Sub-Commission 1.3 - Regional Reference Frames Regional Sub-Commission 1.3c - North America www.naref.org

SC1.3c-WG1
North American Reference Frame Densification (NAREF)
Working Group

NOTICE

Although the members of this working group continue to produce daily and weekly coordinate solutions, their combination into NAREF weekly solutions has been suspended until further notice. We will consider resuming this effort after release of the new North American Terrestrial Reference Frame (NATRF2022). All of the historic NAREF weekly coordinate solutions, together with the regional solutions used to produce them, are still available from the NAREF data archive.

The purpose of this working group is to densify the ITRF and IGS global reference frame in the North American region by organizing the computation of weekly coordinate solutions and associated accuracy information for continuously operating GPS stations that are not part of the current IGS global network. A "cumulative" solution of coordinates and velocities will also be determined on an annual basis. The Subcommission will organize, collect, analyse and combine solutions from individual agencies, and archive and disseminate the weekly and cumulative solutions.

NAREF Data Archive

All of the NAREF WG coordinate solutions, together with the regional solutions used to produce it, as well as data for GPS stations operated by NRCan/GSD are available from the NAREF data archive at the following FTP server. Access to the server requires a password. Please contact Mike Craymer for access.

FTP Server: gauss.geod.nrcan.gc.ca
Login Name: narefftp
Password: [contact Mike Craymer]
Directory: /pub
URL: ftp://narefftp@gauss.geod.nrcan.gc.ca/pub/
Web Access: http://www.naref.org/archive/

Members/Contributors

Publications/Presentations

• Densification of the ITRF through the weekly combination of regional and global GNSS solutions (poster), Eos Transactions, AGU, ??(51), Fall Meeting Supplement, Abstract G53B-1144, 2012.
• An updated GPS velocity field for Canada (poster), Eos Transactions, AGU, 92(51), Fall Meeting Supplement, Abstract G21A-0793, 2011. (4.2 MB)
• Preliminary results of an updated North American GPS velocity field (poster), Eos Transactions, AGU, 91(51), Fall Meeting Supplement, Abstract G23B-0825, 2010. (7.5 MB)
• Predicting Present-Day Rates of Glacial Isostatic Adjustment Using a Smoothed GPS-Based Velocity Field for the Reconciliation of NAD83 Reference Frames in Canada (poster), Eos Transactions, AGU, 89(53), Fall Meeting Supplement, Abstract G31A-0638, 2008. (2.3 MB)
• IGS [IAG] Working Group "Regional Dense Velocity Fields": Objectives and Work Plan (poster), Eos Transactions, AGU, 89(53), Fall Meeting Supplement, Abstract G33B-0689, 2008. (0.5 MB)
• SNARF 2.0: A Regional Reference Frame for North America (presentation), Eos Transactions, AGU, 89(23), Joint Assembly Supplement, Abstract G31B-01, 2008. (2.9 MB)
• IGS [IAG] Working Group "Regional Dense Velocity Fields": Objectives and Future Plan (poster), IGS Analysis Center Workshop, Miami Beach, June 2-6, 2008. (2.2 MB)
• NRCan-Determined GPS Velocity Fields: Contributions to the definition of the Stable North American Reference Frame (SNARF) (presentation), CGU-CGRG Joint Annual Meeting, Banff, Alberta, May 11-14, 2008. (3.8 MB)
• Contributions of the North American Reference Frame Working Group to the next realization of the Stable North American Reference Frame (SNARF) (poster), Eos Transactions, AGU, 88(52), Fall Meeting Supplement, Abstract G21B-0498, 2007. (11.5 MB)
• The North American Reference Frame (NAREF) project to densify the ITRF in North America, ION GNSS 2007, Fort Worth, Texas, September 25-28, 2007. Preprint. (2.1 MB)
• NRCan Velocity Fields and Comparisons to Some Plate Motion Models, SNARF Workshop 7, UNAVCO Science Workshop, Denver, CO, March 14-16, 2006. (4.3 MB)
• NAREF Analysis and ITRF2004 Densification, SNARF Workshop 3, Santa Ana Pueblo, NM, March 28, 2005. (5.8 MB)
• The NAREF Perspective on a New Plate-Fixed Reference Frame for North America (poster), Joint AGU-CGU Meeting, Montreal, May 17-21, 2004. (343 KB)
• North American Reference Frame (NAREF) Working Group, SNARF Workshop 2, AGU-CGU 2004 Joint Assembly, Montreal, May 19, 2004. (352 KB)
• Report of the Sub-Commission for North America, IAG Commission X (Global and Regional Geodetic Networks), 1999 to 2003, Report to the XXIII General Assembly of IUGG, Sapporo, Japan, June 30 - July 11, 2003. (127 KB)
• Canadian Contributions to the NAREF Initiative to Densify the ITRF in North America (poster), AGU 2002 Fall Meeting, San Francisco, December 6-10, 2002. (1094 KB)
• Densification of the ITRF: The NAREF experience in North America, IGS Network, Data and Analysis Center Workshop 2002, Ottawa, Canada, April 8-11, 2002. (2040 KB)
• IGS Position Paper: Regional Networks Densification, Proceedings of the IGS Network, Data and Analysis Center Workshop, Ottawa, April 8-11, 2002.
• The North American Reference Frame: Densification of the ITRF in North America, Plate Boundary Observatory US/Canada Workshop, Seattle, WA, March 5, 2002. (658 KB)
• Report of the Subcommission for North America, IAG Commission X (Global and Regional Geodetic Networks), IAG Scientific Assembly 2001, Budapest, Hungary, June 2-7, 2001. (80 KB)
• The NAREF Initiative to Densify the ITRF in North America (poster), IAG Scientific Assembly 2001, Budapest, Hungary, June 2-7, 2001. (627 KB)
• The North American Reference Frame (NAREF): An Initiative to Densify the ITRF in North America, KIS 2001, Banff, June 4-8, 2001. Revised July 13, 2001. (1024 KB)
• The NAREF Initiative to Densify the ITRF in North America, EUREF Permanent Network Third Local Analysis Centres Workshop, Warsaw University of Technology, Warsaw, Poland, May 31 - June 1, 2001. (1208 KB)
• The NAREF Initiative to Densify the ITRF in North America (poster), Canadian Geophysical Union Annual Scientific Meeting, Ottawa, May 14-17, 2001. (96 KB)
• NAREF: Densification of the ITRF in North America, IGS Analysis Center Workshop, Washington, September 25-29, 2000. (909 KB)
• NAREF: An Initiative to Densify the ITRF in North America, AGU Spring Meeting, Washington, May 30 - June 3, 2000. (93 KB)
• Canadian Regional Solutions for NAREF: Initial Investigations, AGU Spring Meeting, Washington, May 30 - June 3, 2000. (173 KB)

