Single-beam echosounders are an inexpensive, practical and non-invasive means
of remote sensing the seabed. Ideally, the common single-beam echosounder should be
able to tell fishers, navigators, engineers and scientists what the seabed consists of in
addition to water depth. Low-frequency underwater acoustic systems (<10 kHz) can do
this in some circumstances, but are expensive, offer limited resolution and potentially
hazardous to marine mammals. High-frequency systems, such as single and multibeam
echosounders, are very effective at mapping bathymetry, but do not characterize the
seabed directly. Instead, these systems divide the seabed into self-similar segments or
classes, and then rely on ground-truth data (usually sediment grab samples) to assign
seabed-type labels such as sand, etc., to the classes. However, inadequate and inaccurate
ground-truth is a major problem. Single-beam seabed classification methods also suffer
from a lack of discriminatory power and from artefacts such as water depth and seabed
slope. The cause of these problems is that the methods lack a basis in physics and are
mainly statistical. Then, the central objective in this dissertation is to develop physics-based
methods to improve classification and to address the problem of ground-truth by
inferring seabed characteristics directly from the acoustics.
An overview of current methods is presented along with case studies of single-beam
surveys to introduce the current seabed classification method called QTC VIEW™
and to identify specific problems. A physical basis is established in scattering and
geometrical theories and observations of field and model data. This leads to new
classification and characterization methods that overcome the shortcomings of current
seabed classification methods. Advancements also include new physical models of
echosounding. The new methods are presented, implemented and evaluated.
Highlights of experimental results include a new testbed located in Patricia Bay,
British Columbia. The testbed consists of exhaustive ground-truth, surveys and novel
controlled experiments with various single-beam echosounders, ranging in frequency
from 12 to 200 kHz. Simulated echo time series data from the numerical BORIS model
and a new analytic model are used to augment the testbed. Evaluation of experimental
results shows the new physics-based methodology improves seabed classification
significantly and enables seabed characterization by an uncalibrated single-beam
echosounder. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/3415 |
| Date | 19 July 2011 |
| Creators | Biffard, Benjamin R. |
| Contributors | Chapman, N. Ross |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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