Tim Springer

The Extended CODE Orbit Model, an empirical orbit model proposed by Beutler et al. [1994], was used for the first time in the actual parameter estimation procedures (using the Bernese GPS Software), to model the orbits of the GPS satellites at the CODE Analysis Center of the IGS. Apart from six Keplerian elements this orbit model consists of nine instead of the usual two parameters to take into account the deterministic part of the force field acting on the satellites. In this article we focus on the optimum use of this Extended CODE Orbit Model for the CODE IGS activities. Of particular interest are the generation of rapid orbits, with only 12 hour delay after the last observation, and (IGS) orbit prediction.

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<p>The availability of highly accurate Earth Orientation Parameters (EOPs) in near real time is of major importance for any type of positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for all ESA missions and the EU space programs Galileo, EGNOS and Copernicus.</p><p>To ensure operational capability, ESA’s Navigation Support Office developed independent EOP products and services.</p><p>The EOPs are estimated based on a rigorous combination of the ESA’s contributions to the International Association of Geodesy (IAG) that are used as an input for the generation of the International Earth Rotation Service (IERS) products. For the ESA/ESOC EOP products, the individual parameters are combined on normal equation level and propagated with the contribution of model-based predicted Effective Angular Momentum (EAM) functions.</p><p>The ESA/ESOC’s EOP product generation is currently running in pre-operational mode.</p><p>This presentation will provide a high-level overview of the methodology and the status of ESA’s EOP products and services. In this context, the accuracy achieved in the test operations and the roadmap for the publication of ESA’s EOP products and services will be outlined.</p>

<p>For the previous ITRF calls for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with a single software package (NAPEOS), running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the techniques themselves, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models.</p><p>At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GNSS) into one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using “space ties”. Of course these space ties are not perfectly known but they still allow for a rigorous combination of the different reference frames. Furthermore, and very important for the GNSS technique, they allow for the direct estimation of the GNSS satellite transmitter phase centre offset. We solve not only for integer ambiguities of the GPS satellites but also for those of the LEO satellites, which is also providing GPS phase observations on two frequencies. </p><p>Our poster presents an overview of this multi-technique combination approach at observation level (COOL). We have included all observations provided by the following satellites in a single parameter estimation process: GNSS, JASON, SPOT, Sentinels, GRACE, LAGEOS and Etalon satellites. We demonstrate the benefits of such a rigorous approach compared to processing the various space geodetic techniques separately.</p>

In the recent years, GPS only dual-frequency GNSS receivers are increasingly developing into multi-constellation, multi-frequency receivers. This development poses a new set of technical challenges. A key factor for precise GNSS applications is the stability of receiver induced inter-frequency/signal biases. The consequences of receiver induced bias instabilities on GNSS analyses are of particular importance for analyses applying more than two signals types per link. Certainly, most up-to-date applications maintain the common ionosphere free (dual-frequency) processing. This implementation allows the absorption of these biases by ionosphere and clock estimates. However, to releasing the full potential of the multi-constellation, multi-frequency GNSS environment a joint processing of all available signals is inevitable. Based on experimental results the presented paper shows different sources for bias instabilities and changes as among other internal receiver temperature antenna etc....

Over the recent years the Navigation Package for Earth Orbiting Satellites, NAPEOS, has evolved to a great tool for satellite geodesy. It is developed and maintained at the European Space Operations Centre (ESOC) of the European Space Agency (ESA) NAPEOS is capable of processing data from all GNSS systems, all DORIS, and all SLR observations. And, NAPEOS is used for generating state of the art products for all three satellite-geodetic techniques and there corresponding services: IGS, IDS, and ILRS. ESA owned software is in general available free of charge to any entity in the ESA member states as the developments have been paid by public funding. Thus NAPEOS is, in principle, available free of charge but under a strict license agreement with ESA. However, ESA does not provide any support on how to use the software. And like most research oriented packages learning such software from scratch is at the very least an "adventure". In 2009 we therefore started a company, called...

