G53A-0103 1340h
GPS Measurement Corrections for Geophysicists: A Calibration Experiment for C/A-P Code Biases
The existence of pseudorange biases between the C/A and L1-code (P1) has been recognized for several years. Although pseudorange is a secondary data type for geophysicists and geodesicists, the satellite dependent biases between the two pseudorange observables, C/A and P1, can affect the carrier phase ambiguity resolution as well as timing errors. We report results of several experiments conducted to accurately determine pseudorange biases. In the first case, we use receivers that report both C/A and P1, and average the observations over a day to estimate satellite specific bias es. In this way, we are able to evaluate the long-term stability of the transmitter biases, and compare results between different receivers. Many receivers record C/A or P1, but not both. To evaluate possible receiver specific biases for these units, we conducted zero-baseline experiments. We evaluate the accuracy of the pseudorange bias estimates by assessing abmiguity resolution results with and without these corrections.
G53A-0104 1340h
Low-Multipath Antenna for Real-Time High-Accuracy GPS in Earth and Atmospheric Sciences
Novel applications of high-accuracy GPS, such as GPS seismology and meteorology, require time-dependent, real-time, and near-real-time positioning at data acquisition times of only a few seconds. This fast observation rate enables the analysis of dynamic phenomena that are often encountered in Earth and atmospheric sciences. The most critical source of error in high-accuracy GPS, especially for dynamic applications, is multipath, the interference of multiple reflections with the direct GPS signal. For observations made over 24 hours, multipath effects can sometimes be removed by averaging, but for time dependent measurements performed over a few seconds there is currently no effective way to mitigate the errors introduced by multipath. Therefore, there is an urgent need for the development of new methods to reduce or eliminate this critical source of error for advanced GPS applications. The best way to mitigate multipath is to build an antenna that rejects multipath at reception. The only GPS antenna available today that can somewhat reduce multipath is the Choke Ring antenna. This antenna only partly rejects multipath (mainly at one frequency), presents a lower gain at low elevation angles, and is massive, heavy, and relatively expensive. In this work we propose and test a novel GPS antenna for real-time high accuracy applications. The antenna performance is enhanced through an innovative design of the antenna ground plane. GPS test measurements show that the proposed GPS antenna achieves an improved multipath rejection and eliminates multipath uniformly at L-Band, while allowing for a smaller and lighter antenna.
G53A-0105 1340h
Absolute local sea surface in the Vanuatu Archipelago from GPS, satellite altimetry and pressure gauge data
Water height measurements provided by seafloor tide gauges are a combination of sea level variation and local ground motion. Both signals are of scientific interest, but they must be separated in order to be useful. A reliable estimation of the vertical ground motion is important in very seismically areas such as the Pacific Ocean rim. One promising method to separate the two contributions is to use satellite altimetry which gives absolute water height that is independent of the local ground motion. However, the altimeter data must be calibrated using ground truth measurements. Once different components of the signal are separated, bottom pressure gauges can be used to detect vertical movements of the seafloor. The Vanuatu Archipelago is part of the Pacific "ring of fire", where plates are quickly converging. In this area, movements are very rapid and the seismic activity is intense, which gives a good opportunity to study deformation and seismic cycle. To get an integrate picture of vertical deformation over one plate and between the two plates, one needs to be able to monitor vertical movements on both underwater and emerged areas. We conducted an experiment in this area to compare measurements from bottom pressure gauges located beneath altimetry satellite tracks with sea surface altitude measurements from GPS. Two bottom pressure gauge are immerged since Nov. 1999 in this region. In order to perform absolute calibration for multiple satellite altimeters that overfly the region, we conducted 2 campaigns of GPS measurements of instantaneous sea surface height onboard the R/V Alis and using a GPS buoy. We present results of GPS computations for the March 2003 and March 2004 campaigns. These sea level GPS measurements are compared with multiple altimeter-measured sea surface heights, and sampling differences and high frequency variations were removed using continuous pressure gauge data. The observed discrepancies are likely to be explained by local geoid variations or dynamic topography and we conducted GPS surveys to map these differences.
