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Monitoring geoid change in Canada

Explore the Geodetic Survey Division's efforts in monitoring geoid change in Canada, with a focus on height modernization, GNSS infrastructure, gravity networks, satellite altimetry, and more. Learn about the adoption of new vertical networks and the validation of geoid models for scientific applications.

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Monitoring geoid change in Canada

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  1. Monitoring geoid change in Canada Marc Véronneau, Joe Henton, Jianliang Huang*, Jacques Liard, Michael Craymer and Pierre Héroux Geodetic Survey Division , CCRS, NRCan 2009 Workshop on Monitoring North American Geoid Change Boulder, CO 21-23 October 2009

  2. Outline • Geodetic Survey Division … 3 • Height Modernization … 4 • GNSS infrastructure (h and h-dot) … 7 • Gravity infrastructure (g and g-dot) … 11 • Satellite altimetry (sea level) … 24 • Conclusion … 26

  3. Geodetic Survey Division • The primary role of the Geodetic Survey Division (GSD) is to maintain, continuously improve, and facilitate efficient access to the Canadian Spatial Reference System (CSRS). This includes the responsibility to maintain the Canadian Gravity Standardization Net (CGSN) that provides datum control for gravity observations across Canada. • In order to better contribute to the definition of the vertical component of a highly accurate, multi-purpose, active and integrated Canadian Spatial Reference System (CSRS), GSD is in the process of consolidating the CGSN primary control sites with geometric reference stations (e.g. continuous and episodic GPS) of the CSRS

  4. Height Modernization - 2013 The geoid model: 1. Entire coverage of the Canadian territory (land, lakes and oceans) 2. Compatible with space- based positioning (e.g., GNSS, altimetry) 3. Less expensive for maintenance 4. Fairly stable reference surface Levelling Networks: 1. Established over the last 100 years 2. 120,000 km of levelling lines 3. Some 80,000 benchmarks 1. Time consuming 2. Expensive 3. Limited coverage 4. BMs are unstable 5. BMs disappear 6. Local networks H = hGNSS – NModel

  5. Unifying Vertical and Horizontal Networks Horizontal network (f, l) NAD27 NAD83 4-D network (f, l, H = h – N, t) 3-D network (f, l, H = h – N ) NAD83(CSRS) Geoid model h-dot & N-dot NAD83(CSRS) Geoid model NAD83(CSRS) 3-D network (f, l, h) Direct transformation Vertical network (H) Adopted in the USA, but not in Canada CGVD28 NAVD88 ITRF SNARF

  6. Vertical Reference System • Definition of the Vertical Reference system • Equipotential surface (W0) • Specific potential value determined by NA agencies or IAG • Physical height realization at one or several CACS/CBN • Realization of the Vertical Reference System • Mean static solution representing a 1-to-2-year period • Remove-restore approach; Degree banded Stokes Kernel • GRACE, GOCE, Altimetry, Terrestrial gravity data, DEM, Topo density • Error estimates • Maintenance of the Vertical Reference Frame • Monitoring height (h and h-dot) • CACS/CBN + collaborative stations (e.g., provincial) • Monitoring gravity (g and g-dot) • Improvement at GRACE wavelengths only • Absolute gravity stations co-located at CACS/CBN/Tide Gauges • No plans for short wavelengths (unless something is observed locally that requires action) • Actions to be taken regarding significant changes in geoid models • What is a significant change in the geoid model?

  7. Federal active and passive stations • CACS: • 50 stations • Concrete pillar anchored to • bedrock • GNSS receivers (9 stations) • 3 stations at St-Johns, ARO, • Yellowknife, and Penticton • (all former VLBI sites) • Real-time (1 sec.) • CHAIN (New): • 9 stations (some co-located • with CACS) • CBN: • 151 stations • 5-year obs. cycle • Not shown: active • Provincial active stations • NB, QC, BC • Private RTK networks • Not shown: passive • High Precision Network • (HPN) • Provincial

  8. National Velocity Grid v1.0 Churchill, MB 10.14 mm/yr Halifax, NS -1.29 mm/yr

  9. GPS on BMs Validation of geoid models (monitoring static solutions) Nmodel = hGPS - HLev • GPS surveys: 1986 to 2008 • 2729 stations • h accuracy: ± 1-2 cm to ± 10-15 cm • h are not corrected for PGR • Current levelling data have somewhat • reach their limitation in evaluating geoid • models • Deflections of the vertical may be the • most suitable data to validate • geoid models

  10. GPS on Tide Gauges Tide gauges with more than 100 months of observations GPS on Tide gauges GPS on BMs (near tide gauge) Arctic Halifax, NS 3.22 mm/yr Churchill, MB -11.12 mm/yr West Coast East Coast

