| Date: | 2009-01-13 00:28:00 | |
| Sender: | Via IGS Central Bureau <Carey Noll <Carey.E.Noll@nasa.gov>> | |
| Subject: | [SLR-Mail] No. 1744: IGS Reference Frame Coordinator - Call for Participation | |
| Author: | Via IGS Central Bureau | |
| Content: | ******************************************************************************** SLR Electronic Mail 2009-01-13 00:28:00 UTC Message No. 1744 ******************************************************************************** Author: Via IGS Central Bureau Subject: IGS Reference Frame Coordinator - Call for Participation *Apologies for multiple postings* INTERNATIONAL GNSS SERVICE CALL FOR PARTICIPATION January 9, 2009 IGS REFERENCE FRAME COORDINATOR 2010 -2013 Summary The IGS invites proposals for a new Reference Frame (RF) Coordinator, whose key responsibilities include forming the weekly SINEX combination of Analysis Center solutions for global station coordinates & velocities, Earth rotation, and apparent geocenter parameters. The new RF coordinator will replace Remi Ferland (Natural Resources Canada) by the end of 2009 with a prior transition and validation phase of no less than six months. This is a core task within the IGS. Expressions of interest are requested at the earliest opportunity, with a proposal due by 31 March 2009. It is expected that a final selection will be made by 1 May 2009 and a hand-over process begun by 1 June 2009. The charter for the reference frame working group can be found at: http://igs.org/projects/reference_frame/rfwg_charter.html (also attached). Background The IGS Reference Frame Coordinator, who also chairs the Reference Frame Working Group (RFWG), forms the official combination of Analysis Center (AC) solutions for station coordinate, Earth rotation, and other frame-related parameters. Weekly submissions of AC solutions in SINEX format, including full variance-covariance information, are combined using rigorous mathematical methods. The results of this step are subsequently used by the Analysis Center Coordinator (ACC) to form the IGS combined orbits and clock products in a way that maintains a high level of overall internal consistency. Since May 1999, Natural Resources Canada (NRCan) has supported Remi Ferland as IGS RF Coordinator, and since March 2000 (week 1050), the NRCan SINEX combination has provided the official frame products for the IGS [Ferland, 2000]. A new orbit alignment procedure was adopted at the same time to ensure consistency in the IGS Final products [Springer, 2000a,b]. The general methodology now used was discussed and agreed at the IGS Analysis Center Workshop held in Darmstadt in 1998 [Kouba et al., 1998]. After more than a decade, NRCan will terminate their sponsorship of this important activity at the end of 2009. In order to provide an orderly transition of responsibilities and modify inter-agency interfaces, it is expected that parallel operations and testing by the new RF Coordinator will begin by 1 June 2009. Full operational responsibility should be in place by 1 January 2010. The RF Coordination requires approximately one full-time person plus additional backup support to provide year-round coverage. Proposals where resources are leveraged with other closely related activities and experience will be considered. Weekly SINEX combinations are normally released by the RF Coordinator each Wednesday, 11 days after the end of each GPS week, followed the next day by the production of consistent IGS orbits and clocks by the ACC. Specific Tasks The tasks of the RF Coordinator are to: 1) Chair the IGS RFWG and direct its activities. Details are given at: http://igs.org/projects/reference_frame/index.html In this capacity, the RF Coordinator is also a voting member of the IGS Governing Board. 2) Lead the RFWG in specifying and selecting a globally distributed set of GNSS stations to realize an IGS reference frame, and ensure its accurate alignment to the International Terrestrial Reference Frame (ITRF). The coordinates and velocities of the IGS RF are determined from a long-term accumulation of IGS combined SINEX solutions. New RF realizations are issued at irregular intervals, usually synchronized to new ITRF releases. The continued reliability and consistency of individual RF stations must be continuously monitored and occasional updates announced to users. 3) Combine the weekly SINEX submissions from the IGS ACs into a unified global frame aligned to the current IGS RF. This involves checking and validating the input AC solutions, detection and removal of outliers, reweighting of input solution covariances, alignment of all input frames to the current IGS RF, rigorous combination of AC solutions with full covariance information, and the output and distribution of the combination products, consisting of weekly station coordinate frames and covariances, daily Earth rotation parameters, weekly geocenter offsets, and other frame-related parameters. This processing is normally done each Wednesday, 11 days after the end of each GPS week. Suitable electronic interfaces must be established with the ACC and IGS Data Centers to enable the subsequent orbit and clock combination to be performed in a consistent way. In addition, an accumulation of weekly frame solutions is updated weekly to form a continuously evolving secular GNSS RF with linear station velocities. A summary of the weekly combination statistics shall also be prepared. 