Impact of loading effects on determination of the International Terrestrial Reference Frame

The International Terrestrial Reference Frame (ITRF), as a realization of the International Terrestrial Reference System (ITRS), is represented by a set of station positions and linear velocities. They are intended to be used as regularized coordinates to which some corrections should be added to access instantaneous coordinates. The latest ITRS realization is the ITRF2005, which has integrated time series of station positions to form long-term solutions for the four space geodetic techniques. Currently, a purely linear model is used to parameterize station displacements in the estimation process, plus occasional discontinuities in case of earthquakes or equipment changes. However the input data have been derived without applying surface loading models and so surface loading effects are supposed to be embedded in the coordinates as measured quantities. We evaluate the effect of applying a posteriori loading corrections, which include the effect of atmospheric, non-tidal ocean, and continental water loading, to time series of positions estimated from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS) data. We notice that they reduce about 50% or more of the annual signals in the translation and scale parameter time series of the SLR and VLBI techniques, except in SLR Z translation. In general, the estimated secular frame definition is negligibly affected and estimated positions and velocities are not significantly modified for stations that have accumulated a large number of observations. A multi-technique combination of such derived frames allows concluding that, for some cases, loading model corrections might degrade co-located station coordinates almost as much as they benefit them. However, most significant improvement of the estimated secular coordinates is observed for stations with less than 100 estimated positions as demonstrated with a multi-technique combination

The Role of Laser Ranging for Calibrating Jason-1 : the Corsica Tracking Campaign

Marine Geodesy, v. 27, n. 1-2, p. 333-340, Special Issue on Jason-1 Calibration/Validation, 2004. http://dx.doi.org/10.1080/01490410490476272International audienc

Single-Frequency Receivers as Permanent Stations in GNSS Networks: Precision and Accuracy of Positioning in Mixed Networks

Continuous Operating Reference Stations (CORSs) are widely used for many purposes including precise positioning, mapping and monitoring. These architectures are composed of a control centre and a number of permanent stations consisting of geodetic antennas and dual frequency receivers. This infrastructure is costly due to the instruments used and has the additional disadvantage in that inter-station distances between CORSs, that are often too high if a single-frequency receiver acts as a rover. This study focuses on the usefulness of permanent single-frequency stations in order to increase density of existing CORSs for monitoring purposes. In this connection, some innovative GNSS networks composed of geodetic and mass-market L1 receivers have been developed and tested, analyzing the performance of rover positioning in terms of quality, accuracy and reliability in real time. Some tests have been carried out considering different types of receivers (geodetic and mass market) and antennas (patch and geodetic), in real-time mode. The results obtained show that with a "classical" network (where the mean inter-station distances between CORSs are about 40 km) an accuracy of about 5 cm can be achieved after fixing the phase ambiguity with a mass-market L1 receiver acting as rover. In addition, the Time-To-Fix period is very short, being less than 2 min. Despite the obvious fact that increased inter-station distance leads to reduced accuracy, the degree of precision obtainable remains useful for many applications, such as mobile mapping and traffic control. In short, the experiments under examination performed with low-cost GNSS receivers will be useful for many types of applications (landslide monitoring, traffic control), especially where the inter-station distances of permanent GNSS stations are around 40 km

Recent advances in the determination of a high spatial resolution geopotential model using chronometric geodesy

International audienceThis work aims to evaluate the contribution of optical atomic clocks in the determination of the geopotential at high spatial resolution. The quality of the geopotential reconstruction is evaluated by comparing solutions computed from synthetic gravimetric data, combined or not with synthetic clock data. Our synthetic tests are performed in a French area with a moderate relief, which leads to variations of the gravitational field over a range of spatial scales. We show that adding few clock data into a gravimetric network permits to reduce the reconstruction bias significantly and to improve the standard deviation by a factor 3. Optimization of a clock data network with a genetic algorithm is also investigated

Satellite Laser Ranging

International audienc

Geocenter motion measured by DORIS and SLR and geophysical expectations

Journal of Geodesy, v. 80, n. 8-11, p. 637-648, 2006. http://dx.doi.org/10.1007/s00190-006-0079-zInternational audienc

OCA/GEMINI-GRGS BECOMING AN OFFICIAL ILRS ANALYSIS CENTER

National audienceOCA/GEMINI-GRGS is currently moving from its status of an associate ILRS analysis center to an official ILRS analysis center. The ILRS (International Laser Ranging System) is one of the nine services of the International Association of Geodesy (IAG). This new status should permit to GRGS to validate and, especially, enlighten in an easy way its scientific results coming from SLR data, within this international organization