Lesson 2 Flashcards
(27 cards)
What is the definition of sound?
Periodic vibration in pressure, particle displacement or particle velocity in an elastic medium
What is the decibel scale?
It’s a logarithmic scale which doubles every 3db. It has a reference value in which it is based upon. Means we don’t have to deal with big numbers
What are the different types of underwater detection?
Active
Passive
What is active sonar?
Detects objects by transmitting sound and recieving an echo. Intensity measured in Dbs
What is passive sonar?
Sound received at a sensor produced from an external source
What is the main difference between active and passive sonar?
Active is 2 way transmission path, passive is 1 way
What are the different levels on ocean topography?
Continental shelf Continental slope Continental rise Abyssal plane Trench (area significantly deeper than abyssal plane) Ridge (plate boundaries)
What are the different types of sea mounts?
Jagged (pinnacles)
Flat topped (guyots)
What are the different types of ocean bottom?
Sand
Rock
Mud/silt
Ooze
What are the characteristics of a sand ocean bottom?
Smooth surface
Good reflector
Common in shallow water
What are the characteristics of rock ocean bottom?
Good reflector
Irregular surface
May scatter
What are the characteristics of mud and silt ocean bottom?
Extremely smooth surface
Poor reflector as absorbs energy
Very low frequencies <300Hz may be refracted instead of reflected back
What are the characteristics of ooze ocean bottom?
Mud with high carbonate content (dead shit)
What are the different water depth measurements?
Feet
Meters
Fathoms 1 = 6ft
What connects lines of equal depths?
Contours
What is sound pressure measured in?
Decibels (dB)
What is frequency measured in?
Hertz
What is a choke point?
A geographical feature, above or below the water which restricts the movement of submarines
What is ambient noise?
Any background noise which is not target related
What are the 2 catagories of ambient noise?
Man made
Natural
What are the 4 examples of man made ambient noise?
Shipping noise
Sonar noise
Seismic survey
Oil rig noise
What are the 4 examples of natural ambient noise?
Sea state (waves etc)
Precipitation (weather)
Biological noise (whales etc)
Ice noise
What is the problem with ambient noise? Is it better or worse at low frequencies
Ambient noise is worse at lower frequencies
It masks the target noise and makes it harder to detect
3 examples of a choke point
The English Channel
Straights of Gibraltar
Greenland - Iceland -UK Gaps
