Exam 1

Question 1

Name the NATO Designators and give brief description (5)

Answer 1

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

Question 2

What does the snort system allow?

Answer 2

Batteries to be charged without surfacing properly

Question 3

A sub may surface/come to periscope depth when?

Answer 3

Emergency
Recharge Batteries
Comms
Attack Solutions

Question 4

What is Rarefraction?

Answer 4

Sound vibration away from a point (lengthened wavelength)

Question 5

What is compression?

Answer 5

Sound vibration towards a point (shorter wavelength)

Question 6

What is the effective pressure level?

Answer 6

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

Question 7

What is frequency?

Answer 7

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

Question 8

Give some decibel levels and what they are linked to

Answer 8

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

Question 9

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

Answer 9

10Log2 (equals 3dB)

Question 10

4 types of sea bed composites and their characteristics?

Answer 10

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

Question 11

What are modern charts measured in?

Answer 11

Fathoms (6 feet)
Metres

Question 12

2 types of underwater sound detection?

Answer 12

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

Question 13

Two types of Spreading Loss?

Answer 13

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

Question 14

Types of Attenuation loss?

Answer 14

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)

Question 15

2 types of Propogation Loss?

Answer 15

Spreading
Attenuation

Question 16

What is Ambient Noise?

Answer 16

Any background noise that is non target related

Question 17

Man made Ambient Noises?

Answer 17

Drilling
Shipping
Seismic Surveying
Active transmissions

Question 18

Natural ambient noise?

Answer 18

Bio
Ice
Weather
Sea State
Tectonic/Seismic

Question 19

What is Lloyd’s mirror?

Answer 19

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

Question 20

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

Answer 20

Own ship noise
Aircraft on top
Geographical
Biological
Buoys

Question 21

What types of sub noises could we hear?

Answer 21

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

Question 22

What is CIS?

Answer 22

Cavitation Inception Speed

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

Question 23

Two factors that affect TPK

Answer 23

Depth
Number of Shafts

Question 24

What could we possibly see between 0-75Hz?

Answer 24

Blade and Shaft

Question 25

What could we possible see between 75-150Hz?

Answer 25

2 S/C engines

Question 26

What could we possibly see above 150Hz?

Answer 26

4 S/c engines

Question 27

What equation do we use to find Speed?

Answer 27

1450 x (Fmax-Fmin) ------------------------------- F0

Question 28

What equation do we use to find CPA?

Answer 28

Speed x Time x 17

Question 29

What is the equation to find Relationship of EDA to Engine

Answer 29

Main gearing teeth ÷ Reduction Gear Teeth All times number of lobes

Question 30

3 Factors that effect waves at Sea?

Answer 30

Wind Strength Wind Duration Fetch

Question 31

What are the components of a passive Sonobuoy?

Answer 31

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

Question 32

What is the DIFAR SSQ 53?

Answer 32

Directional Frequency Analysis and Recording

Question 33

How many hydrophones does a DIFAR buoy have? What are their functions?

Answer 33

4 hydrophones Frequency Pilot at 7.5KHz Constant Shallow Omni (CSO) @45Ft Calibrated Omni (15KHz) 2 Directional Sensors (2.4KHz)

Question 34

What depths can the DIFAR operate at? What life can they have? What channels are selectable?

Answer 34

90, 200, 400, 1000 Ft 0.5, 1, 2, 4, 8 hrs 1-99 (apart from 57,58,93)

Question 35

What time to depth are each setting for the DIFAR?

Answer 35

90- 40 secs 200- 65 secs 400- 100 secs 1000- 180 secs Can take up to a minute for buoy to stabilise

Question 36

What does DICASS stand for?

Answer 36

Directional Command Activated Sonobuoy System

Question 37

What types of beams are used on DIFAR?

Answer 37

Cardioid Limacon Used to find directionality

Question 38

What does the Bathy measure? What is its activation time? What is its life?

Answer 38

Temperature against Depth Activation time 0.5-3 mins 12 mins life

Question 39

What is the descent rate of the Bathy? What does it measure down to?

Answer 39

5ft / Sec 2625 ft (800 m)

Question 40

What life does the DICASS have?

Answer 40

60 mins/ 50 ping seconds

Question 41

What are the cable length depths for the DICASS?

Answer 41

D1- 50,150,300 ft D2- 90,400,1500ft

Question 42

What kind of ocean effects can attribute to sub detectability?

Answer 42

Surface wind Ocean current Sea Waves

Question 43

What are ocean currents affected by? What can they cause?

Answer 43

Surface wind flow Affected by Coriolis effect Sonobuoy drift

Question 44

What types of ocean fronts are there?

Answer 44

Semi Perminent Temporary

Question 45

What is an ocean front?

Answer 45

The boundary between 2 water fronts of different thermal characteristics

Question 46

How can ocean fronts affect acoustic prosecution?

Answer 46

Poor sound Propogation Increased ambient noise (up to 25dBs) Confused bearing activity (change in velocity profiles causes innacurate crossfixes as sound travels through)

Question 47

What is the ocean swell?

Answer 47

Ocean waves that have departed the fetch

Question 48

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

Answer 48

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

Question 49

What is a LOFAR Event?

Answer 49

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

Question 50

What two mediums can sound be exploited?

Answer 50

Transmitting medium (source/environment) Receiving medium (sensor, weapon system, operator)

Question 51

What is the function of the APS?

Answer 51

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

Question 52

What is the APS?

Answer 52

Acoustic Processing System

Question 53

What is FFT carried out by?

Answer 53

The ADP (Acoustics Data Processor) within the APS

Question 54

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

Answer 54

Sampling Rate Ailiasing

Question 55

What is the sampling rate?

Answer 55

Rate/number of times the amplitude of a wave is sampled (FFT) Needs to be double the bandwidth needed in order to avoid ailiaising

Question 56

What is aliasing?

Answer 56

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

Question 57

What factors affect ADP performance?

Answer 57

Data Collection Time Resolution Integration Time Frequency History Normalisation

Question 58

What is DCT?

Answer 58

Time taken to resolve a signal Inversly proportional to Resolution

Question 59

What is resolution?

Answer 59

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

Question 60

How do we work out resolution?

Answer 60

Bandwidth ÷ Number of Display Cells

Question 61

3 types of res criteria?

Answer 61

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

Question 62

Two types of Integration Times? What is IT?

Answer 62

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

Question 63

What is the critical angle Ray?

Answer 63

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

Question 64

Diesel electrical prop make up

Answer 64

Diesel engine Generator Battery Motor Prop