  11. Gravimetry at NRCan • CSRS objectives, including: • Datum support for gravity surveys • Support time evolution of vertical component of geometric RF • Maintenance of a new gravity-based/geoid height reference system (e.g. direct measurement of g-dot/h-dot ratio to provide simplified connection for corresponding reference standards) • Scientific applications/priorities (with NRCan partners): • Subduction/earthquake zone deformation studies • Sea-level rise studies • Hydrological/ground-water mass monitoring • Post-glacial rebound studies

  12. Instrumentation • Superconducting gravimeter (CAGS) • Observing since November 1989 (no activities between 1994 and 1996) • Absolute gravimeters • FG5-236 NRCan/GSD (field operation) • FG5-106 NRCan/GSC (field operation) • FG5-105 NRC Watt Balance • JILA-2 NRCan/GSD (CAGS) • A-10 NRCan/GSD • No absolute gravimeters with universities or private industry in Canada • Relative gravimeters • CG5 (4) • L&R (8) • SL-1 dynamic gravimeter (shipborne and airborne surveys) • Tidal gravimeter • 1 instrument in preparation for field operation

  13. Absolute gravity survey Survey tent A-10 FG-5 Vertical gradient of gravity

  14. Canadian Absolute Gravity Site (CAGS) Fundamental Absolute Gravity Station in Canada CAGS was established in 1987. The site is located on bedrock. • Superconducting gravimeter • Canadian Active Control Station • Four absolute gravity stations • Weather station • Two wells • Possible North American Inter-Comparison site (4 inst. max.) GWR superconducting gravimeter at CAGS CAGS TMGO

  15. Canadian Absolute Gravity Array • Absolute Array • 63 sites co-located with • ACP, CBN and/or TG • (1) (15) (37) (10) • 8 proposed new sites • 44 other sites • CGSN Primary stations • 74 stations Mid-continent Profile Vancouver Island Laurentian Profile

  16. Regular GSC Survey Sites in SW-BC

  17. Preliminary Uplift Rate Comparisons Eastern Canada • GPS Uplift Rates • Co-located at/near AG •Continuous & Episodic (CBN & CACS) •Data period equivalent to JILA AG surveys [after Henton et al., 2004] • AG to Uplift Conversion • -0.15 μGal/mm • Theoretical relationship for Laurentide GIA [Lambert et al., 2001] • PGR Model • ICE-4G (VM1) [Peltier, 1994]

  18. CGSN (relative gravity network) Primary gravity ties in Canada Primary and secondary gravity stations • 50+ years of relative gravity observations in Canada. • g-dot determination (Pagiatakis and Salib) • Absolute gravity stations are tied to primary stations of CGSN by relative measurements

  19. “G-dot” (Relative Gravity Change) ▪CGSN (Relative) Primary Control Points [Pagiatakis & Salib, 2003 – JGR] ▪

  20. Satellite Gravity Missions • GRACE • Analysis of monthly and static solutions • CSR, GFZ, JPL • Analysis of combined solutions (e.g., EGM08) • Estimation of monthly and secular variations of the geoid • Validate variation models against ground terrestrial gravity measurements • Availability of secular and monthly geoid variations (preliminary stage) • GOCE • Will analyze GOCE-contributing global gravity models • Will contribute to the static geoid for half-wavelength components between ~700 km and 100 km (1 cm) in North America • Evaluate needs for surface/airborne gravity measurements in Canada

  21. Secular geoid velocity The secular geoid change from the monthly GRACE models (2002-2008). The solution represents the effect due to total mass changes in the Earth interior. The solution uses a 400-km Gaussian filter.

  22. Monthly geoid change - 2008 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Color scale: -10 mm to 10 mm, GIA trend removed, and wrt to mean static 2002-2003 model

  23. GRACE comparison GRACE gravity vs SG gravity data Canadian Absolute Gravity Site GRACE gravity vs mean abs. surface gravity Southern Vancouver Island

  24. Sea Surface Topography SST = SSHAlt – N SSH: DNSC08 (Denmark) N: PCG08I (Canada)

  25. MSS variation and currents: East coast Data: AVISO TOPEX-POSEIDON SSH; GEOID CGG2005 (RIM) Area: N65/N41/W72/W46 SSH: DNSC08 (DK) N: PCG08I (Canada) Speed of ocean currents (DNSC08 & PCG08I)

  26. Conclusion • Canada is moving to a geoid-based vertical reference system by 2013 • Canada has a well-established active and passive GNSS network based on high reliability standards • Canada is presently establishing a national absolute gravity array co-located at GNSS stations • Canada relies heavily on satellite gravity missions in realizing an accurate static geoid model and monitoring geoid change • Canada is making use of tide gauge and altimetry data in monitoring the coastal and marine geoid (sea level)

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