- Sat Sep 03, 2005 6:18 pm
Two different "easy" solutions that I can see, but I don't know how much each will cost:
1) Specific bands of IR will bounce off water. This is how aerial mappings of sea depth is done (one bounces off water, other bounces off the ground... they compare the two). That could be mounted on a pole facing down. I haven't used these, so I can't point you in the direction of where to buy it. You could also use the other band and have a floating sensor pointing down, but it would either have to be battery powered and wireless, or tethered. In each case, having a non-submerged sensor would be easier and safer. Wave bounce compensation would be done in software.
2) Even though ultrasonic sensors don't do well with water, you can just have it bounce off a floating device. Rig up the ultrasonic sensor at the top of a pole, and have the floater attached to it, yet free enough to move up and down with the water. Bounce reduction from waves can be done in software, or changing the "RC" of the floater (add more weight to dampen its movement).
The last ultrasonic sensor I used I got through my university. It had a range of 7ft, which should be enough. Use math to figure out the water depth based on the pole height (obviously).
Capacitive sensors would require too much calibration, and dielectric property of the water changes based on other factors, such as pollutants, natural organism count, a duck, etc... plus, it's not KISS.