1. U.S. Department of the Interior U.S. Geological Survey ESTABLISHMENT OF THE USGS GPS COMMITTEE, CHARGE AND CURRENT PROGRESS NAVD 88 DATUM CONVERSION UPDATE Paul H. Rydlund Jr. PLS U.S. Geological Survey Missouri Water Science Center

2. Current Guidance – Vertical Datum Techniques of Water-Resources Investigations of the United States Geological Survey Chapter A19 LEVELS AT STREAMFLOW GAGING STATIONS Suggested criteria for tying to NGVD 29 control. Suggested distance under 8 miles, greater than 8 miles should wait or defer to other agencies to establish benchmarks. “Ordinary Levels” – describes Third Order levels run with ordinary equipment and procedures (as opposed to special equipment and meticulous procedures designed to minimize systematic errors). Fourth order levels are run for the purpose of referencing gaging-station datums to NGVD 29. First order (ft) Second order Class I & II (ft) Third order (ft)

3. Current Guidance – Vertical Datum Techniques of Water-Resources Investigations of the United States Geological Survey Chapter A19 LEVELS AT STREAMFLOW GAGING STATIONS Suggested criteria for tying to NGVD 29 control. Double run lines Sight lengths limited to 300 feet Rods read to 0.01 ft Closure errors kept under Third Order, exceptions due to rough or hilly terrain. Third order (ft) Rough/Hilly exception (ft)

4. Establishment of the USGS GPS Committee, charge and current progress GPS Why???? Stuff OSW sponsored, Liaison Robert R. Holmes, Jr.,PhD,PE Committee Members Paul H. Rydlund Jr., PLS, Chair (MOWSC) Brian Fiehler (MCGSC) Doug Nagle (SCWSC) Chad Ostheimer, PE (OHWSC) Kenneth Skinner (IDWSC) Brenda Woodward (NEWSC)

5. Establishment of the USGS GPS Committee, charge and current progress Charge Action Plan : Addressing needs of technically strong GPS activities in the USGS and a set of actions that will address such needs and set a firm foundation for sound and robust use of GPS to achieve accurate and defensible survey data Completion of 2 or 3 highest priority actions from the Action Plan Accomplishment of the remainder of priority action items

6. USGS GPS Survey Web Portal Introduction Mission & Members USGS State Contacts National Equipment Inventory Training And Workshops On-line References Status Of GNSS

7. Coastal Storm Surge Sensors Coastal State Control Evaluation GPS Campaign Guidence Pre-deployment preparedness Methods Data dissemination USGS publications Real-Time Networks State Network Overview & Contacts Method USGS GPS Survey Web Portal - Linked Pages

8. USGS Projects Involving GPS Well Field Surveys Flood Studies Land Science Aerial and Ground-based LiDAR Verification Hydrographic Surveys USGS GPS Survey Web Portal - Linked Pages

9. Techniques and Methods Anticipated Publication Methodology in establishing datum by GPS methods Variable methods of practice and guidelines in ensuring minimum solution standards Survey grade RTK Single base Network RTN Survey grade Post Processed Static Kinematic Fast Static Data Dissemination CASE STUDIES

10. Techniques and Methods Anticipated Publication Guidelines and Procedures for Different Real-Time Accuracy Classes CLASS RT1 CLASS RT2 CLASS RT3

11. 12 miles 13 miles 4 miles 5 miles 3 rd Order 2 nd Order Occupy approximate midpoint 5 mile baseline Redundant rover observations (180 epochs each) tied to bridge Occupy approximate midpoint 4 mile baseline Redundant rover observations 180 epochs tied to bridge and 3 rd Order check Occupy different base location near midpoint 5 mile baseline (best 2 nd Order control source) Redundant rover observations (180 epochs) tied to bridge Derivation of Class RT1 or Class RT2 Procedures, Bridge & Gage Autonomous field base at midpoint Autonomous field base at midpoint 2 nd OrderBridgeDifference3 rd OrderBridgeDifference Given751.75?763.25? 1 st Autonomous 152.36123.45-28.91143.88103.48-40.40 2 nd Autonomous 161.54132.71-28.83138.5298.25-40.27 Elevation722.88-28.87avg722.91-40.34avg Techniques and Methods Anticipated Publication “RTK as a level”

12. Consider beginning with outer network first. Consider minimally and fully constraining inner network. Datum brought in using Static Benchmark Autonomous Benchmark Techniques and Methods Anticipated Publication “GPS over large areas”

13. NGS-NWS-USGS Streamgage Datum Conversion Committee NGS: Renee Shields, Christine Gallagher NWS: Victor Hom, Laurie Hogan (NY), John Sikora (WV), Jonathon Brazzell (LA) USGS: Jim Kolva, Paul Rydlund (MO), Brenda Woodward (NE) NCGS: Gary Thompson, Scott Lokken Objective: To develop a coordinated effort to convert existing NVGD 1929 datum to NAVD 1988 while ensuring a datum quality sufficient for public and cooperative interest

14. NGS-NWS-USGS Streamgage Datum Conversion Committee VERTCON 2 cm at 1 sigma 68% confidence 4 cm at 2 sigma 95% confidence Cooperative GPS Campaigns Methods sufficient to meet accuracy needs

15. USGS database updated to include NWS location IDs NCGS setting control to aid USGS gaging stations Additional parameter dissemination from USGS database to local partners Missouri conducting local pilot study Local spreadsheet (database) nearly complete (needed to scope) 3-4 cm accuracies at NWS forecast sites (other criteria?) Anticipated cooperation with NGS state advisor, NWS, and USACE NGS-NWS-USGS Streamgage Datum Conversion Committee