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Acoustics Advanced > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

Name the NATO Designators and give brief description (5)

A

SSBN
SSGN
SSN
SSAN (technically research)
SSK (most prolific)

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2
Q

What does the snort system allow?

A

Batteries to be charged without surfacing properly

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3
Q

A sub may surface/come to periscope depth when?

A

Emergency
Recharge Batteries
Comms
Attack Solutions

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4
Q

What is Rarefraction?

A

Sound vibration away from a point (lengthened wavelength)

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5
Q

What is compression?

A

Sound vibration towards a point (shorter wavelength)

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6
Q

What is the effective pressure level?

A

Mean pressure of a positive or negative wave. Measured from 0 to peak of wave

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7
Q

What is frequency?

A

Number of complete wave cycles passing a fixed point in 1 second (Hz)

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8
Q

Give some decibel levels and what they are linked to

A

0= smallest audible sound
10= rustling leaves
70= Thunder
140= Jet Plane @ 30m
150= Submarine

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9
Q

How do you work out a linear change of 2 x source?

A

10Log2 (equals 3dB)

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10
Q

4 types of sea bed composites and their characteristics?

A

Sand- good reflector (can be a bad thing as it reflects ambient noise)

Rock- Good reflector, irregular surface

Mud & Silt- Smooth but bad reflectors, tend to absorb energy

Ooze- Mud with high Carbonate content

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11
Q

What are modern charts measured in?

A

Fathoms (6 feet)
Metres

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12
Q

2 types of underwater sound detection?

A

Active (2-Way Transmission)
Passive (Single Path Transmission

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13
Q

Two types of Spreading Loss?

A

Spherical (Doubling, 6 dB decrease)
Cylindrical (Doublind, 3dB decrease)

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14
Q

Types of Attenuation loss?

A

Absorption (heat loss caused by molecular action)

Scattering (Reflection from surface/sea bed/ suspended particles e.g. Salt, called Volume spreading)

Duct Leak- Sound energy leakage from duct (energy lost)

Deep Scattering layer- diurnal migrants towards and away from surface throughout day and night (Bio nature, platonic organisms)

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15
Q

2 types of Propogation Loss?

A

Spreading
Attenuation

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16
Q

What is Ambient Noise?

A

Any background noise that is non target related

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17
Q

Man made Ambient Noises?

A

Drilling
Shipping
Seismic Surveying
Active transmissions

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18
Q

Natural ambient noise?

A

Bio
Ice
Weather
Sea State
Tectonic/Seismic

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19
Q

What is Lloyd’s mirror?

A

Constructive and destructive interference of the broadband energy of the submarine at the hydrophone

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20
Q

What could we see on a LOFAR gram that isn’t sub related?

A

Own ship noise
Aircraft on top
Geographical
Biological
Buoys

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21
Q

What types of sub noises could we hear?

A

Shaft rub
Compressed cavitation
In/Out
Cavitation Interception Speed (speed of which you can hear blade & shaft)
Vortex shredding
Blade tip cavitation
Sheet Cavitation

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22
Q

What is CIS?

A

Cavitation Inception Speed

The point (or RPM) at which a blade starts to cavitate.

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23
Q

Two factors that affect TPK

A

Depth
Number of Shafts

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24
Q

What could we possibly see between 0-75Hz?

A

Blade and Shaft

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25
Q

What could we possible see between 75-150Hz?

A

2 S/C engines

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26
Q

What could we possibly see above 150Hz?

A

4 S/c engines

27
Q

What equation do we use to find Speed?

A 
          F0
28
Q

What equation do we use to find CPA?

A

Speed x Time x 17

29
Q

What is the equation to find Relationship of EDA to Engine

A

Main gearing teeth ÷ Reduction Gear Teeth

All times number of lobes

30
Q

3 Factors that effect waves at Sea?

A

Wind Strength
Wind Duration
Fetch

31
Q

What are the components of a passive Sonobuoy?

A

Flip Plate & Parachute
Ariel and Flotation bag
Surface Unit
Cable Drum
Compliant Cable
Strum Net and Damper
Hydropone

32
Q

What is the DIFAR SSQ 53?

A

Directional Frequency Analysis and Recording

33
Q

How many hydrophones does a DIFAR buoy have?

What are their functions?

A

4 hydrophones

Frequency Pilot at 7.5KHz

Constant Shallow Omni (CSO) @45Ft
Calibrated Omni (15KHz)
2 Directional Sensors (2.4KHz)

34
Q

What depths can the DIFAR operate at?

