Detection of Submarines and Evading Detection--- A Primer for Fanboyz
I thought I would write some sort of primer for the fanboyz here on various issues that go into detection of submarines. Later if I feel like it, I will give you a full fledged treatment of invisibility of aircraft, stealth and even Prandtl's boundary layer theory and bleeding of the boundary layer so you can appear erudite with other fanboyz when discussing SU-30 MKI, LCA yada, yada These are all areas I have contributed very deeply with papers with citations way, way beyond what I thought was possible as a young boy when I wrote them.
OK you know the song don't you "There is a hole in the bottom of the sea...." and there like the log in the song, the evil submarine lurks.
https://www.youtube.com/watch?v=UK6UNRnbfnw
There are four factors to keep in mind now.
1.
Salinity of the water
2.
Temperature of the water
3.
Pressure of the water
and of course 3 is related to
3(b)
Depth of the water where the submarine is operating.
Next what is a sound wave? Its a pressure wave and the speed depends on the density of water and other factors. Let us list the effects of 1- 3(b) on the speed of sound in water.
1. More salinity increases sound speed.
2. Higher the temperature increases sound speed, so the deeper you are in the water the colder and sound speed is lower.
3. Increasing pressure, the deeper you are in the water sound speed increases.
So 2 and 3 are competing conditions. The deeper you go one lowers sound speed and one increases sound speed. Lastly in polar regions the salinity increases with depth and so the deeper you go sound speed increases. In equatorial and tropical regions due t surface evaporation of water, salinity decreases generally with depth and so the sound speed is slower at depth. So there are many competing conditions for the sound speed to decrease and increase.
Well what does this have to do with submarine detection? See did you fanboyz ever do an experiment in school of taking a glass block and tracing a ray of light through the glass block using pins? You would have seen that the light ray bends because the light speed in glass is less than in air. The same thing happens with sound waves and when the sound waves travel through material of different densities it bends. Now imagine your great big submarine and a ship/s on the surface pinging with sonar and the sound emitted by the sonar bends and misses the submarine because it is a certain depth where the sound ray just bends and goes back to the surface, because your Navy has used its hydrographical ships well and has produced a map of the oceans where you can lie in certain pockets where the sound waves cannot hit your submarine. Simply because your hydrographical ships have plotted the sound speed at different depths. There you can lie in wait away from the prying eyes of sonar if need be.
Well about a 100 years ago two men independent of one another developed mathematical tools to find the sound speed at different depths of the Earth and find the density at various points of the Earth 100's of miles underneath. How did they do it, yiu cannot did a 100 miles below. They did it by "travel time tomography". You have a surface station or ship and it send out a sequence of pings that sound and then there is another station on the Earth or ship far away that measures the time taken for the signal to reach it. If you do it for a whole bunch of measurements you can then compute the sound speed at any one point under the Earth. However, the formulae and proof of these gentlemen one Herglotz and one Wiechert( same as the Lienard-Wiechert potentials in Electromagnetism) assumes the Earth is a layered body and so obviously a simplified model. Treating the Earth or the oceans as completely inhomogenous leads to more complicated formula and thus reconstructing the densities from the time taken by the pulses to reach your ship is now something that can still be done with assistance of high speed computers. ALl this has been done by the leading Navies of the world, all over because these navies have been in the SSBN business for years and not like Johnny who has just come lately. Of course you want to know the proof these results by Herglotz and Wiechert here is a nice well-written set of slides, notice the bending picture of waves in one of the slides, that should give you an idea what I am talking about.
The idea is to be in a pocket which the waves avoid due to the bending effect. Where are they in the ocean, at what depths? Are these depths compatible with the design of the submarine?
https://www.google.com/url?sa=t&source= ... 5K9XMOvqfK
German U boat captains were already aware and using such evasion techniques in WW2.
Oink, oink, oink.