G53A-0106 1340h
The European Sea Level Service (ESEAS): The Continuous GPS Coordinate Time Series Analysis Strategy
The European Sea Level Service (ESEAS) was established in June 2001 and has the objective to provide sea-level and sea-level related information for the European waters to scientific and non-scientific users both from inside and outside Europe. The ESEAS-RI (Research Infrastructure) commenced its work in November 2002 for a three year period, included 25 institutions from 17 countries and aims to provide substantial resources to ESEAS for improving the observational network as well as the tools for exploitation of the data. Within ESEAS-RI, data from continuous GPS (CGPS) stations co-located with tide gauges in Europe are analyzed and vertical station velocity estimates at the 1\,mm/yr accuracy level with uncertainties of $<$\,0.5\,mm/yr are envisaged. Therefore, an ESEAS CGPS coordinate time series analysis strategy was developed in order to separate real geophysical signals from the underlying noise. Coordinate time series pre-processing identifies outliers and discontinuities in the time series. The following parameterization includes a mean value, a constant rate, periodic terms with annual and semi-annual frequencies, and offset magnitudes for the identified discontinuities. Maximum Likelihood Estimation then determines all parameters plus the magnitudes of different stochastic noise. Empirical Orthogonal Function (EOF) analysis allows the discrimination between local, station-specific, deterministic processes and inter-station, correlated transient signals, i.e. common mode errors. Using the common mode errors from the EOF analysis, the coordinate time series of the continuous and eventually also campaign data from the ESEAS GPS network are filtered and improved. After outlining the ESEAS CGPS coordinate time series analysis strategy this presentation shows initial results for coordinate time series from a selection of CGPS stations in Europe for a four year (2000-2003) test period.
G53A-0107 1340h
SURFACE DEFORMATION DUE TO NON-LINEAR TIDES IN THE NORTH SEA
The indirect deformations of the Earth caused by variations in the surface load from non-linear tides are detectable by measuring e.g. surface displacements, tilt or gravity changes. To predict these shallow water loading deformations, an ocean tide model (describing the spatial and temporal distribution of the surface load) and a visco-elastic Earth model (describing how the Earth responds to the surface load) are needed. The ongoing satellite altimetry missions have improved considerably to model these effects. In this study, we use Topex/Poseidon (T/P) data to construct a model of the shallow water loading deformations at the third-diurnal and higher frequency tidal band. Furthermore, we compare our T/P results with vertical surface deformation observed using GPS at some selected locations in the coastal region of the North Sea.
G53A-0108 1340h
Eleven Years of Continuous GPS Observations and Inference of Three-Dimensional Deformation in Fennoscandia
The land uplift processes in Fennoscandia have been subject to scientific research for more than a century. The cause of this land uplift phenomenon is a glacial isostatic adjustment (GIA) process, which has its origin in the last ice age that culminated about 20 kyr ago. In 1993, the Baseline Inferences for Fennoscandian Rebound Observations Sea Level and Tectonics (BIFROST) project was started, with a primary goal to establish a 3D observable, able to constrain models of the GIA process in Fennoscandia. In this study we have analysed continuous GPS observations from August 1993 until August 2004. We also present results from different methods used to re-analyse the BIFROST data. The Precise Point Positioning technique (PPP) available for the GIPSY software has been applied, the elevation cut-off angle is lowered from 15,a to 10,a making especially the vertical component of the solution stronger. In addition we also solve for integer ambiguities. To be able to study possible software specific effects, we have performed additional analyses using the GAMIT/GLOBK and Bernese software packages. A detailed description of the different GPS processing results, analysis of the GPS time series, and comparisons with GIA model predictions are presented. Finally, we present error analyis, spatial and temporal correlations, and additional signals visible in the data.
G53A-0109 1340h
Observation and Modeling of Thermoelastic Strain in SCIGN Daily Position Time Series
The Southern California Integrated GPS Network (SCIGN) is now well established, and daily position time series for its stations clearly show seasonal variations. With our analysis we suggest that these fluctuations are caused by strain in the elastic part of the earth's crust induced by temperature variations at the surface (thermoelastic strain). We compute the predicted crustal thermoelastic strain using the observed local atmospheric temperature record and compare the seasonal variation in thermoelastic strain to the horizontal position time series of regional GPS stations. We use a crustal model that consists of an elastically decoupled (soil) layer over a uniform elastic half-space. Temperature variations at the base of the decoupled layer results in strain in the underlying elastic half-space. The decoupled layer has the effect of delaying, attenuating, and low-pass filtering the source temperature field. For our analysis we consider three regions (Palmdale, Pinon Flat, and 29 Palms), each with a radius of about 50 km. In each region we analyze data from one temperature station and three or four GPS stations. The temperature time series is used to compute the thermolastic strain at each GPS station, based on its relative location in the temperature field. For each region we assume a wavelength for the temperature field that is related to the local topography. The depth of the decoupled layer is inferred from the phase delay between the temperature record and the GPS time series. In order to compare our predicted strains to the GPS position time series, an arbitrary scale factor is applied. The amplitude of the strain variation at each GPS station is related to the relative location of that GPS station in the temperature field. The goodness of fit between model and data is evaluated from the relative amplitudes of the seasonal signals, as well as the appropriateness of the chosen temperature field wavelength and decoupled layer depth. Our analysis shows a good fit between the predicted strains and the GPS time series and suggests that thermoelastic strain is a primary contributor to the seasonal variations observed by the SCIGN network.
