types, respectively. The importance of accurately defining the measurement height is emphasized in the context of the SAE. The accuracy and advantages of referring gravity measurements to an effective position of the free-fall solution are demonstrated together with a simple and accurate empirical estimation of this effective position. © 2012 BIPM & IOP Publishing Ltd.
Dousa J.,Research Institute of Geodesy |
Vaclavovic P.,Research Institute of Geodesy
Advances in Space Research | Year: 2014
The Geodetic Observatory Pecný (GOP) routinely estimates near real-time zenith total delays (ZTD) from GPS permanent stations for assimilation in numerical weather prediction (NWP) models more than 12 years. Besides European regional, global and GPS and GLONASS solutions, we have recently developed real-time estimates aimed at supporting NWP nowcasting or severe weather event monitoring. While all previous solutions are based on data batch processing in a network mode, the real-time solution exploits real-time global orbits and clocks from the International GNSS Service (IGS) and Precise Point Positioning (PPP) processing strategy. New application G-Nut/Tefnut has been developed and real-time ZTDs have been continuously processed in the nine-month demonstration campaign (February-October, 2013) for selected 36 European and global stations. Resulting ZTDs can be characterized by mean standard deviations of 6-10 mm, but still remaining large biases up to 20 mm due to missing precise models in the software. These results fulfilled threshold requirements for the operational NWP nowcasting (i.e. 30 mm in ZTD). Since remaining ZTD biases can be effectively eliminated using the bias-reduction procedure prior to the assimilation, results are approaching the target requirements in terms of relative accuracy (i.e. 6 mm in ZTD). Real-time strategy and software are under the development and we foresee further improvements in reducing biases and in optimizing the accuracy within required timeliness. The real-time products from the International GNSS Service were found accurate and stable for supporting PPP-based tropospheric estimates for the NWP nowcasting.
Dousa J.,Research Institute of Geodesy |
Elias M.,Research Institute of Geodesy
Geophysical Research Letters | Year: 2014
A new concept is described for calculating the tropospheric zenith wet delay (ZWD) and its vertical approximation derived from the original profile of meteorological data. A new parameter of ZWD exponential decay is introduced which, together with a reference value, represents ZWD corrections accurately up to 10 km altitude. The new parameter considerably improves ZWD vertical reduction and surface ZWD calculation using the model of Askne and Nordius (1987). This development reduces the original large data set of a numerical weather model to an accurate grid representation at a reference level that may be more effectively disseminated. This can be used in regional augmentation models for precise positioning and navigation.
Dousa J.,Research Institute of Geodesy
GPS Solutions | Year: 2010
The impact of precise GPS ephemeris errors on estimated zenith tropospheric delays (ZTD) is studied for applications in meteorology. First, the status of IGS ultra-rapid orbit prediction is presented and specific problems are outlined. Second, a simplified analytical solution of the impact of ephemeris errors on estimated ZTDs is presented. Two widely used methods are studied-the precise point positioning technique (PPP) and the double-difference network approach. A simulation experiment is additionally conducted for the network approach to assess the capability of ephemeris error compensation by the ambiguities. An example of marginal requirements for ephemeris accuracy is presented, assuming the compensation by ZTD only and admitting the error of 1 cm in ZTD. The requirement for the maximum orbit error 1 cm for radial and 8 cm for tangential position components using PPP approach, versus 217 cm (radial) and 19 cm (tangential) using network solution. Furthermore, an assessment of possible compensations of ephemeris errors by other estimated parameters was considered. In radial orbit position, an error of a few meters can be still absorbed by satellite clocks (96%) and phase ambiguities (96%) even for the PPP technique. A tangential orbit position error up to 16 cm for PPP and 38 cm for network solutions should not bias ZTD by more than 1 cm, but any bigger error could, in general. The error impact on ZTD in such cases depends on the compensation ability of ambiguities and clocks (PPP). © Springer-Verlag 2009.
