Experiments in DIY Audible Frequency Digital Chirp Sonar
Working prototypes in air
Digital Sonar Experiment Part 1
For the last 10 years or so, I have wanted to build an underwater robot of some sort. I assume this is the result of reading too much Cussler, and doing a bit of SCUBA diving, but I can’t seem to shake it. I’ve been following a number of projects, particularly OpenROV, with great interest. One of the challenges that does not seem to have been tackled much by hobbyists is an affordable underwater sonar. There are plenty of inexpensive sonar units for land and aerial robotics — modern RC drones makes good use of them for low altitude sensing — but there don’t seem to be any for water use yet.
I figured it made the most sense to understand the algorithms and get them debugged in air first, since sound travels much faster in water, and there are issues with acoustic coupling and waterproofing in water that are not a problem in air.
I chose to explore what could be done on a PC first, just for ease of programming. I found that it has been done before, successfully, and documented well by this gentleman. His page gave some very useful information about echo detection, introducing me to the idea of correlation functions to detect a short signal in another signal stream. With that information, I found an…
