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Alaska Heights Workshop

Join the Alaska Heights Workshop by John Oswald, PLS, CHS to learn about tidal datums, National Tide Datum Epoch, datum planes, MSL, geoid, and more.

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Alaska Heights Workshop

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  1. Alaska Heights Workshop Tidal Datums John Oswald, PLS, CHS

  2. Tidal Datum Definitions (1) • National Tide Datum Epoch (NTDE) • 19 years • 1960 – 1978 • 1980 – 2001 • Special 5 year 1st Reduction • Datum Planes • MSL • Geoid approximates • USGS Quad Elevations • NGVD29, NAVD88 • MHW • Uplands ownership • Nautical chart land elevations • MLLW • Soundings on nautical charts

  3. Tidal Datum Definitions (2) • Tide Station Protocol • Primary Tide Station • 19 year (metonic) • National Water Level Observation Network (NWLON) • Secondary • 1 year • Tertiary • 30 days/calendar month • Short • 1 minute to upwards of 10 days

  4. Tide Station Locations • NWLONS • 17 in Alaska • About 200 in lower 48 • NTDE 83-01 (April 2003) • NTDE 60-78 • NTDE 42-59 • Unpublished Tide Stations

  5. Where to Get Tide Data • NOAA/COOPS • Center for Observational Oceanograhic Products and Services • co-ops.nos.noaa.gov • Corps of Engineers • National Data Buoy Center • PMEL – Dart Program

  6. What Does the Data Mean? • Verified vs. Unverified • Time • UTC, Local • Datum Plane • MLLW, MSL, MHW, Station Datum • Water Level Observations • “Stage”, “Tide Readings” • 6 minute interval • Hourly Heights • Used to compute Monthly Means • MSL • Daily Highs and Lows • HH, H, L, LL

  7. Tide Gauge Operations (1) • Equipment • Tide Gauges • Digital bubbler • Nitrogen or Pump • Submersible pressure • Strain • Acoustic • Radar • Laser-Lidar • Securing the Orifice • Power • Shelter • Data Telemetry

  8. Tide Gauge Operations (2) • Installation • Boat • Helicopter • Wet Surveyor • Operation • Observation Interval • Observation Averaging • Staff Shots • Leveling Benchmarks • Water Density • Atmospheric Pressure

  9. Tide Gauge Operations (3) • Data Flow • Flash Memory • Satellite Telemetry • Automated Internet Database • Quality Control • Staff Shots • Gauge to Gauge comparisons • Measurement Sigma

  10. Tide Curve Examples: Nome & Prudhoe Bay (1)

  11. Tide Curve Examples: Nome & Prudhoe Bay (2)

  12. Tide Curve Examples: Nome & Prudhoe Storms (1)

  13. Tide Curve Examples: Nome & Prudhoe Storms (2)

  14. Tide Curve Examples: Cook Inlet

  15. Tide Curve Examples: Aleutians

  16. Tide Curve Examples: Seward Peninsula

  17. Datum Computations • 1st Reduction • Tide by Tide • Monthly Means • Quick and Dirty Water Level Shots

  18. Sea Level Changes – Seasonal (1)

  19. Sea Level Changes – Seasonal (2)

  20. Sea Level Changes – Long Term (1)

  21. Sea Level Changes – Long Term (2)

  22. Ellipsoid Heights and Tide Datums • Ellipsoid Heights now being required on Tidal Benchmarks • Relationship of Ellipsoid Heights to Tide Datums • EH more stable • Used for Aircraft positioning (LIDAR, photogrammetry) • Repeatable • Separation is not constant • NOS/NGS 58 Standards • GEOID99, GEOID2004 • Seamless vertical datum • Vertcon • Documentation of Results

  23. Ellipsoid Heights and The Ocean

  24. Ellipsoid – MSL - Geoid

  25. The End R/V JOASurveys.com

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