IAG Sub-Commission 1.3c
Regional Reference Frames for North America
Canadian Geodetic Survey
U.S. National Geodetic Survey
IAG Commission 1 Symposium 2014
Reference Frames for Applications in Geosciences (REFAG)
Luxembourg, October 13-17, 2002
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Provide international focus and cooperation for issues involving the horizontal, vertical and three dimensional geodetic networks of North America, including Greenland, Mexico and the
Caribbean

Co-Chairs
• Mike Craymer, Canada
• Neil Weston, USA (replaced Jake Griffiths in 2013)
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Working Groups
• SC1.3cWG1 – North American Reference Frame (NAREF)
• SC1.3cWG2 – New Plate-Fixed North American Reference Frame
• SC1.3cWG3 – Reference Frame Transformations
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Objective
• Densify the ITRF/IGS global reference frame in North America
• Combine regional networks into a continental one
• Integrate into ITRF via the IGS global network
• Include most continuous GPS sites in N.A. (2500+ stations)
• Follow IGS processing guidelines
– IGS orbits and EOPs
– Current absolute antenna phase center models

Products
• Weekly coordinate solutions (combinations of regional solutions)
• Periodic multi-year cumulative (velocity) solutions
• Presently on hold pending release of IGS repro2 products
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America
Contributor Since Software
NGS
MIT/PBO 1
SOPAC
INEGI
2000 PAGES
2004
2000 GAMIT
CGS-B 2000 Bernese
CGS-G 2 2001 GIPSY
PGC 2 2001 Bernese
2010
GLOBK
GAMIT
Region (# sta used wk 1631)
North+Central America (762)
Plate Boundary Obs (183)
North+Central America (140)
Northern N.A. (568)
Canada (43)
Pacific Northwest (55)
Mexico (44)
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Combo of GIPSY & GAMIT solutions
2 Not contributing since GPS week 1631 (switch to IGS08 & igs08.atx)
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Last weekly combination to GPS Week 1513
• Too many stations for combination software (2000+)
• Began development of new software

Last cumulative solution to GPS Week 1399
• Prior to switched to IGS05 and absolute phase centre calibrations
• Need to reprocess all data with new calibrations
• Not all contributors reprocessed right away

Problem – uneven overlap & redundancy
• Few stations in all regional solutions
• Most stations (72%) in only one solution (NGS CORS) – no checks on these sites
• Causes uneven weighting of stations in combination
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America
Horizontal Vertical
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

US NGS multi-year solution
• Covers continental US, Mexico and Caribbean + global RF sites
• Based on weekly PAGES solutions up to GPS week 1631 (2011.3)
• Used repro1 products and igs05.atx antenna calibrations with a posteriori correction to igs08.atx using IGS model

NRCan/CGS multi-year solution
• Covers northern North America, including Greenland (685 stations)
• Based on weekly Bernese 5.0 solutions up to GPS week 1631
• Also used repro1 products and igs05.atx calibrations with a posteriori correction to igs08.atx
• Densified sparse continuous GPS sites in Canada with 160 Canadian
Base Network (repeated high accuracy campaign surveys)
• Aligned weekly & campaign solutions to IGS08 using global RF sites
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America
Horizontal* Vertical
* ITRF2008 plate motion removed
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Developed by Remi Ferland

Features
• Dynamic memory allocation (number stations limited only by RAM)
• Highly optimized and efficient matrix library (LAPACK)
• Some limited parallelization (adding more)
• At least 10 times faster than pervious software

Estimates
• Coordinates & velocities
• Seasonal signals (annual & semi-annual)
• Transformations between SINEX files
• Optional velocity equivalencing: before/after offsets & btwn stations
• Variance component estimation
• Post-seismic modelling to be added later
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Reprocessing of regional solutions with repro2
• Most contributors plan to reprocess
• Will include more overlap among networks
• NGS may be delayed due to their large network

Restart NAREF combinations in IGS13
• Current weekly combinations & submissions to IGS
• Weekly regional combinations of repro2 regional solutions
• Cumulative solutions with monthly updates

Need discontinuity detection software
• Can’t manually inspect thousands of stations
• Will evaluate various software for automatic detection
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Problems with NAD83
• Offset ~2 m from geocentre (ITRF)
• Defined by transformation from ITRF but biased by 2 mm/y error in NUVEL-1A

Objective
• Establish a new high-accuracy, geocentric reference frame, including velocity models, procedures and transformations, tied to the stable part of the North American tectonic plate.
• Replace NAD83 together with US vertical datum by 2022

Reference frame definition – current thinking
• Use current ITRF in 2022 at some adopted reference epoch
• Estimate plate motion to keep frame aligned to N.A. plate
• Need to select a set of frame sites representing stable N.A.
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Begin discussions with public
• Initial discussions held at the Federal Geospatial Summit in 2010
• NGS plans to begin active promotion in near future

US Foundation CORS
• To provide a more stable network to define the new frame
• Creating a network of 10-20 highly stable CORS sites
• Owned and operated by NGS (complete control)
• Using highly stable monumentation
• Will try to collocate with other other techniques (GGOS stations)
• Will contribute stations to the IGS network
• First site currently being installed in Miami this week
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Objectives
• To determine consistent relationships between international, regional and national reference frames/datums in North America
• Maintain and update these relationships
• Provide tools for implementing the transformations
• Primarily involves maintaining the adopted relationship between
ITRF and NAD83

NAD83 – ITRF
• NAD83 is now defined by a transformation from ITRF96
• Transformation is incrementally updated to new ITRF’s using adopted IERS transformations between ITRF realizations
• NNR-NUVEL-1A is used to keep the frame fixed to N.A. (now known to be biased by about 2 mm/yr)
• Will update transformation for new ITRF2013
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America

Commercial RTK networks
• Commercial RTK networks effectively acting as access points to
NAD83 for many users
• Problem – RTK networks integrated into different realizations of
NAD83
• Canada is now integrating 6 largest RTK networks in latest realization of NAD83 (600+ stations)
• Also implementing a validation process based on these results
• NGS planning to implement a similar RTK validation program
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IAG Sub-Commission 1.3c
Regional Reference Frames for North America
Thank you for your attention
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