Exam 1 Flashcards
Name the NATO Designators and give brief description (5)
SSBN
SSGN
SSN
SSAN (technically research)
SSK (most prolific)
What does the snort system allow?
Batteries to be charged without surfacing properly
A sub may surface/come to periscope depth when?
Emergency
Recharge Batteries
Comms
Attack Solutions
What is Rarefraction?
Sound vibration away from a point (lengthened wavelength)
What is compression?
Sound vibration towards a point (shorter wavelength)
What is the effective pressure level?
Mean pressure of a positive or negative wave. Measured from 0 to peak of wave
What is frequency?
Number of complete wave cycles passing a fixed point in 1 second (Hz)
Give some decibel levels and what they are linked to
0= smallest audible sound
10= rustling leaves
70= Thunder
140= Jet Plane @ 30m
150= Submarine
How do you work out a linear change of 2 x source?
10Log2 (equals 3dB)
4 types of sea bed composites and their characteristics?
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
What are modern charts measured in?
Fathoms (6 feet)
Metres
2 types of underwater sound detection?
Active (2-Way Transmission)
Passive (Single Path Transmission
Two types of Spreading Loss?
Spherical (Doubling, 6 dB decrease)
Cylindrical (Doublind, 3dB decrease)
Types of Attenuation loss?
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)
2 types of Propogation Loss?
Spreading
Attenuation
What is Ambient Noise?
Any background noise that is non target related
Man made Ambient Noises?
Drilling
Shipping
Seismic Surveying
Active transmissions
Natural ambient noise?
Bio
Ice
Weather
Sea State
Tectonic/Seismic
What is Lloyd’s mirror?
Constructive and destructive interference of the broadband energy of the submarine at the hydrophone
What could we see on a LOFAR gram that isn’t sub related?
Own ship noise
Aircraft on top
Geographical
Biological
Buoys
What types of sub noises could we hear?
Shaft rub
Compressed cavitation
In/Out
Cavitation Interception Speed (speed of which you can hear blade & shaft)
Vortex shredding
Blade tip cavitation
Sheet Cavitation
What is CIS?
Cavitation Inception Speed
The point (or RPM) at which a blade starts to cavitate.
Two factors that affect TPK
Depth
Number of Shafts
What could we possibly see between 0-75Hz?
Blade and Shaft
What could we possible see between 75-150Hz?
2 S/C engines
What could we possibly see above 150Hz?
4 S/c engines
What equation do we use to find Speed?
F0
What equation do we use to find CPA?
Speed x Time x 17
What is the equation to find Relationship of EDA to Engine
Main gearing teeth ÷ Reduction Gear Teeth
All times number of lobes
3 Factors that effect waves at Sea?
Wind Strength
Wind Duration
Fetch
What are the components of a passive Sonobuoy?
Flip Plate & Parachute
Ariel and Flotation bag
Surface Unit
Cable Drum
Compliant Cable
Strum Net and Damper
Hydropone
What is the DIFAR SSQ 53?
Directional Frequency Analysis and Recording
How many hydrophones does a DIFAR buoy have?
What are their functions?
4 hydrophones
Frequency Pilot at 7.5KHz
Constant Shallow Omni (CSO) @45Ft
Calibrated Omni (15KHz)
2 Directional Sensors (2.4KHz)
What depths can the DIFAR operate at?
What life can they have?
What channels are selectable?
90, 200, 400, 1000 Ft
0.5, 1, 2, 4, 8 hrs
1-99 (apart from 57,58,93)
What time to depth are each setting for the DIFAR?
90- 40 secs
200- 65 secs
400- 100 secs
1000- 180 secs
Can take up to a minute for buoy to stabilise
What does DICASS stand for?
Directional Command Activated Sonobuoy System
What types of beams are used on DIFAR?
Cardioid
Limacon
Used to find directionality
What does the Bathy measure?
What is its activation time?
What is its life?
Temperature against Depth
Activation time 0.5-3 mins
12 mins life
What is the descent rate of the Bathy?
What does it measure down to?
5ft / Sec
2625 ft (800 m)
What life does the DICASS have?
60 mins/ 50 ping seconds
What are the cable length depths for the DICASS?
D1- 50,150,300 ft
D2- 90,400,1500ft
What kind of ocean effects can attribute to sub detectability?
Surface wind
Ocean current
Sea Waves
What are ocean currents affected by?
What can they cause?
Surface wind flow
Affected by Coriolis effect
Sonobuoy drift
What types of ocean fronts are there?
Semi Perminent
Temporary
What is an ocean front?
The boundary between 2 water fronts of different thermal characteristics
How can ocean fronts affect acoustic prosecution?
Poor sound Propogation
Increased ambient noise (up to 25dBs)
Confused bearing activity (change in velocity profiles causes innacurate crossfixes as sound travels through)
What is the ocean swell?
Ocean waves that have departed the fetch
What is the annulus of a CZ?
What are the two ranges we know?
What rules must sound meet to cause a CZ?
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
What is a LOFAR Event?
A change or addition to the target signature that may provide tactical information
What two mediums can sound be exploited?
Transmitting medium (source/environment)
Receiving medium (sensor, weapon system, operator)
What is the function of the APS?
Fast Fourier Processing
Processing time based signals into a frequency based signal (usable format)
What is the APS?
Acoustic Processing System
What is FFT carried out by?
The ADP (Acoustics Data Processor) within the APS
What two things is the performance of the ADP affected by?
Sampling Rate
Ailiasing
What is the sampling rate?
Rate/number of times the amplitude of a wave is sampled (FFT)
Needs to be double the bandwidth needed in order to avoid ailiaising
What is aliasing?
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
What factors affect ADP performance?
Data Collection Time
Resolution
Integration Time
Frequency
History
Normalisation
What is DCT?
Time taken to resolve a signal
Inversly proportional to Resolution
What is resolution?
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
How do we work out resolution?
Bandwidth ÷ Number of Display Cells
3 types of res criteria?
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
Two types of Integration Times? What is IT?
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
What is the critical angle Ray?
The steepest angle at which there is 100% reflection from the seabed/surface
Diesel electrical prop make up
Diesel engine
Generator
Battery
Motor
Prop
