Wiki Wednesday – Ultra-short baseline

11 07 2007

When it comes to blogging, as with so many things in life, I am a perfectionist. And this blog is by no means perfect. I decided that “theme days” might spice the place up, put the “interest” in “general interest blog” . One of the themes will be a weekly Wiki Wednesday (try saying that quickly when you’re drunk). I saw this meme on a few other blogs. The basic idea is to go to Wikipedia every Wednesday (which would be today) and use the “random article” option. At the very least we may all learn something, including me. Today’s article is…

Ultra-short baseline

From Wikipedia, the free encyclopedia

USBL (Ultra-short baseline) is a method of underwater acoustic positioning. A complete USBL system consists of a transceiver, which is mounted on a pole under a ship, and a transponder/responder on the seafloor, a towfish, or on a ROV. A computer, or “topside unit”, is used to calculate a position from the ranges and bearings measured by the transceiver.

An acoustic pulse is transmitted by the transceiver and detected by the subsea transponder, which replies with its own acoustic pulse. This return pulse is detected by the shipboard transceiver. The time from the transmission of the initial acoustic pulse until the reply is detected is measured by the USBL system and is converted into a range.

To calculate a subsea position, the USBL calculates both a range and an angle from the transceiver to the subsea beacon. Angles are measured by the transceiver, which contains an array of transducers. The transceiver head normally contains three or more transducers separated by a baseline of 10cm or less. A method called “phase-differencing” within this transducer array is used to calculate the angle to the subsea transponder.

Ok, that wasn’t the most auspicious of starts but things can only get better.


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