How Highs the Water

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Ross Mackay Kentucky Geodetic Advisor
How Highs the Water? Elevation and Kentucky
Height Modernization
Well, the rails are washed out north of townWe
gotta head for higher groundWe can't come back
till the water comes down, Five feet high and
risin'
- Johnny Cash
2007 KAMM Conference Kentucky Dam Village State
Resort Park May 8, 2007
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National Spatial Reference System (NSRS)
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National Spatial Reference System (NSRS)

• Since 1807 NGS has provided a consistent
  National coordinate system
• Latitude
• Longitude
• Height
• Gravity
• Shoreline
• and how these values
• change with time

The linchpin of geographic systems in the USA
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36 33 42.15986 N 105 12 15.67754 W
1855.973 m
(NAD83/NAVD88)
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National Spatial Reference System (NSRS)
Geodetic Datum a set of constants specifying
the coordinate system used for geodetic
control and the set of all points and lines
whose coordinates, lengths, and directions have
been determined by measurement or calculation.
Geodetic Datum a set of constants specifying
the coordinate system used for geodetic
control and the set of all points and lines
whose coordinates, lengths, and directions have
been determined by measurement or calculation.
realization of the datum
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National Spatial Reference System (NSRS)
We begin with a grid, the Horizontal Datum
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National Spatial Reference System (NSRS)
Whats a vertical datum?
Image credit Universität Stuttgart
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National Spatial Reference System (NSRS)
Equipotential gravity field
The geoid can be as low as 106 meters (350 feet)
below the ellipsoid or as high as 85 meters (280
feet) above.
NASAs GRACE Gravity Recovery and Climate
Experiment
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National Spatial Reference System (NSRS)
Image credit University of Texas at Austin
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National Spatial Reference System (NSRS)
Vertical Datums

• Mean Sea Level Datum Of 1929
• name changed
• National Geodetic Vertical Datum of 1929
• - NGVD 29 (July 2, 1973)
• North American Vertical Datum of 1988
• - NAVD 88 (June 24, 1993)

• NGVD 29 NAVD 88
• Datum Definition 26 Tide Gauges in Fathers
  Point
• the
  U.S. Canada Quebec, Canada
• Bench Marks 100,000
  450,000
• Leveling (Km) 102,724
  1,001,500
• Geoid Fitting Distorted Fit
  Best Fit
  to MSL Gauges Continental Model

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National Spatial Reference System (NSRS)
NAVD 88
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National Spatial Reference System (NSRS)
Declining Infrastructure
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National Spatial Reference System (NSRS)
Why height matters?
NOAA Press Release Dec. 17, 2002 Recent studies
by the NOAAs NGS, in partnership with LSU,
indicate the states hurricane evacuation routes
are growing increasingly vulnerable to coastal
storm surge and flooding.
Image credit AP Photo/Rick Bowmer
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Height Modernization
enter GPS
(GNSS)
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Height Modernization

Topographic Surface
H
h
Ellipsoid
Geoid
h Ellipsoidal Height
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Height Modernization
H Elevation (Orthometric Height)
h Ellipsoidal Height (from GPS)
N Geoid Height (from Geoid model)

Topographic Surface
H
h
Ellipsoid
N
N
h - N
H
h
Geoid
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Height Modernization

• Hybrid geoid model
• Gravity
• Leveling
• GPS
• best fit to NAVD 88

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Height Modernization
Geoid model in Kentucky (Geoid03)
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Height Modernization
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Height Modernization
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Height Modernization
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Height Modernization
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Height Modernization
These look like some of the best CORS sites that
I've seen. Don Haw, NGS CORS team member
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Kentucky Height Mod Whats next?
H h - N
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Kentucky Height Mod Whats next?
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Height Modernization
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Height Modernization
LIDAR and its Products Light Detection and
Ranging
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National CORS
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National CORS
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National CORS

• Submit GPS data file to NGS website
• Processed automatically with NGS computers
  software
• With respect to 3 suitable CORS
• Solution via email (usually in minutes)
• Fast, easy consistent access to the
• National Spatial Reference System

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National CORS
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National CORS
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Many Flavors of OPUS Planned
National CORS

• OPUS
• one receiver, hours of data
• OPUS Rapid Static
• one receiver, minutes of data
• OPUS-DB
• one receiver, hours of data, archive results
• OPUS Projects
• multiple receivers, archive result
• OPUS GIS
• receiver, minutes of data, no archive

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National CORS

• 1009 National CORS
• 166 Cooperative CORS
• April 30, 2007

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International GNSS
International GNSS Service
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International GNSS
GPS Observed Vertical Velocities
Clear pattern of positive velocities around
Hudson Bay that decreases going southwards to
zero (hinge line), beyond which velocities are
initially negative and then rise to near
zero All sites north of the hinge line and those
up to a 100 km south are interpreted as being due
to Glacial Isostatic Adjustment
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International GNSS
GPS-derived ITRF Horizontal Velocities
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International GNSS
ITRF vs. NAD 83 Height Relationship
h-NAD83
Earths
h-ITRF
Surface
ITRF
Origin
2.2 meters
NAD 83
Both systems use GRS-80 ellipsoid a
6,378,137.000 meters (semi-major axis) 1/f
298.25722210088 (flattening)
Origin
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International GNSS
NAD83 vs. ITRF Ellipsoid Heights (meters)
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Relative Positioning
International GNSS
Mapping Accuracy (m-level) - Post-Processed -
Real-Time Differential (NDGPS, WAAS,
etc.) Survey Accuracy (cm-level) -
Post-Processed - Real-Time Kinematic (RTK,
Network RTK)
Data or Correction
NSRS Reference Station
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International GNSS
Autonomous Positioning Today
lt13m
Vertical accuracy 22 m

• C/A Code on L1
• No Selective Availability
• (since 5/1/00)

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International GNSS
Autonomous Positioning 2015 (?)
Better resistance to interference
0.1 m -- 1 m

• C/A Code on L1
• L2C Code on L2
• L5 Code

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Ross Mackay Kentucky Geodetic Advisor
ross.mackay_at_ky.gov on the web at ngs.ky.gov (502
) 564-1450 x290