4) Maintain the combination software, either that developed at NRCan (which may be exported to the new RF Coordinator under agreement), or an independent combination system, provided that it possesses similar functionality. The NRCan combination uses standard least-squares adjustment theory for the various component tasks [Ferland et al., 2000]: • variance factor estimation • removing constraints • addition of normals • rejection of outliers • addition of inner constraints. Comparable estimation schemes and algorithms are well documented in most geodesy textbooks on least-squares. In actual practice, most effort is needed to interpret and check results in a ”relatively automated” way to give reliable results, rather than on the mechanics of the combination process itself. 5) Detect station discontinuities. In order to accumulate the time series of weekly frames, it is necessary to detect and accommodate any discontinuities in the linear evolution of station positions, which are caused by changes of receiver equipment, tectonic events, or other causes, both known and unknown. Abnormal station behaviors should be reported via the agreed to procedures, to the IGS Central Bureau, station operators and data analysts. The set of coordinate and velocity discontinuities shall be continuously documented, updated, and published in SINEX format for general use. 6) Accumulate Earth Rotation Parameters (ERP) files. The weekly SINEX combinations also produce an update of the accumulated estimates of daily Earth rotation parameters, consisting of the coordinates of the pole of rotation, the rates of change of the polar coordinates, and the excess length of day. While other ERP files are also generated by the ACC from the various IGS orbit combination processes, the weekly Final ERPs from the RF Coordinator are the definitive IGS products. 7) Report the residuals of the coordinates, ERPs, and apparent geocenter estimates of the AC solutions with respect to the weekly combined solution, as well as the residuals of the AC solutions with respect to the reference frame realization and the cumulative solution. 8) Compute and report accumulated coordinates, residuals, and summary files. Time series of the coordinates and residuals files shall also be updated weekly and made available. Plots of those time series and residuals shall also be updated weekly and made available. Time series and plots from the summary files shall also be reported. 9) Provide the official IGS submissions to the ITRF. Based on the regular combined RF products, the IGS RF Coordinator will interact with the ITRF Product Center of the International Earth Rotation and Reference Systems Service (IERS) and provide the official submissions for the ITRF updates. 10) Provide satellite antenna offsets. Certain other frame-related parameters may be reported in AC SINEX solution files, such as the phase center offsets of the GNSS satellite antennas. From time to time, the RF Coordinator will assist the chair of the IGS Antenna Working Group in examining and updating estimates of the satellite offsets based on these parameter estimates. 11) Periodically reprocess and recombine new AC submissions. From time to time, the IGS expects to reprocess all GNSS observational data using the latest models and procedures to achieve the highest possible product accuracy and to maintain long-term consistency. The RF Coordinator should be prepared to contribute to such irregular campaigns by reprocessing and recombining new AC submissions similar to the regular weekly tasks. 12) Investigate improvements and assess performance of participating ACs. The RF Coordinator, in collaboration with the RFWG, IGS ACC, the IERS, and other scientists, will investigate improvements in the IGS products through refinements in analysis, modeling, and combination algorithms. As needed, feedback should be provided to existing ACs when significant changes occur and to new candidate ACs to assess their performance. 13) Provide, as needed to the users, information about the combined SINEX products. 14) Document and submit regular reports of results of each weekly SINEX combination to be distributed by the IGS. An example of the SINEX combination report for GPS week 1500 is given at: http://igscb.jpl.nasa.gov/mail/igsreport/2008/msg00942.html 15) Prepare other reports and scientific papers to document accomplishments and future developments. Responses Expressions of interest should be addressed to the IGS Central Bureau at anytime to igscb@igscb.jpl.nasa.gov Proposal responses to this CfP are due by March 31, 2009 and should contain at least the following information: • Names of key personnel, especially the proposed new RF Coordinator • Level of support to be provided • Software system to be used for tasks • Available starting date • Duration of commitment Schedule • 12 Jan 2009 Call for proposals released • Jan – March Expression of interest, email to igscb@igscb.jpl.nasa.gov • 31 Mar 2009 Due date for submission of proposal responses • 01 May 2009 Selection of new Reference Frame Coordinator • 01 Jun 2009 Beginning of test and validation phase • 01 Jan 2010 Full operational responsibility by new Coordinator Any questions on proposal preparation and submission, or clarifications on the above technical tasks, can be directed to: John Dow, Chair, IGS Governing Board John.Dow@esa.int, +49-6151-90-2272 Remi Ferland, IGS Reference Frame Coordinator Remi.Ferland@NRCan-RNCan.gc.ca,+1-613-995-3215 Ruth Neilan, Director, IGS Central Bureau Ruth.E.Neilan@jpl.nasa.gov, +1-818-354-8330 References R. Ferland (2000) SINEX Products Status Changes, IGS Mail 2740, 10 Mar 2000, http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00080.html R. Ferland, J. Kouba, D. Hutchison (2000) Analysis methodology and recent results of the IGS network combination, Earth Planets Space, 52, 