First SNARF Workshop: Introduction Stable North America Working Group UNAVCO Inc., 27 Jan 2004 Geoff Blewitt University of Nevada, Reno

Agenda –NAREF and National Survey Agency Perspectives on SNARF 1:20 pm - Mike Craymer 1:40 pm - Richard Snay Discussion and Planning –2:00 pm - Underlying Models: What is useful and what is possible? –2:30 pm - A working definition of the "stable plate interior" –3:00 pm - Criteria for selecting stations that define SNARF –3:30 Break for coffee/tea –3:45 pm - Work plan for producing and testing SNARF –4:15 pm - Decide on a specific baseline version of SNARF (0.0) Conclusions 4:45 pm - Workshop report and action items 5:00 pm - end workshop. Introduction –9:00 am - Welcome –9:05 am - Brief Self-Introductions –9:15 am - WG Charge/Status of NSF Funding Technical Presentations –Reference Frame Theory & Practice, and Implications for SNARF 9:30 am - Geoff Blewitt 9:50 am - Tom Herring 10:10 am - Kristine Larson 10:30 am - Break for coffee –Intraplate Deformation, Evidence, Models, and Implications for SNARF 10:40 am - Eric Calais 11:00 am - Goivanni Sella 11:20 am - Mark Tamisiea –Current Reference Frame Treatment and Future Needs: Regional Arrays 11:40 am - Meghan Miller 12:00 pm - Rick Bennett 12:20 pm - Break for lunch 1:00-1:20 - Tour of UNAVCO

PBO Needs What are PBO reference frame needs? How can we meet those needs?

PBO stated requirements: PBO needs –“…that plate boundary deformation be adequately characterized over the maximum ranges of spatial and temporal scales common to active continental tectonic processes.” [ES Facility Proposal] How broad is the plate boundary? Is there a “stable plate interior”? –to within potential GPS accuracy ~ 0.1 mm/yr –would require accurate modeling of non-tectonic deformation –If so, where is this stable plate interior? PBO will address these questions by –Network design including broad GPS spatial coverage across North America –Research (SNARF WG)

Working Group Charge (1) International Association of Geodesy (IAG) –NAREF: Special Commission on the North America Reference Frame –Proposed and under the new IAG structure (Sapporo July 2003) –SC1.3c-WG3: Stable North American Reference Frame (SNARF) –The objectives of this working group are to establish a high-accuracy, standard reference frame, including velocity models, procedures and transformations, tied to a "stable North America" which would serve the scientific and geomatics communities by providing a consistent and stable reference with which scientific and geomatics results (e.g., positioning in tectonically active areas) can be produced and compared. –Chair: Geoff Blewitt (USA) Members: M. Craymer (Canada), Mitrovica (Canada), D. Argus (USA), R. Bennet (USA), J. Davis (USA), J. T. Dixon (USA), T. Herring (USA), D. Lavalleee (USA), M. Miller (USA), W. Prescott (USA), R. Snay (USA), F. H. Webb (USA)

Working Group Charge (2) UNAVCO Charge (Annual Board of Directors Meeting, July 2003) –The Stable North America Reference Frame (SNARF) Working Group (WG) is charged with producing a standard reference frame (for studies in North America) and specifying standard procedures to realize such a frame to meet the needs of the UNAVCO community. –The WG's responsibility is to: design an appropriate ideal reference system (which includes philosophy, axioms, and models) and implement a strategy to produce a specific reference frame (which includes site coordinates, velocities, and offsets); produce a preliminary SNARF in SINEX format and iteratively assess it (and possible alternatives) through testing by different analysis groups using different software; produce the first official SNARF along with published procedures that enable and facilitate correct realization of the frame by users; make available useful information regarding the relationship between SNARF and other reference systems, frames, and other geodetic solutions; produce a comprehensive final report (potentially a refereed publication) on SNARF with an assessment of its accuracy, and with recommendations for further development and continuing maintenance; complete the above first phase of the work and present a report at the UNAVCO Annual Members Meeting. –Board concurs NSF proposal is needed to facilitate expert participation

Working Group Charge (3) National Science Foundation –Proposal submitted July 2003 PIs: Larson and Davis –Recommended Dec 2003 –Funded Jan 2004 ($44K) Stated Plan: –Frame for PBO By group of experts that works cooperatively with UNAVCO, and NAREF under IAG –3 workshops First “mid-January 2004” Second “AGU/CGS, May 2004” Third “January 2005” –Tasks: Design ideal reference system Realize reference frame Initial SNARF by Fall 2004 Procedures for users Transformations and software Final SNARF and report 2005

Charge for First Workshop According to NSF Proposal…. –“The initial workshop (tentatively scheduled for mid-January 2004) will be an organizational workshop to assign priorities, identify problems to be solved. –“Tasks must be itemized and subgroups of the main WG must be assigned to work on these tasks.” –“Some of the issues to be discussed will be disseminated through in Fall This will allow various members to perform preliminary studies.”

Development Principle Consider SNARF always as a “work in progress” At any given point in time there needs to be a well-defined current version of SNARF similar to ITRF philosophy incremental improvement to ideal frame but also means doing the best we can right now having an early “baseline version” is not so difficult in principle motivates early improvement provides an early ability to measure incremental improvements