Re: [PSUBS-MAILIST] 3D Sonar

[SJSVOB@aol.com]

> What kind of data would you need.  As far as real time goes, at the speeds we are travelling underwater .5 seconds to 1 second might be okay.  It takes a bit for these vehicles to respond any way.


I suppose the phrase 'real-time' can differ greatly depending on the system.  For a psub this would obviously be less of a problem than the echocardiographic system I worked on.  The system I worked on ran real time with 30 frames per second and a lag-time less than a small fraction of a second.  It was necessary to design custom hardware which cost upwards of a million dollars.   In order to test the algorithm I wrote a program for my computer which processed the data for one frame.   It would be much easier for a psub.

So in order to describe the data I would be interested in I will describe how I imagine the psub system would be designed.  There would be an array of hydrophones mounted in front of the psub, (the more the better).  There would also be a sound emitter.  The hydrophones are all fed into an analog-digital converter board mounted in a computer.  The emitter would ping and the sound waves would be transmitted.  As the transmitted pulses return to the microphones they are recorded by the computer.  An algorithm in the computer would analyze the returned signal and generate the appropriate 3D image.  The algorithm would have to be fed the position in space of each microphone in reference to the emitter.  

Has anyone read about how the underwater caves at Wakulla springs were mapped?  The Digital Wall Mappers they used had 32 sonar transducers.  However they did not work like the system I descibed.  Each sonar transducer was only capable of recording the distance to the cave wall.  Anyone interested in this might find them interesting just the same so I will include the link:

http://www.usdct.org/mapper.htm

-Stephen