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The goal of the project “Co-location of Space Geodetic Techniques on Ground and in Space”, in the DFG funded research unit on reference systems and founded by the Swiss National Foundation (SNF), is the improvement of existing and the establishment of new ties between the space geodetic techniques, together with the assessment and reduction of technique-specific biases. To achieve this, the wealth of co-located instruments at the Geodetic Observatory Wettzell (Germany) are used, where systematic errors in the space geodetic techniques can be detected, assessed and removed on very short, well-known baselines. Within this paper we summarise results for three intra-technique co-location experiments in Wettzell. Firstly, an assessment of the GNSS to GNSS baselines in relation to the surveyed local ties shows discrepancies of up to 9 mm, for solutions based on the ionosphere-free linear combination. Secondly, an analysis of the short VLBI baseline shows that the use of a clock tie achieves a sub-mm agreement with respect to the local tie. And finally, initial results on the usage of differencing approaches on the short SLR baseline show that double-difference residuals are within ±4 mm. The results of this work show the potential of intra-technique studies on short baselines for the understanding of technique-specific biases and errors and for the monitoring of local ties., International Association of Geodesy Symposia, 152, ISSN:0939-9585, ISSN:2197-9359, Beyond 100: The Next Century in Geodesy, ISBN:978-3-031-09856-7, ISBN:978-3-031-09857-4

Local ties (LTs) at co-located sites are currently used to align different space geodetic techniques for the determination of a global terrestrial reference frame (TRF). However, the currently available LT measurements are typically characterized by an inhomogeneous accuracy, which may cause inconsistencies within the TRF and limit the final TRF accuracy. An alternative strategy is a combination of common parameter types to which the individual geodetic techniques are sensitive. In this study, we combine Global Navigation Satellite Systems (GNSS) and Satellite Laser Ranging (SLR) data without using LTs but by combining the common pole coordinates and by adding proper datum constraints. In addition, we constrain the velocities at co-located sites to be the same for all markers. This allows an independent validation of measured LT components. Our data are based on a homogeneous reprocessing of GPS+GLONASS and SLR to LAGEOS-1 and LAGEOS-2 over 17 years in the time span of 1994–2010. A preliminary analysis including the elimination of outliers and the selection of core datum stations was performed based on the station position time series of the single-technique solutions. Applying our combination approach, the north and height components of the LTs can be directly derived from our combined coordinate solution. The differences of the measured and the estimated LTs remain below 1 cm for 96% in the north component and for 50% in the height component of all co-located sites.

Journal of Geodesy, 87 (5), ISSN:0949-7714, ISSN:1432-1394

The German geoscience satellite CHAMP (CHAllenging Minisatellite Payload) provides global atmospheric measurements almost continuously since early 2001. It currently generates a unique and operationally available long-term set of GPS radio occultation (RO) data. RO data from the US-German GRACE-A satellite (Gravity Recovery and Climate Experiment) are in addition operationally available since May 22, 2006. Data and analysis results from both satellites are provided to the international scientific community and stimulated several activities to improve GPS RO data analysis and the application in atmospheric research and for global weather forecasts. The data are currently in use by more than 40 research groups worldwide. A near-real time data provision from CHAMP and GRACE was installed and is demonstrated by GFZ within the GEOTECHNOLOGIEN research project NRT-RO (Near-Real-Time Radio Occultation) funded by the German Federal Ministry of Education and Research (BMBF). An average delay between measurement aboard the satellites and provision of corresponding analysis results below 2 h is operationally reached. This successful research activity was one of the preconditions for the beginning of the operational GPS RO data use to improve global weather forecasts in 2006 by Met Office and ECMWF (European Centre for Medium-Range Weather Forecasts). This result is a milestone and a breakthrough for the acceptance of the innovative GPS RO data in Numerical Weather Prediction (NWP).

