Many Vertical Datums that are not part of the NGRS have been used throughout the years in Alaska

1. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums

2. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsOVERVIEW of THIS SESSION • Many Vertical Datums that are not part of the NGRS have been used throughout the years in Alaska • I am going to briefly discuss SOME of these datums explaining: History, Reference Planes, Names and Uses • I will present where to find information and data for each • I will then discuss issues about use of these DATUMS and how to relate “local” vertical DATUMS to other vertical DATUMS

3. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsVERTICAL DATUM CATAGORIES • Non-National vertical datums can be divided into five main groups: • Federal • State • Municipal/Borough • Project • “Other”

4. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsCOE VERTICAL DATUMS IN ALASKA • Local Orthometric datums for Military Bases such as Elmendorf, Galena, Adak, Shemya • Have gone to NAVD88 generally for active Bases • Local Tidal datums at ports/harbors/channels to support dredging activities • River Flood Height References at villages • COE Contacts: • Harlen Lagaire (907) 753-2610 for Flood Heights • Andrew Brewer (907) 753-2757 for Tidal BMs • Jerry Zuspan (907) 753-2660 for Base Datums

5. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsOTHER FEDERAL VERTICAL DATUMS IN ALASKA • USFWS Water Heights Studies – Used NAD83 ellipsoid heights • FAA for Airports – Varied drastically over years, call now to go to NAVD88 (discussed more later in this session) • Alaska DEM Initiative led by USGS – “Pseudo NAVD88” (NAD83 ellipsoid w/ GEIOD computed by observation of IFSAR & gravitometer)

6. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsSTATE VERTICAL DATUMS • NO official state of Alaska vertical datum • ADOT&PF largest state agency directing and working with vertical surveys • ADNR has been involved in some vertical surveys, such as “Dinkum sands” litigation • Possibly some other state agency surveys referenced to vertical, but most likely referenced to national datums or are “local”

7. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsSTATE VERTICAL DATUMS – ADOT&PF • ADOT&PF provides vertical control in three Regions: Southeast, Central & Northern, and also AIA • Typically all highway, airport, and harbor projects have associated Survey Control Sheet detailing vertical datum referenced • Additional vertical data obtainable through regional Survey Managers

8. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums ADOT&PF VERTICAL DATUMS – HISTORY • Past ADOT&PF vertical datums varies on era of project and project location • When NGRS BM’s available (mostly in CR & NR along roads) Dept. used NGVD29 and then NAVD88 or GAAB72 in Anchorage • Outlying areas vertical datums widely varied from use of VABMs, short-term tidal, Tidal BMs (either MLLW or MTH), and even assumed local based on need for project. • Airports needed MSL, projects affected by tidal design issues needed MLLW

9. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsVERTICAL DATUMs – AIRPORTS 2003 & BEYOND • FAA desires NAVD88 for all airports (FAA Section 405 Specifications) • NAVD88 unobtainable in most of Alaska away from NGS NGRS Benchmark Loops • GPS cannot truly return NAVD88 as all present geoid models are uncorrelated to BM network in Alaska • FAA willing to accept “Pseudo NAVD88” in remote areas using NAD83 ellipsoid height with uncorrected geoid undulation correction

10. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsVERTICAL DATUMs – AIRPORTS 2003 & BEYOND • Problems with “Pseudo NAVD88” Approach • Geoid Model bias change – Geoid96 vs Geoid99 in many areas 1-2 meters different • Mis-identification of title of datum confusing and misleading • Advantages with “Pseudo NAVD88” Approach • Well documented of what was done • Consistent between airports regionally • Able to easily update in future as more refined Geoid Models develop • Consistent with aviation GPS navigation equipment

11. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsVERTICAL DATUMs – AIRPORTS 2003 & BEYOND • HOW TO DESCRIBE “PSEUDO NAVD88” • A local orthometric vertical datum established by applying GEOID99 ellipsoid-to-geoid separations directly to NAD83 ellipsoid height for point “NAME”. This datum approximates NAVD88 plus or minus the un-removed bias of GEOID99 geoid model correlation to the NAVD88 vertical network.

12. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project DatumsSTATE VERTICAL DATUMS – ADOT&PF CONTACTS • Southeast: Randal_Davis@dot.state.ak.us • Central: Michael_Schoder@dot.state.ak.usftp.cadastral.info/dot-cadastral/Highway-and-Airport-Control-System • Northern: Scott_Sexton@dot.state.ak.us • AIA: Bob_Ramsey@dot.state.ak.us www.dot.state.ak.us/anc/Engineering-Construction/engineering.html

13. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums BOROUGH VERTICAL DATUMS • Many of the Boroughs have done additional leveling and monumenting to establish vertical control. Some of these include: • Municipality of Anchorage – GAAB72 • Matanuska-Susitna Borough • Kenai Peninsula Borough • City/Borough of Fairbanks • Information normally available through the respective Borough Surveyor or Engineering Department

14. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums MAT-SU BOROUGH VERTICAL DATA • Leveling from NGRS NGVD29 Benchmarks as source • Established new BMs on Old Glenn Highway Palmer to Knik River Bridge and Knik Goose Bay Road from Wasilla to Pt. McKenzie Road • Project was performed by contract, project report is final data source. • Old Glenn Line has issue with value used of originating BMs in Palmer and does not connect well to Glenn Highway NGS Benches

15. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums KENAI PENINSULA BOROUGH VERTICAL DATA • Leveling from NGRS NGVD29 Benchmarks as source • Established new BMs off of Sterling Highway to Kenai River for flood/hydrological reference • Project was performed by contract, project report is final data source.

16. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums MUNICIPALITY OF ANCHORAGE VERTICAL DATA • GAAB72 established to densify vertical data in Anchorage • Local orthometric leveling referenced to “post quake” NGVD29 NGRS values • Originally included only Anchorage Bowl, Eagle River and Girdwood added later • Data published in “Benchmark Book”, now on-line: www.ci.anchorage.ak.us/ProjectMgmt/survey.cfm

17. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums MUNICIPALITY OF ANCHORAGE VERTICAL DATA • No future plans for re-monumentation or re-observation by MOA • MOA requests BM updates through MITS recovery form • Other Agencies and Private Firms will continue to use, and supplement • Monument stability is fairly good, will become more of an issue in future years

18. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums PROJECT SPECIFIC VERTICAL DATUMS • Many large, or long-term projects have established local vertical datums • Oil Fields – “West Dock” for Prudhoe Bay and Kuparuk (See BP & Arco Survey Contractors) • TAPS (See TAPS Survey Contractor) • Mines (Red Dog, Fort Knox, Usibelli, Greens Creek are all examples – contact mine operators) • Other Large-Scale commercial developments • With the advent of GPS there are now less reasons to create independent local vertical datums for projects

19. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums INTERNAL USE OF VARIOUS VERTICAL DATUMS • Simple issue if using locally, with spirit levels and conventional terrestrial equipment • Always need data concerning monument setting, height value, and date of issue • Use with GPS requires “site calibration” with RTK, or shift,tilt, slope fitting of external geoid model to network of static vectors • IMPORTANT: Always consider monument stability when evaluating fit with any method!

20. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums MIXING VARIOUS VERTICAL DATUMS • More care needs to be placed when mixing vertical datums and establishing relationships • The old adage: Don’t mix Apples & Oranges • Comparing single point creates first-level comparison of datum offset. • Comparison of a number of well distributed points throughout study are with stable monuments best method to remove slopes, tilt and average monument stability/accuracy errors • “Over-determine” comparison if possible to provide a truer evaluation statistically and provide check points of final solution

21. Alaska Heights Short Course – February 2004Session 3- State, Municipal, Borough and Project Datums EVALUATING VARIOUS VERTICAL DATUMS • The best tool to provide a long-term, stable reference plane: GPS ELLIPSOID HEIGHT! • Ellipsoid heights referenced to either NAD83 or ITRF ellipsoids is easily determined with GPS, repeatable, not effected by tectonic and monument stability issues and will be supported with rigorous transformations to other future world-wide ellipsoids. • These attributes make GPS Ellipsoid Heights the best Benchmark to evaluate different datum correlations.