GPS Requirements for the National Water Level Program

1. GPS Requirements for the National Water Level Program Applications of GPS/GNSS in NOAA Cross-NOAA Workshop Boulder, Colorado October 24-25, 2007 Thomas F. Landon NOAA/National Ocean Service Center for Operational Oceanographic Products and Services

2. Presentation Overview • National Water Level Program • National Water Level Observation Network • Leveling at Water Level Stations • Long-Term Sea Level Trends • National Tidal Datum Epoch • Areas of Anomalous Sea Level Trends • NWLON GPS Operational Plan • Relating the Tidal and Geodetic Datums by leveling and GPS • GPS Applications

3. NOAA OCEAN SERVICE NATIONAL WATER LEVEL PROGRAM • PROVIDES TIDAL DATUM AND WATER LEVEL DATUM REFERENCES FOR THE ENTIRE U.S COASTAL ZONE • PROVIDES FOR GEODETIC DATUM CONNECTION AND REFERENCES TO TIDAL DATUMS FOR THE ENTIRE COASTAL ZONE • PROVIDES FOR UPDATED NATION-WIDE INFORMATION ON RELATIVE SEA LEVEL TRENDS AND LAND MOVEMENT

4. National Water Level Observation Network 200 Stations as of 2007 (planned expansion to 300 stations pending increased base funding) Remote Pacific Island Stations Not Shown

5. THE NWLON AS A GEOPHYSICAL TIME SERIES

6. WATER LEVEL STATION CONFIGURATION • Supporting Structure • Water Level Sensor(s) • Data Collection Platform (DCP) • Bench Mark Network • Ancillary Sensor(s)

7. Typical NWLON and Short-Term Stations

8. REFERENCING OF THE SENSOR ZERO TO STATION DATUM THROUGH LEVELING AND BENCH MARKS Primary Bench Mark and GPS Mark: BG4867 87209840 M TIDAL

9. Leveling at Water Level Stations • NGS Accuracy Standards • 2nd Order, Class I for long-term stations • 3rd Order for short-term stations • Electronic Digital Barcode Leveling Equipment preferred • Annual leveling for NWLON; installation and removal levels for short-term stations • Emergency leveling for storm events

11. NATIONAL TIDAL DATUM EPOCH (NTDE) A common time period to which tidal datums are referenced • A specific 19 year period that includes the longest periodic tidal variations caused by the astronomic tide-producing forces. • Averages out long term seasonal meteorological, hydrologic, and oceanographic fluctuations. • Provides a nationally consistent tidal datum network (bench marks) by accounting for seasonal and apparent environmental trends in sea level that affects the accuracy of tidal datums. • The NWLON provides the data required to maintain the epoch and make primary and secondary determinations of tidal datums.

12. 1983-01 EPOCH ACTUAL IDEALIZED CHANGE OF TIDAL EPOCH

13. COMPUTING TIDAL DATUMS IN AREAS OF ANOMALOUS SEA LEVEL TRENDS There are areas of Louisiana, Texas, SE Alaska and SW Alaska where there are anomalous sea level trends compared to most other geographic regions of the United States. “New Procedures” have been developed to address these regions so that published tidal and geodetic relationships are representative of current conditions

16. NWLON GPS Operational Plan • Requirements: NOS NGS-58, CO-OPS User’s Guide for GPS Observations, CO-OPS Standing Project Instructions, and contractor specifications • Frequency: coordinated with rate of sea level rise – annually or every five years • Station GPS mark identified in project instructions • Documentation: all data required for OPUS-DB submissions • Monitoring: Track and compare solutions over time

17. Operational Plan for Periodic GPS Observations National Water Level Observation Network GPS Annually at Selected stations, Every 5 Yrs at others GPS Every 5 Yrs GPS Every 5 Yrs GPS Annually

18. CORS Co-located with NWLON • Coordinate with NGS to co-locate CORS sites with long-term NWLON stations • Level to the CORS GPS reference marks bi-annually as a minimum • 12 co-located sites in the Great Lakes • NGS performing recons at seven NWLON sites on the east coast; Key West completed in January 2007 • NGS planning to install CORS at many of the Alaskan NWLON stations

19. 9099004 Point Iroquois, Lake Superior 9087044 Calumet Harbor, Lake Michigan CORS antenna on houses

20. 3.150 m Tidal Bench mark 4811 G 2004 2.736 m MHW 1.220 m MLLW Geodetic Tie to Tidal Datums at Bradmoor Island (Standard Levels Example) Once leveled, you can transform between tidal and geodetic datums. Tide Gauge Pier NOAA 1.150 m (example value) Tidal Bench mark 4811 G 2004 Geodetic Benchmark (and its NAVD88 value) Relative to Tidal Datum 2.000 m Bench mark with geodetic control (NAVD88, WGS84,etc.) NAVD88 Orifice 0.7428 m Station Datum

21. 3.150 m Tidal Bench mark 4811 G 2004 2.736 m MHW 1.220 m MLLW Geodetic Tie to Tidal Datums at Bradmoor Island (GPS Example) Ellipsoid GPS Receiver GPS Receivers collecting simultaneous data over existing bench marks allow for datum transformation. Tide Gauge Pier NOAA 1.150 m (example) Tidal Bench mark 4811 G 2004 Geodetic Benchmark (and its WGS84 value) Relative to Tidal Datum 2.000 m Bench mark with geodetic control (NAVD88, WGS84,etc.) NAVD88 Orifice 0.7428 m Station Datum

23. Visual Representation of Tidal and Geodetic Datums

24. Relationship of Tidal Datums to the Ellipsoid

25. Assessing Sea Level Rise

26. Marsh Restoration Barren Island, MD • Using known plant habitat criteria elevations relative to the tidal datum were grouped together for each species. • Plant specifications • Spartina alterniflora MLLW – MHW • Spartina patens MHW-MHHW

27. Measuring Subsidence, Sea Level & Storm Surge

28. Questions?