G53A-0110 1340h
Techniques for Reducing Spatially-Correlated Errors in High-Rate GPS Positioning
Even with continuing advances in GPS data analysis techniques and receiver technology, sub-daily GPS position time series exhibit a high noise level relative to the desired geophysical signal (e.g. volcanic uplift, seismic waves). Several sources of positioning noise are spatially-correlated, meaning that these errors depend on the position of a GPS satellite relative to the location of the receiving GPS antenna. Examples of spatially-dependent errors include multipath, residual phase center variations, and positioning precision based on satellite constellation geometry. We present here two different but complementary methods for removing spatially-correlated errors, sidereal filtering and signal-to-noise ratio (SNR)-based multipath corrections. By applying these methods to both high-rate (1 Hz) and low-rate (30-second) GPS data, we analyze and discuss the respective differences in position noise reduction.
G53A-0111 1340h
Strain From Small-Scale GPS Networks: Differences in Apparent Noise Levels
Time series from permanent GPS stations are usually shown as variations in station positions. Such series usually show correlations between stations in a region; these correlations are often removed using regional filtering. Another mode of analysis is to solve for a time series of strain changes across a network (as well as a mean displacement) from the series of station displacements. This automatically removes common-mode signals, and produces an output (strain change) of immediate geophysical relevance. Applying this method to time series for small (10-20 km span) subnetworks of the SCIGN and BARGEN networks shows that the resulting strain series show interesting signals not obvious in the original time series (such as local annual signals). The level in strain (as judged by day-to-day scatter) ranges from 40 to 100 nanostrain for a network size of 10 km, with the higher values for subnetworks in more coastal areas, and lower ones in desert sites. A large variation comes from the mode of processing used to create the displacement series, with point-positioning giving much larger apparent strain noise than baseline processing. This suggests that the sensitivity of GPS data to many geophysical signals will depend on the way in which the original phase data are processed.
G53A-0112 1340h
Assessment of GPS Derived Velocity Solutions in the Mediterranean Area
The GPS data collected from permanent receivers are now widely used to compute time series of site coordinates and to infere the kinetic behaviour of tectonically active regions. The daily (or weekly) coordinate solutions are often considered as high level products obtained by a complex propagation of the raw GPS observations into the coordinate space. A number of highly sofisticated GPS analysis tools have been developed in the past years and are now available to a great deal of applications. Nevertheless, differences in the setup approach, misconceptions or real software bugs could lead to hidden errors in the final geodetic product. The apparently simple-to-use softwares could therefore give the impression of easy-to-obtain results and often geophysical interpretations relay on data that have not been cross validated. This work will test the contribution to the error budget of long lasting GPS time series (1995-2004), computed by different analysis groups and different softwares (Gipsy, MicroCosm and Gamit) in a regional network context. The current work focuses on time series of permanent GPS solutions located in the Central Mediterranean area, already published or that have been used for regional tectonic studies. Site velocities has been derived from these time series with a standardized approach and using the complete covariance matrices. The different velocity fields are then compared in a homogeneous reference frame. Eventual differences are purely due to the raw data analysis procedures and should never exceed the given standard error. The site noise content derived from the coordinate time series will also be discussed and compared in order to possibly isolate the error sources. Since the expected velocities in the central mediterranean area are only on the order of a few mm/y, there is a strong demand on the stability of the coordinate and covariance time series. If the repeatability among different data-analysis approaches is not at the level of the declared standard error, the geophysical interpretation can be, at high probability, seriously distorted by impredictible (human) factors.
