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AVISO (Archiving, Validation and Interpretation of Oceanographic Satellite data) is a service set up by the French spatial agency, CNES (Centre National d'Etudes Spatiales) to process, archive and distribute data and derived products from satellite missions. Its web portal AVISO+ (www.aviso.altimetry.fr) is the entry point to freely access more than 40 products from CNES and CTOH (Center for Topographic studies of the Ocean and Hydrosphere) not only for ocean-oriented applications but also for hydrology, coastal, biology and sea ice applications. In addition, the website proposes information (handbooks, use cases, outreach material, etc.) to discover the products and their use. New operational (or demonstration) products are regularly added to the AVISO+ catalogue. In 2022, the catalogue has been for instance enriched with several along-track and gridded SSALTO/DUACS experimental products, simulated SWOT Sea Surface Heights, costal products of Sea Level Anomaly (X-TRACK L2P), the Floating Sargassum detection index and climate indicators for the ocean heat content and earth energy imbalance. In 2023, new versions of the models produced by CNES and CLS for the Mean Sea Surface (MSS CNES-CLS 2022) and for the Mean Dynamic Topography (MDT CNES-CLS 2022) will be available for AVISO+ users, as well as the upcoming SWOT oceanographic products. A visualization tool will also be available online to discover the AVISO+ products, including the KaRIn measurements of the SWOT mission over the oceans. An overview of these new AVISO+ products will be presented.

On 1 July 2023, the International DORIS Service (IDS) will celebrate the 20th anniversary of its creation under the umbrella of the International Association of Geodesy (IAG). The IDS was established to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associated Analysis Center, a Combination Center, and several partner groups.The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 32 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system, ... Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF. This year, a 9th satellite joins the current constellation of DORIS satellites. It is SWOT, launched on 16 December 2022. Never before have so many DORIS instruments been in operation simultaneously.This presentation addresses the recent achievements made by IDS and its components, and the future plans of the service.

The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 30 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system. Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF.The International DORIS Service (IDS) was created in 2003 under the umbrella of the International Association of Geodesy (IAG) to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products from an expanded set of DORIS Analysis Centers. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associate Analysis Centers, and a Combination Center. Using the experience gained in the preparation of the ITRFs, many improvements were made all along both in data analysis and on technical aspects. After the IDS Retreat held in June 2018, the IDS GB worked on the development of a strategic plan for the IDS. In the coming years, IDS will focus on growing the community, extending the DORIS applications, and improving the technology, the infrastructure and the processing.This presentation addresses the recent achievements made by IDS and how the service is preparing the future.

Aviso (Archiving, Validation and Interpretation of Satellite Oceanographic data) is a service set up by CNES to process, archive and distribute data and products from altimetry satellite missions. Its portal AVISO+ (www.aviso.altimetry.fr) is the entry point to freely access more than 40 products from CNES (Centre National d'Etudes Spatiales) and CTOH (Center for Topographic studies of the Ocean and Hydrosphere) not only for ocean-oriented applications but also for hydrology, coastal, ice applications. In addition, the website proposes information (handbooks, use case, outreach material, …) to discover the products and their use. New products are regularly added to the catalogue, whether they are operational or demonstration products. For example, in 2019, the catalogue has been enriched with L2P level products from the Copernicus Sentinel-3A & 3B missions, the new version of the Mean Dynamic Topography CNES/CLS 2018, the mesoscale Eddy Trajectory Atlas in Near Real Time, several datasets of along-track and gridded SSALTO/DUACS experimental products, and some others. In 2020, some products of the CFOSAT (China-France Oceanography SATellite) mission devoted to the monitoring of ocean surface winds and waves, as well as CTOH ice and snow products will be available via Aviso+.This presentation gives an overview of available products and services. We also present here all the recent novelties, and those to come in 2020.

Within the frame of the International DORIS Service, the CNES/CLS Analysis Center, previously known as LCA and renamed GRG, contributes to the geodetic and geophysical research activity through DORIS data analysis. The main work carried out in the past two years concerns the processing of the measurements collected by the DORIS-equipped satellites over 22 years, in order to provide a homogeneous series of station coordinates and Earth pole parameters for the IDS contribution to the ITRF2014. First, we brought several upgrades to the processing and the modeling. Some of them are corrective actions to issues raised during or shortly after the production of our contribution to the ITRF2008 (ground station frequency offsets, attitude laws and macromodels). Recent models have been assessed with the aim to update our analysis configuration. Among others, we adopted the time variable gravity (TVG) model EIGEN-6S2 and applied tropospheric gradients. Then we processed almost all the DORIS data collected between January 1993 and December 2014. The series of weekly SINEX solutions derived from this processing is labeled grgwd40. This new series performs better than the series produced for ITRF2008. Especially, the results discussed in this paper show a decrease of 2% of the DORIS orbit residuals as well as a strong reduction of the annual terms of the TRF scale and Tz translation which can be explained by the application of the TVG model.

