1. The Importance of Accurate Elevations & Case Studies Edward Carlson Pacific Region Geodetic Advisor National Geodetic Survey Ed.Carlson@noaa.gov (808) 532-3205

2. The ability to establish highly accurate horizontal positions has become much simpler in the last 10 years. –Full constellation of GPS satellites. –More affordable GPS receivers and software. –Establishment of statewide HARNs. –Proliferation of the national CORS network. ESTABLISHING HORIZONTAL POSITIONS

3. ESTABLISHING VERTICAL POSITIONS Unlike the horizontal component, establishing accurate elevations is becoming increasingly more difficult. –Reduction in the number of benchmarks. –Loss of accuracy of benchmarks over time. –Unavailability of benchmarks for GPS observations.

4. PROBLEMS WITH VERTICAL NETWORK Major problem is land development and construction activities, destroying an estimated 40 percent (or more) of the existing monuments. Many existing vertical monuments are not well-suited for GPS observations… –Tree canopies. –Walls of buildings. –Urban canyons. In some counties… the problem is much worse.

5. CHARLESTON BRIDGE PROJECT

6. PURPOSE Determine the precise “AIR GAP” of the bridges (distance at Mean High Water and the bottom of the bridge) METHODS TO BE USED GPS Trig-Leveling Classical Leveling

7. MOUNTING THE ANTENNAS

8. TRIG-LEVELING

9. GPS OCCUPATION

10. CLASSICAL LEVELING

11. CHARLESTON BRIDGE NETWORK C 69 TBM SILE ARP HOLLINS 10 012 TIDAL 13 CBPA CHA1 CORS NAVD88 Bench Mark Temporary (Project) CORS

12. BOTTOM OF GPS ANTENNA BOTTOM OF BRIDGE MEAN HIGH WATER GPS ANTENNA NAVD88 BM h (Determined by GPS ) HI (Determined by trig-leveling) H GPSBotBr MHW

13. COMPARISION OF ORTHOMETRIC HEIGHTS NAVD88 GPS METHOD HGPSANT = 65.211 m TRIG-LEVELING HGPSANT = 65.203 m DIFFERENCE = 0.8 cm

14. Relating the ship to the bottom of the channel, shoreline, and docking areas Determining the vertical clearances for large vessels navigating beneath bridges MARINE APPLICATIONS

15. HAMILTON AIR FORCE BASE To assist in making vertical geographical representation for the wetlands restoration.

16. EXISTING NAVD88

18. HAMILTON AFB CONTROL POINTS

24. ORTHO PHOTO OVERLAID ON DITIGAL ELEVATION MODEL(DEM)

26. DETERMINING GPS ORTHOMETRIC HEIGHTS FOR THE MAUI PUMPING WELLS

27. PROBLEM TWO DIFFERENT MEASURING POINT ELEVATIONS FOR THE KANOA WELL IN THE WAIHEE AQUIFER SECTOR

28. KNOWNS LEVELING TO 1/100 th OF A FOOT WAS DONE TO EACH WELL UNKNOWNS 1.WHAT BENCH MARK WAS USED. 2.HOW WAS THE BENCH MARK DETERMINED. 3.HOW GOOD IS THE BENCH MARK WHEN LEVELING DONE.

29. PROJECT AREA

30. MAUI WELLS SITES & NGS BENCH MARKS

31. MAUI WELLS SITES & RECOVERED BM

35. TIDAL BENCH MARK NGS BENCH MARK CORS SITE

36. Designation Pub Elevation Vertical Free Orthometric Shift (cm) 161 5680 TIDAL C 1.461 1.461 0.0 * A 6 137.775 137.684 -9.1 * F 6 146.390 146.324 -6.6 * M 22 1.981 1.750 23.1 R22 RESET 5.972 4.234 173.8 V 6 48.173 48.118 -5.5 * * Fixed Elevation Free Vertical Adjustment Compared to Published Elevations

37. WAIHEE BRIDGE AREA ELEVATION ON TOP OF WING WALL 122.48 ft LEVELING – WING WALL TO MARK -0.91 ft LEVELED ELEVATION OF MARK 121.58 ft GPS DETERMINED ELEVATION 121.52 ft DIFFERENCE.06 ft

38. CONCLUSION GPS METHODS WORK FOR DETERMINING HEIGHTS

39. Find Your Way With Height Modernization