the importance of accurate elevations & case studies edward carlson pacific region geodetic...
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The Importance of Accurate Elevations
&Case Studies
Edward CarlsonPacific Region Geodetic Advisor
National Geodetic Survey [email protected]
(808) 532-3205
• 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
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.
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.
CHARLESTON BRIDGE PROJECT
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
MOUNTING THE ANTENNAS
TRIG-LEVELING
GPS OCCUPATION
CLASSICAL LEVELING
CHARLESTON BRIDGE NETWORKC 69 TBM SILE
ARPHOLLINS
10 012
TIDAL 13
CBPA CHA1CORS
NAVD88 Bench Mark
Temporary (Project) CORS
BOTTOM OF GPS ANTENNA
BOTTOM OF BRIDGE
MEAN HIGH WATER
GPS ANTENNA
NAVD88 BM
h (Determined by GPS)
HI (Determined by trig-leveling)
HGPSBotBr
MHW
COMPARISION OF
ORTHOMETRIC HEIGHTSNAVD88
GPS METHOD
HGPSANT = 65.211 m
TRIG-LEVELING
HGPSANT = 65.203 m
DIFFERENCE = 0 .8 cm
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
HAMILTON AIR FORCE BASE
To assist in making vertical geographical representation for the wetlands restoration.
EXISTING NAVD88
HAMILTON AFB CONTROL POINTS
#S
#S
#S
#S
M 1393F 466
C
HPGN D CA 04 J E
941 5252 D
941 5126 D
#S
#S
San Pablo Bay
Project Area
ORTHO PHOTO OVERLAID ON DITIGAL ELEVATION MODEL(DEM)
DETERMINING GPS ORTHOMETRIC
HEIGHTS FOR THE MAUI PUMPING WELLS
PROBLEM
TWO DIFFERENT MEASURING POINT ELEVATIONS FOR THE KANOA WELLIN THE WAIHEE AQUIFER SECTOR
KNOWNS
LEVELING TO 1/100th 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.
PROJECT AREA
MAUI WELLS SITES&
NGSBENCH MARKS
G
G
%%
%% G
%
%
%
G
G
%
%
G
%
% G
%
%
%
%%%
¯0 8 164 Miles
Geodetic Reference Locations
% Well Location
G Geodetic Bench Mark
MAUI WELLS SITES&
RECOVERED BM
G
G
%
%
%
%G
%
G
%
%
%G
%
%
%
%
%%
V 6
F 6
A 6
LUKE
TEST HOLE E
DWS MOKUHAU
TEST HOLE A1
WAIHEE BRIDGE
161 5680 TIDAL C
WAIKAPU 1 MONITOR
DWS WAIEHU HEIGHTS
WAIKAPA SHAFT WELLS
WAIEHU DEEP MONITOR
DWS WAILUKU BOOSTER
KANOA WELL GAUGE STATION
WAIKAPU WELL GAUGE STATION
NORTH WAIHEE
WAIHEE GUAGE STATION
DWS WAILUKU SHAFT 33
¯0 2 41 Miles
Geodetic Reference Locations
% Well Location
G Geodetic Bench Mark
G
G
G
%
%
G
%
G
%
F 6
A 6
M 22
R22 RESET
161 5680 TIDAL C
MAUI HALEAKALA MA
WAIKAPA SHAFT WELLS
KIHEI RECYCLING CENT
KEALIA POND GAUGE STATION
¯0 2.5 51.25 Miles
Geodetic Reference Locations
% Well Location
G Geodetic Bench Mark
TIDAL BENCH MARK
NGS BENCH MARK
NGS BENCH MARK
NGS BENCH MARK
CORS SITE
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
WAIHEE BRIDGE AREA
ELEVATION ON TOP OF WING WALL 122.48 ftLEVELING – WING WALL TO MARK -0.91 ftLEVELED ELEVATION OF MARK 121.58 ft
GPS DETERMINED ELEVATION 121.52 ft
DIFFERENCE .06 ft
CONCLUSION
GPS
METHODS
WORK
FOR
DETERMINING
HEIGHTS
Find Your Way
With Height
Modernization