Dousa J.,Research Institute of Geodesy
International Association of Geodesy Symposia | Year: 2012
Observations from up to 51 GPS+GLONASS satellites are available as of September 2009. Mainly (near) real-time GNSS analyses, particularly navigation, warning systems or atmosphere monitoring, will benefit from the data from all these satellites. The International GNSS Service (IGS) has been providing precise GPS ultra-rapid orbits since 2000, but up to these days, due to a lack of contributing analysis centers, it does not provide GLONASS ultra-rapid orbit product. The Geodetic Observatory Pecný has been contributing to the IGS ultra-rapid orbits since 2004. In 2008/2009 an extension of the orbit determination procedure was prepared for the GLONASS system. Although the GLONASS global data coverage is far from optimal, we focused on a robust and satisfactory routine product already usable in (near) real-time GNSS analysis. We have tested the system for different schemes of processing - (1) common GNSS solution and (2) stand-alone GLONASS or GPS solutions. Resulting orbits and ERPs were evaluated with respect to the IGS final products. The use of the GLONASS ultra-rapid orbits was demonstrated in near real-time water vapor monitoring using the European network of 38 GNSS stations. © Springer-Verlag Berlin Heidelberg 2012.
Dousa J.,Research Institute of Geodesy |
Bennitt G.V.,UK Met Office
GPS Solutions | Year: 2013
The EUMETNET EIG GNSS Water Vapour Programme (E-GVAP) is responsible for the coordination of near real time GPS Zenith Total Delay (ZTD) production in Europe and for aiding the development of ZTD assimilation into Numerical Weather Prediction (NWP) models. Since 2000, the Geodetic Observatory Pecný (GOP) has been routinely estimating regional ZTDs in near real time. In 2010, GOP developed a modified processing system in order to provide the first optimal and robust ZTD solution with a global scope and hourly upgrade, fulfilling the requirements for assimilation into operational NWP models. Since July 2010, the GOP global tropospheric product has consisted of about 90 sites and has contributed routinely in a testing mode into the E-GVAP database. Global near real time ZTDs generated over ten months have been evaluated with respect to IGS and EUREF routine post-processed ZTD products, ZTDs integrated from radiosonde profiles, and ZTDs calculated from the Met Office global NWP model. Comparison with the GNSS post-processed solutions gives standard deviations of 3-6 mm in ZTD and biases of 1-2 mm, which is comparable to GOP regional near real time solution, however, for some isolated or low data quality stations up to 20 % quality decrease can be found. Comparison with NWP shows a latitudinal trend in the standard deviation with values as low as 4 mm at high latitudes, increasing to almost 20 mm in the tropics, and a lack of variability in the model background ZTD in the tropics. The evaluation with global radiosondes gives ZTD standard deviation of 5-16 mm, which is comparable with previous studies in European scope. Since the 10-month comparison gave satisfactory results, GOP was asked by UK Met Office to disseminate the global product to the end users via the Global Telecommunications System. Since 10 October 2011, the GOP global ZTD product configuration has been extended to about 164 global stations and still processed within 10 min. However, in GOP routine contribution to E-GVAP, about 124 stations are available in general due to hourly data latency above 30 min or data gaps. © 2012 Springer.
Holota P.,Research Institute of Geodesy
Studia Geophysica et Geodaetica | Year: 2011
In the introductory part of the paper the importance of the topic for gravity field studies is outlined. Some concepts and tools often used for the representation of the solution of the respective boundary-value problems are mentioned. Subsequently a weak formulation of Neumann's problem is considered with emphasis on a particular choice of function basis generated by the reproducing kernel of the respective Hilbert space of functions. The paper then focuses on the construction of the reproducing kernel for the solution domain given by the exterior of an oblate ellipsoid of revolution. First its exact structure is derived by means of the apparatus of ellipsoidal harmonics. In this case the structure of the kernel, similarly as of the entries of Galerkin's matrix, becomes rather complex. Therefore, an approximation of ellipsoidal harmonics (limit layer approach), based on an approximation version of Legendre's ordinary differential equation, resulting from the method of separation of variables in solving Laplace's equation, is used. The kernel thus obtained shows some similar features, which the reproducing kernel has in the spherical case, i. e. for the solution domain represented by the exterior of a sphere. A numerical implementation of the exact structure of the reproducing kernel is mentioned as a driving impulse of running investigations. © 2011 Institute of Geophysics of the ASCR, v.v.i.