What life can they have?

What channels are selectable?

A

90, 200, 400, 1000 Ft

0.5, 1, 2, 4, 8 hrs

1-99 (apart from 57,58,93)

35
Q

What time to depth are each setting for the DIFAR?

A

90- 40 secs
200- 65 secs
400- 100 secs
1000- 180 secs

Can take up to a minute for buoy to stabilise

36
Q

What does DICASS stand for?

A

Directional Command Activated Sonobuoy System

37
Q

What types of beams are used on DIFAR?

A

Cardioid
Limacon

Used to find directionality

38
Q

What does the Bathy measure?

What is its activation time?

What is its life?

A

Temperature against Depth

Activation time 0.5-3 mins

12 mins life

39
Q

What is the descent rate of the Bathy?

What does it measure down to?

A

5ft / Sec

2625 ft (800 m)

40
Q

What life does the DICASS have?

A

60 mins/ 50 ping seconds

41
Q

What are the cable length depths for the DICASS?

A

D1- 50,150,300 ft

D2- 90,400,1500ft

42
Q

What kind of ocean effects can attribute to sub detectability?

A

Surface wind
Ocean current
Sea Waves

43
Q

What are ocean currents affected by?

What can they cause?

A

Surface wind flow

Affected by Coriolis effect

Sonobuoy drift

44
Q

What types of ocean fronts are there?

A

Semi Perminent
Temporary

45
Q

What is an ocean front?

A

The boundary between 2 water fronts of different thermal characteristics

46
Q

How can ocean fronts affect acoustic prosecution?

A

Poor sound Propogation
Increased ambient noise (up to 25dBs)

Confused bearing activity (change in velocity profiles causes innacurate crossfixes as sound travels through)

47
Q

What is the ocean swell?

A

Ocean waves that have departed the fetch

48
Q

What is the annulus of a CZ?
What are the two ranges we know?
What rules must sound meet to cause a CZ?

A

10% of its range

28-32 N Atlantic
14-18 Med

Must be at SLD (warmest point in first 1000ft of water), with sea bed at 9000ft minimum
Sound velocity must be greater than 10m/s increase in order to work

49
Q

What is a LOFAR Event?

A

A change or addition to the target signature that may provide tactical information

50
Q

What two mediums can sound be exploited?

A

Transmitting medium (source/environment)

Receiving medium (sensor, weapon system, operator)

51
Q

What is the function of the APS?

A

Fast Fourier Processing

Processing time based signals into a frequency based signal (usable format)

52
Q

What is the APS?

A

Acoustic Processing System

53
Q

What is FFT carried out by?

A

The ADP (Acoustics Data Processor) within the APS

54
Q

What two things is the performance of the ADP affected by?

A

Sampling Rate
Ailiasing

55
Q

What is the sampling rate?

A

Rate/number of times the amplitude of a wave is sampled (FFT)

Needs to be double the bandwidth needed in order to avoid ailiaising

56
Q

What is aliasing?

A

An unwanted effect when processing frequencies through FFP

Required bandwidth needs to be doubled in order to mask erroneous data (Niquis), this is Anti Aliasing

57
Q

What factors affect ADP performance?

A

Data Collection Time
Resolution
Integration Time
Frequency
History
Normalisation

58
Q

What is DCT?

A

Time taken to resolve a signal

Inversly proportional to Resolution

59
Q

What is resolution?

A

A measure of the systems capability to distinguish two separate lines of frequency close together

Measured in Hz

Inversly proportional to DCT

Smaller the number, finer the res

60
Q

How do we work out resolution?

A

Bandwidth ÷ Number of Display Cells

61
Q

3 types of res criteria?

A

Matched Res (perfect)

Over Res (Bandwidth exceeds bin size), weak signals may not be seen as blocked out

Under Res- bandwidth less than the res, weak signals may not be detected, strong signals as faint lines

62
Q

Two types of Integration Times? What is IT?

A

Adds up constant frequencies to stand out more against AN.

LTI (Long Term Integration)
40, 80, 160, 320 secs

STI
3.3, 6.6, 13.3

25% New and 75% old data

63
Q

What is the critical angle Ray?

A

The steepest angle at which there is 100% reflection from the seabed/surface

64
Q

Diesel electrical prop make up

A

Diesel engine
Generator

Battery

Motor
Prop

Acoustics Advanced (1 decks)

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