Analysis Center Workshop 2008

Improvements in the analysis strategies and modeling of the IGS Analysis Centers are an ongoing process. This session will concentrate on pending and proposed updates in models for tropospheric delays, higher-order ionospheric corrections, and GNSS orbital dynamics. The current procedures of the ACs will be compared with each other and with recent and future likely updates, including those from the IERS Conventions.

Presentations:

• P. Steigenberger, J. Böhm, V. Tesmer — Comparison of GMF/GPT with VMF1/ECMWF & implications for atmosphere loading
• M. Hernandez-Pajares, M. Fritsche, M.M. Hoque, N. Jakowski, J.M. Juan, S. Kedar, A. Krankowski, E. Petrie, J. Sanz — Methods & other considerations to correct for higher-order ionospheric delays in GNSS
• M. Ziebart, A. Sibthorpe, C. Flohrer, T. Springer, Y. Bar-Sever, B. Haines — Refinements in GNSS orbit modeling
• S. Loyer, F. Perosanz, H. Capdeville (abstract) — CNES-CLS dynamical modelling of GPS orbits & SLR residuals
• J. Ray, J. Griffiths — Overview of IGS products & Analysis Center modeling
• discussion of recommendations

Posters:

• F. Mercier, D. Laurichesse (abstract) — Zero difference integer ambiguities, integer phase clocks

Background materials:

• IERS Conventions Center updates
• Presentations at IERS Conventions Workshop 2007
• IERS Conventions Workshop 2007 -- Position Paper on Principles for Conventional Contributions to Modeled Station Displacements
• Summary of IERS Conventions Workshop 2007
• A survey of some systematic errors in IGS products, by J. Ray (EGU 2008)

This session includes a summary of the activities of the IGS Working Groups and wil focus on current status, pending, and future developments of the core IGS products, e.g., ionosphere, troposphere, satellite orbits, clocks, ERPs, etc.

Presentations:

• A. Krankowski, M. Hernandez-Pajares — Status of the IGS ionosphere products & future developments
• K. Senior — New IGS timescale & new UT1/LOD series
• Y. Bar-Sever, S. Byun — The new IGS tropospheric delay production
• R. Ferland, M. Piraszewski — Reference Frame Working Group report
• discussion of recommendations

GNSS observations are sensitive to a wide-range of natural and man-made phenomena, including ionospheric disturbances, tropospheric fluctuations, tidal displacements, surface mass loading, and earthquake deformations. This sensitivity not only allows GNSS observations to be used to investigate these phenomena, but it also creates a market for the development of improved models of these phenomena when they are needed to reduce and/or interpret GNSS observations. This session will be a forum for discussing sources of systematic errors that limit the accuracy of GNSS models and products, including but not limited to errors in tropospheric models, tide models, surface mass loading models, and multipath signal models.

Presentations:

• C. Flohrer, G. Beutler, R. Dach, W. Gurtner, U. Hugentobler, S. Schaer, T. Springer — Validation of GNSS satellite orbits
• P. Barrett — The relative contribution of the annual & draconitic periods in GPS station position spectra
• A.W. Moore, S.L. Granger, S.E. Owen, F.H. Webb, E.J. Fetzer, E.J. Fielding, E.F. Fishbein, C.F. Bjorndahl, J. Lofgren — Toward correcting InSAR images for tropospheric delay
• K. Larson, A. Bilich, V. Zavorotny, J. Braun, E. Small — Making good from bad: Can we use GPS multipath to measure soil moisture content?
• summary of posters
• discussion of recommendations

Posters:

