I was very excited when i started to read the first line of your post but sad after reading the last line.
is there is any documents even related to underwater acoustics please provide me.
i am really struggling in this research. I want to build up my foundation strong.
please.
As for acoustics .. can't say much about documents. But there are books. They are low edition size, so expensive. I was recommended this book:
Principles of Underwater Sound 3rd Edition: Robert J. Urick: 9780932146625: Amazon.com: Books
And I must say it's a great book. But keep in mind, most acoustic problems won't apply with lasers.
As for lasers, all I can do without specific questions is to guide you to google .. search terms like 'laser underwater detection' seems to result in 'something', though I admit it's nothing much.
As for what I heard .. lasers were tested recently especially for detecting mines in shallow waters, from helicopter. Helicopter would fly low over water, shining its lasers down and scanning the bottom for irregularities. Green lasers seemed to work surprisingly well.
I also hear about lasers being considered for communication with submerged submarines in cold war years. Again green lasers were considered, with either airplane or satellite which would shine laser in rather wide cone into expected friendly submarine location, which would then intercept the signal. I'm not sure if the system was ever tested at all.
Anyway .. what is clear .. green light seems to be used. If the light is to be transmitted from air, laser should hit the water as perpendicular as possible, as at such angle reflection losses are best. I guess surface waves would be major factor for bottom scanning, also water purity.
With the laser itself underwater the set of problems would be similar to active sonar, but I never heard about such system.