953-957 http://acc.igs.org/trf/sinex-combi_ferland_eps00.pdf J. Kouba, J. Ray, M.M. Watkins (1998) IGS Reference Frame Realization, in 1998 IGS Analysis Center Workshop Proceedings, European Space Operations Centre, Darmstadt, Germany, pp 139-171, available at: http://igscb.jpl.nasa.gov/igscb/resource/pubs/wksp_2.pdf T. Springer (2000a) IGS Final orbit changes, IGS Mail 2750, 17 Mar 2000, http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00090.html T. Springer (2000b) Clarification of IGS Final orbit changes, IGS Mail 2751,18 Mar 2000, http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00091.html ============================================================== CHARTER For the IGS REFERENCE FRAME WORKING GROUP Remi Ferland Geodetic Survey Division Natural Resources Canada Ottawa, Ontario, Canada INITIAL GOALS The collective effort of the working group participants is to generate the official IGS station coordinates and velocities, Earth Rotation Parameters (ERP) and geocenter estimates along with the appropriate covariance information. The estimated parameters will be aligned to the International Terrestrial Reference Frame (ITRF). The group will strive for consistency, reliability and accuracy of the above products. The station coordinates and ERP information from the Analysis Centers (AC), the Global Network Associate Analysis Centers (GNAAC), the Regional Network Associate Analysis Centers (RNAAC) and potentially other sources will be compared and used to generate and validate the IGS official products. A new solution will be computed and made available regularly. It will initially contain station coordinates, daily ERP, weekly geocenter estimate, and relevant information on the equipment used at each station. The ”epoch” estimated station coordinate solutions will be added to the cumulative solution. The cumulative solution will contain at least a set of estimated coordinates and velocities at a reference epoch for each station. The AC, GNAAC, RNAAC, ”epochs”, cumulative, ITRF and potentially other solutions will be compared and residual files will be made available. The cumulative solution will be submitted as needed to IERS in order to contribute to the definition of ITRF. The solutions will be limited to about 200 to 250 well distributed and high quality stations, forming an IGS polyhedron. Abnormal station coordinates behavior will be reported. Potential inconsistencies in the past and current coordinates solutions will be investigated and corrected whenever possible. The performance and long term characteristics of the network based on the station coordinate time series will be monitored and reported. The network will consist of a number of well-distributed and quality stations. In collaboration with interested users, the network will be reassessed regularly as part of the maintenance. The IGS Reference Frame working group will promote improvements to the products through refinement in the analysis, modeling and algorithms. As a result, enhancements to current exchange standards and reports may be proposed. This group will collaborate with other groups and scientific organizations to improve the IGS products and to promote their use. The use of the IGS realization of ITRF will also be promoted. The products will be suitable for other IGS products as well as various studies such as plate tectonic, regional deformations, temporal variations. The definition of national reference systems can also benefit from the IGS realization of ITRF. STRUCTURE The working group will be composed of one coordinator with a number of active members. The working group reports to the IGS Governing Board. Modifications to the goals and working plan will be arrived at through consultation among the working group. WORKING PLAN In coordination with the group members, the ongoing objectives are to: • Analyze the time series station coordinates residuals; report on the findings and if appropriate implement improvements to the processes. • Compare the products with other solutions/models, report the findings and if appropriate implement improvements to the processes. • Analyze/compare ERP solutions, report the findings and if appropriate implement improvements to the processes. • Inform responsible groups/organizations to help resolve station related inconsistencies. In coordination with the group members, the objectives for the first year are to: • Get the weekly combination and reporting procedure to run smoothly, with a concise and informative weekly report. • Reanalyze the AC and/or GNAAC and/or RNAAC stations coordinates solutions available since GPS week 837 and report the results. • In coordination with the group members, the objectives for the second year are to: • Monitor and report the performance and long term characteristics of the network based on the stations coordinates time series • Continue the analysis with emphasis on the reliability and accuracy of the products • Include AC and/or GNAAC and/or RNAAC stations coordinates solutions available before GPS week 837 and report the results. In coordination with the group members, the following objectives will be considered as time and resources are available to: • Provide graphical interface for the reporting of the time series residuals and other types of data. MEMBERS The working group will be potentially composed of the IGS coordinator, the Director of the IGS Central Bureau, one representatives from each AC, one from each GNAAC and one from the ITRF/IERS section. Other members may be added as required. From: Carey Noll ******************************************************************************** |