Surveying tiny passage
Posted: May 9, 2013 8:29 am
I've already asked for tips on wet and muddy passage, now for tiny. My upcoming survey is a resurvey of a cave currently listed at 688 feet. Years ago, before I knew there was such a thing as cave maps, I pushed a small passage far beyond what I now know is the "too tight" stopping point on the current map. Since then, we have confirmed a connection to a nearby sinkhole that we are waiting to unsump so that we can survey all the way through.
There are approx. 500 feet of unsurveyed passage that is too small to turn around in. The first 100' is 1' - 1.5' wide and 1.5' -2' tall and the rest is 2' - 3' wide and 1' -1.5' tall. The passage has bedrock floor for the first hundred, and sand and cobbles for the rest.
The survey will be a two person effort, and I'm looking for advice on how to divide the responsibilities, and how to set stations. I don't think it's realistic to expect the lead man to back through this entire section of cave. There are many difficult squeezes that may be impossible to negotiate in such an awkward fashion.
Here's what I'm thinking. Lead man carries the book and a stick of chalk or some other marking device. As he crawls, he marks the stations with chalk and then continues past the station until his feet are even with the mark. The instrument man stops at each mark and shoots the lead's boot sole with the laser, then takes azimuths to the center of the passage. In each case it would be assumed that the station is floating in the center of the passage. This would allow passage dimensions to be taken as two measurements (width and height) instead of four (lrud).
Obviously this method would sacrifice some accuracy. Do you think that's acceptable given the conditions? Is there another way to survey this kind of junk that would allow for better accuracy while still maintaining some sort of efficiency?
Thanks!
There are approx. 500 feet of unsurveyed passage that is too small to turn around in. The first 100' is 1' - 1.5' wide and 1.5' -2' tall and the rest is 2' - 3' wide and 1' -1.5' tall. The passage has bedrock floor for the first hundred, and sand and cobbles for the rest.
The survey will be a two person effort, and I'm looking for advice on how to divide the responsibilities, and how to set stations. I don't think it's realistic to expect the lead man to back through this entire section of cave. There are many difficult squeezes that may be impossible to negotiate in such an awkward fashion.
Here's what I'm thinking. Lead man carries the book and a stick of chalk or some other marking device. As he crawls, he marks the stations with chalk and then continues past the station until his feet are even with the mark. The instrument man stops at each mark and shoots the lead's boot sole with the laser, then takes azimuths to the center of the passage. In each case it would be assumed that the station is floating in the center of the passage. This would allow passage dimensions to be taken as two measurements (width and height) instead of four (lrud).
Obviously this method would sacrifice some accuracy. Do you think that's acceptable given the conditions? Is there another way to survey this kind of junk that would allow for better accuracy while still maintaining some sort of efficiency?
Thanks!