Nathan Williams laser profiling
Just stumbled over his image of laser cross-section snapshots. I wonder if this technic could find an application in u/w cave survey.
Walk Scan Test by Realms(Nathan Williams), on Flickr
I would think the laser technology would have a tough time in water.
Joe
Originally Posted by Richard Pyle
Yes, even with very clear water, the laser beam is diffused and can't be used the same as in air. There was a similar map made in Wakulla using sonar.
A green laser should do considerably better.
http://www.seafriends.org.nz/phgraph/water.htm:
“I firmly believe that any man's finest hour, his greatest fulfillment to all he holds dear, is the moment when he has worked his heart out in a good cause and lies exhausted on the field of battle - victorious.” - Vince Lombardi
Penetration yes, but it will still diffuse.
Determening distance via a laser underwater can and has been done. As long as the water isn't too sility it should work. Think about how much your primary light diffuses underwater compared to land. A laser isn't going to diffuse to the point it can't be used. I'm not sure about long distances underwater, but shorter distance like those found in an underwater cave would work. This technology (called lidar) is used extensivly to determine elevation from aerial plateforms and ground based units and it has been used to map rooms in dry caves. The problem with lidar in UW caves is that it wouldn't be pratical or economical to do so. I would think just waterproofing the equipment would be a major job. I'm not a survayor, but I do work with lidar data using GIS software (I work for a GIS company). This is something I have an interest in and I have researched it a little.
One of the big problems is determing location underwater in a cave. I think it would be relatively easy to make a waterproof device that would measure to some reasonable distance, but plotting that distance on a map with thousands of other measurements is what really needs to happen. That's hard to do without many many $$$ right now. GPS won't work in that environment for obvious reasons, and an INS system accurate enought to plot location within a foot or two would be extrodinarily expensive. The error compounds on each position measurement, and quickly grows to ridiculous error numbers.
People have used thumpers, but it takes a lot of guesswork and manpower to do, I would suspect. I have no experience with those.
Bob K
Why not use some sort of wall mapping in conjunction with traditional means of survey? Use the survey to plot the general direction, and the laser to map the contours of the cave.
In a slightly related note, Microsoft is releasing the Kinect for Windows early next year. The SDK is already out. It uses an infrared laser to do 3d mapping, and a ccd for texturing. It is absolutely capable of mapping the surface of an object, but probably far from powerful enough to be of use in an underwater cave. It would be a pretty serious hack, but one might be able to replace the laser with a much more powerful one, possibly one with a higher frequency (green?), and make some use of one in a cave.
“I firmly believe that any man's finest hour, his greatest fulfillment to all he holds dear, is the moment when he has worked his heart out in a good cause and lies exhausted on the field of battle - victorious.” - Vince Lombardi
BOBk is correct in saying the difficult part of lidar in a UW cave would be determining the sensors position as it moves though the cave. To be accurate the sensor would have to know its position for each laser burst. I admit that I am intrigued by lidar in a cave environment and I think this would make a great research project for a graduate student. I'm way beyond that stage of my life.
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