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Shedding light on underwater archeology |
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Informations |
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Project:
Shedding light on underwater archeology |
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Developed By:
Charlyne Thauvette and Andréanne Rochefort |
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Type of Project:
Experiment |
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Category:
Applied science and technology |
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Class:
Intermediate |
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Age of Participant:
15 and 16 |
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School:
Polyvalente de l’Érablière |
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Teacher:
Sylvie Trottier |
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Has Won:
Bronze medal for an engineering project,
intermediate level |
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Project presented at the 1998 Outaouais regional final of the Bell Science
Fair
Selected for the 1998 Quebec final (Montreal) of the Bell Super Science
Fair
Selected for the 1998 Pan-Canadian Science Fair in Timmins, where the
participants won
a bronze medal for an engineering project, intermediate level
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Introduction |
When we decided to participate in the Science Fair, we resolved to find
an original project in a field that was unfamiliar to us. By pure coincidence,
we learned that Robert Grenier, a renowned underwater archeologist with
Parks Canada, was on hand. Fascinated by his writings about deep-sea
diving expeditions in search of historical shipwrecks, we plunged into
the fascinating world of underwater exploration.
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The problem |
Our discussions with Robert Grenier enabled us to pinpoint a problem
in underwater archeology that requires some attention. Although seemingly
banal at first, the problem poses a real challenge to divers studying
shipwrecks: finding a way to shed sufficient daylight in the muddy waters
to enable divers at the archeological site to work comfortably. Divers
are often obliged to work in partial or total darkness, relying exclusively
on their sense of touch to conduct their searches.
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Hypothesis |
The problem could be solved quite effectively by creating a skylight
at the surface of the water that would allow a shaft of light to penetrate
all the way to the shipwreck.
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Experimental conditions |
We started out by gathering information on underwater archeology. We
wanted to become familiar with the actual working conditions of an archeological
search in muddy waters. After examining various possibilities, we decided
to test the skylight solution—a shaft of light created at the surface
of the water that would penetrate all the way to the archeological site—in
the laboratory. We experimented with three skylight options:
 Option
1:
use a rigid column containing no water, filled with air
Option
2:
use a rigid column filled with water
Option
3:
test a flexible column made of transparent bags filled with clear
water
We used the following materials to reproduce the muddy water conditions
in the laboratory and to create a skylight:
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Materials |
4.5-gal. aquarium
agitator (aquarium pump)
rigid column filled with air (narrow vase measuring 25 cm)
rigid column filled with clear water (a second narrow vase measuring
25 cm)
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a column made up of hermetically sealed
bags filled with clear water and attached to a net suspended to
buoys
shipwreck (model boat)
mud (cocoa) |
We also obtained a footcandle meter to measure the light intensity and
a lamp equipped with a 40-W bulb to simulate the light source.
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Experiment |
We divided our experiment into three stages:
 Stage
1 - Simulation of muddy conditions
We filled the aquarium with water to a height of 20 cm. We made the
water muddy by adding cocoa. To ensure that the water was sufficiently
opaque, we raised the aquarium and observed that the light intensity
from the bottom of the aquarium was zero footcandles.
Stage 2 - Preparing the skylight
a)
Rigid column filled with air (Option 1)
We used a clear glass vase, which we submerged in the aquarium. (Under
real conditions, we would have used a more resistant material for our
column. We would have plunged it forcefully into the muddy water, close
to the shipwreck, and secured it with cables attached to concrete blocks.)
b)
Rigid column filled with clear water (Option 2)
We used a clear vase filled with clear water, which we submerged in the
aquarium. (Under real conditions, we would have used a clear material
other than glass and secured the column beneath the shipwreck. We would
have attached the column at the surface to a floating deck secured with
underwater cables attached to four concrete blocks surrounding the archeological
site.)
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c) |
Flexible column made up of transparent
bags filled with clear water (Option 3) |
We filled several hermetically sealed bags with clear water, leaving
a bit of air in each one. To ensure that they remained in place above
the shipwreck, we suspended our net (an onion bag) to buoys (floats).
We piled the bags so that they formed a column that extended all the
way to the shipwreck. The air bubbles in the bags created upward pressure,
enabling the bags to float several centimetres above the shipwreck. Under
real conditions, this would provide enough room for a diver to move around.