NAREF Combinations

Regional Solutions

Regional and local network solutions are obtained from various agencies. Presently, only solutions from the northern half of North America are being contributed. We are always seeking new solutions, especially from Mexico and Central America.

Current Contributions

• GSB -- Northern North American Network by Geodetic Survey Division, NRCan (Bernese GPS Software)
  
• GSG -- Canadian Reginal Network by the Geodetic Survey Division, NRCan (GIPSY/OASIS II)
  
• MIT -- Official Plate Boundary Observatory by the Massachusetts Institute of Technology (combination of Bernese GPS Software & GIPSY/OASIS II)
• NGS -- U.S. CORS Network by the U.S. National Geodetic Survey, NOAA (PAGES)
  
• PBO -- Preliminary Plate Boundary Observatory by the Scripps Institution of Oceanography (GAMIT)
  
• PGC -- Western Canada Deformation Array by the Pacific Geoscience Centre, NRCan (Bernese GPS Software)
  

We would most welcome your contribution if you have any regional solution in North American that meet the criteria described in the above publications. For further information, please contact Mike Craymer.

NAREF Combinations

The NAREF weekly combination of regional solutions is obtained using SINEX Software version 1.0 by Remi Ferland. It is the same software used to produce the official IGS coordinate solutions. The combination procedure is based on that used for the IGS solutions and is performed in two steps: alignment of each regional solution to the IGS weekly solution and combination of the (aligned) regional solutions. The procedure is summarized as follows:

Alignment of Each Regional Solution
1. A priori datum constraints are removed.
2. Solution is aligned to the IGS weekly solution of the same week using 3 translations, 3 rotations and a scale change.
3. Covariance matrix is scaled by the weighted root mean square (WRMS) of the residuals from the above transformation.
4. Residuals are tested for outliers. If any outliers are found, they are removed and steps 2 to 4 are repeated.
Combination of Regional Solutions
5. Regional solutions are combined together by summation of the normal equations for the (scaled) regional solutions.
6. Combined solution is aligned to IGS weekly solution of same week using 3 translations., 3 rotations and a scale change.
7. Covariance matrix is scaled by the WRMS of residuals from the above transformation.
8. Residuals are tested for outliers. If any outliers are found, they are removed from their solution and steps 2 to 8 are repeated (only steps 2 to 4 for the regional solution with the outlier needs to be repeated).
9. A minimum constraint is applied to the combined solution for further testing and comparison with the IGS weekly solution. Presently, IGS station DRAO is constrained to itŐs IGS97 coordinates and weights at the epoch of date to facilitate comparisons among all the solutions (itŐs the only station common to all solutions).

The combination results are analysed using the combination residuals for each regional solution and comparing the NAREF combations to the IGS weekly solutions. It is also planned to use other combination software for further quality control.

Recent NAREF Results

The North American Reference Frame (NAREF) project to densify the ITRF in North America, ION GNSS 2007, Fort Worth, Texas, September 25-28, 2007. Preprint. (2.1 MB)

Map of NAREF contributions as of November 2006
Horizontal velocities (updated May 2008)
Horizontal residual velocities after removal of ITRF2005 plate motion estimate for North America (updated May 2008)
Vertical velocities (updated May 2008)

Maps of the velocities fields for the combined NAREF and Canadian Base Network solutions. The CBN solution is based on repeated occupations of highly stable, forced centering pillars over the years 1994 to 2006. It provides greater spatial sampling of the velocity field in Canada where there are fewer continuous GPS sites then in the US.

Horizontal velocities (updated May 2008)
Horizontal residual velocities after removal of ITRF2005 plate motion estimate for North America (updated May 2008)
Vertical velocities (updated May 2008)