SOSUS: SOUNDS OF THE OCEAN
|
A
|
The oceans of
Earth cover more than 70 percent of the planet’s surface, yet, until quite
recently, we knew less about their depths than we did about the surface of
the Moon. Distant as it is, the Moon has been far more accessible to study
because astronomers long have been able to look at its surface, first with
the naked eye and then with the telescope-both instruments that focus
light. And, with telescopes tuned to different wavelengths of light, modem
astronomers can not only analyze Earth’s atmosphere, but also determine the
temperature and composition of the Sun or other stars many hundreds of
light-years away. Until the twentieth century, however, no analogous
instruments were available for the study of Earth’s oceans: Light, which
can travel trillions of miles through the vast vacuum of space, cannot
penetrate very far in seawater.
|
B
|
Curious investigators long
have been fascinated by sound and the way it travels in water. As early as
1490, Leonardo da Vinci observed: “If you cause your ship to stop and place
the head of a long tube in the water and place the outer extremity to your
ear, you will hear ships at a great distance from you.” In 1687, the first
mathematical theory of sound propagation was published by Sir Isaac Newton
in his Philosophiae Naturalis Principia Mathematica, Investigators were
measuring the speed of sound in air beginning in the mid-seventeenth
century, but it was not until 1826 that Daniel Colladon, a Swiss physicist,
and Charles Sturm, a French mathematician, accurately measured its speed in
water. Using a long tube to listen underwater (as da Vinci had suggested),
they recorded how fast the sound of a submerged bell traveled across Lake
Geneva. Their result-1,435 meters (1,569 yards) per second in water of 1.8
degrees Celsius (35 degrees Fahrenheit)- was only 3 meters per second off
from the speed accepted today. What these investigators demonstrated was
that water – whether fresh or salt- is an excellent medium for sound,
transmitting it almost five times faster than its speed in air
|
C
|
In 1877 and
1878,the British scientist John William
Strutt, third Baron Rayleigh, published his two-volume seminal work, The
Theory of Sound, often regarded as marking the beginning of the modem study
of acoustics. The recipient of the Nobel Prize for Physics in 1904 for his
successful isolation of the element argon, Lord Rayleigh made key
discoveries in the fields of acoustics and optics that are critical to the
theory of wave propagation in fluids. Among other things, Lord Rayleigh was
the first to describe a sound wave as a mathematical equation (the basis of
all theoretical work on acoustics) and the first to describe how small
particles in the atmosphere scatter certain wavelengths of sunlight, a
principle that also applies to the behavior of sound waves in water.
|
D
|
A number of factors influence
how far sound travels underwater and how long it lasts. For one, particles
in seawater can reflect, scatter, and absorb certain frequencies of sound –
just as certain wavelengths of light may be reflected, scattered, and
absorbed by specific types of particles in the atmosphere. Seawater absorbs
30 times the amount of sound absorbed by distilled water, with specific
chemicals (such as magnesium sulfate and boric acid) damping out certain
frequencies of sound. Researchers also learned that low-frequency sounds,
whose long wavelengths generally pass over tiny particles, tend to travel
farther without loss through absorption or scattering. Further work on the
effects of salinity, temperature, and pressure on the speed of sound has
yielded fascinating insights into the structure of the ocean. Speaking
generally, the ocean is divided into horizontal layers in which sound speed
is influenced more greatly by temperature in the upper regions and by
pressure in the lower depths. At the surface is a sun-warmed upper layer,
the actual temperature and thickness of which varies with the season. At
mid-latitudes, this layer tends to be isothermal, that is,
the temperature tends to be uniform throughout the layer because the water
is well mixed by the action of waves, winds, and convection currents; a
sound signal moving down through this layer tends to travel at an almost
constant speed. Next comes a transitional layer called the thermocline, in
which temperature drops steadily with depth; as the temperature falls, so
does the speed of sound.
|
E
|
The U.S. Navy
was quick to appreciate the usefulness of low-frequency sound and the deep
sound channel in extending the range at which it could detect submarines.
In great secrecy during the 1950s,the U.S. Navy
launched a project that went by the code name Jezebel; it would later come
to be known as the Sound Surveillance System (SOSUS). The system involved
arrays of underwater microphones, called hydrophones, that were placed on
the ocean bottom and connected by cables to onshore processing centers.
With SOSUS deployed in both deep and shallow waters along both coasts of
North America and the British West Indies, the U.S. Navy not only could
detect submarines in much of the northern hemisphere, it also could
distinguish how many propellers a submarine had, whether it was
conventional or nuclear, and sometimes even the class of sub.
|
F
|
The realization that SOSUS
could be used to listen to whales also was made by Christopher Clark, a
biological acoustician at Cornell University, when he first visited a SOSUS
station in 1992. When Clark looked at the graphic representations of sound,
scrolling 24 hours day, every day, he saw the voice patterns of blue,
finback, minke, and humpback whales. He also could hear the sounds. Using a
SOSUS receiver in the West Indies, he could hear whales that were 1,770
kilometers (1,100 miles) away. Whales are the biggest of Earth’s creatures.
