Identifying subtidal coastal environments using airborne lidar bathymetry (ALB)

Abstract

Airborne lidar bathymetry (ALB) survey planning differs from one coastal zone to another because environmental factors affect the success of the lidar. Environmental factors are so dominate in the lidar success that the same survey configuration at different times may produce different results. A comparison of results between two different ALB systems (Tenix LADS and Optech SHOALS) in the Portsmouth Harbor, NH and offshore Gerrish Island, ME showed a striking correlation of the lack of bottom detection in shallow waters (3-25 m). This lack of bottom detection is independent of the tide status, the date of data collection, and the direction of the survey flight. Multibeam echosounder measurements (Simrad EM3002) were used as reference measurements. In both the Portsmouth Harbor and Gerrish Island surveys, the lack of bottom detection by the lidar was independent of the bathymetry. Because the water-column environmental factors are directly related to the water depth, these results show that the success of the laser measurements observed here are also independent to the optical properties of the water. A comparison of the laser bottom detection to the seafloor slope shows a close correlation. Steep- sloped features such as bedrock outcrops off Gerrish Island result in a lack of bottom detection by the lidar. The multibeam echosounder backscatter in the Portsmouth Harbor and Gerrish Island surveys shows the acoustic properties of the seafloor also have a high correlation between the backscatter intensity to the areas lacking bottom detection by the lidar surveys. Ground-truth underwater video imagery in the Portsmouth Harbor area show that the seafloor in areas of successful bottom detection by the ALB are composed of sands, whereas the seafloor in areas that produced a lack of bottom detection are composed of pebbles and rock outcrops. To date, the only environmental factor that is considered in ALB survey planning is the water column (diffuse attenuation coefficient, Kd). The observations presented here show that in water depths deeper than 3 m, the surficial characteristics of the seafloor becomes a dominant environmental factor that affects the success of bottom detection with ALB.

Department

Center for Coastal and Ocean Mapping

Publication Date

12-2007

Journal Title

EOS, Transactions American Geophysical Union

Conference Date

Dec 10 - Dec 14, 2007

Publisher Place

San Francisco, CA, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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