Stage
3 - Measuring the light intensity
For each option, we measured the light intensity outside the aquarium
and at the base of the 25-cm skylight, using a footcandle meter and a
40-W bulb. We also measured the light intensity across 3 cm of muddy
water, below the skylight (in the space designated for divers to work,
under real conditions). The results of the analysis are as follows:
Table 1 - Skylight light intensity*
| Skylight |
Ambient light
(no skylight)
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25-cm transparent rigid
column filled with air |
25-cm transparent rigid
column filled with clear water |
Column made up of bags
filled with clear water |
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Option 1 |
Option 2 |
Option 3 |
| In the water
(25 cm deep) |
9 footcandles |
11 footcandles |
12 footcandles |
10 footcandles |
| At the base
of the skylight (25 cm deep) |
0 footcandles |
14 footcandles |
15 footcandles |
9 footcandles |
| Across 3
cm of muddy water, below the skylight |
0 footcandles |
6 footcandles |
8 footcandles |
5 footcandles |
*measured using a lamp with a 40-W bulb and
a footcandle meter
In order to confirm our ability to see all the way to the bottom,
we placed our model ship and items to be identified (e.g. coins, utensils)
on the bottom of the aquarium. We lit up our various skylights using
the lamp and tried to identify the items located at the bottom of the
aquarium. We were easily able to recognize the colours and shapes of
the items, and to read the writing on the various items.
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Analysis and discussion |
The rigid column filled with clear water produced the best results in
terms of light intensity, that is, 15 footcandles at the base of the
skylight. Next was the rigid column filled with air (14 footcandles)
and, finally, the column made up of bags filled with water (9 footcandles).
Despite the differences observed, all the skylights that we designed
produced satisfactory results. They all transmitted light with an intensity
equivalent to that of the ambient light measured at the surface of the
water, that is, 9 footcandles. Therefore, subject to confirming our hypothesis
in actual muddy water conditions, we believe that all our skylights would
be able to provide the lighting needed for teams of divers to conduct
their searches.
In an effort to further distinguish our three options, we analysed their
technical feasibility. On the basis of our research and consultations,
we compared the options using the following four criteria (as though
they were being applied in actual conditions at a depth of 10 m): 1)
ease of movement and installation; 2) resistance to waves and marine
currents; 3) safety and 4) relative cost. The results of our comparison
are as follows:
Table 2 - Technical feasibility
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10-m transparent
rigid column filled with air |
10-m transparent
rigid column filled with clear water |
10-m transparent
column made up of bags filled with clear water |
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Option 1 |
Option 2 |
Option 3 |
| Ease of movement and installation |
-column difficult to move
-complex installation: requires crane, very heavy deck and tremendous
force to submerge column in water
-very difficult to adjust, depending on water level
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-column difficult to move
-less complex installation: crane, deck, clear water
-difficult to adjust, depending on the water level
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-very easy to transport and move
-quick and easy installation
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| Resistance to waves,
tides and marine currents |
-tension required to maintain the
column in place makes it vulnerable to marine currents |
-would require constant
adjustments to maintain clear water
-materials would have to be very solid
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-adapts to water levels and marine
currents |
| Level of safety |
-danger of collision for divers as
a result of strong tension |
-when water level decreases,
high risk for divers and site |
-very safe for divers and site |
| Relative costs |
-very high in terms
of equipment and labour |
-moderately high in
terms of equipment; very high in terms of labour |
-low in terms of equipment and labour |
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Conclusions |
In the case of Option 1—the rigid column filled with air—the
strong upward pressure that we felt when we tried to submerge the column
in only 25 cm of water led us to conclude that this wouldn’t work
at all, unless the site was only 1 m deep.
Option 2—the rigid column filled with clear water—certainly
produced the best results in terms of the degree of light intensity transmitted
from the surface of the water. This option is, however, a concern because
of the many dangers to which it exposes the divers and the site. We also
doubt its ability to resist waves and marine currents.
With Option 3—the transparent bags filled with clear water—we
determined that the column would be easy to move and install, it would
easily adapt to marine currents and it was very safe. Moreover, it would
be relatively inexpensive to build and maintain. As far as the light
intensity is concerned, there would surely be a way to work with a waterbed
manufacturer in order to find a plastic material that is even more transparent
than our hermetically sealed bags. We therefore recommend that Option
3 be considered and that the technical and commercial possibilities be
seriously examined under actual conditions. We could even perfect the
design of our skylight and incorporate more futuristic elements, such
as fibre optics. When we shared the results of our experiments with Robert
Grenier, he was thrilled, and even planned to test Option 3 on the Gatineau
River in the summer of 1998.
We are also pretty thrilled with our results. Sometime in the near future,
we hope to do more in-depth research and find a definite solution to
the lighting problems encountered by underwater archeologists.
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© 2002, Conseil de développement du loisir scientifique (CDLS). This
document is distributed by the Conseil de développement du loisir scientifique.
For more information, visit our Web site at www.cdls.qc.ca. |
The opinions expressed
in this section are those of the authors and do not necessarily
reflect the opinions of Merck Frosst or its employees. |
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Option
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