SNARF Working Group - FINAL REPORT (2004-2006)
Workshops for Establishing a Stable North American Reference Frame (SNARF) to Enable Geophysical and Geodetic Studies with EarthScope: Final Report (2004-2006).
Prepared by SNARF Working Group, UNAVCO Inc., Boulder, CO.
G. Blewitt (Chair), K. Larson (PI), J. Davis (Co-PI), D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer (NRCan rep.), T. Dixon, J. Freymueller, T. Herring, D. Johnson, M. Miller, G. Sella, R. Snay (NGS rep.), and M. Tamisiea.
PART 1: PROJECT ACTIVITIES
GOALS AND OBJECTIVES
The goal of this project is to define a geodetic reference frame attached to stable North America in some useful way for EarthScope investigators. This project proposed a model whereby this goal would be achieved by a group of a dozen (or so) expert participants of a working group who meet in a series of three to four workshops. Note that the funding covers only travel for the experts to the workshops, and the research is conducted on a kind of 'volunteer' basis (i.e., funded by other means). Being a 'worshop proposal', it is therefore pertinent to describe the methods and activities involved in implementing this collaboration model, as well as the scientific research itself.
As proposed, the outcome of the working group activities would be the realization of a new standard reference frame suitable for scientific investigations of the North American plate and its boundary with the Pacific Plate. Such a 'Stable North American Reference Frame' (SNARF) would be fundamental in the analysis of data from EarthScope's Plate Boundary Observatory, and should be useful in the broader public and legal sense of a North American Datum adopted jointly by the national surveys of the USA and Canada (NGS and NRCan, respectively). Apart from resolving fundamental research issues related to reference frame definition and realization, the objectives of this project include educating the scientific community on the use of reference frames and their limitations as to the interpretation of station coordinate time series within such defined frames. This is achieved by posting the research findings of the SNARF working group on-line at:
and by giving presentations (oral and poster) at major conferences. This combination of research and education activites will ultimately result in improved use and interpretation of EarthScope data for scientific purposes.
OVERVIEW OF ACTIVITIES
Activities for this project can be broadly categorized as follows:
1. Establishing the Stable North Amerian Reference Frame (SNARF) Working Group (WG).
2. Selecting the project participants (WG members), with an emphasis on engaging the highest levels of scientific expertise in the USA and Canada on defining a new reference frame for North America.
3. Organizing SNARF WG workshops.
4. Research activities (including fundamental research and workshop participation).
5. Education activities, including web publication at UNAVCO, presentations by the participants (e.g., at AGU) on SNARF and SNARF-related research, and journal articles co-authored by the participants.
Each of these areas of activity are now discussed in further detail.
ESTABLISHMENT OF THE SNARF WG
Much work was conducted prior to grant approval to establish the SNARF WG, so that activities could commence immediately upon approval of funding. This pre-award work was possible because the activities were conducted entirely on a volunteer basis, with only travel funding made available to participants.
The initial concept of the SNARF WG arose about one year prior to this award, when the UNAVCO President, Will Prescott, identified the need to develop a plan to develop a consistent reference frame for EarthScope. Geoff Blewitt (UNAVCO Chairman of the Board at the time) then developed a plan for a working group to address this need. In 2003, the SNARF WG was officially approved and charged by two very different organizations: (1) UNAVCO Inc, by appointment of the Board of Directors, primarily in preparation for the Plate Boundary Observatory and as a service to UNAVCO member organizations in North America, and (2) the International Association of Geodesy, as part of a more global collaborative effort to standardize reference frames, under the committee 'NAREF' (North American Reference Frame), which has organizational links to the national geodetic surveys of both the USA (NGS) and Canada (NRCan).
The SNARF WG thus includes key representatives from both the NGS (Richard Snay) and NRCan (Mike Craymer). Geoff Blewitt was appointed Chair of the SNARF WG. Kristine Larson (University of Colorado) was appointed to take the lead as PI on this NSF proposal to fund workshops of the SNARF WG, and Jim Davis (Harvard-Smithsonian Center for Astrophysics) was appointed Co-PI.
The plan for the SNARF WG was presented to potential EarthScope investigators at the Fall 2004 AGU Meeting by the chair of the WG:
Blewitt, G., A reference frame for PBO: What do we have; what do we need? Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract G32B-02 INVITED, 2003
PARTICIPANT SELECTION
Expert participants were selected by an open invitation to the broad community of geodetic investigators in North America, by mass emailing to the entire UNAVCO membership plus additional individual investigators who were recognized as performing research of relevance to the project goals. Members of the SNARF Working Group (i.e., the participants listed for this project) were identified as those who responded positively to the invitation, and who subsequently became active participants in the project by attending the workshops and being involved in the discussions outside of the workshops. The resulting group of 16 participants covers a broad range of expertise in problems relating to SNARF research and development, ranging from mathamatical geodesy and reference frames, to physical Earth models, tectonophysics, and GPS observation modeling. The participants come from the US and Canada, and from university or governmental institutions. In addition to scientific expertise, the group also includes key experts on legal and public implications related to the definition of a North American Datum.WORKSHOP ORGANIZATION
The scientific organization of workshops was led by the chair, and conducted by the participants. The logistical organization of the workshop was conducted by UNAVCO Inc. staff.