• J. Dousa — GOP AC's development for the Ultra-rapid orbit product
• J. Dousa — GOP near-real time processing background
• T.A. Springer, F. Dilssner, E. Schoenemann, M. Otten, I. Romero, J. Tegedor, F. Pereira, J. Dow — ESOC new developments & innovations
• C. Hackman, P. Barrett, V. Slabinski, J. Tracey, W. Wooden — Progress at the United States Naval Observatory Analysis Center
• J.C. Tracey, P.C. Kammeyer, N.G. Stamatakos — Usage of the UT1-like quantity UTGPS at the United States Naval Observatory
• S. Schaer, R. Dach, M. Meindl, H. Bock, C. Flohrer, A. Jäggi, S. Lutz, L. Ostini, L. Prange, A. Steinbach, D. Thaller, P. Walser, G. Beutler — Activities at CODE Analysis Center
• H. Bock, R. Dach, S. Schaer, M. Meindl, G. Beutler — CODE's new high-rate GPS clock product
• S. Desai, W. Bertiger, B. Haines, D. Kuang, M. Miller, C. Lane, F. Webb, J. Weiss — Recent developments & plans at the JPL Analysis Center
• S. Owen, D. Dong, F. Webb, B. Newport, S. Kedar, A. Moore, Z. Liu — Improvements in analysis of large GPS networks at JPL
• R. Gross — An improved empirical model for the effect of long-period ccean tides on polar motion
• R.F. Leandro, R.B. Langley, M.C. Santos — GNSS data analysis in GAPS, the GPS Analysis and Positioning Software, using IGS products
• F. Perosanz, R. Biancale, J.-C. Marty, S. Melachroinos, S. Loyer — Surface load models and validation by GPS positioning
• R. Dach, T. Springer, Z. Altamimi — Experiment on impact of constrained orbit parameters on station coordinates

During the IGS history several TRFs were applied and the ACs have implemented many changes for software and technology improvements; all led to various inconsistencies in the IGS products. A major change was the introduction of the absolute antenna models, which entered only with some approximation into the recent IRTF2005. The IGS has to overcome these inconsistencies in their time series with a reprocessing of its historical data since 1994 using the latest models and the latest AC's software implementations. The improved homogeneous products will allow better geophysical interpretations and will result in a significantly better contribution to the next realization of the ITRF. The reanalysis will also include more stations to better address the requirements of the user community.

The session will concentrate on all activities related to the IGS reprocessing. Evaluations of the reprocessing test campaign, which shall identify problems in an early stage, and first results from the IGS reprocessing, available up to this IGS Workshop, are welcome. Also welcome are experiences from any reprocessing activities outside the IGS, which can give valuable feedback to the IGS reprocessing project.

Presentations:

• P. Steigenberger, G. Gendt, R. Ferland, I. Romero — Current status of the IGS reprocessing
• I. Romero — Examination of reprocessing network coverage
• R. Ferland — Report of the Analysis Centers reprocessed SINEX solutions
• G. Gendt, Th. Nischan — Combination of reprocessed orbit, clock and ERP products
• discussion of recommendations

Presentations:

• M. Fritsche, R. Dietrich, A. Rülke, P. Steigenberger, M. Rothacher — Reprocessing of a global GPS network: Experiences & results
• T.A. Springer, F. Dilssner, E. Schoenemann, I. Romero, J. Tegedor, F. Pereira, J. Dow — ESOC IGS reprocessing
• A. Kenyeres, J. Legrand, C. Bruyninx, M. Figurski, H. Habrich — Regional re-analysis: Expectations & experiences within the EPN
• G. Wöppelmann, T. Schöne — Reprocessing GPS data at the observation level for tide gauge monitoring: Main raison d'être of TIGA
• discussion of recommendations

Posters:

• P. Steigenberger, M. Rothacher, M. Fritsche, A. Rülke, R. Dietrich — PDR GPS satellite orbits
• I. Thomas, M. King, P. Clarke — Water vapour estimates over Antarctica from 12 years of globally reprocessed GPS solutions
• J.R. Rohde, M. Cline, W.H. Dillinger, R.L. Dulaney, J. Griffiths, S. Hilla, W.G. Kass, J. Ray, G.F. Sella, R. Snay, T. Soler, N.D. Weston — The GPS data reanalysis campaign at the National Geodetic Survey
• T.A. Springer, F. Dilssner, E. Schoenemann, I. Romero, J. Tegedor, F. Pereira, J. Dow — ESOC IGS reprocessing (details)

The first half of the session will catalog the various biases that affect IGS products and goals, including inter-frequency biases, phase biases, and inter-system biases. The current status of IGS efforts to address these biases will be described. Recommendations will be made for modernizing the conventions used in bias calibration and for the direction of future efforts.