Within the frame of the International DORIS Service (IDS), the CNES/CLS Analysis Center contributes to the geodetic and geophysical research activity through DORIS data analysis. A strategy was developed for the processing of the measurements of the DGXX instruments in RINEX/DORIS format, as it will be the only type of DORIS format made available by CNES, starting with the Jason-3 and Sentinel-3A missions launched at the beginning of the year 2016. The purpose of this paper is to describe the method implemented in the CNES/CLS Analysis Center orbit computation software GINS to process RINEX/DORIS data files. Phase measurements are converted into Doppler counts and then into relative satellite-to-beacon velocities. In this approach, the iono-free phase centers have to be used as the end points of the measurement instead of the 2 GHz phase centers. Given that, the processing results with RINEX/DORIS data are similar to the ones obtained with the usual doris2.2 data, except the scale factor of the Terrestrial Reference Frame in the 7-parameter transform of the network solution. We also address the issue of the scale factor increase from 2012 observed by all the IDS Analysis Centers in their solutions for the ITRF2014 combination. We show that the scale increase in 2012 is dependent on the type of DORIS data used. This scale increase is also enhanced by a bias due to the inclusion of HY-2A data, but which can be eliminated by adopting different coordinates of the onboard DORIS antenna phase center.

The anisotropy of propagation of radio waves used by global navigation satellite systems is investigated using high-resolution observational data assimilations produced by the European Centre for Medium-range Weather Forecast. The geometry and the refractivity of the neutral atmosphere are built introducing accurate geodetic heights and continuous formulations of the refractivity and its gradient. Hence the realistic ellipsoidal shape of the refractivity field above the topography is properly represented. Atmospheric delays are obtained by ray-tracing through the refractivity field, integrating the eikonal differential system. Ray-traced delays reveal the anisotropy of the atmosphere. With the aim to preserve the classical mapping function strategy, mapping functions can evolve to adapt to high-frequency atmospheric fluctuations and to account for the anisotropy of propagation by fitting at each site and time the zenith delays and the mapping functions coefficients. Adaptive mapping functions (AMF) are designed with coefficients of the continued fraction form which depend on azimuth. The basic idea is to expand the azimuthal dependency of the coefficients in Fourier series introducing a multi-scale azimuthal decomposition which slightly changes the elevation functions with the azimuth. AMF are used to approximate thousands of atmospheric ray-traced delays using a few tens of coefficients. Generic recursive definitions of the AMF and their partial derivatives lead to observe that the truncation of the continued fraction form at the third term and the truncation of the azimuthal Fourier series at the fourth term are sufficient in usual meteorological conditions. Delays’ and elevations’ mapping functions allow to store and to retrieve the ray-tracing results to solve the parallax problem at the observation level. AMF are suitable to fit the time-variable isotropic and anisotropic parts of the ray-traced delays at each site at each time step and to provide GPS range corrections at the measurement level with millimeter accuracy at low elevation. AMF to the azimuthal anisotropy of the neutral atmosphere are designed to adapt to complex weather conditions by adaptively changing their truncations.

