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Problems With The Vertical Reference Frame In Alaska

Problems With The Vertical Reference Frame In Alaska. JOA Surveys Erik Oppegard. Two Problems for Today. Distribution and density of vertical control Time. Where Is this?. State of Wisconsin 295 miles E-W 320 miles N-S 11,090 NAVD88 published stations

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Problems With The Vertical Reference Frame In Alaska

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  1. Problems With The Vertical Reference Frame In Alaska JOA Surveys Erik Oppegard

  2. Two Problems for Today • Distribution and density of vertical control • Time

  3. Where Is this? • State of Wisconsin • 295 miles E-W • 320 miles N-S • 11,090 NAVD88 published stations • Average 1 NAVD88 benchmark every square 8.5mi

  4. Where Is This? • State of Alaska • 800 miles E-W (Canada border to Hooper Bay) • 800 miles N-S (Barrow to Seward) • 3608 NAVD88 published stations • Average 1 NAVD88 benchmark every square 177mi

  5. Density Comparison AK & WI

  6. Effects of NAVD88 Network • Vertical surveys very expensive, especially if performed off the road system • Sparseness of adequate vertical control in remote AK leads to weak strength of figure in adjustments • Vertical surveys impractical, especially if performed under NGS-58 and NGS-59 requirements

  7. NGS-58 & 59 • Minimum 3 HARN (A or B order) within 75km of same or higher order • Minimum of 3 Primary Bases within 50km of same or higher order • Secondary Bases within 20km of same or higher order • User Densification Network within 20km of same or higher order For 5cm guidelines, 2cm is denser

  8. OPUSDB • Online publishing of GPS observations • “For the people by the people” • Linked to datasheets • Allows for easy reconnaissance

  9. OPUSDB Submissionsas of 2/21/2010

  10. AdakOPUSDB DataSheet Dave Doyle: Not surprised that this Position is more than 2m off published HZ He is surprised that The orthometric height Is 4.328m from NWLON LMSL

  11. Time • The position of a station is only truly known the moment of its last observation • Stations are destroyed • Stations move due to plate tectonics and isostatic rebound • Stations move due to local geology

  12. NAVD88 in Seward • X74 • 72ft copper clad rod • VERT ORDER - FIRST CLASS II • Stability Code B

  13. NAVD88 in Seward • 945 5090 TIDAL 10 • Set in a massive structure • VERT ORDER - FIRST CLASS II • Stability Code B

  14. NAVD88 in Seward • Stability: B = Probably hold position/elevation well • 2005: Required to level through these marks during annual maintenance of NWLON • The two stations were 2.25 miles apart • 0.234m – The difference in Difference of Elevation between 2005 and 1967 published levels • Which station moved? • Perhaps both

  15. NAVD88 in Seward

  16. Uplift of the Kenai Peninsula • Cumulative crustal uplift between 1964 and 1995 relative to a site in Seward • Cohen and Freymueller, 1997 • http://denali.gsfc.nasa.gov

  17. Sea Level in Seward and Anchorage

  18. Sea Level Falling in Nikiski

  19. Land Rising at Nikiski Copper clad Steel rod driven 12.2m (40ft)

  20. Land Rising at Nikiski • 24 hour annual sessions during NWLON maintenance trips • NGS OPUS Solutions • REF FRAME: ITRF00 • 2006 Ellipsoid Height: 15.975(m) • 2007 Ellipsoid Height: 16.006(m) • 2008 Ellipsoid Height: 16.055(m) • 2009 Ellipsoid Height: 16.044(m)

  21. Sea Level is Falling in Skagway

  22. Land Rising at Skagway Copper clad Steel rod driven 5.8m (19ft)

  23. Land Rising at Skagway • 24 hour annual sessions during NWLON maintenance trips • NGS OPUS Solutions • REF FRAME: ITRF00 • 2007 Ellipsoid Height: 12.674(m) • 2008 Ellipsoid Height: 12.706(m) • 2009 Ellipsoid Height: 12.735(m)

  24. New NWLON at Elfin Cove

  25. Tidal BM Elevations at Elfin Cove • Datasheets published less than 2 years apart • Benchmarks rose 0.234m in 13.5years

  26. Hooper Bay Tide Station June 2007 • SS Rod driven 8.53 m (28.0 ft) to refusal, June 2007 • Ice lens collapsed the ground around the benchmark • The benchmark did not move – only the ground as confirmed through 3 wire levels September 2007

  27. Conclusion • Distribution and density of NAVD88 stations very sparse off the road system • Benchmark elevations are dynamic with time – user beware

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