International GNSS Service

Analysis Center Workshop 2008

2-6 June 2008, Miami Beach, Florida, USA



Summary of Recommendations

1 June 2008

12:00 - 18:00 IGS Governing Board meeting (invitation only) — Fisher Room
  chair: J. Dow

18:00 - 20:00Informal Gathering (cash bar) — Di Lido patio

2 June 2008

08:00 - 08:40 Registration
08:40 - 09:00 Welcome remarks
  G. Mader — Convenor & Chief, Geosciences Research Division, NGS/NOS/NOAA
D. Zilkoski — Director, National Geodetic Survey, NOS/NOAA
09:00 - 09:45 Keynote address
  Hon. Jeff Kottkamp — Lt. Governor of Florida
09:45 - 10:00 The International GNSS Service, June 2008: Perspectives & Key Issues
  J. Dow — Chair, IGS Governing Board
10:00 - 10:30coffee break
10:30 - 12:00Pending & proposed model changes
  chairs: J. Ray, J. Böhm (not attending), M. Hernandez-Pajares, M. Ziebart

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.



Background materials:

12:00 - 13:30complimentary buffet lunch
  poster viewing
13:30 - 15:30Pending & proposed product changes
  chairs: Y. Bar-Sever, A. Krankowski, K. Senior, R. Weber

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.


15:30 - 16:00coffee break
16:00 - 17:30Other analysis center developments & studies of general interest
  chairs: R. Gross, S. Desai, U. Hugentobler, B. King

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.



17:30 - 18:00Poster viewing

18:00 - 20:00Welcome Reception hosted by NGS — Di Lido South patio

3 June 2008

08:30 - 10:00Reanalysis campaign — Status of test periods
  chairs: G. Gendt, R. Ferland, I. Romero, P. Steigenberger

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.


10:00 - 10:30coffee break
10:30 - 12:00Reanalysis campaign — Next steps & consequences
  chairs: G. Gendt, R. Ferland, I. Romero, P. Steigenberger



12:00 - 13:30complimentary buffet lunch
  poster viewing
12:20 - 13:20Real-time Pilot Project committee meeting (members only) — Fisher Room
  chair: M. Caissy

13:30 - 15:30Progress in receiver calibrations & future developments
  chairs: Y. Gao, G. Petit (not attending), T. Humphreys, L. Young, Th. Pany

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.



15:30 - 16:00coffee break
16:00 - 17:30Progress in antenna calibrations
  chairs: R. Schmid, G. Wübbena (not attending), G. Mader, B. Haines

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.



17:30 - 18:30Poster viewing

17:40 - 18:30Analysis Center splinter meeting (AC members only) — Fisher Room
  chair: J. Ray

19:00 - Analysis Center group dinner (AC members only)
  chair: J. Ray

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.

4 June 2008

08:30 - 10:00Real-time & near-real-time user requirements
  chairs: G. Dick, J. Wang, G. Blewitt, P. Fang

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.



10:00 - 10:30coffee break
10:30 - 12:00Real-time & near-real-time IGS products
  chairs: R. Weber, S. Gutman, T. Fuller-Rowell, Y. Mireault (not attending)

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.



12:00 - 13:30complimentary buffet lunch
  poster viewing
13:30 - 15:30IGS network issues & challenges
  chairs: B. Twilley (not attending), C. Bruyninx, Z. Altamimi, T. Herring

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.



15:30 - 16:00coffee break
16:00 - 17:30Status of real-time & Pilot Project operations
  chairs: M. Caissy, G. Weber, M. Ge (not attending), C. Garcia-Martinez

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.



17:40 - 18:00GO Forum demonstration
  G. Walia, R. Neilan

18:00 - 18:30Poster viewing

5 June 2008

08:30 - 10:00Improvements in station installations
  chairs: P. Elosegui, E. Hill, S. Williams, C. Meertens

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.



10:00 - 10:30coffee break
10:30 - 12:00Data center operations & issues
  chairs: C. Noll, H. Habrich, S. Cho, P. Jamason

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.



12:00 - 13:30complimentary buffet lunch
  poster viewing
13:30 - 15:30Future IGS & inter-technique SINEX combinations: Issues & challenges
  chairs: D. Lavallée, R. Ferland, D. Thaller, T. Herring

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
The evolution of IGS products into their current form has been driven by the need for robust, reliable and precise products. This session will investigate issues for the IGS combination products with a strong focus on the form of future IGS combination products and how they can integrate into inter-technique products.

Subject areas of concern in current products/combination input and ideas for future:

  • Need for clear IGS procedures/conventions
  • Direct and indirect constraint issues
  • Products consistency
  • New IERS proposed parameterisations
  • Discontinuities
  • Local surveys
  • SINEX format issues (probably best addressed in File Formats Session)


15:30 - 16:00coffee break
16:00 - 17:30Multi-GNSS & regional combined IGS products
  chairs: R. Dach, F. Perosanz, M. Craymer, G. Wöppelmann, C. Bruyninx

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.



17:30 - 18:30Poster viewing

17:40 - 18:30Data Center splinter meeting (invitation only) — Fisher Room
  chair: C. Noll

6 June 2008

07:30 - 08:30complimentary continental breakfast
08:30 - 10:00Product file formats & related issues
  chairs: T. Springer, Th. Nischan, L. Estey, S. Hilla, W. Gurtner (not attending)

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:

  • SP3c
  • Clock-Rinex
  • IGS ERP-file
  • Antex
  • 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?)
In addition, there are various AC and combination summary reports, which generally do not have rigid formats.

The focus of this session is threefold:

  1. Where are format changes needed?
  2. How can future formats be set up to be more extensible? (like SINEX or XML?)
  3. Does the IGS need a more formal process to handle format changes, other than just group email? Should the IGS do more to bring in the opinions of the world community when deriving new IGS formats? Are there instances where the IGS could hand off the responsibility of creating some new formats to some other international body or national agency?

10:00 - 10:30coffee break
10:30 - 12:00Closing discussions & recommendations
  chairs: G. Mader, J. Ray, G. Gendt

13:30 - 14:30 IGS Governing Board summary meeting (invitation only) — Fisher Room
  chair: J. Dow

Send comments to Jim Ray (updated 31 July 2008)