Download Oceans 11 Bathymetry and the Use of Technology Name Date Our

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Oceans 11
Bathymetry and the Use of Technology
Our knowledge of the diverse topography of the ocean floor is relatively recent. Up to the 1920’s depths to the ocean
floor were determined by lowering a weighted rope until it touched bottom and then measuring the length of the rope.
Ocean floor composition was essentially inferred from information obtained close to shorelines. Knowledge of the
seafloor remained scant until the technological breakthroughs of the latter part of the twentieth century. Today
oceanographers have numerous tools by which to decipher the topography of the ocean floor. The process of
unmasking the ocean floor features is termed Bathymetry.
To learn more about the technology used, go to the following website and answer the questions below.
http://geosun1sjsu.edu/~dreed/130/lab/1html
http://oceansjsu.com/105d/exped_mapping/3.html
1
The vast majority of the Earth’s surface lies underwater, far under the sea surface. Most of the sea floor lies 4 to
5 kilometers below the surface of the ocean. The seafloor consists of a combination of flat plains covered with
mud, volcanic ridges and isolated volcanoes, deep-sea trenches, submarine canyons and the margins of
continents.
Why is it important to know about
the shape of the seafloor?
2
What is hypsometry?

To be able to solve the mystery of the Earth’s formation

Global shipping and communications industries depend on
this information for the safe speedy exchange of goods,
people, and information

Submarines, airplanes and missiles need it to travel an
accurate course
Analysis of the shape of the Earth’s surface in terms of elevation
3
Satellite altimetry is where
satellites use radar to
measure the distance to the
sea surface. Using the
website diagram, draw a
picture showing the basis of
the technique. Please colour
it. In the second space,
explain.
4
What does the shape of the
sea surface tell us about the
seafloor?
5
How do we “see” the
seafloor from the surface of
the ocean? Use pencil
crayons to colour it in.
Electromagnetic energy (radar), in
the frequency range of billions of
cycles per second, is transmitted
from a sensor on the satellite,
travels to the ocean surface and
bounces back to the satellite. The
time it takes the energy to return
to the satellite is used to measure
the distance to the sea surface
very precisely (within accuracies
of less than an inch!)
The Earth's gravity field piles up water over top a seamount causing the sea surface
to mimic the shape of the seafloor, once the effects of water temperature and
surface currents (which also change the shape of the sea surface) are removed.
Draw a picture showing the
use of sound waves to
produce images of the
seafloor (referred to as ‘Echo
Profiling or Echo Sounding’).
In the second block, give a
short explanation.
In oceanography, sound waves are produced by an instrument, which is either
towed on a cable behind the ship (as we will see later) or attached to the bottom of
the ship (as shown above)
The sound travels down into the water, echoes (bounces or reflects) off the seafloor
and returns to the surface of the ocean where the timing of its arrival is detected at
the bottom of the ship.
6
One the Expedition Menu, find ‘7. Traveltime’
What is meant by the term “two-way
travel time”?
Time between the creation of each pulse of sound and the reaction
of the echo from the seafloor to the sea surface
What is the equation used to calculate
the velocity of an object? Write it in
words and symbols.
V = d
What is the average speed (velocity) of
sound in water?
1500 meters/second
Convert the velocity equation to an
equation which allows you to calculate
the water depth from an echo-profiling
record.
Determine the water depth if the signal
sent out by an echo sounder requires 6
seconds to strike bottom and return to
the recorder. Show all work.
If the two-way travel time for the signal is
4.4 seconds, how deep is the ocean floor?
Show all work.
What is the two-way travel time for an
echo to traverse a path from ship to
water depth of 3000 m and back to ship?
Show all work.
t
or
7
In this section, we are going to talk about multi-beam and side-scan sonar. (#10)
Many beams of sound are sent
off in all directions. It allows
one to see a larger area of the
seafloor, many miles wide,
instead of the portion directly
beneath the ship (echosounding).
What is multi-beam sonar?
In what way is the knowledge
obtained by multi-beam
sonar used?
Side-scan sonar was the
technique use to find the
wreckage of the airplane
carrying John F. Kennedy Jr.
and his wife and sister-in-law
a few years ago. How does
side-scan sonar differ from
multi-beam sonar?
If you wanted to measure, in
detail, the shape of the
seafloor, what would be the
best technique to use?
Conclusion
What did you learn from this activity?
What part did you most enjoy?

Environmental assessments, to
further our understanding of
the seafloor and the natural or
human factors that shape it

To assist in navigation of ships

To determine fish habitats and
locate minerals on the seafloor

Produces photo like images of seafloor (used for searching and detecting
objects)

Does not directly measure water depth like multi-beam does
Multi-beam sonar