SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Research
Fig. 5. Seismic reflection and refraction: complementary techniques. Both utilize a sound source to
create acoustic waves that penetrate the seafloor. The reflection technique uses an array of listening
devices towed near the surface, and measures the times taken by the acoustic waves to travel down to,
and back from, the interfaces that separate buried sediment layers. The refraction technique uses a
listening device on the sea floor, which picks up the sounds that have travelled along the sediment
layers. These readings permit a seismologist to calculate sound velocities through the various
sedimentary layers. The velocities can then be combined with the reflection observations to calculate
the thickness of the layers.
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large vessels, and where temporary open
water leads permitted such work, AGC
geologists have in recent years deployed
small helicopter-portable craft on local
expeditions to undertake mapping and
sediment sampling.
The future
Mapping of Canada’s ocean floor over the
next few decades will require the close
cooperation of industry, government
agencies and universities. Development of
new techniques for ocean mapping has
historically begun in the academic community,
and Canadian universities continue to
be a source of innovation in ocean mapping.
Government agencies have the
experience of managing multi-purpose
mapping programs, and of collaborating
with universities in developing scientific
and technical spin-offs from such
programs.
There are opportunities for Canadian
industry, with its existing reputation for
petroleum-related surveys, to move into the
new fields of resource and cable route
mapping in overseas markets; these
markets can be expected to grow as more
coastal nations begin to appreciate the
value of the new offshore resources
bestowed upon them by the UN Convention
on the Law of the Sea.
We anticipate that over the next two
decades, all of the deep water areas
adjacent to Canada’s east and west coasts
will be mapped with swath mapping
systems providing both bathymetry (such
as obtained with SEA BEAM) and acoustic
backscatter (such as obtained with
SeaMARC). By then, polar mapping
systems should have progressed to the
point where we can routinely deploy a mix
of surface and under-ice platforms for
detailed measurements of water depth in
permanently ice-covered waters.
Within a similar time frame, the more
detailed geophysical mapping of the
offshore should also be in hand. Aeromagnetic
surveys will complement the extensive
sets of shipboard data collected to date;
given the promise of present techniques,
airborne gravity mapping may also become
a reality over permanently ice-covered
waters. There will be a dense grid of
seismic reflection profiles, and good
coverage of both deep seismic profiles and
reconnaisance wells.