For the first time, the International DORIS Service (IDS) has produced a technique level combination based on the contributions of seven analysis centers (ACs), including the European Space Operations Center (ESOC), Geodetic Observatory Pecny (GOP), Geoscience Australia (GAU), the NASA Goddard Space Flight Center (GSFC), the Institut Geographique National (IGN), the Institute of Astronomy, Russian Academy of Sciences (INASAN, named as INA), and CNES/CLS (named as LCA). The ACs used five different software packages to process the DORIS data from 1992 to 2008, including NAPEOS (ESA), Bernese (GOP), GEODYN (GAU, GSC), GIPSY/OASIS (INA), and GINS (LCA). The data from seven DORIS satellites, TOPEX/Poseidon, SPOT-2, SPOT-3, SPOT-4, SPOT-5, Envisat and Jason-1 were processed and all the analysis centers produced weekly SINEX files in either variance–covariance or normal equation format. The processing by the analysis centers used the latest GRACE-derived gravity models, forward modelling of atmospheric gravity, updates to the radiation pressure modelling to improve the DORIS geocenter solutions, denser parameterization of empirically determined drag coefficients to improve station and EOP solutions, especially near the solar maximum in 2001–2002, updated troposphere mapping functions, and an ITRF2005-derived station set for orbit determination, DPOD2005. The CATREF software was used to process the weekly AC solutions, and produce three iterations of an IDS global weekly combination. Between the development of the initial solution IDS-1, and the final solution, IDS-3, the ACs improved their analysis strategies and submitted updated solutions to eliminate troposphere-derived biases in the solution scale, to reduce drag-related degradations in station positioning, and to refine the estimation strategy to improve the combination geocenter solution. An analysis of the frequency content of the individual AC geocenter and scale solutions was used as the basis to define the scale and geocenter of the IDS-3 combination. The final IDS-3 combination has an internal position consistency (WRMS) that is 15 to 20 mm before 2002 and 8 to 10 mm after 2002, when 4 or 5 satellites contribute to the weekly solutions. The final IDS-3 combination includes solutions for 130 DORIS stations on 67 different sites of which 35 have occupations over 16 years (1993.0–2009.0). The EOPs from the IDS-3 combination were compared with the IERS 05 C04 time series and the RMS agreement was 0.24 mas and 0.35 mas for the X and Y components of polar motion. The comparison to ITRF2005 in station position shows an agreement of 6 to 8 mm RMS in horizontal and 10.3 mm in height. The RMS comparison to ITRF2005 in station velocity is at 1.8 mm/year on the East component, to 1.2 mm/year in North component and 1.6 mm/year in height.

DORIS is one of the four space-geodetic techniques participating in the Global Geodetic Observing System (GGOS), particularly to maintain and disseminate the Terrestrial Reference Frame as determined by International Earth rotation and Reference frame Service (IERS). A few years ago, under the umbrella of the International Association of Geodesy, a DORIS International Service (IDS) was created in order to foster international cooperation and to provide new scientific products. This paper addresses the organizational aspects of the IDS and presents some recent DORIS scientific results. It is for the first time that, in preparation of the ITRF2008, seven Analysis Centers (AC’s) contributed to derive long-term time series of DORIS stations positions. These solutions were then combined into a homogeneous time series IDS-2 for which a precision of less than 10 mm was obtained. Orbit comparisons between the various AC’s showed an excellent agreement in the radial component, both for the SPOT satellites (e.g. 0.5–2.1 cm RMS for SPOT-2) and Envisat (0.9–2.1 cm RMS), using different software packages, models, corrections and analysis strategies. There is now a wide international participation within IDS that should lead to future improvements in DORIS analysis strategies and DORIS-derived geodetic products.

For Precise Orbit Determination of altimetry missions, we have computed a data set of DORIS station coordinates defined for specific time intervals called DPOD2005. This terrestrial reference set is an extension of ITRF2005. However, it includes all new DORIS stations and is more reliable, as we disregard stations with large velocity formal errors as they could contaminate POD computations in the near future. About 1/4 of the station coordinates need to be defined as they do not appear in the original ITRF2005 realization. These results were verified with available DORIS and GPS results, as the integrity of DPOD2005 is almost as critical as its accuracy. Besides station coordinates and velocities, we also provide additional information such as periods for which DORIS data should be disregarded for specific DORIS stations, and epochs of coordinate and velocity discontinuities (related to either geophysical events, equipment problem or human intervention). The DPOD model was tested for orbit determination for TOPEX/Poseidon (T/P), Jason-1 and Jason-2. Test results show DPOD2005 offers improvement over the original ITRF2005, improvement that rapidly and significantly increases after 2005. Improvement is also significant for the early T/P cycles indicating improved station velocities in the DPOD2005 model and a more complete station set. Following 2005 the radial accuracy and centering of the ITRF2005-original orbits rapidly degrades due to station loss.

DORIS is a French precise orbit determination system. However, in the past four years, through the creation of the International DORIS Service, a larger international cooperation was involved. Furthermore, the precision of its scientific applications (geodesy, geophysics) gradually improved and expanded to new fields (atmospheric sciences), leading, for example, to the publication of a special issue of the Journal of Geodesy. The goal of this manuscript is to present and explain these changes and to put them in perspective with current results obtained with other space geodetic techniques, such as GPS or Satellite Laser Ranging.