The ITRF2005 solution constituted a significant improvement over all earlier ITRF solutions. Nevertheless significant issues surfaced when the different services, IDS, IGS, ILRS and IVS, started to use the ITRF2005. The most noticeable issue being the scale difference between the SLR and VLBI solution, leading to a special "rescaled" version of the ITRF2005. Within each individual technique service, IDS, IGS, ILRS, and IVS, the reference frame issues are relatively well understood and a very good agreement between the technique specific analysis centres reference frame realisations is achieved. However, the scale discrepancy of the ITRF2005 demonstrated that across the different techniques significant systematic differences still exist. The origin of these systematic differences between the techniques dependent reference frame realisations is unknown, not understood, and seems to be very difficult to resolve. One possible way to resolve these "inter technique" bi...

The upcoming the Galileo GNSS and the modernisation of the GPS and Glonass systems offers many exciting opportunities and challenges in the field of geosciences in the next decade. However, in order to obtain any positive effects on our geodetic and geophysical estimates the different GNSS systems will have to be observed by multi system receivers that track all systems

The accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications. Among others, these include global positioning, near-Earth and deep-space navigation, the realisation of precise reference and time systems as well as studies of geodynamics and global change phenomena. In this paper, we present a refined strategy for processing and combining Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations at the normal equation level and formulate recommendations for a consistent processing of the space-geodetic input data. Based on the developed strategy, we determine final and rapid Earth rotation parameter (ERP) solutions with low latency that also serve as the basis for a subsequent prediction of ERPs involving effective angular momentum data. Realising final E...

For the ITRF2008 call for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with one and the same software package NAPEOS, running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the technique itself, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models. At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GPS/GLONASS) in one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using "space-ties". Of course these space-ties are not perfectly known but nevertheless they allow for a rigorous combination of the different reference frames. And, very important for the...

The IGS is facing ever increasing demands for more precise and more rapid (real-time!) products. The computation of the rapid orbits and especially the orbit predictions, which are available in real-time, therefore are becoming more important and deserve ...

We derive phase center offsets (PCOs) and variations (PCVs) for almost all GPS Block II/IIA/IIR/IIF transmitting antennas by processing multi-year GPS dual-frequency code and phase observables from Jason-1/2 together with ground-based data from a globally well-distributed set of International GNSS Service (IGS) tracking stations in a common least-squares (LS) analysis. To alleviate the effect of unmodelled Jason-1/2 receiving antenna PCOs and PCVs propagating into the GPS transmitting antenna parameters, we estimate the PCOs and PCVs for Jason-1/2 as well. The quality of the new antenna corrections, in particular with regard to the IGS standard, and their impact on precise orbit determination (POD) of low-Earth orbiting (LEO) satellites will be discussed. The 1336-km orbital altitude of the Jason-1/2 spacecraft is particularly favourable as it allows determination of the GPS antenna PCVs up to 17 boresight angle without the need of setting up additional troposphere parameters. Rathe...

Context: Calibration of radiometric tracking data for effects in the Earth atmosphere is a crucial element in the field of deep-space orbit determination (OD). The troposphere can induce propagation delays in the order of several meters, the ionosphere up to the meter level for X-band signals and up to tens of meters, in extreme cases, for L-band ones. The use of media calibrations based on Global Navigation Satellite Systems (GNSS) measurement data can improve the accuracy of the radiometric observations modelling and, as a consequence, the quality of orbit determination solutions. Aims: ESOC Flight Dynamics employs ranging, Doppler and delta-DOR (Delta-Differential One-Way Ranging) data for the orbit determination of interplanetary spacecraft. Currently, the media calibrations for troposphere and ionosphere are either computed based on empirical models or, under mission specific agreements, provided by external parties such as the Jet Propulsion Laboratory (JPL) in Pasadena, Calif...