The second half of the session will concentrate on desirable features of future GNSS receivers for the IGS and for other high-precision geodetic applications. The relative performance of several example observables subsets will be analyzed to illustrate how the IGS can benefit from modern GNSS signals. A hypothetical "dream receiver" will be introduced along with practical alternatives for the near-term, including commercial receivers and open-architecture software-defined receivers. A dual-frequency software receiver will be demonstrated.

Presentations:

• Y. Gao — GNSS biases, their effect and calibration
• G. Petit (presented by Y. Gao) — Calibration of geodetic (dual frequency) GPS receivers: Implications for TAI and the IGS
• S. Schaer — Differential code biases (DCB) in GNSS analysis
• L. Young — What makes a GNSS signal great?
• Th. Pany — Survey of the "ipexSR" software receiver
• T. Humphreys, L. Young, Th. Pany — IGS receiver considerations
• position paper by T. Humphreys, L. Young, Th. Pany: Considerations for future IGS receivers (version updated 17 July 2008)
• discussion of recommendations

Posters:

• Th. Pany — Status of software receiver technology at University FAF Munich and IFEN GmbH
• H. Habrich, P. Neumaier — GLONASS single-difference phase biases

Since 5 November 2006, IGS products are based on an absolute model for the phase centers of both the transmitting and receiving GNSS antennas. This model comprises phase center estimates from global terrestrial data for the satellite antennas, and robot-based calibrations as well as converted field calibrations for the receiver antennas. Due to the adoption of the ITRF2000 scale in the determination of satellite antenna corrections, the transition from the relative to the absolute IGS model led to an improvement of the consistency between the IGS and the ITRF scale. Moreover, the consistency amongst the ACs could be improved.

However, there are still a lot of open issues. Ground-based and space-based satellite antenna models agree well on the nadir- and azimuth-dependent phase center variations (PCVs), but the z-offsets show a considerable bias. The latest robot-based calibration of a Block IIA antenna may help to clear up that problem. A combination of ground- and space-based satellite antenna corrections could allow to consider azimuth-dependent PCVs and to provide nadir-dependent PCVs beyond 14 degrees that are particularly important with regard to LEO missions.

As regards the receiver antennas, several institutions initiated additional robot-based calibrations as well as anechoic chamber measurements: on the one hand in order to replace converted field calibrations, on the other hand to provide correction values for uncalibrated antenna/radome combinations. However, the question of how to add additional correction values to the IGS model without getting consistency problems is not yet answered. In addition, there is an increasing demand for calibrations using the GLONASS or the (future) Galileo frequencies. Mitigation and empirical calibration of multipath are additional topics of high relevance for the antenna session.

Presentations:

• N. Weston, S. Hilla — Impact of the antenna model change on IGS products
• G. Wübbena, M. Schmitz — GPS Block II/IIA antenna calibration with the Geo++ robot
• R. Schmid, P. Steigenberger — First activities of the IGS Antenna Working Group: Comparison of ground- and space-based satellite antenna maps
• B. Haines, Y. Bar-Sever, W. Bertiger, S. Desai, A. Sibois, F. Webb, L. Young — Space-based satellite antenna maps; Impact of different satellite antenna maps on LEO & terrestrial results
• discussion of recommendations (updated)

Posters:

• G. Wübbena, M. Schmitz, M. Propp — Antenna group delay calibration with the Geo++ robot
• G. Wübbena, M. Schmitz, M. Propp — Sensibility of Dorne Margolin chokering antennas to rainfall: Analysis of a sprinkled antenna site on a short baseline
• G. Hedling, L. Jivall, M. Lidberg, B. Jonsson — Impact of the antenna Rooftop antenna calibration field of the National Land Survey of Sweden

• agenda

An opportunity for the members of the IGS Analysis Centers to dine out together at The Playwright Irish Pub & Restaurant, 1265 Washington Ave., for informal discussions.

