Questions about Underwater Depth Sounders

[inverted_bear]

Do any of you have any experience using underwater depth sounders to gather walls data for cave survey?

How accurate was the data? What model of sounder did you use? What are the depth limitations?

I'm looking to use one for deep cave survey (250-400 ffw), and from what I've heard the available models are only good to 150'. Are there any that are good past that depth?

Thanks,
Frank

[FW]

I use a couple different depth sounders, but I don't remember the brand off hand. One says ScubaPro on it. They aren't as accurate as tape, but in low visibility, they are better than nothing. I suspect it might be hard to find any with a depth rating over 150'.

[inverted_bear]

Any idea where I could get one of those sounders? If there's nothing commercially available that's good to that depth, I'll give it to an engineer buddy, so he can take it apart and redesign one that is.

[FW]

Any idea where I could get one of those sounders? If there's nothing commercially available that's good to that depth, I'll give it to an engineer buddy, so he can take it apart and redesign one that is.

I can loan you one for your buddy to look at.

Here are ads for a couple:
https://www.amazon.com/Norcross-Hawk.../dp/B000781CY8
https://www.amazon.com/Vexilar-Inc-H..._&dpSrc=detail

[OFG-1]

I have one of the Vexilar units, actually a older version. I have used it to 160 feet with no issue, and it is reasonably accurate.

I know the military has several units that can go deeper, the DNS300 and the Artemis are rated to 80 meters I believe, but you have best get a real big bag of money for either of those.

[Jim Coke]

I have used them for collecting LRUD's in a couple of caves. I used an earlier Scuba Pro model, it was reasonably accurate. I found that depending on the wall contour, or more importantly the lack of a smooth-wall contour (the surface being measured to), data from the measurements varied. Hold the instrument level if possible. Shooting at an angle might bring up some wild readings.

If you are diving a phreatic tube, you will get better results than if you are measuring to an incut wall or sloping rubble pile against the wall. If you can see the left and right walls from the survey station, you will know what you are measuring and sketching.

Take three measurements for each wall measurement and weed out the two outlying data readings. You can always run a tape or a knotted line at random stations just to check how close you are. I would suggest testing your machine in a shallow cave first. There are other ways to get LRUD's. but at the depths you mention those methods might take too much time.

[Kelly Jessop]

I have used them for collecting LRUD's in a couple of caves. I used an earlier Scuba Pro model, it was reasonably accurate. I found that depending on the wall contour, or more importantly the lack of a smooth-wall contour (the surface being measured to), data from the measurements varied. Hold the instrument level if possible. Shooting at an angle might bring up some wild readings.

If you are diving a phreatic tube, you will get better results than if you are measuring to an incut wall or sloping rubble pile against the wall. If you can see the left and right walls from the survey station, you will know what you are measuring and sketching.

Take three measurements for each wall measurement and weed out the two outlying data readings. You can always run a tape or a knotted line at random stations just to check how close you are. I would suggest testing your machine in a shallow cave first. There are other ways to get LRUD's. but at the depths you mention those methods might take too much time.

I have to echo what Jim Coke said, wall contour can cause accuracy issues. From my experience, if you are trying to get a grade 3C map, you'll want to pull tape.

[inverted_bear]

My concern is drift as you run out the tape. If you’re swimming the tape out perpendicular to the line in massive passage with mediocre viz, it wouldn’t be hard to drift several feet to the side. This would really mess with the accuracy of the reading.

[Kelly Jessop]

My concern is drift as you run out the tape. If you?re swimming the tape out perpendicular to the line in massive passage with mediocre viz, it wouldn?t be hard to drift several feet to the side. This would really mess with the accuracy of the reading.

You have two ways you can measure side walls, visual estimation or some valid measuring device like a tape measure. I will take the take tape measure over other methods, even with some drift. I experimented with one of the Scubapro handheld sonar devices at a cave that we were surveying and measuring side walls with tape. The error rate with the sonar device was huge because of side walls that were incongruous, and determined very quickly that it is not a survey grade tool. Also, I understand your concern for sidewall accuracy. One cave I surveyed the visibility would be 10' at times,but side walls were frequently 60' away. On occasion when visibility would improve I would validate my measurements which would include some sidewall stations, and found very little deviation. A compass and tape measure can seem to be old school, but with practice, practice, practice, it can produce amazingly accurate results. A side note- when using tape in very low visibility to measure side walls that are far away, this is your guideline back to the mainline and treat it as so. I was recalling a story with a primary survey buddy that we can laugh now about,but wasn't funny at the time

[jlillest]

I have to echo what Jim Coke said, wall contour can cause accuracy issues. From my experience, if you are trying to get a grade 3C map, you'll want to pull tape.

A survey grade here is not dependent on the accuracy of the LRUDs, survey grade only has to do with the lineplot survey.

I look forward to the day when we have sonar devices that will help us collect 3D information, until then the depth finders are a good tool for collecting basic information. They're pretty pricey though for the limited information you get from them.