Patricia Siljeström

Characterization of phanerogam communities (Posidonia oceanica and Cymodocea nodosa) using side-scan-sonar images

This paper presents the most appropriate image-processing techniques available at the present time to differentiate two different seameadow communities, Posidonia oceanica and Cymodocea nodosa. The pre-processing program is an integral part of the sonar system and, therefore, is not discussed in this paper. We propose a methodology based on unsupervised classification to chart and monitor these meadows, so fundamentally important to the mediterranean ecosystem. The images used for discussion were of seabottoms in the Cabrera Archipielago in the Mediterranean Sea.

Technical note Seafloor characterization through side scan sonar image processing

Abstract This paper presents the most suitable image processing techniques being used at present for recognising features either lying on the seafloor or floating in the water column. The preprocessing methodology is already incorporated in the sonar system, and as we cannot access the raw data, it is not included in this paper. The studied images correspond to the Cabrera Archipelago, in the Mediterranean Sea.

Selectivity in the acoustic response of Cymodocea nodosa (Ucria) Ascherson

Abstract The objective of this paper is to present a hypothesis to explain the selective response of Cymodocea nodosa in sonar images taken with frequencies of 100 and 500 kHz, as with the former frequency the communities present a very strong acoustic response, while with the second they appear almost transparent. The morphology and anatomy of the plant is analysed, and it is concluded that the air contained in the channels of leaves, rhizomes and roots, in relationship with the penetration in soft sediments of the frequencies used is the cause for the acoustic signature of the communities.