CHAMP CHAllenging Minisatellite Payload.- CHAMP Mission 5 Years in Orbit.- Remarks on CHAMP Orbit Products.- Harmonic Analysis of the Earth's Gravitational Field from Kinematic CHAMP Orbits based on Numerically Derived Satellite Accelerations.- Earthquake Signatures in the Ionosphere Deduced from Ground and Space Based GPS Measurements.- Global Atmospheric Sounding with GPS Radio Occultation aboard CHAMP.- GRACE The Gravity Recovery and Climate Experiment.- Design and Operation of the GRACE ISDC.- De-aliasing of Short-term Atmospheric and Oceanic Mass Variations for GRACE.- Integrated Sensor Analysis GRACE.- Static and Time-Variable Gravity from GRACE Mission Data.- Gravity Field Recovery from GRACE-SST Data of Short Arcs.- Mapping Earth's Gravitation Using GRACE Data.- High Frequency Temporal Earth Gravity Variations Detected by GRACE Satellites.- GOCE The Gravity Field and Steady-State Ocean Circulation Explorer.- From Kinematic Orbit Determination to Derivation of Satellite Velocity and Gravity Field.- Mission Simulation and Semi-analytical Gravity Field Analysis for GOCE SGG and SST.- GOCE Gravity Field Modeling: Computational Aspects - Free Kite Numbering Scheme.- An Integrated Global/Regional Gravity Field Determination Approach based on GOCE Observations.- High-Performance GOCE Gravity Field Recovery from Gravity Gradient Tensor Invariants and Kinematic Orbit Information.- The Impact of Temporal Gravity Variations on GOCE Gravity Field Recovery.- Quality Assessment of GOCE Gradients.- Color Figures.- IERS The International Earth Rotation and Reference Systems Service.- IERS Data and Information System.- IERS Analysis Coordination.- Analysis and Refined Computations of the International Terrestrial Reference Frame.- Combination of VLBI Analysis Results.- Towards a Rigorous Combination of Space Geodetic Observations for IERS Product Generation.- CONT02 Analysis and Combination of Long EOP Series.- Conventional and New Approaches for Combining Multi-Satellite Techniques.- GEOsensor Ring Laser for Seismology.- The GEOsensor Project: Rotations - a New Observable for Seismology.- Airborne Gravimetry.- Evaluation of Airborne Vector Gravimetry Using GNSS and SDINS Observations.- SAGS4 - StrapDown Airborne Gravimetry System Analysis.- Further Development of a High Precision Two-Frame Inertial Navigation System for Application in Airborne Gravimetry.

This report is divided into two parts: the first part gives an overview of the combination studies performed by the Forschungseinrichtung Satellitengeodasie TU Munchen (FESG) and the Deutsches Geodatisches Forschungsinstitut (DGFI) based on the data of the continuous IVS campaign CONT02. The close cooperation of the two institutions established the basis for a detailed adaption of the GPS and the VLBI software concerning models and parameterization to avoid systematic differences between the technique contributions. Special attention was payed to parameters with a high temporal resolution; in this study tropospheric parameters and Earth rotation parameters (ERP) are considered. Including the troposphere parameters offered a good possibility to study the correlation between troposphere parameters and station coordinates. It was found that this interaction can deliver a very important contribution to validate the available local tie information. For comparison of the troposphere results derived for the 14-days campaign CONT02, long time series for VLBI and GPS were used as well, and it turned out that the results are in good agreement. Regarding the sub-daily Earth rotation parameters it can be shown that a combination of the space techniques improves the results compared to single-technique solutions. Furthermore, it is illustrated that UT1-UTC can be combined from VLBI together with the satellite techniques. All in all, the presented results demonstrate the high potential of a combination of VLBI, GPS and SLR data. The second part is devoted to the combination of long sub-daily EOP time series from VLBI and GPS. Space geodetic techniques like the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) can provide Earth Orientation Parameter (EOP) time series with very high sampling rates. This offers the opportunity to study sub-daily tidal excitations and the influences of high-frequency or episodic geophysical effects on Earth rotation. Therefore we need sub-daily time series as consistent and homogeneous as possible. Based on the Combined Smoothing method of Vondrak and Cepek (2000), we developed a new combination scheme for sub-daily EOPs to obtain a new sub-daily time series which benefits from the longterm stability of VLBI and the continuity of GPS. Furthermore we can remove the weakness of UT1 estimations of the satellite techniques. We analysed the combination using spectral imaging methods and the results from sub-daily tidal harmonic estimation.

Purely kinematic precise orbit determination (POD) was performed for the CHAMP satellite over 11 days in the framework of the CHAMP Orbit Comparison Campaign. For the same period, reduced-dynamic orbits were computed and both types of orbits were independently validated by SLR. The tests with SLR showed that the accuracy of CHAMP reduced-dynamic POD is at the level of 4-5 cm, whereas kinematic orbits have a quality of 5-6 cm. Neither in the kinematic nor in the dynamic orbits a significant SLR range bias could be detected. In adition, we will present results concerning the ambiguity resolution techniques used.

Using the GPS data of a special antenna calibration campaign involving most of the current high-precision geodetic receivers, mean antenna offsets and elevation- and azimuth-dependent phase center variations were estimated. The phase center variations were modeled using spherical harmonics. Due to the fact that the antennas were rotated by 180° and also interchanged between sessions, it was possible to estimate site coordinates and horizontal antenna phase center offsets at the same time. Rotating the antennas also made it possible to distinguish between multipath and real antenna phase patterns in the azimuth and to solve the problem posed by the “northern hole” in the satellite distribution.