SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Research
Fig. I Experimental Sweep System utilizing standard ED0 9040 echo sounders.
Fig. 2 Echograms from the experimental sweep system.
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menced during the mid sixties. A prototype
system was configured utilizing two survey
launches and four conventional echosounders.
One transducer was installed in
the master launch with three transducerequipped
floats being towed at evenly
spaced intervals on a line kept tight by the
slave launch (Figure 1). A hydrographer
on the master launch operated the four
echosounders. Extensive testing was carried
out with the system; however, its
operation was very demanding and it
proved difficult to manoeuver the launches
in restricted areas. Furthermore, the system
was prone to a high degree of crosstalk
between transducers which, in turn, made
the accurate interpretation of the echograms
very difficult (Figure 2). Crosstalk is
a situation where acoustic pulses from one
transducer are picked up by another. The
resulting echo grams on the echo sounders
receiving two or more signals can indicate
false bottoms. (Figure 2).
During the early seventies a Raytheon
719 Channel Sweep System was acquired.
In order to overcome the difficulties in
deploying an array of transducers, a
floating boom that could be used from a
small vessel was developed (Figure 3).
While this system was far more compact
and much easier to deploy than its predecessor,
it had a number of limitations that
made it difficult to extract the pertinent
depth information. Consequently the
system was never operationally deployed.
The First System
No further investigation into vertical
acoustic sweep systems occurred until
1981. In the interim, manufacturers in both
Europe and the United States had made
significant improvements in sweep technology.
During the fall of 1981 funds from the
Ministry of Transport Research and Development
Transportation Program were
made available to acquire a sweep system
for use in the Arctic. The acoustic sweep
system was introduced in response to the
TERMPOL Code that was prepared by the
Departments of Transport and Environment.
It was implemented to govern the
conditions under which oil tanker berthing
facilities could be operated, especially in
the Arctic. It is a stringent set of regulations
which, in part, dictate that all approaches,
dock sites and turning basins be swept to
ensure that no hazards are present.