This session will focus on identifying current and future users and their requirements for the RT/NRT and other IGS products, assessing the status of current products to meet the requirements, and proposing future improvements. Main topics could include, but are not limit to, the emerging needs of users for tsunami warning, earthquake monitoring, operational numeric weather prediction (NWP) and weather research in general, E-GVAP perspectives, climate applications, space weather, time transfer, and LEO satellite tracking.

Presentations:

• T. Song, G. Blewitt (abstract) — GPS requirements for tsunami detection
  • tsunami warning announcement (MP3)
  • 26 Dec. 2004 tsunami animation (AVI)
• J. Dousa — Case study for the IGS ultra-rapid orbit requirements
• G. Dick, J. Dousa — E-GVAP: EUMETNET GPS water vapor programme
• J. Wang — Climate applications of a global, 2-hourly atmospheric precipitable water dataset derived from IGS tropospheric products
• F. Pang — Survey of requirements of realtime/near realtime applications in terms of current & potential IGS Ultra-rapid products
• discussion of recommendations

Posters:

• F. Vespe, R. Pacione, B. Pace — Accuracy of regional near-real time GPS ZTD & site coordinate estimates versus IGS Ultra-Rapid products
• B. Miyahara (abstract) — Results of GEONET real-time analysis
• J. Dousa — Case study for the IGS ultra-rapid orbit requirements

This session will discuss how current and possible future RT/NRT products are (or may be) used, and what changes or improvements are required to optimize these products. Presentations will focus on NRT applications which could be based on upgraded orbit and clock products as well as on atmospheric (ionospheric and tropospheric) models with medium to low spatial and temporal resolution.

Presentations:

• R. Weber, M. Opitz, G. Thaler — Real-time quality control for IGS clocks & orbits
• S.I. Gutman — Need for IGS real-time/near real-time tropospheric products
• T. Fuller Rowell, M. Codrescu, E. Araujo-Pradere — Need for an IGS real-time/near real-time ionospheric product
• Y. Mireault, P. Tétreault, F. Lahaye, P. Collins, M. Caissy — Real-time & near real-time GPS products & services from Canada
• P. Wielgosz, A. Krankowski — Real-time kinematic GPS positioning supported by predicted ionosphere model
• discussion of recommendations

Posters:

• A. Karabatic, R. Weber, S. Leroch, T. Haiden — Near real-time zenith wet delay estimation
• S. Gleason — Real-time applications of long-term GPS orbit predictions
• O.L. Colombo — Precise real-time differential navigation using NTRIP streams from continuously operating, wide-area GNSS networksM
• A. Komjathy, B. Wilson, V. Akopian, X. Pi, M. Dumett, A.J. Mannucci, C. Wang — JPL/USC GAIM: New developments in using COSMIC & ground-based GPS data to estimate high precision ionospheric products including VTEC

This session will focus on data quality and latency of the IGS network data, their influence on the IGS products, and will investigate possible means for improvement. Example topics are:

• stability of the IGS network, quality of the IGS reference frame sites and what can be learned from the ITRF2005 and IGS coordinate residuals;
• methods of detecting coordinate discontinuities, relation to the IGS standards, and dissemination to the IGS users;
• relation between the completeness and latency of IGS data files relative to IGS Rapid and Ultra-rapid products;
• methods of assessing and disseminating quality of IGS stations, e.g. coordinate discontinuities, knowledge of effects such as snow/ice on the antenna, failed sites and antennas;
• relationship between regional networks and the IGS.

