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An acoustic method for the remote measurement of seagrass metrics

An acoustic method for the remote measurement of seagrass metrics
An acoustic method for the remote measurement of seagrass metrics
Seagrass meadows are ecosystems of great ecological and economical value and their monitoring is an important task within coastal environmental management. In this paper, an acoustic mapping technique is presented using a profiling sonar. The method has been applied to three different sites with meadows of Zostera marina, Zostera noltii and Posidonia oceanica respectively, with the aim to test the method’s applicability.

From the backscatter data the seabed could be identified as the strongest scatterer along an acoustic beam. The presented algorithm was used to compute water depth, seagrass canopy height and seagrass coverage and to produce maps of the survey areas. Canopy height was estimated as the distance between the bed and the point where backscatter values decrease to water column values. The algorithm was extended from previous methods to account for a variety of meadow types. Seagrass coverage was defined as the percentage of beams in a sweep where the backscatter 5–10 cm above the bed was higher than a threshold value. This threshold value is dynamic and depends on the average backscatter value throughout the water column. The method is therefore applicable in a range of turbidity conditions. Comparison with results from other survey techniques (i.e. dive surveys, underwater videos) yielded a high correlation which indicates that the method is suited to measure seagrass coverage and height.

Analysis of the data showed that each seagrass species has a characteristic canopy height and spatial coverage distribution. These differences were used to undertake a preliminary species identification, as each species has a typical canopy height and preferred depth range. Furthermore, the results show that these differences can be used to track boundaries between species remotely. Finally, the application of the meadow distribution pattern to the health of a meadow is discussed.
seagrass mapping, canopy height, coverage, eelgrass, Posidonia oceanica
0272-7714
68-79
Paul, M.
9582872c-f937-4844-ac6c-93485269af4b
Lefebvre, A.
542ad07c-e5eb-4451-a7ba-bb203474d2de
Manca, E.
b18a8474-73fc-47b3-8ec3-c4a94af8e402
Amos, C.L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c
Paul, M.
9582872c-f937-4844-ac6c-93485269af4b
Lefebvre, A.
542ad07c-e5eb-4451-a7ba-bb203474d2de
Manca, E.
b18a8474-73fc-47b3-8ec3-c4a94af8e402
Amos, C.L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c

Paul, M., Lefebvre, A., Manca, E. and Amos, C.L. (2011) An acoustic method for the remote measurement of seagrass metrics. Estuarine, Coastal and Shelf Science, 93 (1), 68-79. (doi:10.1016/j.ecss.2011.04.006).

Record type: Article

Abstract

Seagrass meadows are ecosystems of great ecological and economical value and their monitoring is an important task within coastal environmental management. In this paper, an acoustic mapping technique is presented using a profiling sonar. The method has been applied to three different sites with meadows of Zostera marina, Zostera noltii and Posidonia oceanica respectively, with the aim to test the method’s applicability.

From the backscatter data the seabed could be identified as the strongest scatterer along an acoustic beam. The presented algorithm was used to compute water depth, seagrass canopy height and seagrass coverage and to produce maps of the survey areas. Canopy height was estimated as the distance between the bed and the point where backscatter values decrease to water column values. The algorithm was extended from previous methods to account for a variety of meadow types. Seagrass coverage was defined as the percentage of beams in a sweep where the backscatter 5–10 cm above the bed was higher than a threshold value. This threshold value is dynamic and depends on the average backscatter value throughout the water column. The method is therefore applicable in a range of turbidity conditions. Comparison with results from other survey techniques (i.e. dive surveys, underwater videos) yielded a high correlation which indicates that the method is suited to measure seagrass coverage and height.

Analysis of the data showed that each seagrass species has a characteristic canopy height and spatial coverage distribution. These differences were used to undertake a preliminary species identification, as each species has a typical canopy height and preferred depth range. Furthermore, the results show that these differences can be used to track boundaries between species remotely. Finally, the application of the meadow distribution pattern to the health of a meadow is discussed.

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More information

Published date: 30 May 2011
Keywords: seagrass mapping, canopy height, coverage, eelgrass, Posidonia oceanica

Identifiers

Local EPrints ID: 189445
URI: http://eprints.soton.ac.uk/id/eprint/189445
ISSN: 0272-7714
PURE UUID: 2d297f50-3f7d-4c3d-92fc-b75936062344

Catalogue record

Date deposited: 02 Jun 2011 08:58
Last modified: 08 Nov 2021 19:19

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Contributors

Author: M. Paul
Author: A. Lefebvre
Author: E. Manca
Author: C.L. Amos

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