1. Underwater Detection and Tracking Systems
Naval Weapons Systems

2. Format for Lecture Terms, systems Pictures, slide recognition
BG Operations

3. Basic Sonar Systems Active Passive Echo Ranging Systems
Listening Systems
Already discussed differences between active and passive systems as lead-in to sonar equations. Here, it is meant as a review and as included in various forms of detection equipment.

4. Transducer Theory
Transducer: Device for converting one form of energy into another.
In sonar, electrical energy is transformed into acoustic energy (oscillation of water molecules through which sound travels)
Three ways to change electrical energy into acoustic energy....
Three electrical => acoustic conversions:
- Electrostrictive
- Piezoelectric
- Magnetostrictive
Discuss the differences between the energy conversion processes, and various materials that would be used in each process.
Transducer Directivity: Function of the mechanical arrangement of the transducer elements and the associated electrical and electronic circuitry.
Control of beam patterns is needed so that directivity matches operational needs.
Discuss “shading a transducer” by:
- physically arranging the spacing, size, or number of elements
- electrically, by the number of turns on magnetostrictive elements
- mechanically, by the physical shape of the active surface of the tranducer
Transducer Power: Limited by hydrostatic pressure at transducer...increases with depth. Size also increases w/increased power => limitations.

5. Searchlight SONAR SLOW Search Easily Saturated
Have to TRAIN the transducer
Old Knox class FF’s and before
{Pg 256, fig 9-6 in Old Book}

6. Scanning Echo Ranging SONAR
360 degree search on each transmission
Range and Bearing on a number of targets
No Mechanical rotation, electronic
Greater Power

7. Advantages & Disadvantages of Sonar Types
Limitations of sonar due to the physical properties of sound travel in water
Active vs Passive sonar in detection
Active vs Passive sonar in tracking
Lead discussion to draw from students what type of sonar may be used for various applications, and why? (i.e.-Would one use active or passive sonar to identify a type of submarine? What about to obtain a fire control solution? Why?)
Concentrate on limitations such as:
- Slow search with active sonar. After transmitting a ping, transducer must remain trained in same direction to await sonar return. (For 5000 metres, that equates to about 7 seconds.)
- Saturation vulnerability. When echo-ranging sonar is being used, it can be used only on one target, and it cannot simultaneously be used for search. Introduce scanning echo-ranging systems.
- Transducer size limitations:
> Limits output due to cavitation.
> Requires use of relatively high frequencies .

8. Other Sonar Equipment Tactical Towed Array Sonar (TACTAS) Sonobouys
Passive
Active
Special purpose
Dipping Sonar
Sound Surveillance System (SOSUS)
VISUAL!
TACTAS: Line of hydrophones (passive) towed astern of an ASW platform. (CRUDES ships)
- Hydrophones are grouped according to the beam patterns desired and the frequency band covered.
- Advantage: Sensing array can be towed more than meters astern, far from machinery noise of towing vessel.
(Improve S/N ratio)
Sonobouys: Expendable detection device, designed to be dropped from aircraft and ships. Detect underwater sounds and transmit the sounds to nearby vessels via low-powered VHF radio transmission.
- Depth of hydrophone/transducer may be variable.
- May be active, passive, or special purpose; may be directional or omni-directional.
- Special purpose:
- To obtain temperature vs. depth profiles
- Communications link between aircraft and friendly submarines
Dipping Sonar: Sonar transducer attached to line and lowered by helicopter.
SOSUS: Permanent hydrophones at bottom of GI-UK gap to track underwater traffic.

9. Magnetic Anomaly Detection (MAD)
Principle: A metallic submarine disturbs the magnetic lines of force of the earth.
The magnetic distortion - or anomaly - caused by a sub below the surface can be detected from the air above the sub.
P-3, SH-60B
Talk about the permanent magnetic lines of flux about a ship, especially how that is formed during construction (from heat (welding) and impact (riveting).
[Allude to construction of wooden-hulled mine countermeasures vessels.]
Talk about the “induced field” which varies with ship’s head.
Comment on combination of permanent and induced fields => the ship’s magnetic signature, and possible reductions of it by degausing coils.
MAD can detect up to 500 meters from source to sensor.
[Visual sighting of submarines is also a possible means of detection.]

10. Underwater Communications
AN/WQC-2
Short range
Most of the time, they just surface and use RF

11. Doppler Shift Oh no, not again!!!
Same principles apply to sound in water
Doppler shift not as great as in the air
Varies with the speed of sound
Increased frequency?
Decreased frequency?

12. EMCON EMCON for USW! Similar to RADAR and RF Set quiet ship
Reduce self noise!

13. Introduction (Platforms)
Surface Ships (DDG, CG, DD, FFG)
Advantages:
more available manpower
greater time on station
variety of detection equipment
variety of available weapons and better fire control systems
ability to operate in foul weather
embarked LAMPS aircraft

14. Introduction (Platforms)
Surface Ships
Disadvantages:
NOT “in” the submarine’s environment
Relatively Slow
Noisy
ASW prosecution is protracted

15. Introduction (Platforms)
Aircraft Carriers
Advantages:
NONE
Disadvantages:
Same as for Surface Ships
Aircraft Carrier is a High Value Target, its importance to naval operations requires many assets to be employed to protect it.

16. Introduction (Platforms)
Aircraft (S-3, P-3, SH-60B)
Advantages:
Speed
ability to deploy sensors over a large area
Surprise through use of passive detection systems
Not in submarine’s environment
Altitude increases radar horizon.

17. Introduction (Platforms)
Aircraft
Disadvantages:
Low time on station
Limited weapons capacity
Limited range
Vulnerable to weather

18. Introduction (Platforms)
Submarines
Advantages:
Shares the advantages of the target
passive detection
concealment
less distracted by sound refracting properties of water
Speed vs. Surface Ships
Nuke subs can stay submerged for months

19. Introduction (Platforms)
Submarines
Disadvantages:
To detect targets, subs must run deep
To communicate, subs must be in shallow water
Capable of high speed, but at the expense of increased noise levels
Diesel subs must “snorkel” to recharge batteries

20. SH-60
Dipping SONAR
MAD gear
Sonobouys
Torpedo is equipped

21. CRUDES ships
Long on station time
SONAR
TACTAS
NIXIE
Prairie/Masker
Acoustic countermeasures
Torpedoes
BAD if surface ship is shooting at a submarine!
What is the #1 means if positive submarine ID? MK1 Mod 1 Eyeball!

22. Submarines!
Operating in its own environment, BEST USW Asset!
Long station time
SONAR
TASS Towed array sonar system
torpedoes
acoustic countermeasures

23. Questions?