While accuracy of tracking station coordinates is of key importance for Precise Orbit Determination (POD) for altimeter satellites, reliability and operationality are also of great concern. In particular, while recent ITRF realizations should be the most accurate at the time of their computation, they cannot be directly used by the POD groups for operational consideration for several reasons such as new stations appearing in the network or new discontinuities affecting station coordinates. For POD purposes, we computed a new DORIS terrestrial frame called DPOD2008 derived from ITRF2008 (as previously done by DPOD2005 with regards to ITRF2005). In a first step, we will present the method used to validate the past ITRF2008 using more recent DORIS data and to derive new station positions and velocities, when needed. In particular, discontinuities in DORIS station positions and/or velocities are discussed. To derive new DORIS station coordinates, we used recent DORIS weekly time series of coordinates, recent GPS relevant time series at co-located sites and also dedicated GPS campaigns performed by IGN when installing new DORIS beacons. DPOD2008 also contains additional metadata that are useful when processing DORIS data, for example, periods during which DORIS data should not be used or at least for which data should be downweighted. In several cases, a physical explanation can be found for such temporary antenna instability. We then demonstrate improvements seen when using different reference frames, such as the original ITRF2008 solution, for precise orbit determination of altimeter satellites TOPEX/Poseidon and Jason-2 over selected periods spanning 1993–2013.

The transformation between European Center for Medium-range Weather Forecast (ECMWF) model level assimilations and the refractivity at any given point of the neutral atmosphere has been investigated. We first present the IFS interpolations and extrapolations of each physical parameter done in operations at ECMWF. These formulae are used to compute, for example, pressure levels from model levels at ECMWF. We use this formulation to compute the pressure levels, the large majority of which are found similar to the pressure levels provided by ECMWF with an appropriate accuracy for ray-tracing. The IFS-based scheme (IFS-BS) is then presented. It is an adaptation of the interpolations and extrapolations done at ECMWF for troposphere delay computation by ray-tracing. This scheme ensures the coherence with the ECMWF meteorological model and is used in our software Horizon designed to compute the Adaptive Mapping Functions (AMF). In the IFS-BS, vertical interpolations are adapted for each thermodynamic parameter necessary to precisely rebuild the refractivity along the ray path according to the physical laws. In order to take into account the atmospheric part between the lowest model level and the Earth’s topography during the ray-tracing, extrapolation of physical parameters below the lowest model level are included. The proposed scheme is expected to be relevant for applications where accuracy of refractivity is important as troposphere delay modelling for high-accuracy geodesy.

The International DORIS Service (IDS) was created in 2003 under the umbrella of the International Association of Geodesy (IAG) to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). We first present some general background related to the DORIS system (current and planned satellites, current tracking network and expected evolution) and to the general IDS organization (from Data Centers, Analysis Centers and Combination Center). Then, we discuss some of the steps recently taken to prepare the IDS submission to ITRF2013 (combined weekly time series based on individual solutions from several Analysis Centers). In particular, recent results obtained from the Analysis Centers and the Combination Center show that improvements can still be made when updating physical models of some DORIS satellites, such as Envisat, Cryosat-2 or Jason-2. The DORIS contribution to ITRF2013 should also benefit from the larger number of ground observations collected by the last generation of DGXX receivers (first instrument being onboard Jason-2 satellite). In particular for polar motion, sub-milliarcsecond accuracy seems now to be achievable. Weekly station positioning internal consistency also seems to be improved with a larger DORIS constellation.

The aim of the DORIS Pilot Experiment is to assess the need and feasibility of an International DORIS Service. A Call for Proposals was broadcasted in September 1999 to prompt qualified organizations to submit proposals for components of the future IDS. DORIS Days were held in Toulouse (May 2–3, 2000). This second version of these Doris days was in particular devoted to a review of the start-up of the Doris Pilot Experiment. This paper recalls the objectives of the future IDS, points out its components and structure, and gives information on the current and future activities.

