Sonin rangefinders for mapping

[rockprof]

Anyone ever use Sonin electronic rangefinders for cave mapping? I'd like to do some simple mapping in local mines and it seems a lot easier than constantly rolling up a muddy tape after each measurement.

Also, some models emit sound waves (others IR). Does the sound (I'm assuming it's ultrasonic) annoy bats at all? Just wondering.

[Caverdale]

To my knowledge, Sonin makes two types of rangefinders. One is strictily ultrasonic. It sends out a sound beam that reflects back. Distance is found from the time of flight. I think you will find these almost useless for mapping mines or caves. They require a fairly large reflective surface. I have used my unit for determining ceiling heights in lava tubes and sometimes wall distances, but was never satisfied. The other type uses a transponder target. The user instrument sends out an IR beam to the transponder, which sends back an ultrasonic signal. No large reflective surface is required. They can be accurate if used properly. A typical product is the "Sonin 250". I have never heard of a strictly IR unit.

A few hints: I ruined my first 250 after the first summer and fall's use. It was winter and the unit was left in the cold front seat of my truck over night. I took it into a warm cave. At first it worked in a fashion, but then I noticed condensation, the display turned dim, and it never worked after that. My assumption was that condensation trashed the electronics. The dealer gave me a price to fix it but it was unreasonable. After hearing my story, a friend gave me an identical instrument that has worked perfectly for several years.

Sonin says the instrument is temperature compensated, but if you are worried about accuracy, let both units get adjusted to the average mine temperature before using them. Take along a tape and calibrate the instrument at something like 50 feet before using at the temperature of mine. Don't do what one of my point men did. He put the transponder in his shirt pocket under his coveralls between each station, a temperture difference of about 40 degrees. I could see the distance drift at each station before it was figured out what he was doing.

When I worked with Scott Earl of the Idaho Cave Survey several years ago, he used a Sonin 250 for all his measurements when surveying lava tubes. He swore by it. He should be in the NSS members manual if you want his opinion.

However, if I had use for such an instrument today, I wouldn't hesitate to buy one of those $100 radar rangefinders that was recently posted on the Cave Diggers forum and would sell the Sonin on eBay.

I have no idea what the ultrasound does to bats.


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[NZcaver]

I have heard a few stories about using ultrasonic rangefinders in caves - but unfortunately none of them were very positive.

A group that I've been surveying some lava tubes with tried out a hardware store one, and declared it virtually useless. It had a really short range, and needed a nice big flat surface to get anything like an accurate reading. They quickly went back to using a tape for most of their surveying. And if there are bats around, I would think you'd be interfering with their biosonar signals too.

Laser rangefinders are definitely more effective. I'll stick with my Leica Disto. If you use a white target plate (or brown for longer ranges) to measure between stations, you can get hundredths of a foot accuracy for up to a few hundred feet with the common models. You usually get acceptable accuracy with side or ceiling shots without a target plate, too. Just avoid reflective surfaces like water, and take the average of a few shots.

You might do well to keep eye out for any cheap used Leica Distos on eBay...