Underwater position tracking - Page 1
Forum section: electronics / projects

author: diegosfb
author_rank: Contributor
timestamp: March 17, 2014, 06:30:41 pm
content: Hi;I need to track the position of an underwater object (to which I can add circuitry) relative to the measuring point (it will be on a boat).Max distance about 35mt in any direction and accuracy must be better than 0.5mtI was thinking in some form of ultrasound, but seems that accurate systems don't have enough range.RF underwater systems seem to be short distance and still in experimental phase.Anyone here has some ideas as to what type of technology can I use.Thanks in advance,

author: fcb
author_rank: Super Contributor
timestamp: March 17, 2014, 06:48:46 pm
content: Commercial systems are both accurate and have significantly more range. But they are fantastically expensive. USBL bywww.sonardyne.co.ukfor example.You could certainly build yourself a USBL type system, they work in at least two modes:1-1 (one pinger on the UW object) and a receiver with multiple transducers - typically used in diver tracking.6-1 (numerous pingers on seabed, typically six) and at least a single receiver - used for dynamic positioning.Also, everything tends to be half-duplex so you can extract time-of-flight, ID, sequence the pingers etc...Forget RF.

author: diegosfb
author_rank: Contributor
timestamp: March 17, 2014, 07:56:40 pm
content: Thanks fcb for your input.Do you know how they figure the position of the object?Is it by measuring phase difference between signals (asuming the emiter sends at least 2 signals)Do you know some place I can research a bit deeper into this ?I am trying to desing a custom system; but cant seem to find much info on this topic.Regards,

author: fcb
author_rank: Super Contributor
timestamp: March 17, 2014, 08:07:34 pm
content: Quote from: diegosfb on March 17, 2014, 07:56:40 pmYes.QuoteYes/No/Sort of. You should look-up the principles of phased array directional SONAR (as used on tactical submarines). The emitter only needs to send a single burst.QuoteErm. Google, patents, whitepapers, etc...QuoteThat's because it is proprietary technology and/or military stuff.Sorry I can't be much more help, other than the above. I strongly suggest you get yourself (or make) some hydrophones and start playing - it's not as difficult as it looks.

author: zapta
author_rank: Super Contributor
timestamp: March 26, 2014, 04:03:59 pm
content: What you are trying to do is not trivial, and may require budget and engineering skills.As you said, the two main methods are time of flight (~350 m/sec, one way) and phase differences. The configuration you choose need to match your requirements. How fast the object moves, can you place the boat such that the object is always on one side, is it a 2D or 3D problem (how deep the object can dive), is it an easy to use product or a one time experiment, do you need the data in real time and can post-process later, can you instrument the boat (e.g. place multiple hydrophones), can you place static hydrophones surrounding the area of movement, etc. You will also need a body of water to test while you develop, if you use a swimming pool, pay attention to reflections.I would start with building a simple two nodes, one way prototype. Send a ping from one, receive in another and go from there. It will allow to to estimate your changes to succeed. You will need to pick a frequency and pulse width, build power amplifier, receiver/detector, etc. Place the hydrophones in your target distance and see how well you measure the time of flight. Be aware that the electrical characteristics of hydroponics are different air and water (impedance matching and such) so at least have them in a bucket of water (still not the same as a large open mass of water). Once you will master this (it's not as simple as as it sounds) you will be on good track to success. Alternatively, you can search for off the shelf system or subsystems.BTW, some cities install this kind of systemhttp://en.wikipedia.org/wiki/Gunfire_locator. It uses multiple stationed microphones

author: qno
author_rank: Frequent Contributor
timestamp: March 27, 2014, 07:25:14 am
content: Tie a rope to it with a scale. this gives you the distance.The angle with your boat give you direction.Depth can be estiated with a string of floats.