G53A-0113 1340h
Effect of reference stations on continuous GPS (CGPS) time series
Time series of CGPS sites in the ITRF2000 reference frame show a significant "bump" in late 2002. The time series suggest that the position of the GPS monument has moved significantly compared to the expected steady velocity prediction. Although the change has only a slight effect on computed velocities for long time series, it may introduce a significant bias in the computed velocity for shorter time series and in time series only using data collected during episodic GPS campaigns. The "bump" is easily recognized in North American sites but can also be observed in sites around the world, indicating a global effect. It is also present in time series produced by different analysis groups with different software packages (GIPSY-OASIS, GAMIT). We propose that the bump is related to "misbehavior" of one or more references sites used to transform raw GPS positions into ITRF2000. The "bump" appears to coincide with discontinuity in the operation of some reference stations. We also find that daily positions estimates are particularly sensitive to the behavior of some reference stations.
G53A-0114 1340h
Reference frame induced noise in CGPS coordinate time series.
Global scale studies of changes in the Earth's geometry due to geodynamics and surface loading, including problems related to global change (such as sea level changes) require access to a highly accurate global reference frame with spatially homogeneous accuracy. Today, such access is only easily available through GPS, which allows to determine point coordinates relative to the International Terrestrial Reference Frame (ITRF). The International GPS Service (IGS) provides global products (satellite orbits and clocks, SOC) as well as time series of the reference coordinates for the IGS tracking stations that can be used to determine coordinates of new points either through single point positioning relative to the SOC or by using additional information from nearby reference sites. We will discuss the quality of the IGS products in terms of long-term stability and accuracy relative to ITRF and discuss potential noise introduced by these products into coordinate time series determined from Continuous GPS (CGPS) observations. Through comprison to homogeneous SOC provided by the Jet Propulsion Laboratory (JPL), we will assess the noise due to the IGS products and also quantify the noise introduced by inconsistencies in the processing used to generate the global products and the single point positioning processing.
G53A-0115 1340h
Data Quality Monitoring and Noise Analysis at the EUREF Permanent Network
The EUREF Permanent Network (EPN) includes now more then 150 GNSS stations of different quality and different observation history. The greatest portion of the sites is settled on the tectonically stable parts of Eurasia, where only mm-level yearly displacements are expected. In order to extract the relevant geophysical information, sophisticated analysis tools and stable, long term observations are necessary. As the EPN is operational since 1996, it offers the potential to estimate high quality velocities associated with reliable uncertainties. In order to support this work, a set of efficient and demonstrative tools have been developed to monitor the data and station quality. The periodically upgraded results are displayed on the website of the EPN Central Bureau (CB) (www.epncb.oma.be) in terms of sky plots, graphs of observation percentage, cycle slips and multipath. The different quality plots are indirectly used for the interpretation of the time series. Sudden changes or unusual variation in the time series (beyond the obvious equipment change) often correlates with changes in the environment mirrored by the quality plots. These graphs are vital for the proper interpretation and the understanding of the real processes. Knowing the nuisance factors, we can generate cleaner time series. We are presenting relevant examples of this work. Two kinds of time series plots are displayed at the EPN CB website: raw and improved time series. They are cumulative solutions of the weekly EPN SINEX files using the minimum constraint approach. Within the improved time series the outliers and offsets are already taken into account. We will also present preliminary results of a detailed noise analysis of the EPN time series. The target of this work is twofold: on one side we aim at computing more realistic velocity estimates of the EPN stations and on the other side the information about the station noise characteristics will support the removal and proper interpretation of site-specific phenomena .
G53A-0116 1340h
Choosing Geodetic Monuments Based on Noise in New Zealand GPS Time Series
Geodetic signals of tectonic or volcanological interest recorded by geodetic instrumentation may be degraded or obscured by the presence of noise in the geodetic data. Limiting the noise is therefore important for the detection and interpretation of such signals. One source of noise is random motion occurring within the connection of the geodetic instrument to the ground. In the case of surface instruments such as GPS, the connection to the ground is through a geodetic monument. The motion of this monument, with respect to a representative volume of the Earth's near surface in its vicinity, is termed monument noise. Monument noise results from processes such as soil swelling in response to rainfall, and general rock and soil weathering effects. In this paper we investigate the noise levels within time series of continuous GPS (CGPS) positions collected on concrete pillar monuments in New Zealand. We compare these noise levels with those from drilled, braced monuments in several U.S. CGPS networks. We investigate under what conditions monument noise is the limiting noise source in the CGPS data, and attempt to provide a basis for decisions on what type of monument to deploy under certain scenarios.
