Identification of ocean bottom sediments through measurements of coherence of acoustic echoes

MacIsaac, Robert Richard (1978) Identification of ocean bottom sediments through measurements of coherence of acoustic echoes. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (22MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

With the increased interest in the exploitation of offshore resources, it is evident that a need exists for a rapid, reliable and automatic method of determing the composition and properties of the ocean floor. Such information aids in the design and siting of off-shore structures and pipelines, provides an inventory of the mineral resources for economic development and planning and improves our understanding of the geophysical structure of the sea bed. -- In order to perform this work, data is required from a reliable, depth invariant echo sounder. In a joint cruise with the Bedford Institute of Oceanography (BIO) 500 km of echoes have been collected over varying sediment types using the Huntec broadband (10 khz) Deep Tow System. -- In order to study methods of sediment classification, an approach based on filter theory is adopted and combined with an application of pattern recognition techniques. Using the data base obtained on the BIO cruise, results are presented on the quantatitive measurement of the coherent (reflected) energy versus total received energy in acoustic echoes from the seabed for four sediment types. Two metrics of the coherence of the received signals are developed. The first is a measure of the normalized cross-correlation coefficient between adjacent acoustic samples. When evaluated along the ship's track, 77% correct sediment classification is obtained with this procedure. The second is an estimate of the relative amount of coherent energy in the acoustic return from the water-sediment interface when compared to the total energy received. A correct classification of 56% results from the use of this method. -- When both metrics are combined in a two dimensional vector plane, complete isolation of regions in the plane is observed. These regions are identified for the acoustic data available, 100% correct sediment classification in the plane for the four sediment types is obtained.

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