Temporal variations of surface mass redistribution among atmosphere, oceans, and continental water reservoirs deform the Earth's crust, in particular in the vertical direction. These displacements can now be measured by space geodesy and predicted from climatic loading data. In this study we first compute globally theoretical vertical displacements of the Earth's crust caused by the main annual surface mass redistributions (atmosphere and ocean mass, soil moisture, and snow load). For that purpose we consider atmospheric pressure data from the National Centers for Environment Prediction (NCEP), soil moisture data from Huang et al. [1996] and from the Global Soil Wetness Project (GSWP), snow data from the International Satellite and Surface Climatology Project (ISLSCP) and GSWP, and ocean mass data from the Parallel Ocean Climate Model (POCM) and from TOPEX-Poseidon satellite altimetry after correcting for steric effects. Annual vertical displacements are computed for each load individually as well as for the total climatic contribution on global 2.5°×2.5° grids. We then present space geodesy-derived annual variations of vertical coordinates of 16 Doppler orbitography and radiopositioning integrated by satellite (DORIS) stations globally distributed around the globe. A comparison is then performed for each station between observed (by DORIS) and predicted (from climatology) results.

The New Hebrides experiment consisted of setting up a pair of DORIS beacons in remote tropical islands in the southwestern Pacific, between 1993 and 1997. Because of orbitography requirements on TOPEX/Poseidon, the beacons were only transmitting to SPOT satellites. Root-mean-square (RMS) scatters at the centimeter level on the latitude and vertical components were achieved, but 2-cm RMS scatters affected the longitude component. Nevertheless, results of relative velocity (123 mm/year N250°) are very consistent with those obtained using the global positioning system (GPS) (126 mm/yr N246°). The co-seismic step (12 mm N60°) related to the Walpole event (MW = 7.7) is consistent with that derived from GPS (10 mm N30°) or from the centroid moment tensor (CMT) of the quake (12 mm N000°).

Sea level difference (Topex-Poseidon minus tide gauge) time series have been computed over 1993–1997 at 53 selected gauges sites. Comparison of these sea level differences with vertical crustal motions derived from the DORIS space geodesy system at 6 colocated sites shows good consistency. At one site (the Socorro volcanic island), a striking correlation is reported between sea level differences and DORIS height time series. The observed trend likely reflects a post eruptive deformation associated with a volcanic eruption that occurred in early 1993. At several other gauge sites, the sea level differences present large linear trends possibly bearing evidence of land motion. This may be the case at Rabaul (Papua New Guinea) where a volcanic eruption took place in autumn of 1994. The sea level differences at Rabaul show a negative trend from this date, likely related to the volcanic event.

Five years (1993–1997) of DORIS data on the SPOT and Topex-Poseidon satellites have been analyzed to estimate vertical motions at 33 sites of the permanent DORIS network. Rates have been determined assuming constant velocity over the 5-year time span. Except for a few stations, vertical rates are lower than 5 mm/yr. Comparison with solutions provided by GPS, SLR or VLBI at colocated sites shows good agreement for most stations. Some space-geodesy vertical rates however disagree significantly. This may result from interannual to decadal fluctuations affecting the vertical motions, giving rise to different apparent linear trends if estimated over different time spans. Except for six high-latitude stations, post-glacial rebound produces negligible signal and cannot explain the observed motions. Other local or regional phenomena from geophysical or anthropogenic origin may be responsible for the estimated vertical motions.

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) data acquired between January 1993 and December 1996 from the SPOT-2, SPOT-3, and TOPEX/Poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates. For 28 sites far from deformation zones, the velocity estimates agree with plate model predictions. Least squares computation of poles of rotation, which model the plate motions, shows that for Eurasia, Africa, Pacific, and South America plates, the agreement is better with NUVEL-1, while for Australia, Antarctica, Nazca, and North America plates the DORIS Euler vectors are closer to NTJVEL-1A. In general, DORIS results do not differ significantly from other space geodetic techniques determinations but provide better estimates for plates poorly or inhomogeneously covered by Global Positioning System (GPS), Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) networks, such as Africa. The DORIS coverage of this plate allows discussion of intraplate deformations due to the motion of the eastern Africa part which constitues the Somalia plate. Sites located in deformation zones, such as western Eurasia boundaries, central Asia, southwestern America coast, South East Asia, show motion with respect to their own plates. Comparisons with other geodetic measurements for colocated stations, or with regional geodynamical models, show the interest of DORIS in active zones where global plate models are not valid.

