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Mapping Shorelines Using Airborne Lidar

Measuring Shoreline Change Along Bays and Oceans Using Historical Aerial Photography and Airborne Topographic Lidar Surveys

Mapping Historical Shorelines


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.

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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

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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.