| |
|
|
Introduction
Lidar
surveys provide a contour line to represent the shoreline.
However, lidar data are acquired as heights above the ellipsoid
(HAE) and must be converted to heights above a local tidal
datum. Furthermore, the contour chosen to represent the shoreline
should correlate with a geomorphic feature such as a high-tide
berm. It should also be high enough so that it is usually
above water. Finally, the line needs to be "cleaned"
to remove undulations caused by structures or reentrants into
runnels.
|
|
| Schematic
of the Airborne Laser Terrain Mapping (ALTM) system that illustrates
its three major components: a solid-state laser (1,064-nm wavelength)
that scans back and forth across the terrain, an Inertial Motion Unit
(IMU) for monitoring aircraft attitude, and geodetic-quality Global
Positioning Receivers for accurate aircraft positioning. |
| |
|
Survey
Plan
The
Bureau uses a network of tidal stations, National Geodetic
Survey monuments, and Bureau-installed reference points along
the Gulf of Mexico coast as Global Positioning System (GPS)
base stations during lidar surveys. Base stations are chosen
along the flight path no farther than 50 km apart. Representative
beach profile locations are also being established and surveyed
with geodetic GPS.
Click
on image to enlarge.
|
|
|
| |
|
|
Lidar
Flight Parameters
Altitude:
500-700 m AGL
Speed: 85-110 knots
Swath width: 350-500 m
Pulse rate: 25 kHz
Scanning frequency: 25 Hz
Scan angle: ±20 degrees
Number of shoreline passes: 2-4
Baseline length: <50 km
Navigation: Down-looking video
Click
on image to enlarge.
|
|
| A
videocamera with the same view as the laser is used for navigation
along the Gulf of Mexico shoreline. The pilot uses the videocamera
to monitor position above the land/water interface, wet/dry line,
vegetation line, or dune crest. For complicated bay shorelines real-time
DGPS guidance along predefined parallel-flight lines is used. |
|
|