We have analysed approximately 3 years of Doppler tracking measurements of the DORIS system on the SPOT2 and Topex-Poseidon satellites. Absolute velocities of 19 stations of the DORIS network have been computed through a dynamic orbit computation method. These stations are located on 9 major tectonic plates. For 14 stations, relative velocities across 28 plate boundaries involving 8 different plates, agree quite well with the NUVEL-1 geological estimates, with a correlation coefficient of 0.982 and a slope of 1.00±0.02. This study provides the first space geodesy-derived motion of the African plate which is based on data taken at 4 stations. Computed rotation vectors for the relative motions between the Eurasian, Pacific and African plates show a good agreement with NUVEL-1 vectors. For the remaining sites which are typically located close to plate boundaries, measured motions depart significantly from the ones predicted by NUVEL-1. The site of Fairbanks (Alaska) appears to move anomalously compared to earlier VLBI results.

The long-term stability of the scale of Terrestrial Reference Frames is directly linked with station height determination and is critical for several scientific studies, such as global mean sea level rise or ocean circulation with consequences to global warming studies. In recent International Terrestrial Reference Frame (ITRF) solutions, the DORIS technique was not considered able to provide any useful information on scale (derived from VLBI and SLR). We have analyzed three different DORIS time series of coordinates (GSFC, IGN/JPL, LEGOS/CLS) performed independently using different software packages. In the long-term, we show that the DORIS technique, due to its very stable and geographically distributed network, has extremely good stability (

International audience; In the framework of the activities of the Combination Research Centers (CRC) of the International Earth Rotation and Reference Systems Service (IERS), the French Groupe de Recherche en Géodésie Spatiale (GRGS) studies the benefit of combining space-geodetic techniques (Doppler orbitography and radiopositioning integrated by satellite, GPS, satellite laser ranging, and very long baseline interferometry) at the observational level. This combination aims to produce a global and consistent solution for Earth orientation parameters (EOPs), polar motion xp and yp, and universal time UT1 with a 1-day or a 6-hour sampling, as well as weekly station positions. In this paper we present a methodology for multitechnique combination at the observational level. We process the measurements of the four techniques over a 1-year period (the year 2002) in order to illustrate and validate our method. All techniques are processed with the same computational framework, thus with the same models and a priori values for parameters. By using the same software and conventions, we avoid inconsistencies in individual computations. We process each technique individually and inside the combination. The comparison between these solutions is a way of analyzing the power of our method even if the actual status of our software does not reproduce the state-of-the-art analyses of each technique. However, we produce an analysis of the quality of our individual computations so that readers can get an informed appreciation of the current capabilities of our software. Finally, we present the capability of such combinations in terms of accuracy and precision, we underline the main issues of our method and propose solutions to solve them in the future.

International audience; A rigorous approach to simultaneously determine both a terrestrial reference frame (TRF) materialized by station coordinates and Earth Orientation Parameters (EOP) is now currently applied on a routine basis in a coordinated project of the Groupe de Recherches de Géodésie Spatiale (GRGS). To date, various techniques allow the determination of all or a part of the Earth Orientation Parameters: Laser Ranging to the Moon (LLR) and to dedicated artificial satellites (SLR), Very Large Baseline Interferometry on extragalactic sources (VLBI), Global Positioning System (GPS) and more recently DORIS introduced in the IERS activities in 1995. Observations of the different astro-geodetic techniques are separately processed at different analysis centres using unique software package GINS DYNAMO, developed and maintained at GRGS. The datum-free normal equation matrices weekly derived from the analyses of the different techniques are then stacked to derive solutions of station coordinates and Earth Orientation Parameters (EOP). Two approaches are made: the first one consists to accumulate normal equations (NEQs) derived from intra-technique single run solution in a single run combined solution; the second one leads to weekly combinations of NEQs. Results are made available at the IERS site (ftp iers1.bkg.bund.de) in the form of SINEX files. The strength of the method is the use of a set of identical up-to-date models and standards in unique software for all techniques. In addition the solution benefits from mutual constraints brought by the various techniques; in particular UT1 and nutation offsets series derived from VLBI are densified and complemented by respectively LOD and nutation rates estimated by GPS. The analyses we have performed over the first four months of the year 2006 are still preliminary; they show that the accuracy and stability of the EOP solution are very sensitive to a number of critical parameters mostly linked to the terrestrial reference frame realization, the way that minimum constraints are applied and the quality of local ties. We present thereafter the procedures which were applied, recent analyses and the latest results obtained.