During this project, six workshops have been held:
(1) at the UNAVCO Inc. headquarters, January 27, 2004, immediately following the announced approval of funding (hitting the ground running, so to speak). The workshop featured 10 presentations followed by in-depth discussion.
(2) at Montreal, during the week of the Joint Assembly of the AGU and CGU, 17-21 May, 2004.
A special session at the Joint Assembly was convened by Blewitt and Craymer, which constituted the first half of the Montreal workshop:
Sessions G21C and G21D: 'Toward a Stable North America-Fixed Reference Frame', Presiding: G Blewitt, University of Nevada, Reno; M Craymer, Natural Resources Canada; W E Holt, State University of New York at Stony Brook (joint sessions with Geodesy, Seismology, and Tectonophysics).
These sessions featured 6 oral presentations and 4 posters by the workshop participants, including a collaborative poster:
Blewitt, G., R. Bennett, E. Calais, T. Herring, M. Miller, G. Sella, R. Snay, and M. Tamisiea, First Report of the Stable North America Reference Frame (SNARF) Working Group, Eos Trans. AGU, 85(17), Jt. Assem. Suppl., Abstract G21C-01, 2004.
The second half of the Montreal workshop was a several-hour discussion of the WG participants outside of the Joint Assembly in a nearby hotel.
(3) at Santa Ana Pueblo, NM, March 28 2005, immediately preceding the EarthScope National Meeting. The workshop featured 8 presentations followed by in-depth discussion. Conclusions of this workshop were then presented at the EarthScope National Meeting:
Blewitt, G., D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer, J. Davis, T. Dixon, J. Freymueller, T. Herring, D. Johnson, K. Larson, M. Miller, G. Sella, R. Snay, and M. Tamisiea, Workshops for Establishing a Stable North American Reference Frame (SNARF) to Enable Geophysical and Geodetic Studies with EarthScope: Annual Report 2004-2005, Abstracts of the 2005 EarthScope National Meeting, p. 81, 2005.
(4) at Stevenson, WA, during the Joint UNAVCO/IRIS Workshop, with presentations and discussions aimed at educating interested users of SNARF in the UNAVCO/IRIS community in preparation for EarthScope:
Blewitt,G., D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer, J. Davis, T. Dixon, J. Freymueller, T. Herring, D. Johnson, K. Larson, M. Miller, G. Sella, R. Snay, and M. Tamisiea, A Stable North American Reference Frame (SNARF): First Release, abstracts of the Joint UNAVCO/IRIS Workshop, June 2005.
Davis, J., and T. Herring, Stable North American Reference Frame (SNARF) Version 1, presentation and discussion given at the SNARF WG meeting of the Joint UNAVCO/IRIS Workshop, June 2005.
(5) at the Brown Palace Hotel, Denver, CO, on March 15, 2006, during the UNAVCO Science Workshop. This workshop featured 9 presentations followed by in-depth discussion.
(6) at Natural Resources Canada, Ottawa, on Nov 16, 2006. This workshop featured 9 presentations followed by in-depth discussion.
(7) (planned) at Monterey, March 27, 2007, immediately preceding the EarthScope National Meeting. The attendance by 13 participants have so far been confirmed.
SCIENTIFIC ACTIVITIES
The scientific activities can be considered in two parts: (1) fundamental research toward SNARF goals, thus forming a scientific basis for discussion, and (2) participation in workshops, including discussion of the research and its implications with regard to defining SNARF, and the creative activity that pulls together various strands of research toward the common goal of realizing a new standard reference frame. More details on the research findings and progress on developing SNARF are given in the next section on 'findings'.
The main areas of scientific research in which the participants were active and which were discussed at workshops are listed below:
(1) Reference frame theory and practice;
(2) Geodetic analysis for reference frame realization, including optimal analysis, station motion model, validation studies (e.g., software intercomparisons), error analysis, etc.;
(3) Earth models, especially GIA (glacial isostatic adjustment) and secular loading associated with current climate change, and an assessment of whether such effects can be accurately included in the SNARF reference system definition;
(4) Tectonic considerations regarding proximity to plate boundary effects;
(5) Quality-affecting issues, such as data quality, multipath, monument stability, local- to broad-scale subsidence, hardware configuration, site selection, etc.
(6) Transfer from research-mode activities to the operational activities of EarthScope's Plate Boundary Observatory and to the national geodetic agencies (NRCan in Canada, and NGS in USA). Specifically, in October 2006, SNARF was officially adopted as the reference frame for the production of PBO geodetic products, thus closing the loop on a major objective of the SNARF Workshops.
The list of publications and presentations given in this report provide more specific detail on each specific research activity.
EDUCATION ACTIVITIES
Due to the highly specialized nature of this research, education activities are directed toward the scientific community itself. These activities can be categorized as:
(1) a collaborative project web-page hosted by UNAVCO:
which contains information on the project goals and objectives, materials presented at workshops, and conclusions of the research and workshop discussion ('major findings', which are discussed later).
(2) presentations at SNARF workshops, at conference special sessions such as the AGU co-authored by the participants, and plenary sessions of the UNAVCO Science Meetings and EarthScope National Meetings.
(3) journal articles on fundamental research related to SNARF co-authored by the participants.
References to publications and presentations are attached with the second half of this report (Project Findings).
Comments or questions about this page? Send e-mail to Geoff Blewitt (gblewitt
unr.edu).
Last modified: 2019-12-24 02:12:52 America/Denver