# Underwater Distance Sensing

I'm looking to measure distances from a submersed robotics project in the range of 1 to 20 feet (around there at least). However, the only options I seem to come across are rather heavy sonar modules that cost hundreds of dollars. Are there lighter, cheaper alternatives? I don't need great resolution or accuracy, just a decent measurement. Perhaps it's possible to waterproof a normal distance sensor (IR or ultrasonic)?

I intend to interface the sensor with a microcontroller so it would be nice to have something that outputs 0-5 V, but that's not a requirement.

Thanks.

• IR probably will not work very well, water absorbs red light. Ultrasonic sounds good, but i have no idea how well it works underwater. Mar 7, 2011 at 7:59
• I have a feeling you should be able to waterproof piezo elements rather easily for underwater operation, both as a speaker and a mic. I have never tried through, so don't hook up anything expensive to it if you do ;) Mar 7, 2011 at 10:12

Ultrasound would be your best shot. A quick search on the web tells me that unless you want do do a significant amount of work yourself it's not going to be cheap. Transducers from Senix cost about $500, but if you can get a hold of a waterproof ultrasound sensor for parking aid systems and is able to build the tx-amplifier, the transmit/receive switch, and do the signal processing in a uC you should be done for a lot less than that. Fish-finders like this Garmin unit are quite inexpensive at about$100. Buy one of those and use the transducer. You might even be able to buy the transducer quite cheaply as a spare.