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[OneShot]

I moved it to the right forum ...

To answer your question, the gram or XBT display will have a notation somewhere like Layer : xxx ft if there is actually a layer. A layer means that you see a clear and sometimes sharp bend in the line drawn, regardless of which direction. The point at which the line bends marks the layer. For more detailed information check out one of the various available manuals, like the TACMAN or the P-3C OWTOP (both available here and at subguru's).



P.S. : I suggest you take the time to register here, as it allows you more access to the CADC (and its absolutly free).

Cheers
OS

[Subguru]

Check out this link for a good introduction to sonar and underwater sound:

http://www.fas.org/man/dod-101/sys/ship/acoustics.htm

[soundken]

althrough this is really clear in my head its hard to put into words. and i havent had to explain this since college so please pactince, for those that understand already apolagies in advance for simplifying things a lil

first lets look at the air because its the easiest :wink: sound travels at diff speeds/ distance throught the air dependent on mostly, temp and pressure its quite common to think of the "speed of sound" as a hard figure about 1180f/s which is what it is @ sea lvl room temp. dont feel bad this is quite common among a lot of "profesional" "Soundmen" :slap: that i have had the pleasure of working with :rolleyes:

medium: (defenition) the phisical enviorment that the energy passes through eg, water, air, wood, steel anything classafied as "matter"

now lets change the medium lets say steel. does sound travel trough steel well? the answer yes mabey no depends :confused: put your ear up to a railroad track and listen you can hear a train coming from miles away. way before you hear it in air but now there's a catch your ear has to be attached to the track to hear it and all you can hear is the train (or what you assume is the train) nothing else.

refraction: (loose defenition) the bending of light/sound/energy as it passes from one medium to annother. ex: have a friend stick a long pole in a pool of water and look at it from the side.

now for the big one you have alll been reading me rambling on for sound in water . first the surface . lets say your freind with the pole smacks you and pushes you in the water where and holds you under water laughing at you:mad: you hear him but he's all muffled and distorted.

1 there's the refraction thing
2 and this is the biggie, theres a change of medium

sound like all energy, and myself ,always takes the path of least resistance, i mean there you are a happy soundwave passing through the pretty air when you encouter this big surface (the water) it looks inviting but do you really want to get wet? well that depends on what kind of sound wave you are

1) if your a LF wave then your big and burly and like to crash around making things vibrate, (like last night when your "friend" had his stereo cranked and you could hear the bass all through your apartment) so you jump in the water making a big splash showing all the smaller soundwaves how big and powerfull you are but you epend a lot of your energy in the process , your 5 m/s of fame:cool:

2 if your a HF wave then you wanna impress your friends on how fast you can go and getting in the water would only slow you down, so you bounce of the water and in doing so you learn that u gain a little momentum and can travel farther

whats this layer thingie and what am i gonna do about this so called friend

the ocean (for reason's i can only assume ill let someone else answer) at a certain depth changes temp. drasticly , which to our sound waves looks like a change in medium not one as big as from air to water but still enough to pose a problem perfering the path of least resistance most (not all) would rather stay in the medium there in (make sense so far ?) so now in the knowlege of how sound moves you (the sub) dive under the layer while your friend (the FFG) pokes around with his pole (sonar ,hydrophone) carying with you your sound waves who now also want to stay deep , you move to where he least expects sneaking bsck up just above the layer nice and quiet and :attack:

[Deadeye313]

let me see if I get this straight. When a sound wave from a sub below the layer hits the layer, it'll bounce off and go back down and the frigate may never see you. So we use deep bouies for deep subs.

does this work backwards too in that a sound from a ship above the layer may also be reflected? Also, if this is truly realistic when you hear a sound is there a chance that it may bounce and give you your own signature? Or does the sound wave bounce up and down along the layer?

this poses another question. If the sound wave keeps bouncing back and forth as it moves down the range, can sounds go further and/or bounce so that it comes from a different direction?

Does the layer affect an active ping? If so how? will the transmitter pick up nothing or maybe pick up the sub at a further distance than it really is?

