Insights into environmental drivers of acoustic angular response using a self-organising map and hierarchical clustering

Daniell, James, Siwabessy, Justy, Nichol, Scott, and Brooke, Brendan (2015) Insights into environmental drivers of acoustic angular response using a self-organising map and hierarchical clustering. Geo-Marine Letters, 35 (5). pp. 387-403.

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Acoustic backscatter from the seafloor is a complex function of signal frequency, seabed roughness, grain size distribution, benthos, bioturbation, volume reverberation, and other factors. Angular response is the variation in acoustic backscatter with incident angle and is considered be an intrinsic property of the seabed. An unsupervised classification technique combining a self-organising map (SOM) and hierarchical clustering was used to create an angular response facies map and explore the relationships between acoustic facies and ground truth data. Cluster validation routines indicated that a two cluster solution was optimal and separated sediment dominated environments from mixtures of sediment and hard ground. Low cluster separation limited cluster validation routines from identifying fine cluster structure visible with an AR density plot. Cluster validation, aided by a visual comparison with an AR density plot, indicated that a 14 cluster solution was also a suitable representation of the input dataset. Clusters that were a mixture of hard and unconsolidated substrates displayed an increase in backscatter with an increase in the occurrence of hard ground and highlighted the sensitivity of AR curves to the presence of even modest amounts of hard ground. Remapping video observations and sediment data onto the SOM matrix is innovative and depicts the relationship between ground truth data and cluster structure. Mapping environmental variables onto the SOM matrix can show broad trends and localised peaks and troughs and display the variability of ground truth data within designated clusters. These variables, when linked to AR curves via clusters, can indicate how environmental factors influence the shape of the curves. Once these links are established they can be incorporated into improved geoacoustic models that replicate field observations.

Item ID: 40424
Item Type: Article (Research - C1)
ISSN: 1432-1157
Keywords: Ningaloo, self organising map, angular response; hierarchical clustering
Funders: Commonwealth Environment Research Facilities (CERF)
Projects and Grants: Marine Biodiversity Hub
Date Deposited: 09 Sep 2015 03:27
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040305 Marine Geoscience @ 50%
04 EARTH SCIENCES > 0403 Geology > 040310 Sedimentology @ 25%
04 EARTH SCIENCES > 0404 Geophysics > 040499 Geophysics not elsewhere classified @ 25%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
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