Monitoring geoid change in Canada

Canada’s Natural Resources – Now and for the Future 1 of 26

Monitoring geoid change in CanadaMarc 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


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


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


Height Modernization - 2013

1. Time consuming 2. Expensive 3. Limited coverage 4. BMs are unstable 5. BMs disappear 6. Local networks

Levelling Networks:

1. Established over the last 100 years 2. 120,000 km of levelling lines 3. Some 80,000 benchmarks

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 maintenance4. Fairly stable reference surface

H = hGNSS – NModel


Unifying Vertical and Horizontal Networks

NAD27

CGVD28

NAD83

NAVD88

NAD83(CSRS)NAD83(CSRS)

Geoid model

Horizontal network (, )

Vertical network (H)

3-D network (, , h)

Adopted in the USA,but not in Canada

3-D network(, , H = h – N )

4-D network(, , H = h – N, t)

NAD83(CSRS)Geoid model

h-dot & N-dot

Directtransformation

ITRFSNARF


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?


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. cycleNot shown: active• Provincial active stations

• NB, QC, BC• Private RTK networks Not shown: passive• High Precision Network (HPN)

• Provincial


National Velocity Grid v1.0

10.14 mm/yr

-1.29 mm/yr

Halifax, NS

Churchill, MB


GPS on BMs

• 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

Nmodel = hGPS - HLev

Validation of geoid models(monitoring static solutions)


GPS on Tide Gauges

GPS on BMs (near tide gauge) GPS on Tide gauges

Halifax, NS

Churchill, MB

-11.12 mm/yr

3.22 mm/yr

Tide gauges with more than 100 months of observations

West Coast East Coast

Arctic


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


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


Absolute gravity survey

FG-5

Survey tent

Vertical gradient of gravity

A-10


Fundamental Absolute Gravity Station in Canada

• Superconducting gravimeter • Canadian Active Control Station• Four absolute gravity stations• Weather station• Two wells• Possible North American Inter-Comparison site (4 inst. max.)

CAGS

TMGO

Canadian Absolute Gravity Site (CAGS)

GWR superconducting gravimeter at CAGS

CAGS was established in 1987.The site is located on bedrock.


Absolute Array• 63 sites co-located with ACP, CBN and/or TG (1) (15) (37) (10)• 8 proposed new sites• 44 other sitesCGSN Primary stations• 74 stations

Canadian Absolute Gravity Array

VancouverIslandLaurentian Profile

Mid-continent Profile


Regular GSC Survey Sites in SW-BC


Preliminary Uplift Rate Comparisons

Algonquin Park

Louise

Gananoque

Charlevoix

Eastmain

Val D’Or

La Grande-1

La Forge

Schefferville

Kuujjuarapik

9.7 ± 2.2

10.3 ± 3.9

10.8 ± 2.8

12.3 ± 2.7

11.0 ± 2.2

17.5 ± 8.8

4.5 ± 1.3

2.9 ± 0.6

2.2 ± 2.4

2.0 ± 4.4

10.1 ± 2.1

(1 Obs.)

15.9 ± 3.3

(1 Obs.)

(2 Obs.)

18.2 ± 5.9

21.5 ± 19.5

1.5 ± 3.7

8.4 ± 2.7

1.7 ± 2.3

11.5

10.6

4.6

-0.2

1.8

8.3

12.1

Station Name/Location

GPS UpliftRate (mm/yr)

Abs-GravityRate (mm/yr)

PGR Model(mm/yr)

9.4

8.6

0.0

La Pocatiere 2.0 ± 2.0 -0.5

-1.3St. John’s -0.9 ± 1.1 (1 Obs.)

-2.8Halifax -2.6 ± 3.0

(2 Obs.)

-0.7 ± 4.7

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]


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


“G-dot” (Relative Gravity Change)

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

μg

al/

yr

▪ CGSN (Relative) Primary Control Points [Pagiatakis & Salib, 2003 – JGR] ▪


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

Satellite Gravity Missions


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.


Monthly geoid change - 2008

Jan MarFeb

OctSep

AugJulJun

Apr

May

Nov Dec

Color scale: -10 mm to 10 mm, GIA trend removed, and wrt to mean static 2002-2003 model


GRACE comparison

GRACE gravity vs mean abs. surface gravitySouthern Vancouver Island

GRACE gravity vs SG gravity dataCanadian Absolute Gravity Site


Sea Surface Topography

SSH: DNSC08 (Denmark)N: PCG08I (Canada)

SST = SSHAlt – N


MSS variation and currents: East coast

Area: N65/N41/W72/W46

SST Atlantic Ocean

-0.55

-0.5

-0.45

-0.4

-0.35

-0.3

Date

SS

T (m

)

Data: AVISO TOPEX-POSEIDON SSH; GEOID CGG2005 (RIM)

SSH: DNSC08 (DK)N: PCG08I (Canada)

Speed of ocean currents (DNSC08 & PCG08I)


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)

Monitoring geoid change in Canada

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