One of the primary goals of the 1992 test campaign for the International Geodynamics GPS Service (IGS) was the proof of the feasibility of routine orbit and earth rotation parameter determination, with the strong emphasis on ”routine”. In order to be able to collect, preprocess, and process data of some 30 stations every day during three months a highly automated data processing system at CODE had to be set up. The paper first gives an overview of the IGS data flow and describes the automated data processing at the CODE computing center in Berne.

The IGS reprocessing campaign involves processing all the available GPS data from 1994 to 2008 using the current state-of-the-art techniques. This lofty goal can be proposed and accomplished nowadays due to the availability of cheap high-end computing power and of very efficient new GNSS estimation software. The aims of this initial reprocessing effort at the IGS derive from the need to have consistent products from the start of the service back in 1994. Once completed the reprocessed products will become the official IGS Final products. The existing discontinuities in the IGS product lines (orbits, clocks, station positions, etc) have occurred as new ITRF versions have been adopted over time, and as we switched from relative to absolute antenna phase center calibrations. Having continuous IGS products will assist all Earth Science research that uses historical GPS data by providing better orbit and clocks and better stations positions fully consistent over the entire IGS timeframe....

During 2008 and 2009 ESOC has reprocessed the historic data from the IDS, IGS, and ILRS! Our 3 solution were computed with one and the same software running on the same machine and using, as far as possible, identical settings, a unique achievement. ...

Four years have gone since the start of the first Galileo In Orbit Validation Element (GIOVE)-A and nearly two years since the start of the second validation satellite GIOVE-B. Although results from the Galileo Experimental Sensor Stations (GESS) are published in ...

As a satellite-based technique, GNSS should be sensitive to motions of the Earth's center of mass (CM) with respect to the Earth's crust. In theory, the weekly solutions of the IGS Analysis Centers (ACs) should indeed have the "instantaneous" CM as their origin, and the net translations between the weekly AC frames and a secular frame such as ITRF2008 should thus approximate the non-linear motion of CM with respect to the Earth's center of figure. However, the comparison of the AC translation time series with each other, with SLR geocenter estimates or with geophysical models reveals that this way of observing geocenter motion with GNSS currently gives unreliable results. The fact that the origin of the weekly AC solutions shoud be CM stems from the satellite equations of motion, in which no degree-1 Stokes coefficients are included. It is therefore reasonable to think that any mis-modeling or uncertainty about the forces acting on GNSS satellites can potential...

The different space geodetic techniques have different strengths and weaknesses for recovering geodetic parameters. This makes their combination useful. However they may have some systematic behaviour which can be detected and removed at the observation level. In order to review the interest in combining techniques at this level, a Working Group at the Combination Level (WG COL) was set up in the course of 2009 in the frame of the International Earth Rotation and Reference Systems Service (IERS). A major task of the WG COL is to study methods and advantages of combining space geodetic techniques (DORIS, GNSS, SLR, VLBI), searching for an optimal strategy to solve for geodetic parameters. The first action of the Working Group was to organize an inter-comparison benchmark campaign to serve as a test. The period chosen is from August 10 to August 30, 2008. It includes the intensive CONT08 VLBI period. The combination analyses are based on weekly or daily combined SINEX files which cont...

.   In October 1998 the IGEX field campaign, the first coordinated international effort to monitor GLONASS satellites on global basis, was started. Currently about 40 institutions worldwide support this effort either by providing GLONASS tracking data or in operating related data and analysis centers. The increasing quality and consistency of the calculated GLONASS orbits (about 25 cm early in 2000), even after

1 Astronomical Institute of the University of Bern Sidlerstrasse 5; CH–3012 Bern; Switzerland 2 Swiss Federal Office of Topography swisstopo Seftigenstrasse 264; CH–3084 Wabern; Switzerland 3 European Space Operations Centre Robert Bosch Strasse 5; DE–64293 Darmstadt; Germany 4 Centre National d’́ Etudes Spatiales 18, avenue Edouard Belin; FR–31401 Toulouse Cedex 09; Franc e 5 Technische Universität München; Forschungseinrichtun g Satellitengeodäsie Arcisstrasse 21; DE–80333 Munich; Germany