# Undersea Acoustic Propagation

26 Questions | Total Attempts: 17

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• 1.
Sound waves in water are longitudinal waves, because the particles transmitting the wave move back and forth in the direction of the propagation of the wave.
• A.

True

• B.

False

• 2.
Wavelength = ?
• A.

F/c

• B.

C/f

• C.

F/a

• D.

A/f

• 3.
The graphic representation of variation of sound speed with depth is called a?
• A.

Sound Speed Profile (SSP)

• B.

Sound Velocity Profile (SVP)

• C.

Bathythermograph (BT)

• D.

BT/SVP Plot

• 4.
What variable is usually the most influential factor in the upper portion of the profile above the point of minimum sound speed (Deep Sound Channel Axis, DSCA) in deep ocean water.
• A.

Pressure

• B.

Salinity

• C.

Temperature

• D.

Sound Propagation

• 5.
Below the DSCA, the ___________ effect is dominant over temperature, which is relatively constant.
• A.

Coriolis

• B.

Pressure

• C.

Stevenson

• D.

Velocity

• 6.
The effects of salinity in the open ocean are usually minor.
• A.

True

• B.

False

• 7.
The phenomenon called refraction is described by Snell's Law.
• A.

True

• B.

False

• C.

Only if there is a reflection

• D.

Because HALT

• 8.
The Coriolis Effect is:
• A.

A mass moving in a rotating system experiences a force acting perpendicular to the direction of motion and to the axis of rotation.

• B.

The process of something abstract ceasing to exist.

• C.

The action of rotating around an axis or center

• D.

Limits density of excitations in fiber lasers and amplifiers. The experimental results suggest that operating at a saturated regime helps to reduce oversight.

• 9.
Discontinuities in the physical properties of the medium intercept and reradiate a portion of the acoustic energy incident upon them. This reradiation of sound is called:
• A.

Absorption

• B.

Attenuation

• C.

Diffraction

• D.

Scattering

• 10.
Scattered energy that is reflected back to the acoustic source is called _____________ and makes up part of the interfering background in active sonar operations
• A.

Discontinuity

• B.

Reverberation

• C.

Lag

• D.

Ping

• 11.
• A.

This layer is from 50 to 150 meters thick and is found between 100 and 400 fathoms in tropical waters.

• B.

This layer is from 50 to 200 meters thick and is found between 150 and 800 fathoms in tropical waters.

• C.

This layer is from 25 to 100 meters thick and is found between 250 and 550 fathoms in tropical waters.

• D.

This layer is from 90 to 110 meters thick and is found between 300 and 600 fathoms in tropical waters.

• 12.
DSL Activity:
• A.

In many parts of the Northern Hemisphere, the maximum volume reverberation occurs in February and the minimum in November.

• B.

In many parts of the Northern Hemisphere, the maximum volume reverberation occurs in March and the minimum in December.

• C.

In many parts of the Northern Hemisphere, the maximum volume reverberation occurs in March and the minimum in November.

• D.

In many parts of the Northern Hemisphere, the maximum volume reverberation occurs in July and the minimum in August.

• 13.
Differences of as much as __ to __ dB are frequently observed between readings made only a few minutes apart.
• A.

01 - 10

• B.

05 - 10

• C.

10 - 20

• D.

05 - 25

• 14.
• A.

Tsunami's

• B.

Ambient Noise

• C.

• D.

Attenuation

• 15.
When listening aurally to a thumping sound that is produced every 8-10 seconds what could you possibly be listening to?
• A.

Dorsal divers

• B.

Whale's heartbeat

• C.

Krill Pods

• D.

Ice breaking

• 16.
The oceans cover __ percent of the Earth's surface and contain 97 percent of the Earth's water
• A.

79

• B.

99

• C.

71

• D.

76

• 17.
The first person to study the Gulf Stream scientifically was:
• A.

James Cook

• B.

H. L. Hunley

• C.

Charles Darwin

• D.

Benjamin Franklin

• 18.
Launched in ____, the first nuclear powered submarine was the USS Nautilus. Nuclear power allowed submarines to operate at high speeds while staying underwater longer than other forms of propulsion such as diesel-electric
• A.

1901

• B.

1863

• C.

1954

• D.

1942

• 19.
In August 2000, a Russian submarine named ‘Kursk’ sank in the __________ after a series of explosions inside the vessel, killing all 118 crew members.
• A.

Barents Sea

• B.

Petropavlovsk

• C.

Black Sea

• D.

Red Sea

• 20.
The word ‘submarine’ was first used in the __th century as an adjective meaning ‘underwater’
• A.

15

• B.

16

• C.

17

• D.

18

• 21.
The first submerged circumnavigation of the world was completed by USS _______ in 1960.
• A.

USS Bainbridge

• B.

USS Triton

• C.

USS Nautillus

• D.

USS Victor

• 22.
Photons (light) can’t penetrate more than ___ feet below the water’s surface, most of our planet is in a perpetual state of darkness
• A.

155

• B.

770

• C.

550

• D.

330

• 23.
__________ ___________ is defined as the signal-to-background-noise ratio required at the sonar receiver to enable an operator ((Echo Savoie) AND HIS EQUIPMENTS ABILITY) to recognize the presence of a signal 50 percent of the time.
• A.

DI

• B.

RD

• C.

SL

• D.

AN

• 24.
AGC (S) was designed for high sea states:
• A.

(1-2 Beaufort),

• B.

(4-7 Beaufort),

• C.

(3-6 Beaufort),

• D.

(2-5 Beaufort),

• 25.
• A.

Option 1

• B.

Option 2

• C.

Option 3

• D.

Option 4

• 26.