North Carolina Geodetic Survey

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North Carolina Geodetic Survey

• National Height Modernization System in
• North Carolina

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National Height Modernization System

• National Height Modernization Study (June
  1998)
• Performed pilot project in Asheville area
• Report to Congress

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Benefits to North Carolina

• Geodetic control network
• Global Positioning System (GPS) base station
  network
• North Carolina Floodplain Mapping Program
• Highway construction
• North Carolina Land Records Management Program
• Environment and natural resources programs
• Emergency management

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NHMS Activities in North Carolina
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North Carolina HARN
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North Carolina HARN
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Operational Proposed GPS Base Stations (CORS)
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NHMS Activities In North Carolina
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NHMS Project Areas
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Effects of Hurricane Floyd on North Carolina

• 51 deaths
• 3.5 billion in damages to homes, businesses,
  roads, and infrastructure
• 31,000 jobs lost

Goldsboro, NC
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North Carolina Floodplain Mapping Program
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Components of a DFIRM

DFIRM
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LIDAR Laser Sensor

• First returns provide Digital Surface Models
  (DSMs)
• Roof tops
• Tree tops

• Last returns can provide Digital Elevation
  Models (DEMs) of the bare earth if fully
  processed to remove buildings and vegetation that
  were not penetrated by the LIDAR pulses

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Multiple Returns
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Bare-Earth Post-Processing
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First Return
Courtesy of the Joint Precision Strike
Demonstration Project Office (JPSD-PO)
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LIDAR Digital Elevation Model
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LIDAR Digital Elevation Model
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TIN
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Intensity Return
Courtesy of the Joint Precision Strike
Demonstration Project Office (JPSD-PO)
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Terrain Data Download
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Bare Earth Terrain Data
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Objective of the QC Surveys

• Establish quality control (QC) checkpoints to
  evaluate the vertical accuracy of the elevation
  data
• 20-cm vertical RMSE for coastal counties
• 25-cm vertical RMSE for inland counties
• Require 120 checkpoints per county
• 20 checkpoints required for the following four
  classes bare earth and low grass, weeds/crops,
  scrub, and built-up
• 40 checkpoints required for the forest class

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Bare-Earth Low Grass Land Class
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Forest Land Class
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QC Assessment Report Halifax County, Tar-Pamlico
Portion

• RMSE summary using
• 100 of the checkpoints
• 95 of the checkpoints
• Checkpoints categorized by land cover type

The LIDAR data for Halifax County met the
specification as per the RMSE criteria of 25 cm.
All figures represented the data with the 95
data set. The data was of good quality with the
smaller data limited to the Tar-Pamlico basin
only. The land class type of built-up was
slightly high, but was well within specifications.
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Providing Access With NC OneMap
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Jones County- Effective Mapping
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New Panels - Statewide
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The North Carolina Flood Insurance Rate Map (FIRM)
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Flood Insurance Rate Map

• 1 annual chance floodplain-cyan dots (FEMA
  Standard)
• Floodway White Hatch (FEMA Standard)
• 0.2 annual chance floodplain-black dots
• Numbered cross sections

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Jones County- 2003 Mapping
Blue 2003 Zone AE
BFE
Cross Section
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The Boundaries
2002 Detail Mapping vs. Effective Approximate
Mapping
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2003 Mapping vs FEMA Q3
Orange Effective Zone A
Green 2003 Zone AE
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2002 Mapping
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Effective vs 2002 Mapping
2002 Limited Detail Boundary (blue)
Old Zone A Boundary (red)
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Features of New Maps
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Vertical Datum Information

• Explains vertical offset from NGVD 29 to NAVD 88
• County Average Vertical Datum Offset Table
  displays datum offset by county

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www.ncfloodmaps.com
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Collection of High Water Marks (HWM)
NHMS supported these activities in NC
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North Carolina FMP Imagery/LIDAR Quality Control
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Monitoring Subsidence
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Network RTK Positioning
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Network RTK Expansion
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Data Flow in the Network
Raw Data
CMR / RTCM
LAN
NMEA Position
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North CarolinaFlood Warning System
Stream Gage
Rain Gage
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Tar River at Tarboro, bank full 22.4 ft.
elevation (12 ft gage ht.)
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Tar River at Tarboro 37 ft. elevation (27.0
gage ht.) Hurricane Fran
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Tar River at Tarboro 44 ft. elevation (34.0
gage ht.)
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Tar River at Tarboro 52 ft. elevation (41.5
gage ht.) Hurricane Floyd
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Tidal Station Surveys
NC NHMS Project
GPS and traditional leveling will be use to
connect tidal stations to the vertical control
network
Tidal station
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Education Outreach
Height Modernization Workshops is a traveling
workshop designed for government agencies,
professional surveyors, academic departments,
school groups, and other interested parties in
North Carolina.

• Workshops are tailored to each groups respective
  needs
• PDH credit

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Questions?
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hits2129
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