Cave Exploration: Capturing left-right-up-down from a series of sensors

Projects General Guidance
1

Greetings all,

I'm a caver, and involved in exploration. However, I'm not a diver. Frequently, while digging, we encounter a wet space, filled with rubble and water, that requires a dive or significant digging to be passable. In those cases, I'd like to be able to use a device to get a sense of width and direction, for sometimes the cave doubles back on itself. While that isn't immediately evident, the water moves in the right direction.

So I'd love to build a device that "follows the water" and can report back a series of datapoints to indicate the direction the water takes. I was thinking of something like a waterproofed semi-flexible "string" embedded with sensors that can relate left/right/up/down coordinates relative to the senor behind them, saved by waterproofed and ruggarized Arduino (perhaps stored within an Otter Box) to a small flash device.

While I can imagine the rig, I'd love thoughts and suggestions about which sensor(s) to use to accomplish this feat. After reading the forums, here's what I've learned:

(1) Some people have thought about calculating distance and direction by ultrasonic sound. This doesn't seem optimal, for caves are wet, noisy places. Likewise, if submerged, light isn't a good option.

(2) I see that there are semiflexible sensors (Flexibend) that output voltage changes based on "bend". This seems like a productive direction; we'd need a series of these sensors, and would also need some way to know more than "bend" alone. The "bend where" is important.

The ideal length would be about 20-30' and the line should be highly flexible and submersible. We don't need inch-by-inch granularity, but should have a good idea about the position/location each 12'' or thereabouts.

Thoughts?
--Dave

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A tethered swimming/amphibious robot with a camera, compasss and pressure transducer might
be a more useful approach, but making a waterproof device would not be that simple...

Alternatively if you have a 9 DoF IMU that can orient to the water flow, you could sample the flow direction at
regular spacings down the cave (if its flooded there).

3

MarkT:
A tethered swimming/amphibious robot with a camera, compasss and pressure transducer might
be a more useful approach, but making a waterproof device would not be that simple...

Alternatively if you have a 9 DoF IMU that can orient to the water flow, you could sample the flow direction at
regular spacings down the cave (if its flooded there).

Ah! Sampling the water flow direction is an interesting possibility. I'll have to look at that.

Many of the spaces are miniature, but maybe a tethered floating device w/ an accelerometer (almost like a fishing bobber) could work?

Another interesting possibility might couple the laser rangefinder, http://lightware.co.za/index.php/prod-kits (although this would message something like passage size, rather than distance. But I suppose we could simply use the tethering to measure distance, a gyroscope to measure and normalize for tilt, and then 2-4 rangefinders to measure passage space.