Active vs Passive sonar and marine life

[TheAlphaMag]

I'm in a Marine Science class at my highschool (we're lucky enough to have a great teacher who actually knows what he's talking about- he's a marine biologist- as opposed to someone writing notes on the board out of a book).

Its a great class since we dont have to know any of it for a standardized test- its all for our benefit instead of to pass the MCAS.. How classes should be, in my opinion.

Anyways, I'm going to enlist in the Marine Corps next may, and we were discussing how most whale and large mammal beachings can be directly correlated to military activity in the area, and patterns of the mammals always seem to be in a straight line, as if they are running [swimming] away from something.

Can anybody elaborate on differences between active and passive sonar, and why passive sonar seems to affect wildlife less. Also, which is more effective at detecting enemy vessels and underwater objects?

Thanks

-Alpha

 

[fishb0y]

Can anybody elaborate on differences between active and passive sonar, and why passive sonar seems to affect wildlife less. Also, which is more effective at detecting enemy vessels and underwater objects?

I'm a submariner on shore duty. While I'm Nuclear trained and kept back aft and treated like a mushroom (kept in the dark and shoveled alot of *****) we have to know a little about what happens in the cone (forward part of the boat).

The only time a sub can see is if we use our periscope, but that is only on or near the surface. When submerged we "see" using sound. Unlike what you see in movies like the Hunt for Red October (a sonarman being the smartest person on a sub... please), we listen to what is happening outside using lots of microphones on the outside of the hull. That is called 'passive sonar' simply listening what is going on in the ocean around us. It is possible to hear other vessels miles away, especially older and/louder vessels.

Unfortunately newer submarines, such as diesel electric submarines are much harder, if not impossible to hear at times. At that point we use sound, sent out of speakers. As this sound moves through the water, it bounces off objects and returns to the microphones, kinda like RADAR. This is called active. Active sonar isn't used very often because it can give away the sub's position, thus rendering it more vulnerable.

My only arguement for the use of active sonar (and to my understanding, only certain frequencies) is that it protects my life. I know people that complain about the use of this sonar will come up with plenty of reasons why it souldn't be used, but they are all ignorant of one thing... my wife and 2 children looked forward to me coming home from an underway, and I am against anything that will cause my family to sit at the pier waiting for me to return, not knowing that I am now on eternal patrol.

Hope this helps, I tried to keep it fairly simple.

 

[Don Burke]

we were discussing how most whale and large mammal beachings can be directly correlated to military activity in the area, and patterns of the mammals always seem to be in a straight line, as if they are running [swimming] away from something.

Actually, they can not be directly correlated.

_All_ strandings are now blamed on the nearest military operation. I imagine some of them are the fault of Navy or scientific work, but certainly not all.

Can anybody elaborate on differences between active and passive sonar, and why passive sonar seems to affect wildlife less.

Passive SONAR is not putting anything out, so the ship has to run over the wildlife to affect it to any significant degree.

Also, which is more effective at detecting enemy vessels and underwater objects?

The answer to that question is yes.

On a noisy target in a very quiet environment, a passive system will outperform an active one by quite a margin.

Submariners fell in love with passive systems because they preserve the stealth of the attacking ship. There is only so much that can be wrung from a passive system and we are beyond the point of diminishing returns.

On a silent or nearly silent target, a passive system will probably not work at all. There are classes of submarines that could only detected with a passive system by how they blocked natural ocean sounds. That only works at short ranges if at all.

More background noise and less target noise means active systems must be used.

 

[Rickg]

TheAlphaMag,

Beware of what professors tell you. Also beware of what you read. That said - the following is a fairly informative website on the subject (even if it is a Navy site).

http://www.surtass-lfa-eis.com/

Also you can find a lot of earlier threads on this subject if you do searchs on LFA, active sonar, passive sonar, etc.

Rickg

 

[DA Aquamaster]

Surface vessels engaged in anti submarine operations are far more likely to use active sonar than submarines as about the last thing a sub wants to do is reveal it's position. This is not really an issue with surface vessels as everyone already knows where they are anyway.

It's the frequencies used that cause the problem, and it is not accidental as what makes those frequencies so effective for whales works the same for the US Navy. The whales had first dibs, but as in most other endevors that conflict with nature, we put ourselves first anyway.