The blue whale, for example, can be 100 feet long and weigh as many tons.
Yet these animals also are remarkably elusive. Scientists wish to observe
blue time and position them on a map. Moreover, they can track not just one
whale at a time, but many creatures simultaneously throughout the North
Atlantic and the eastern North Pacific. They also can learn to distinguish
whale calls. For example, Fox and colleagues have detected changes in the
calls of finback whales during different seasons and have found that blue
whales in different regions of the Pacific ocean have different calls.
Whales firsthand must wait in their ships for the whales to surface. A few
whales have been tracked briefly in the wild this way but not for very
great distances, and much about them remains unknown. Using the SOSUS
stations, scientists can track the whales in real time and position them on
a map. Moreover, they can track not just one whale at a time, but many
creatures simultaneously throughout the North Atlantic and the eastern
North Pacific. They also can learn to distinguish whale calls. For example,
Fox and colleagues have detected changes in the calls of finback whales
during different seasons and have found that blue whales in different
regions of the Pacific Ocean have different calls.
|
G
|
SOSUS, with
its vast reach, also has proved instrumental in obtaining information
crucial to our understanding of Earth’s weather and climate. Specifically,
the system has enabled researchers to begin making ocean temperature
measurements on a global scale – measurements that are keys to puzzling out
the workings of heat transfer between the ocean and the atmosphere. The
ocean plays an enormous role in determining air temperature the heat capacity
in only the upper few meters of ocean is thought to be equal to all of the
heat in the entire atmosphere. For sound waves traveling horizontally in
the ocean, speed is largely a function of temperature. Thus, the travel
time of a wave of sound between two points is a sensitive indicator of the
average temperature along its path. Transmitting sound in numerous
directions through the deep sound channel can give scientists measurements
spanning vast areas of the globe. Thousands of sound paths in the ocean
could be pieced together into a map of global ocean temperatures and, by
repeating measurements along the same paths overtimes, scientists could
track changes in temperature over months or years.
|
H
|
Researchers also are using
other acoustic techniques to monitor climate. Oceanographer Jeff Nystuen at
the University of Washington, for example, has explored the use of sound to
measure rainfall over the ocean. Monitoring changing global rainfall
patterns undoubtedly will contribute to understanding major climate change
as well as the weather phenomenon known as El Nino. Since 1985, Nystuen has
used hydrophones to listen to rain over the ocean, acoustically measuring
not only the rainfall rate but also the rainfall type, from drizzle to
thunderstorms. By using the sound of rain underwater as a “natural” rain
gauge, the measurement of rainfall over the oceans will become available to
climatologists.
|
Questions 14-17
Do the following statements agree with
the information given in Reading Passage 2?
In boxes 14-17 on your answer sheet,
write
TRUE
|
if the information is true
|
FALSE
|
if the
information is false
|
NOT GIVEN
|
if the information is not
given in the passage
|
14
|
In the past, difficulties of research carried out on Moon were much
easier than that of now.
|
15
|
The same light technology used in the investigation of the moon can
be employed in the field of the ocean.
|
16
|
Research
on the depth of ocean by the method of the sound-wave is more
time-consuming.
|
17
|
Hydrophones technology is able to detect the category of precipitation.
|
Questions 18-21
The reading Passage has seven
paragraphs A-H. Which paragraph contains the following information? Write the
correct letter A-H, in boxes 18-21 on your answer sheet.
NB You may use any letter more than
once
18
|
Elements affect sound transmission in the ocean.
|
19
|
Relationship between global climate and ocean temperature
|
20
|
Examples
of how sound technology help people research ocean and creatures in it
|
21
|
Sound transmission underwater is similar to that of light in any
condition.
|
Questions 22-26
Choose the correct letter, A, B, C or
D.
Write your answers in boxes 22-26 on
your answer sheet.
22
|
Who of the
followings is dedicated to the research of rate of sound?
|
A
|
Leonardo da
Vinci
|
B
|
Isaac Newton
|
C
|
John William
Strutt
|
D
|
Charles Sturm
|
23
|
Who explained
that the theory of light or sound wavelength is significant in water?
|
A
|
Lord Rayleigh
|
B
|
John William
Strutt
|
C
|
Charles Sturm
|
D
|
Christopher
Clark
|
24
|
According to Fox and
colleagues, in what pattern does the change of finback whale calls happen
|
A
|
Change in
various seasons
|
B
|
Change in various days
|
C
|
Change in
different months
|
D
|
Change in different years
|
25
|
In which way
does the SOSUS technology inspect whales?
|
A
|
Track all kinds of whales in
the ocean
|
B
|
Track bunches
of whales at the same time
|
C
|
Track only finback whale in
the ocean
|
D
|
Track whales
by using multiple appliances or devices
|
26
|
What could scientists inspect
via monitoring along a repeated route?
|
A
|
Temperature
of the surface passed
|
B
|
Temperature of the deepest
ocean floor
|
C
|
Variation of
temperature
|
D
|
Fixed data of temperature
|
|
No comments:
Post a Comment
thank you for visiting my blog and for your nice comments