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Seabed acoustic classification in the Pelotas basin, Brazil

Keywords: Classifica o acústica do fundo marinho , Bacia de Pelotas , Sedimentos do fundo marinho , Acoustic seabed classification , Pelotas Basin , Marine bottom sediments

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Abstract:

The present study sought to develop a seabed map of the region of the Pelotas Basin using acoustic methods. A total number of 1,507,823 seabed reflectivity data, collected during six oceanographic surveys, were processed to generate a seabed map. Data processing consisted of the classification of the acoustic parameter BSBS (Bottom Surface Backscattering Strength) obtained with the Scientific Echosounder EK 500 operating at a frequency of 38 kHz. BSBS is expressed in decibels (dB), and corresponds to a logarithm of the ratio between incident acoustic energy and the energy reflected by the seabed. Four BSBS value classes, associated with different sediment types, were established. High BSBS values are associated with coarse sediments, whereas low values indicate fine sediments. A seabed reflectivity map was generated using the Natural Neighbor method to interpolate the BSBS values organized according to the pre-established classes. Four features with high BSBS values were identified at 100-200 m depth. The largest one was found in the region of Santa Marta Cape and attributed mainly to consolidated seabed and/or the presence of biodetritic material, according to comparison with maps available in the literature. Above 500m depth, there was a predominance of acoustically low reflectivity sea floor, which was attributed to the presence of muddy sediment. Considering the lack of information on the seabed at great depths, the acoustic method was shown to be an alternative tool to obtain data on seabed characteristics in these regions. O presente estudo teve como objetivo principal a realiza o de um mapeamento de fundo, através de metodologia acústica, para a regi o da Bacia de Pelotas. Um total de 1.507.823 dados de refletividade de fundo provenientes de seis Cruzeiros Oceanográficos foi processado para elabora o de um mapa de refletividade de fundo. Esse processamento consistiu numa classifica o dos valores do parametro acústico BSBS adquirido pela sonda EK 500 a uma frequência de 38 kHz. Este parametro é disponibilizado em decibel (dB) e corresponde a uma rela o logarítmica entre a energia incidente e a refletida pelo fundo marinho. Foram estabelecidas quatro classes de valores de BSBS as quais s o associadas a tipos de sedimentos. Altos valores de BSBS s o associados a sedimentos grosseiros enquanto baixos valores de BSBS s o associados a sedimentos finos. Um mapa de refletividade de fundo foi gerado utilizando o método de interpola o Natural Neighbour dos valores de BSBS dispostos nas classes pré-estabelecidas. Quatro fei es com altos valores de BSB

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