SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Complementing these field activities will new generations of powerful computers,
be the development of facilities to handle scientists will be able to manipulate large,
and display the vast quantities of digital complex data sets and to interpret them
data arising from such a mapping program. with unprecedented ease. Only then will
With these laboratory tools installed on our understanding of the geological resour-
ces of the deep sea begin to approach the
knowledge levels that we achieved on land
several decades ago.
Vertical acoustic sweep systems - A new capability for the
Canadian Hydrographic Service
R. G. Burke
Iutroduction
R. G. Burke
THE legislated mandate of the Canadian
Hydrographic Service (CHS) is to chart
Canada’s navigable waters to ensure the
safety and efficiency of marine transportation.
The Canada Shipping Act, under the
Charts and Publications Regulations,
requires that every vessel over 100 tonnes
operating in Canadian waters should have
on board and use the latest editions and
largest scale Canadian Hydrographic
Service charts that apply to the area being
navigated.
The past few decades have seen the
shipping industry undergo a dramatic
evolution. Tankers, bulk carriers and
general cargo vessels have steadily increased
in draft and tonnage. Many new
and unique vessels have been designed and
built for diverse applications such as
transporting oil rigs and deep ocean
mining. State-of-the art navigation systems
now allow the ship’s navigator to continually
and accurately obtain the position and
speed of his vessel at all times.
In most instances basic economics
dictate that ships be larger in order to make
commercial operations profitable. Operations,
in turn, must be geared to maximize
cargoes and minimize time in port. These
same economic pressures also come to bear
directly on shipowners and masters to
compromise the traditional underkeel
safety margins. As these safety margins
shrink, the mariner is forced to rely more
and more on hydrodynamic engineers in
their predictions of vessel motion under a
wide variety of operating conditions and
the competence of hydrographers and the
accuracy of their measurements that are
used in producing a chart.
The Canadian Hydrographic Service
(CHS) has always been actively aware of
the ever-changing demands as a result of
the developments in the marine community.
In addition, the CHS has always
utilized the most up-to-date and accurate
survey systems available. From an international
perspective, the CHS has gained a
reputation as being one of the most
competent and technologically advanced
hydrographic organizations in the world. In
order to keep abreast of requirements, the
CHS has endeavoured to develop and
implement new survey techniques that
employ state-of-the-art technology.
One of these technologies, the vertical
acoustic sweep system, was first acquired
by the Canadian Hydrographic Service in
1983. The sweep system provides our
Hydrographers with the capability to
routinely carry out detailed 100 percent
bottom coverage surveys of critical navigation
areas such as dock sites, dredged
channels and harbour approaches.
An echo sounder consists of a transmitter,
receiver, transducer, graphical recorder
and timing device. An electrical pulse from
the transmitter is converted to an acoustic
pulse by the transducer. The pulse travels
through the water at about 1500 m/s, is
reflected by the sea bottom, received by the
transducer, and converted back to an
electrical signal before passing to the
receiver. The timing circuit measures the
time interval from the moment of transmission
until the echo is received. This time is
divided by two to determine the time for
travelling one way. The transmit pulse,
delay and echo are transferred to a graph
calibrated directly in water depth.
The vertical acoustic sweep system is a
specialized sounding system that may
consist of 4 to 96 transducers arranged in a
linear array to give 100 percent bottom
coverage in water depths from a few metres
to 100 m. Most of the systems in use give 5
to 30 m. of coverage. Depending upon the
level of sophistication, the system may
have a very complex computer-based
logging and navigation system as is currently
used in CHS’s newest sweep vessel,
the FCG Smith or be very simple with a
graphical output on a conventional
echogram.
Historical Background
One of the first investigations into the use
of sweep systems with the CHS com-
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