SUBSIM Radio Room Forums - View Single Post - Sub-mounted HF Active Sonar

C-Wolf · 01-05-18, 02:39 PM

Acoustic Intercept, more commonly called, "Active Emissions" detection is a separate passive sonar system that shares it's information with the main suite on a submarine. I'm referring to the WLR-9 and it's successors, originally built by Norden, of bombsight fame.

Under-ice sonar is optimized for very short range and the required resolution to detect contours of the ice and polynya delineation. There's no (normal) reason to use active sonar against a target. Passive localizes very well and any active emissions can be detected much further away than the range scale they're set for. ie: If the active system is using a 10k range scale, (5nm) the transmission has to travel 20k to be within the search field. In reality, the transmission is detectable at many times the search scale, so you can be at 11kyds and "invisible" to the searcher, and have an accurate fire control solution establsihed.

An upward-oriented sonar projector (BQS-8) still radiates energy spherically, (though not initially) with multiple reflection paths generated under the ice.

Why do skimmers use active sonar? Because they have to, and it beats throwing rocks or consulting the Psychic Hotline. Towed passive sonar, (SQR-17 TACTAS and later) was useful, but not the primary means of detection --due to own ship's noise.

I spent an interesting week of "familiarization training" sitting in the sonar shack of a frigate, and could immediately tell none of the sonarmen had a clue as to how to interpret passive information, including determining their own screw-blade signature. I ended up giving them an impromptu LOFAR gram-reading lesson they thought was black magic, or PFM in submarine parlance. It was more than embarrassing, it was frightening. We routinely entered the detection zones of battle groups during exercises with impunity and popped flares onto the carrier's flight decks. I would feel safer aboard an old, Q-5-equipped Permit boat than any skimmer yet built.

Better algorithms have made passive sonar more practical for surface ships, but active sonar will be their primary means of detection for awhile yet, especially against the newer adversary submarines which run much quieter.

Good luck ever detecting a 20kHz (click). Most humans cannot hear much above 18k. And torpedoes employ much higher active sonars for localization. That's where AE systems come in. They detect anything emitting as much as a squeak (own ship and biologics included.) way beyond aural detection ranges. With SHT (anechoic coatings) applied, any advantage for using active sonar is reduced as well.

Unless a US submarine was in a very dire situation, there is no practical reason to use any kind of active sonar to reveal their position prior to firing. With the reduction of transients associated with a torpedo launch, the last thing an adversary will hear are high-speed screws. The MK-48 is very, very hard to get away from.

The Russians built the Alpha to go fast and deep, using a submarine that was very expensive to build and power plant that was difficult to maintain. We countered with a torpedo that could go fast and deep, (ADCAP) which was much more economical and dealt with the threat.

In short - passive rules!

CCC

01-05-18, 02:39 PM	#5
C-Wolf Watch Join Date: Dec 2017 Location: New England Posts: 30 Downloads: 2 Uploads: 0	Acoustic Intercept, more commonly called, "Active Emissions" detection is a separate passive sonar system that shares it's information with the main suite on a submarine. I'm referring to the WLR-9 and it's successors, originally built by Norden, of bombsight fame. Under-ice sonar is optimized for very short range and the required resolution to detect contours of the ice and polynya delineation. There's no (normal) reason to use active sonar against a target. Passive localizes very well and any active emissions can be detected much further away than the range scale they're set for. ie: If the active system is using a 10k range scale, (5nm) the transmission has to travel 20k to be within the search field. In reality, the transmission is detectable at many times the search scale, so you can be at 11kyds and "invisible" to the searcher, and have an accurate fire control solution establsihed. An upward-oriented sonar projector (BQS-8) still radiates energy spherically, (though not initially) with multiple reflection paths generated under the ice. Why do skimmers use active sonar? Because they have to, and it beats throwing rocks or consulting the Psychic Hotline. Towed passive sonar, (SQR-17 TACTAS and later) was useful, but not the primary means of detection --due to own ship's noise. I spent an interesting week of "familiarization training" sitting in the sonar shack of a frigate, and could immediately tell none of the sonarmen had a clue as to how to interpret passive information, including determining their own screw-blade signature. I ended up giving them an impromptu LOFAR gram-reading lesson they thought was black magic, or PFM in submarine parlance. It was more than embarrassing, it was frightening. We routinely entered the detection zones of battle groups during exercises with impunity and popped flares onto the carrier's flight decks. I would feel safer aboard an old, Q-5-equipped Permit boat than any skimmer yet built. Better algorithms have made passive sonar more practical for surface ships, but active sonar will be their primary means of detection for awhile yet, especially against the newer adversary submarines which run much quieter. Good luck ever detecting a 20kHz (click). Most humans cannot hear much above 18k. And torpedoes employ much higher active sonars for localization. That's where AE systems come in. They detect anything emitting as much as a squeak (own ship and biologics included.) way beyond aural detection ranges. With SHT (anechoic coatings) applied, any advantage for using active sonar is reduced as well. Unless a US submarine was in a very dire situation, there is no practical reason to use any kind of active sonar to reveal their position prior to firing. With the reduction of transients associated with a torpedo launch, the last thing an adversary will hear are high-speed screws. The MK-48 is very, very hard to get away from. The Russians built the Alpha to go fast and deep, using a submarine that was very expensive to build and power plant that was difficult to maintain. We countered with a torpedo that could go fast and deep, (ADCAP) which was much more economical and dealt with the threat. In short - passive rules! CCC __________________ Sagire, Classis, Destructum! Last edited by C-Wolf; 01-05-18 at 08:05 PM.