High-resolution tracking

[Niclas]

I am working on a project to map river currents in northern Sweden and need a device that allows the position of a small float to be tracked with sub-meter accuracy. The idea is to let the float travel downstream for a few hundred meters and continuously (at least once a second)track its position, either internally (GPS/DGPS) or externally with triangulation techniques.

I wonder if anybody could recommend a technique that would be both cheap and roboust. The float might occasionally be hidden behind boulders in the river, so triangulation based on signal strength seems unreliable. What is the accuracy of the so-called "signal phase shift" technique?

Any suggestions will be highly appreciated!
/Niclas

 

[PKSBrian]

I have worked on some similar problems with ROV's, from my experience you might want to look at an underwater acoustic system try SSBL (super short baseline) or USBL (ultra short baseline). The systems are definately robust and designed to be imersed. They are also relatively expesive

Try

http://www.sonardyne.com/theory.htm#USBL

for some ideas.

GPS systems in bouys will work especially an RTK setup that is self triggered by timing (ie. x number of times per sec.) or by position changes (ie. once per sensed meter movement) , however proximity of the equipment to the water surface can create multipath nightmares, and accidental equipment dunkings and less than 100% recovery rates are expensive