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Jon, One more point that Kyle brought up was the ability of this hydrophone to pick up his own motor sounds and how it masks his search for distant surface traffic... I have strived to produce a hydrophone that could pick up faint and distant contacts under abusive conditions and although be subjected to extreme pressure still continue to perform this task well. In this, I feel I have succeeded well. To avoid hearing close aboard motor and propeller noises is an issue for which I have no answer. I would not know where to even start. So I won't. On a good note, a submarine also so equipped would be easily detected just as the motors aboard the submarine with the hydrophone system installed. If you hear motors and your not running...it must be someone else! David Bartsch > Date: Thu, 10 Sep 2009 09:47:39 -0400 > From: jonw@psubs.org > To: personal_submersibles@psubs.org > Subject: Re: [PSUBS-MAILIST] Test #2 of collision avoidance sonar > > > Good work! > > There are a couple of variables that could influence determining (from > sound alone) whether the unit has any directionality in this kind of > field test. First, the topside boat may have been going more in an > ellipse than a circle, with perigee pointed at the front of the > hydrophone. As the distance of the surface boat increased around the > ellipse, the sound would diminish due to distance not directionality. > The other variable is any drift under water by Kyle's submarine would > cause the same effect. Whether the unit is truly directional can easily > be tested from the surface where better visual clues and a more static > environment would provide a better environment to determine the > directional characteristics of the hydrophone. > > My experience with surface testing, and I think evident on Kyle's > sub-surface video, is that it is pretty easy to determine from sound > alone (non-directional) whether something is moving toward or from you. > The audio cues are pretty self-evident and easy to interpret with > objects getting closer also getting louder, and the reverse for things > moving away. Additionally, with ear training over time, I think one > could easily gain experience with estimating range. Surface boat > propellers have a rather distinctive sound that is easily identifiable. > By just spending some time on the surface and listening/watching boat > traffic, I think you could become accustomed enough to make reasonable > estimations of "that one is too close" or "that one is definitely far > enough away". Of course, this in itself is variable depending upon > depth since depth alone will increase the distance to the source and > change the amount of sound energy intercepted. So it would seem that > for this type of surface collision avoidance that the sub, when using > only audio clues, would have to stop at a certain depth each time so > that the sounds the pilot was hearing, and was use to interpreting, were > consistently from the same surface distance. It doesn't matter what the > distance is (15, 20 feet?) but the pilot would need to consistently stop > at the chosen depth and perform a surface collision avoidance test. > > Jon > > > David Bartsch wrote: > > To all: > > > > This to me is a very interesting clip. It shows his marker buoy as > > it deploys and his boat submerges. This allows his partner to pinpoint > > his location while maneuvering his surface craft sonar target. His > > tests are conducted with a controlled surface contact and still he > > picks up unknown contacts! > > In all, a very fun submarine video! My thanks to Kyle for having > > shared with us this footage. > > It should be noted that the hydrophone used in these tests is a > > special hybrid under investigation. It lacks an air resonance chamber > > hence should be operable to great depths without the fear of imploding > > or flooding. It is directional to some degree as his friend becomes > > loudest as he positions himself to Kyles' forward facing. This > > hydrophone is quite rugged in how it was constructed and could > > withstand a considerable punishment before becoming disabled. Again, > > this hydrophone is still under testing but the initial results look > > promising. > > Dean Ackman is also using this form of hybrid on his new submarines > > underwater communications sonar. Its use as a communications > > hydrophone should be known as soon as these tests are conducted. > > > > From Kyle...Enjoy the video! > > > > > > David Bartsch > > > > > ************************************************************************ > ************************************************************************ > ************************************************************************ > The personal submersibles mailing list complies with the US Federal > CAN-SPAM Act of 2003. 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