David Coulot

Satellite Laser Ranging Biases and Terrestrial Reference Frame Scale Factor

We examine the impact of the strategy adopted regarding range biases on Satellite Laser Ranging data processing results. More especially, we test the stability of the weekly Terrestrial Reference Frame scale factors computed w.r.t. ITRF2000 accord- ing to the two different strategies which are studied in this paper. In the first approach, range biases are not considered in the data processing. In the second approach, we use a temporal de-correlation method to rigorously estimate all station range biases. The first approach provides weekly scale factors with a piece-wise behavior. More precisely, the time se- ries exhibit a drift of −2.5±0.2 mm/yr between 2001.0 and 2006.0 and provide a RMS of 5.2 mm. The second

Global optimization of GNSS station reference networks

The IGS08 reference network, adopted by the International GNSS Service (IGS) in 2011, and IGS08 core network are both of primary importance for the international GNSS community. They were empirically designed so as to fulfill several standards, such as the quality of the ITRF2008 positions and velocities of the involved stations, the reliability of the data they provide, and their global distribution. The present study shows that such global reference networks and well-distributed sub-networks can be objectively and rigorously designed with genetic algorithms (global optimization stochastic algorithms), on the basis of equivalent criteria. The IGS08-like reference networks and IGS08 core-like sub-networks provided by genetic algorithms respectively outperform the IGS08 and IGS08 core networks for the specific criteria in play. This opens the way to future essential applications: objective design of the next IGS reference and core networks, construction of dynamic core networks, and computation of user-specific global or regional GNSS reference networks.

Towards a Combination of Space-Geodetic Measurements

The International Terrestrial Reference Frame (ITRF), the Earth Orientation Parameter (EOP) time series, and the International Celestial Reference Frame are obtained separately and may thus present inconsistencies. To solve this problem, a first step has been made with the latest ITRF realization (ITRF2005), which has been computed, for the first time, with consistent EOP time series. Another approach to better understand this issue is to directly estimate, in the same process, station positions and EOP time series, from all the space-geodetic measurements.

Recent Activities of the GGOS Standing Committee on Performance Simulations and Architectural Trade-Offs (PLATO)

The Standing Committee on Performance Simulations and Architectural Trade-Offs (PLATO) was established by the Bureau of Networks and Observations of the Global Geodetic Observing System (GGOS) in order to support – by prior performance analysis – activities to reach the GGOS requirements for the accuracy and stability of the terrestrial reference frame. Based on available data sets and simulated observations for further stations and satellite missions the committee studies the impact of technique-specific improvements, new stations, and additional co-locations in space on reference frame products. Simulation studies carried out so far show the importance of the individual station performance and additional stations for satellite laser ranging, the perspectives for lunar laser ranging assuming additional stations and reflectors, and the significant impact of the new VGOS antennas. Significant progress is achieved in processing VLBI satellite tracking data. New insights in technique-specific error sources were derived based on real data from short baselines. Regarding co-location in space PLATO members confirmed that E-GRASP could fulfill the GGOS requirements with reaching a geocenter and scale accuracy and stability of 1 mm and 0.1 mm/year, respectively.