posted on Aug, 15 2011 @ 01:21 AM
It sounds like you are wanting to send a sonar pulse from one end of these pipes and receive it at another end, calculating the offset angle?
If I'm interpreting this correctly, your first issue is going to be the angle resolution of your receiver, and a few other factors related to the
water (sound will diffuse just like light will, and a single point of sound will appear to be a mass of fuzz). You can improve your resolution
without retardedly expensive gear by simply using a synthetic aperture. Synthetic aperture simulates a much larger antenna/lens by taking readings
from multiple points along a linear path. Using some rigid extension, perpendicular to the pipe, you can offset your receiver by several meters...
or, with more involved means, several kilometers (I'm really not sure what kind of distances you are dealing with, here). Resolve a bearing from
each side of your pipe, and someone with some trig can plot, within some margin of error, the location of your other pipe's end, and derive your
angles from that.
However, sonar and 'ocean floor' are two words that don't go together without a grimace. Sound will 'channel' based on ocean currents, water
temperature, and a range of other things. Something else you will get is sound rebounding along the ocean floor and the thermocline (cold water below
the thermocline, warm water above - acts like a mirror for sound, and even a physical barrier when hit at velocity). If you are looking for more than
a few hundred feet - things will likely get tricky.
Really, you'd be best off to find yourself some drinking buddies in the Navy and find some sub-surface Sonar Technicians to help you out. They will
be able to give you a much better "this is the way it is." I read books about it and bump into sonar guys every now and then - I'm more of a radar
and laser kind of guy.