Please, Excuse My Ignorance

[ysi_maniac]

Can a radar, at least theoretically, work under water?

[simmie]

I aint no physicist but i do know that radiowaves can travel through water.  But, at the higher wave lengths the range is restricted to 10's of metres.  thus the navy use VLf or Very Low Fequency radio to conntact the SSBN's on patrol.  But I belief that this is also retricted in the depth to which it can penetrate water.

I am sure somebody will point out any mistakes I have just made, I am just working of the top of my head here!

[B777LR]

So if skycaptain was to replace his P-40 with a F-16, he wouldnt be able to detect submarines when swimming around under water :dum:  

[RLBH]

For deep penetration, you could use ELF transmissions. Unfortunately, you need an antenna a few thousand miles long, and massive amounts of power. VLF is only good down to about 40 metres, according to Wikipedia.

[Maverick]

Isn't that what Sonar is all about, similar concept but for the squids amongst us?

[Hobbes]

yep. Sonar has its problems though: short range, propagation depends on water temperature so you get all sorts of weird effects. Having an EM sensor would simplify things, but as the other posters said an underwater radar isn't really feasible.  

[GTX]

Whilst underwater radar isn't possible, it might be possible to use a variation of the Blue/Green Laser system as used in the Laser Airborne Depth Sounder (LADS) system (see here for info).

Another possibility (and more exciting I believe) is a third form of Sonar (or arguably a second form of Passive sonar).  As you will be aware, active sonar sends out a sound pulse (the typical 'ping' in the movies) and then listens for the relections (basically the sound equivalent of radar), whilst passive sonar simply listens.  This third technique is known as acoustic-daylight imaging:

"Noise surrounds any object immersed in the ocean; the object, in turn, modifies this noise field in ways that depend on the object's shape, composition and position. Ambient noise has a familiar optical analogue: daylight in the atmosphere. We can see and photograph outdoor objects because they scatter, reflect and otherwise modify the light in the air. Likewise, noise that permeates the ocean acts as a kind of "acoustic daylight." Recent experiments have shown that we can indeed create images of underwater objects by using ambient noise as a source of illumination."  (Source with full explanation.  Also see here.)

Regards,

Greg

[elmayerle]

Whilst underwater radar isn't possible, it might be possible to use a variation of the Blue/Green Laser system as used in the Laser Airborne Depth Sounder (LADS) system (see here for info).

Another possibility (and more exciting I believe) is a third form of Sonar (or arguably a second form of Passive sonar).  As you will be aware, active sonar sends out a sound pulse (the typical 'ping' in the movies) and then listens for the relections (basically the sound equivalent of radar), whilst passive sonar simply listens.  This third technique is known as acoustic-daylight imaging:

"Noise surrounds any object immersed in the ocean; the object, in turn, modifies this noise field in ways that depend on the object's shape, composition and position. Ambient noise has a familiar optical analogue: daylight in the atmosphere. We can see and photograph outdoor objects because they scatter, reflect and otherwise modify the light in the air. Likewise, noise that permeates the ocean acts as a kind of "acoustic daylight." Recent experiments have shown that we can indeed create images of underwater objects by using ambient noise as a source of illumination."  (Source with full explanation.  Also see here.)

Regards,

Greg

Some of Michael Dimercurio's later submarine novels have an "accoustic daylight" sonar system, the big drawback being the large processing power needed.  I can see that developing eventually, but I can also see work going on with a blue-green lidar.