Underwater Detection and Tracking Systems Naval Weapons Systems

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

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.

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.

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}

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

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 .

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 1000 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.

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.]

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

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?

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

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

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

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.

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.

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

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

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

SH-60 Dipping SONAR MAD gear Sonobouys Torpedo is equipped

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!

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

Questions?