It's not just "newer" diesel electric subs that are quieter, many older diesel electric subs were also very quiet. With a nuclear boat, you basically always have to be running pumps to circulate cooling water whereas with a diesel electric sub, you can shut everything off and drift truly silent or run only on the electric motors and still be very very quiet. On average, diesel electric subs tend to be smaller, much less expensive to build and operate and are very attractive for smaller navies who want to primarily defend their coastlines and do not need a sub with extreme range or endurance.

Diesel electric subs are however at a disadvantage as they have to run at periscope depth and raise a snorkel to run their diesel engines and recharge their batteries every day or two. The US Navy used to have extensive airborne ASW assets in the form of ASW carriers, P-3's, helicopters, etc that were able to keep track of just about anything of interest nuclear or diesel electric. However the number of ASW assets has been reduced significantly since the end of the cold war. In my opinion, the current development and use of extremely powerful and long ranged sonar was done in part to offset the overall reduction in ASW forces.

In that regard, it's probably true to say that active sonar helps keep our ships safe when they are in the coastal waters of countries that operate diesel electric subs. However, it would be extremely difficult for a diesel electric sub to cross either the pacific or atlantic and enter our coastal waters without being detected during the crossing. So it's probably more correct to classify the new generation of very powerful active sonars as more of an offensive weapon than a defensive one.

Part of the problem with US Navy operations, is that active sonar is most useful in noisy coastal waters where strandings are obviously more likely to happen. There are areas in the ocean where there are relatively few fish and very little planton to attract marine mammals and where consequently there are not many, if any, marine mammals, but these areas are also relatively quiet and don't offer a great training environment.

And I disagree with the need to beware of what professors tell you. In my experience, they tend to say it like it is, they just offend people because they are less likely than most people to buy into bogus authoritarian explanations and arguments or confine what they say to only those things that are currently viewed as being politically correct. And it's a good thing because if they didn't disagree with the status quo, we'd still be sitting in caves discussing the benfits of being active versus passive cat food.

 

[fishb0y]

Diesel electric subs are however at a disadvantage as they have to run at periscope depth and raise a snorkel to run their diesel engines and recharge their batteries every day or two. The US Navy used to have extensive airborne ASW assets in the form of ASW carriers, P-3's, helicopters, etc that were able to keep track of just about anything of interest nuclear or diesel electric. However the number of ASW assets has been reduced significantly since the end of the cold war. In my opinion, the current development and use of extremely powerful and long ranged sonar was done in part to offset the overall reduction in ASW forces.

Thats the great thing about opinions, they are just that. I have talked with P-3 guys that have said they had a hard time tracking subs, not as easy as Hollywood says. As for tracking a diesel sub, you are right about snorkeling, but there is more and I am not sure how much I can go into that. http://www.naval-technology.com/projects/kilo877/

In that regard, it's probably true to say that active sonar helps keep our ships safe when they are in the coastal waters of countries that operate diesel electric subs. However, it would be extremely difficult for a diesel electric sub to cross either the pacific or atlantic and enter our coastal waters without being detected during the crossing. So it's probably more correct to classify the new generation of very powerful active sonars as more of an offensive weapon than a defensive one.

Wow, glad to see what side you are sitting. Hate to tell you, but if you follow the news, China is building up their military to some pretty impressive levels, and they do have Nukes and Boomers. You can flaunt your peace sign all you want, but again I loved coming home to my wife and children. http://washingtontimes.com/specialreport/20050626-122138-1088r.htm

Part of the problem with US Navy operations, is that active sonar is most useful in noisy coastal waters where strandings are obviously more likely to happen. There are areas in the ocean where there are relatively few fish and very little planton to attract marine mammals and where consequently there are not many, if any, marine mammals, but these areas are also relatively quiet and don't offer a great training environment.

Again you are wrong, the Navy has moved most of the active sonar testing away from those areas, again if you care to look up the facts, you will see the areas of unrestricted use are getting smaller. http://seattlepi.nwsource.com/local/143752_sonar14.html

And I disagree with the need to beware of what professors tell you. In my experience, they tend to say it like it is, they just offend people because they are less likely than most people to buy into bogus authoritarian explanations and arguments or confine what they say to only those things that are currently viewed as being politically correct. And it's a good thing because if they didn't disagree with the status quo, we'd still be sitting in caves discussing the benfits of being active versus passive cat food.

With that said, you are allowing these professors to give the bogus authoritarian explanations and arguements???

 

[Don Burke]

Surface vessels engaged in anti submarine operations are far more likely to use active sonar than submarines as about the last thing a sub wants to do is reveal it's position.