G53A-0117 1340h
Theoretical Studies And Applications Of Regional 4D GPS Tropospheric Tomography
4D GPS water vapor tomography from GPS dense network (~5 km spacing between GPS stations) is now used in the field of meteorology for local studies or model validations. The typical spacing of dense networks over the world is ~50-100 km. To assess the potentiality for atmospheric studies of such networks, we have performed a field experiment in the South-Eastern France on a region regularly affected by severe precipitations. During three month we continuously record GPS data. We first extract the standard atmospheric GPS outputs (IWV and horizontal gradient) which are useful for monitoring the evolution of the precipitation systems. Several examples of tomographic models will be shown illustrating several cases of severe precipitations. Synthetic data obtained from high resolution numerical simulations provide a realistic field of water vapor and allow to perform synthetic tests. These tests inform about the spatial and temporal resolutions of the tomography.
G53A-0118 1340h
Comparison of TEC Measurements from Dual-Frequency Space Geodetic Techniques
Various space geodetic techniques can provide ionosphere information from their dual frequency measurements. These independent data sources can be used for cross-validation purposes and as multiple data types to improve ionosphere modeling. Global Ionosphere Map (GIM) is generated through mapping of the slant Total Electron Contents (TEC) from satellite to the global ground receiver network to zenith direction. The notable GIM data products include those of the NASA/JPL GIM and the CODE GIM. Dual frequency altimeters (TOPEX/POSEIDON or JASON-1 or ENVISAT) in addition to producing data for oceanographic research also produce ionospheric TEC along their nadir tracks. These data are perhaps the most precise available but have particular geographic and temporal sampling pattern that may reduce their global utility. In addition, these data need to be calibrated and validated against other data types. Global VLBI measurements spanning over two solar cycles, though relatively sparse in terms of global stations, represent another independent data type for relative ionosphere measurements. DORIS tracking system onboard of various altimetric satellites and on Spot-n constitutes another relative ionosphere measuring device from space. In this work, we provide a comparison study of various techniques for assessing their applicability to ionosphere modeling as well as measurements validations.
G53A-0119 1340h
Azimuth-dependent Mapping Functions From Numerical Weather Models in VLBI Analysis for CONT02
In the past few years a significant improvement of VLBI analysis has been obtained by the use of numerical weather models (NWM) for the determination of elevation-dependent mapping functions for the troposphere delays. For the VLBI campaign CONT02, which covers 15 consecutive 24 hour sessions with eight stations in the second half of October 2002, the operational analysis pressure level data from the European Centre for Medium-Range Weather Forecasts (ECMWF) is used to provide the hydrostatic and wet mapping functions not only once per station and epoch but also every 30 degrees in azimuth. The determination is based on a 3D ray-trace program which uses the following properties of the NWM: 20 deg x 20 deg grids with 50 km increments around each of the eight stations, 21 levels (from 1000 hPa to 1 hPa) vertical resolution of the profiles and six hours time intervals. The application of these azimuth-dependent mapping functions in the VLBI analysis of CONT02 shows that the hydrostatic gradients are well determined with this approach, whereas the accuracy of the wet gradients from a NWM as described above still contains some deficiencies. The azimuth-dependent hydrostatic mapping functions are compared to the tilting of the 200 hPa pressure levels, and the residual wet gradients estimated in the VLBI analysis are compared to those derived from the NWM. It is also discussed whether standard gradient models with north and east gradients can properly account for asymmetries of the troposphere. Thus, the presentation describes what presently available numerical weather models can do in terms of asymmetric modeling of the troposphere delays. The results of the VLBI analysis provide a reliable estimation how big the effect will be for GPS.
G53A-0120 1340h
Estimating GPS Satellite Antenna Phase Center Variations Using Data from the Jason-1 and GRACE Missions
Reducing the uncertainty in locating the phase centers on both GPS transmitter and receiver antennas has emerged as an area of active research in the GPS geodetic community. We have used on-orbit data from the Jason-1 (2001-) and GRACE (2002-) missions to develop estimates of GPS satellite antenna phase-center variations (PCV). These missions offer a number of advantages for this exercise. The heights of the Jason-1 and GRACE satellites are well-determined at the 1-2 cm level, and there is no troposphere signal to confound interpretation of the measurements. The multipath environments are also favorable, particularly for the GRACE mission. We discuss several strategies for determining the GPS satellite PCV estimates from these data, and describe evaluations of the candidate solutions using independent data from terrestrial GPS stations. We also compare our GPS satellite PCV estimates with those determined independently from a terrestrial network. These estimates have potential benefits for wide-ranging geodetic applications.