I think I may have seen this in a game just now. there was a layer at 399FT and my dicass S was getting intermitent losses of the sub which was below the layer. did the layer cause that?

[soundken]

well most of my work involves sound in air so this is a little fuzzy plus these are all concepts i havent put into words in a VERY long time

let me see if I get this straight. When a sound wave from a sub below the layer hits the layer, it'll bounce off and go back down and the frigate may never see you. So we use deep bouies for deep subs.
yeppers

this poses another question. If the sound wave keeps bouncing back and forth as it moves down the range and/or bounce so that it comes from a different direction?
congratulations you just figured out reverb however in the naval enviorment not much of this happens it would take a large reflective barrier to cause the wave to do a complete 180 and come back along its original course

Does the layer affect an active ping? If so how? will the transmitter pick up nothing or maybe pick up the sub at a further distance than it really is?
yes it efects it depending on the "strength" of the layer its depth and the distance beween you and the sub plus the anachoic covering ( http://www.naval-technology.com/contractors/advanced_materials/syntech/)
also how powerfull and focused the active beam is, however it wont show the sub "further" than it is more along the not at all lines or it wont "ping" just show a dark spot in the waterfall which can easily be confused with a biologic

as always if anyone wants to add to this please do, any questions i will try to to my best. part of the fun for me of DW is studing how sound travels in the water sonar has always fascinated me. i hear rumor that there's a few guys lurking around that may have spent some time in front of a real sonar suite i would love to hear from ya :wink:

[rschoons]

Basic rule for sound propogation in water is HALT, higher away, lower toward. Sound rays bend away from depths with higher sound velocities, and toward depths with lower sound velocities. This depends somewhat on the angle at which the ray is transmitted; a simple sound source radiates omnidirectionally, with ray paths initially beginning in every direction straight away from the source. The angle of incidence of the ray to barriers such as the surface, bottom and mixed layer depth (mld) determine whether the ray is reflected or penetrates.

BT buoys dropped by P-3s measure changes in temperature at various depths. Temperature and pressure are the two biggest factors affecting the sound velocity profile (svp). The sound velocity profile derived by combining depth and temperature measurements determines the ray paths of sound waves in the ocean. In the upper depths of the ocean, temperature has the strongest effect on sound velocity; deeper, pressure predominates as the factor affecting sound velocity.

A typical deep ocean svp has an upper, isothermal surface, or "mixed" layer ("mixed," because of surface wave action mixing normally warmer surface water with cooler water as the depth increases; the mld is the bottom of this surface layer). In this layer, svp increases because pressure increases with depth. Sound rays can be trapped in this surface layer with initial ray paths heading downward being bent back up toward the surface (HALT), then reflecting off the surface if the angle of incidence permits reflection. (At steeper angles, sound rays penetrate barriers such as the layer depth; sound rays from a target in the layer can penetrate below the layer, with bottom bounce in shallower water and convergence zone propogation in deep water.)

Below the layer, temperature decreases more or less rapidly until it becomes isothermal again deep in the ocean. So, below the layer, sound rays bend downward, at first, because the sound velocity is higher just below the layer than deeper in the water. Deeper in the ocean, pressure has a greater effect on sound velocity, and the sound velocity, after decreasing at first, begins to increase. Eventually, the sound velocity in deep ocean can begin to equal or exceed the sound velocity immediately below the surface layer. This causes (some) sound rays from shallow targets to bend downward at first, than gradually bend back upward toward the surface again. Rays at the correct angles will travel through the ocean like a sine wave, approaching the surface every 25 - 35 nm from the source.

Detection ranges for direct path contacts (ray paths that travel directly from source to receiver; can be in layer, or below layer for deep source and deep buoy hydrophone), bottom bounce (rays reflected off the bottom, which can also reflect back off the surface), and convergence zones are determined by signal strength of the source and attenuating factors such as distance, scattering, etc. Ambient noise (biologic, geologic, manmade such as ships) reduces effective signal strength. Low frequencies attenuate less than high frequencies, and, for equal signal strength, can be detected at greater ranges than high frequencies.