This was more true until the Spruance class destroyers hit the water. Those guys are quiet enough to make passive work.

This is not really an issue with surface vessels as everyone already knows where they are anyway.

During the Iranian hostage crisis, the Soviets lost the entire Kitty Hawk battlegroup for several weeks. The ocean is bigger than it looks.

It's the frequencies used that cause the problem, and it is not accidental as what makes those frequencies so effective for whales works the same for the US Navy. The whales had first dibs, but as in most other endevors that conflict with nature, we put ourselves first anyway.

Whales rarely need to track contacts hundreds of miles away.

It's not just "newer" diesel electric subs that are quieter, many older diesel electric subs were also very quiet. With a nuclear boat, you basically always have to be running pumps to circulate cooling water

You might want to review the specifications of an S8G reactor.

whereas with a diesel electric sub, you can shut everything off and drift truly silent or run only on the electric motors and still be very very quiet.

Under such conditions, a Diesel-electric boat would be making no more than a couple of knots. That is useful mainly when you have already been detected.

On average, diesel electric subs tend to be smaller, much less expensive to build and operate and are very attractive for smaller navies who want to primarily defend their coastlines and do not need a sub with extreme range or endurance.

true enough

Diesel electric subs are however at a disadvantage as they have to run at periscope depth and raise a snorkel to run their diesel engines and recharge their batteries every day or two. The US Navy used to have extensive airborne ASW assets in the form of ASW carriers, P-3's, helicopters, etc that were able to keep track of just about anything of interest nuclear or diesel electric.

I strongly disagree. The P-3s would lose us on a regular basis. In fact, the hardest part of an exercise was often getting the P-3 steered onto us so we could begin the exercise.

However the number of ASW assets has been reduced significantly since the end of the cold war. In my opinion, the current development and use of extremely powerful and long ranged sonar was done in part to offset the overall reduction in ASW forces.

In my opinon, the trend toward long range active SONAR is due to much quieter targets in an ocean with much more merchant traffic.

In that regard, it's probably true to say that active sonar helps keep our ships safe when they are in the coastal waters of countries that operate diesel electric subs.[QUOTE/]That is probably the worst possible place to go active.

However, it would be extremely difficult for a diesel electric sub to cross either the pacific or atlantic and enter our coastal waters without being detected during the crossing.

With a little trickery, it has been done. SOSUS is beatable.

So it's probably more correct to classify the new generation of very powerful active sonars as more of an offensive weapon than a defensive one.

Actually neither is a weapon.

Part of the problem with US Navy operations, is that active sonar is most useful in noisy coastal waters where strandings are obviously more likely to happen. There are areas in the ocean where there are relatively few fish and very little planton to attract marine mammals and where consequently there are not many, if any, marine mammals, but these areas are also relatively quiet and don't offer a great training environment.[QUOTE/]The trend has been to move the training areas farther offshore. The noise is of no benefit for training since it is not heard anyway. In the early stages, shorter transit times were the benefit and that has been superceded by environmental concerns.

And I disagree with the need to beware of what professors tell you. In my experience, they tend to say it like it is,

In my experience, professors modify their science to suit their politics.

they just offend people because they are less likely than most people to buy into bogus authoritarian explanations and arguments or confine what they say to only those things that are currently viewed as being politically correct.

This is precisely incorrect. They are far more likely to say what suits the needs of their politics.

And it's a good thing because if they didn't disagree with the status quo, we'd still be sitting in caves discussing the benfits of being active versus passive cat food.

Since there were no professors in the those days, this is impossible.

 

[DA Aquamaster]

I won't argue the P-3 issue other than to point out the primary mission of P-3 crews is no longer hunting subs in blue water. It's a perishable skill, a fact admitted in the P-3 community.

 

[fishb0y]

I won't argue the P-3 issue other than to point out the primary mission of P-3 crews is no longer hunting subs in blue water. It's a perishable skill, a fact admitted in the P-3 community.

Right, P-3s are now hunting subs in shallow water, a much more difficult environment. You will see that submarine warfare is now done in littoral(sp?) (shallow) water.

 

[DA Aquamaster]

Ahh...you do like to argue. Sub hunting in shallow water is also nothing new. The point was that P-3's today are involved in a lot more than hunting subs. In contrast during the cold war, sub hunting used to be their primary mission and older VP crews were extremely good at it, whether it was mid ocean or along a coast line.

It's a perishable skill that is no longer present to the same degree in VP squadrons that now perform multiple roles. But hey, you have a right to your own opinion.