In the frame of the International DORIS Service (IDS), the Laboratoire d’Etudes en Geophysique et Oceanographie Spatiales (LEGOS)/Collecte Localisation Satellites (CLS) Analysis Center (LCA) processes DORIS measurements from the SPOT, TOPEX/Poseidon and Envisat satellites and provides weekly station coordinates of the whole network to the IDS. Based on DORIS measurements, the horizontal and vertical velocities of 57 DORIS sites are computed. The 3D positions and velocities of the stations with linear motion are estimated simultaneously from the 12-year (1993–2004) combined normal equation matrix. We include 35 DORIS sites assumed to be located in the stable zones of 9 tectonic plates. For the motion of these plates, we propose a model (LCAVEL-1) of angular velocities in the ITRF2000 reference frame. Based on external comparison with the most recent global plate models (PB2002, REVEL, GSRM-1 and APKIM2000) and on internal analysis, we estimate an average velocity error of the DORIS solution of less than 3 mm/year. The LCAVEL-1 model presents new insights of the Somalia/Nubia pair of plates, as the DORIS technique has the advantage of having a few stations located on those two plates. We also computed (and provide in this article) the horizontal motion of the sites located close to plate boundaries or in the deformation zones defined in contemporary models. These computations could be used in further analysis for these particular regions of the Earth not moving as rigid plates.

International audience; All space-geodetic techniques are now organized as separate services of the International Association of Geodesy (IAG), supporting the first pilot project ``Global Geodetic Observing System (GGOS)''. The International DORIS (Détermination d'Orbite et Radiopositionnement Intégrés par Satellite) Service (IDS) was created in mid-2003 to organize a DORIS contribution to this project and to foster a larger international cooperation on this topic. The goal of this paper is to summarize the key steps that were taken to create this structure and to present its current organization and recent results. At present, more than 50 groups from 35 different countries participate in the IDS at various levels, including 43 groups hosting DORIS stations in 32 countries all around the globe. Four Analysis Centres (ACs) provide results, such as estimates of weekly or monthly station coordinates, geocentre variations or Earth polar motion, that will soon be used to generate IDS-combined products for geodesy and geodynamics. As a first test, a preliminary combination was performed for all the 2004 data from these four ACs. Three of them show RMS of weighted station residuals with respect to this combination solution between 1 and 2 cm. The main topic under investigation is a discrepancy in the scale factor of the terrestrial reference frame (TRF) to map the individual solutions into the combination solution, which reaches 6 cm (multiplying the unit-less scale factor by the Earth radius to get convert scale to millimetre in vertical at the Earth's surface). Finally, foreseen improvements of the DORIS technology are discussed as well as future improvements concerning the service organization itself and the accuracy and reliability of its scientific products.

[1] We present observed seasonal and interannual geocenter motion over 1993–1999 based on laser data on the LAGEOS-1, LAGEOS-2, and Topex/Poseidon (T/P) satellites as well as Doppler orbitography and radiopositioning integrated by satellite (DORIS) data from T/P. The amplitude and the phase of the space geodesy-derived seasonal cycles for each coordinate are further compared to the estimates based on surface mass redistribution on the Earth surface derived from various climatic data sources: surface pressure, soil moisture, snow depth, and ocean mass variations. Geodesy and climatic data present good agreement in terms of seasonal, still not for interannual, geocenter motion.

In 1999, an International DORIS Experiment was initiated under the aegis of the International Association of Geodesy. Since then, 3 new DORIS satellites have been launched carrying improved Doppler receivers. In addition, the DORIS tracking network has also been steadily improved. In 2001, a DORIS analysis campaign was launched. Several groups participated using different software and providing weekly and monthly time series of results, making them available on Internet. The goal of this paper is to discuss the status of the DORIS Pilot experiment, to analyze the progress made during the past 2 years and to propose the official creation within the IAG of an International DORIS Service (IDS). Such a service would operate in conjunction with the already existing IGS, IVS and ILRS as part of the proposed International Global Geodetic Observing System (IGGOS).

International Altimetry Team., In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion., At the forefront of this support, we must obviously mention the space agencies CNES, ESA and NASA which have played and still play a decisive role in the development and launch of several prominent altimetry missions from the outset. Other agencies such as DLR, EUMETSAT, ISRO, NOAA, NSOAS and organizations such as CMEMS, also contribute significantly to developments in all forms of altimetry.