Presentations:

• T. Herring (abstract) — Detection of GPS station position errors due to instrumental and environmental effects
• Z. Altamimi — ITRF2005 residuals and co-location tie issues
• I. Romero, T. Springer, P. Alfaro, J. Tegedor, F. Dilssner, F. Pereira, M. Lorenzo, J. Feltens, J. Dow (abstract) — The IGS network and ESA processing
• M. Moore (abstract) — IGS, Regional and local networks
• C. Bruyninx, J. Legrand, F. Roosbeek (abstract) — GNSS network management procedures: Application to the EPN
• discussion of recommendations

Posters:

• J.Tegedor, P. Alfaro, I. Romero, C. Garcia Martinez, F. Dilssner, J. Dow (abstract) — ESOC GNSS stations: Current status & monitoring capability
• W. Söhne, S. Leinen, E. Lewi (abstract) — The IGS station Addis Ababa and its role for geodesy and geodynamics

This session will focus on key activities that are on-going within the context of the IGS Real-time Pilot Project and the work of the Real-time Working Group. Several key activities will be highlighted including:

• the management of the network including station level management;
• the distribution of the data;
• the production and the distribution of real-time products;
• the investigation of formats for the delivery of data and products.

Presentations:

• M. Caissy — Real-time Pilot Project: Overview & status
• G. Weber — Real-time IGS network management & data exchange interfaces
• L. Agrotis — IGS Real-Time Pilot Project: Analysis Centre activities
• A. Hauschild — Real-time clock estimation for precise orbit determination of LEO-satellites
• J. Chen, M. Ge, M. Vennebusch, Z. Deng, G. Gendt, M. Rothacher — Progress of the real-time GNSS software development at GFZ
• Shi C., Lou Y.D., Zhao Q.L., Liu J.N. — Real-time orbit & clock estimation using PANDA software
• discussion of recommendations

Posters:

• J. Dousa — Efficient dissemination of the orbit predictions in real-time
• L. Agrotis, J. Dow, C. Garcia-Martinez, A. Ballereau, P. Alfaro — Real time GNSS processing at ESOC: Infrastructure & initial results
• M. Vennebusch, M. Ramatschi, J. Chen, C. Falck. M. Ge, Th. Nischan, M. Rothacher — Realtime GNSS activities at GeoForschungsZentrum Potsdam
• J.F. Galeral Monico — Experiences operating a real-time network
• G. Weber, L. Mervart — The BKG Ntrip Client (BNC)
• G. Weber, C. Bruyninx — Monitoring the real-time IGS NTRIP interfaces

The characterization, and reduction, of sources of site-dependent GNSS error is vital to producing measurements that can reliably be used for geophysical interpretation. This session will focus on new developments concerning our understanding of these errors, with a view to providing recommendations for their limitation at future site installations. Particularly, we concentrate on studies into the quantification and mitigation of monument motion, multipath (far-field, near-field, and internal) and effects (both physical and electrical) of local environment factors such as temperature, snow cover, vegetation, and rainfall. We also elicit papers that discuss the impact of certain equipment choices, such as deep- versus shallow-braced monuments, the use of radomes (and their calibration), and antenna mount design.

Presentations:

• C. Meertens, M. Jackson, A. Borsa, S. Fisher, D. Maggert — Statistical analysis of site effects on Plate Boundary Observatory time series
• J. Johansson, T. Ning, C. Granström, P. Jarlemark, M. Lidberg, G. Hedling — Site-dependent electromagnetic effects in high-accuracy applications of GNSS
• E. Hill, J. Davis, P. Elosegui, B. Wernicke, E. Malikowski, N. Niemi — Are thermal effects responsible for micron-level motions recorded at deep- and shallow-braced monuments in a short-baseline network at Yucca Mountain, Nevada?
• S. Williams, M. King, J. Langbein — The stochastic characterization of noise & signals in GNSS coordinate time series: What do we know after 10 years of study?
• discussion of recommendations

Posters:

