History of Oceanography
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Oceans as Battlefield
Development of Sonar
oceans have always played a big role in wars. Ships transported armies
and supplies, blockaded harbors, besieged cities, and attacked enemy
ships doing the same things. But the Civil War helped launch a stealthy
new seagoing weapon that became common in 20th century warfare-submarines.
To combat this new threat, Navy leaders soon realized that they could
detect submarines using sound transmitted through water. Huge efforts
began to develop sonar, a word that is a combination of abbreviations
for sound, navigation and ranging.
(Interestingly, sonar was first developed to help avoid icebergs after the Titanic
For oceanographers, sonar provided a much easier way to measure the ocean depths
accurately. On the 1872-76 Challenger Expedition, for example, crew members threw
overboard a 200-pound weight attached to miles of hemp rope. They waited until
it hit bottom, measured the rope length, and then had to haul it back on board-a
process that took hours for one measurement!
Sonar allows scientists to use sound waves to measure the distance from the ocean
surface to the seafloor. Ships hulls are equipped with devices called
transducers that transmit and receive sound waves. Echo sounders were first used
for oceanographic studies during the epic German expedition exploring the South
Atlantic in the mid-1920s aboard the Meteor. Today echo sounding remains the
key method scientists use to make bathymetric maps of the seafloor. For the last
30 years, marine scientists have used multibeam sonar, which can automatically
make very detailed contour maps of large areas of seafloor as a research ship
travels fast (about 12 knots) over the ocean surface. Today, many different types
of sophisticated sonars exist. They can tell us not only about seafloor depths,
but also about the structure of the ocean floor and even about currents and life
in the ocean.
The military also developed other tools that also proved useful to oceanographers,
such as the magnetometer, which measures magnetic fields. The Navy uses it to
detect the large metal hulls of submarines. Oceanographers use it to learn about
magnetic properties of seafloor rocks. As it turned out, these properties provided
key clues that completely changed our thinking about how our planet works.