SNARF Working Group - Annual Report 2004-2005
Workshops for Establishing a Stable North American Reference Frame (SNARF) to Enable Geophysical and Geodetic Studies with EarthScope: Annual Report 2004-2005
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 2: PROJECT FINDINGS
OVERVIEW OF FINDINGS
Year 1 was considered to be primarily a time to consider a broad range of pertinent research problems, in preparation for a synthesis of ideas in Year 2, when more conclusive recommendations would be made. The following summarizes, in a nutshell, the findings that result from all of our basic research and discussions in Year 1:
(1) Demonstrated geodetic precision and accuracy appears to have reached the level that the development of a reference frame with sub-millimeter self-consistency is not limited by geodetic observations, but may be instead limited by our ability to model the observations in a predictive way.
(2) Nevertheless, there are numerous specific examples of poor quality data (in various respects) that careful quality assessment and the judicious selection of stations representing 'stable North America' will be important if a sub-millimeter frame is to be realized, and therefore continuing research into appropriate station selection is vital.
(3) The discussion on Earth models concluded that inconsistencies between various GIA models is currently the most limiting factor toward defining SNARF with sufficient accuracy. It is therefore clear that much research (which we estimate would take many years) will be required to resolve this issue.
(4) Therefore, in the interim (until an accurate GIA model can be adopted), it was agree among the participants that a phased-in approach to SNARF would be appropriate. This implies that incremental improvements would continue to be made to some initial version of SNARF for many years to come, but that the initial version will not be as accurate as the GPS observations would otherwise appear to allow.
(5) Taking the above points together, we can therefore conclude that an initial version of SNARF would help to define a standard so that GPS time series could then themselves be used to help improve the GIA models. In this feedback model toward an improved SNARF, the adoption of interim frames allows for consistent GPS software intercomparisons and consistent GIA model intercomparisons. It would also significantly improve consistency when comparing GIA models with GPS time series.
In summary, the focus of further research should be on (a) specific site selection to define SNARF, and (b) improved GIA models. Both of these problems will be better addressed if we adopt an incremental approach to SNARF (say, with annual updates), which can then itself be used (as in a feedback loop) to help resolve site selection and GIA modeling issues.
Details on the research leading to these findings can be found on-line at:
Last modified: 2019-12-24 02:12:52 America/Denver