• M. King, S. Williams — Apparent stability of GPS monumentation from long-running short baselines
• I. Romero, A. Rodriguez-Santana, V. Mendes, J.A. Montiel-Nelson, P. Abad-Real, M. Martin-Betancor (abstract) — GPS observations & analysis from Macaronesia & western Africa: The Canary GNSS Center (CGC), an effort to promote space-geodetic data & techniques

This session will discuss recent data center developments and proposals for handling equalization and validation of the Global Data Center data and product holdings. Also covered will be data center support of the IGS Real-Time Pilot Project as well as the re-analysis campaign and integration of these products in the archives. Other possible topics include utilities developed for data discovery.

Presentations:

• C. Noll — IGS Data Center operations & issues: Overview
• W. Söhne, H. Habrich, G. Weber — Data centre support for the IGS-RT PP
• P. Jamason, Y. Bock, F. Webb, S. Kedar, M. Pierce, R.-J. Chang, D. Dong, P. Fang, R. Granat, I. MacLeod, J. Parker, L. Prawirodirdjo, M. Squibb, G. Wadsworth — GPS Explorer: Overview & extension to INDIGO
• summary of posters
  • H. Habrich, J. Kuscherka, E. Wiesensarter — New features of the GNSS data center
  • B. Garayt — IGN Global Data Center
  • C. Noll, M. Dube — NASA's Crustal Dynamics Data Information System (CDDIS) and its support of the IGS, ILRS, IVS, and IDS
  • G. Sella, R. Snay, M. Cline, D. Haw — CORS network evolution & future developments
• discussion of recommendations

Posters:

• F. Vespe, G. Colucci — GeoDAF: ASI (Italian Space Agency) local data center
• S. Schaer, S. Lutz, M. Meindl, H. Bock, R. Dach — Availability & completeness of IGS tracking data
• H. Habrich, J. Kuscherka, E. Wiesensarter — New features of the GNSS data center
• B. Garayt, E. Fourestier, P. Rebischung — IGN activities as IGS Data Center & GNSS data analysis center
• C. Noll, M. Dube — NASA's Crustal Dynamics Data Information System (CDDIS) and its support of the IGS, ILRS, IVS, and IDS
• G. Sella, R. Snay, M. Cline, D. Haw — CORS network evolution & future developments

This session will cover:

• IGS combination products and their possible future form
• Impact of other GNSS (GLONASS, Galileo) on the existing products
• The integration of IGS products into inter-technique combination products
• Other techniques' products and their characteristics (strengths, weaknesses, issues)
• New IGS products

Presentations:

• D. Angermann, H. Drewes, M. Kruegel, B. Meisel — GPS in the ITRF combination
• R. Dach, S. Schaer, M. Meindl, H. Bock, A. Jäggi, S. Lutz, L. Ostini, L. Prange, A. Steinbach, D. Thaller, P. Walser, G. Beutler— Aspects of global multi-GNSS processing
• Z. Altamimi, X. Collilieux — IGS contribution to ITRF
• D. Lavallee, R. Ferland, D. Thaller, T. Herring, R. Biancale — Future IGS & inter-technique SINEX combinations: Issues & challenges
  • SINEX Extension proposal 2
  • Unfied Analysis Workshop 2007 action items
• discussion of recommendations

Regarding upcoming new GNSS and the improved GLONASS constellation we will discuss aspects of the combination of corresponding observation data with GPS. We would like to review the user needs concerning combined products from the International GNSS Service, specifically with respect to GLONASS (as it is nowadays common to use GPS/GLONASS receiver models for surveying purposes). The next steps for the IGS and the analysis groups towards IGS-combined GNSS products should be defined. Issues related to the European Galileo, or the Chinese Compass may also be addressed.

Contributions dealing with the combination of multiple GNSS are welcome. This includes the full spectrum: from simulation studies on the benefit for IGS products, up to current analysis limitations or problems. In this context global as well as regional aspects will be discussed.

