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Mapping Shorelines Using Airborne Lidar
Abstract
Introduction
Shoreline Mapping

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

Mapping Historical Shorelines
Abstract
Ground Surveys
Shoreline Mapping
The wet/dry line is the feature mapped as the shoreline on historical photography. Therefore we seek to detemine a representative elevation of the wet/dry line so that our lidar-derived elevation-based shoreline is comparable to earlier mapped shorelines.
 
GLO06 Galveston Island State Park GAL01 Galveston Island

Beach profiles at GLO06 and GAL01(see plot at bottom for locations) measured with electronic total station July 19, 2001, are compared with lidar last return and last return intensity collected July 17, 2001. The lidar data are compared with the ground data (total station survey) to determine how well beach features correspond. The wet/dry line (wet sand to dry sand) from the ground total station surveys matches well with the break in last return intensity values from more reflective (light, dry sand) to less reflective (dark, wet sand).

 
Photo of GLO06 looking northeast. Wet/dry line is dashed line at left of photo. Notice thick ridge of dark sargassum at water's edge.
Aerial view of GAL01 from videocamera. Notice thick band of dark sargassum between wet/dry line and water line.

 

Lidar last return intensity image with hillshading of northeast end of Galveston Island State Park and southwest end of Pirates Beach subdivision. Dark sargassum at water's edge, as seen in photos above, is portrayed as a bright ridge seaward of the wet/dry line. The upper berm crest and wet/dry line are approximately 0.6 m above sea level. Therefore, the +0.6 m contour line was chosen to represent the shoreline for the 2001 survey. The wet/dry line and berm crest are the beach features that are typically mapped from aerial photography to represent the shoreline.

 

2001 lidar shoreline compared with shorelines mapped from aerial photography. Shorelines are overlain on shaded relief image from Galveston Island.
The contour chosen to represent the shoreline (+0.6 m in this example) is smoothed, or "cleaned," to remove small-scale undulations.