G53A-0121 1340h
Choice of Basis Functions for the Representation of Seasonal Surface Loading Signals in Geodetic Time Series
We discuss the relative merits of different techniques and basis functions for (i) the forward modelling of geodetic monument displacements due to surface loading, and (ii) inverse modelling of surface load parameters given geodetic displacements. Forward modelling is frequently performed using gridded datasets and a Green's function approach, but in this method it is difficult to account properly for the effects of geocenter motion on the reference frame. In forward modelling, spherical harmonic representation does not suffer from this drawback, but fine-scale (higher-degree) inversion is unstable due to the continent-rich, ocean-poor distribution of geodetic displacement data. A further problem, which affects both of these methods but is readily correctable using the spherical harmonic approach, is the appropriate treatment of mass conservation and of the oceanic equilibrium-tide response to the total gravitational field. We show how a modified set of basis functions derived from mass-conserving, tidally-equilibrated, area-masked spherical harmonics can be used in the inverse procedure. Although this approach is more stable at higher degrees, the basis functions are no longer orthonormal, even for a global dataset. We compare our method with other local representations such as spherical wavelets.
G53A-0122 1340h
Can Continental and Ocean Water Mass Variability from Satellite Gravimetery be Used to Correct for the Loading Signal in Geodetic Time Series?
Model estimates of the annual variations in continental water storage are of sufficient magnitude to induce peak-to-peak changes in the vertical position of geodetic stations of up to 3 cm seasonally. Signals of this magnitude need to be removed from the geodetic data if the geodetic trend is to be interpreted in terms of geodynamic processes. Unfortunately, considerable errors are probably present in the model-derived water storage estimates due to errors in the model forcing, parameters and model formulation. If these models are used to correct the geodetic data, it is likely that the continental water storage signal is being improperly removed from the geodetic data sets. A number of satellite gravity missions have been recently launched, or will come online in the near future, that will measure changes in Earth's surface hydrology with unprecedented accuracy. Gravity missions such as CHAMP, GRACE and GOCE, and other satellite missions have the potential to significantly improve our understanding of many hydrologic processes, as well as improving our ability to monitor and predict the partitioning of continental water mass into snow, precipitation, soil moisture and ground water. In this paper, we investigate the possibility that estimates of water storage variations derived from satellite gravity missions can be used to correct geodetic data for the long wavelength component of the water storage signal.
G53A-0123 1340h
GPSTk: An Open Source Toolkit for Working With GPS Data
Applied Research Laboratories, The University of Texas at Austin (ARL:UT) has established an open source software project called the GPS Toolkit, or GPSTk. In this poster we present an overview of the GPSTk focusing on structure, functionality, licensing, and applications of interest to the geodetic community. The GPSTk distribution is currently available for download on SourceForge. The GPSTk software distribution consists of source code for a core library, a test suite and a collection of applications. The GPSTk code has an object-oriented design and is written in ANSI C++. We intend the GPSTk to be platform independent; and it has been installed and tested successfully under Linux, Solaris and Windows. The code is released under the terms of the Lesser GNU Public License (LGPL). The functionality supported by the GPSTk, includes reading and writing observations to standard formats including RINEX, algorithms defined in the GPS signal-in-space interface control document (ICD-GPS-200), navigation solutions such as receiver-autonomous integrity monitoring (RAIM), atmospheric delay models, and P-code generation. We will provide a variety of examples of applications developed from the GPSTk, including a QA tool for GPS data, and generation of ionospheric total electron (TEC) values and vertical TEC maps from dual frequency GPS measurements. We will also discuss extensions under development, including applications to relative positioning, and will outline intended future development directions.
http://www.gpstk.org
G53A-0124 1340h
International GPS Service - 10 Years History, New Directions for GNSS and Space Geodesy
The IGS celebrates ten years of successful service this year as an official orrganization of the International Association of Geodesy. This talk will feature the recent and long-term advances in the IGS most relevant to supporting the Earth and Geophysical sciences. The results of a recent workshop and symposium celebrating the ten year anniversary of the IGS will be summarized. These will focus on the new recommendations which provide the framework for continued improvements necessary to meet the demanding requirements of science and applications. IGS plans for integrating the new European Galileo GNSS will be discussed.
http://igscb.jpl.nasa.gov/