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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.

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.

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.

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.

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