In the second part, we want to focus on regional GNSS applications based on multi-GNSS as well as GPS-only data processing. We ask for papers that investigate the mitigation of true signals or introduction of biases in regional networks with respect to global solutions. On the other hand, contributions on methodologies for efficiently mapping regional networks to the global network are also welcome.

Presentations:

• T. Herring & the SNARF Working Group — SNARF 2.0: A regional reference frame for North America based on IGS products
• T. Herring — RNAAC combinations in the IGS
• T. Springer, F. Dilssner, E. Schoenemann, I. Romero, J.Tegedor, F. Pereira, J. Dow — ESOC combined GNSS processing
• F. Amarillo-Fernandez, M. Crisci, A. Ballereau, J. Dow, M. Hollreiser, J. Hahn, J-L. Gerner — The Galileo ground mission segment performances
• Multi-GNSS processing position paper
• discussion of recommendations

Posters:

• G. Wöppelmann, M.-N. Bouin, Z. Altamimi, C. Letetrel, A. Santamaria, X. Collilieux, G. Valladeau, F. Lefèvre — Vertical velocities at tide gauges from a completely reprocessed global GPS network of stations: How well do they work?
• C. Bruyninx, Z. Altamimi, M. Becker, M. Craymer, L. Crombrinck, A. Crombrinck, R. Fernandes, R. Govind, A. Kenyeres, B. King, C. Kreemer, D. Lavallée, J. Legrand, L. Sanchez, G. Sella — IAG Working Group "Regional Dense Velocity Fields": Objectives & future plans
• J. Legrand, C. Bruyninx — Reference frame definition in a regional GNSS network: Global or regional?
• R.M.S. Fernandes, H. Farah, A.Z.A. Combrink, L. Combrinck — Testing processing methodologies for the computation of AFREF solutions
• G. Gendt, W. Soehne, M. Rothacher, the GGSP Prototype Team — The Galileo Terrestrial Reference Frame & its connection to the IGS
• M. Meindl, R. Dach, S. Schaer, U. Hugentobler — Developing a generic multi-GNSS software package

The IGS is using many, many different formats. The maintenance and in particular the evolution of these formats is a very important but also a very difficult task. The constant evolution of the IGS and its products, the move towards real-time, and the future evolution of the different GNSS constellations (e.g. the advent of Galileo, the introduction of a third frequency, etc., etc.) do require changes in several of the formats. A complicating issue in maintaining the formats is that many formats have been adopted outside the IGS and even outside the GNSS world. This makes changing the formats a difficult process. Also the fact that format changes require software updates to be able to handle (read and/or write) the new format is a very important factor, especially economically. This has caused the IGS to prolong support for older formats, just to give users an extended grace period to change over to a newer format.

Current points of discussion within the IGS are changes in the SP3c format. Also there are some ongoing discussions about the RINEX3 format. Needed are also enhancements in formats for handling the biases between different observations like P1 and C1 since in the (near?) future there will be three frequencies and on several of these frequencies different observation types (e.g. Galileo with E5a, E5b, and E5a+b). Here the IGS also should take a leading role in specifying which observations should be delivered as a "minimum" by IGS receivers. With triple frequencies there will be different ionosphere-free linear combinations. Depending on which one is used, the estimated clock might be significantly different. How can the IGS "unify" these clock estimates?

Formats currently used by the IGS are:

• RINEX
• SP3c
• SINEX
• Clock-Rinex
• IGS ERP-file
• Antex
• IONEX
• Tropo Sinex
• IGS site logs
• rcvr_ant.tab (official IGS antenna, receiver, & radome names)
• antenna.gra (is this file still needed for IGS site logs?)

• S. Hilla — Initial ideas & suggestions for a new IGS orbit format
• P. Jamason — XML & geodesy: A SOPAC perspective
• W. Gurtner (presented by S. Schaer) — The RINEX format: Current status, future developments
• M. Caissy — Real-time format issues
  • comparison of stream formats
• discussion of recommendations