Dual Baseline Method?

[skip]

What is the dual baseline method used to survey low viz caves? It was mentioned in the first chapter of the Heinerth & Oigarden cave diving book.

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[Webmaster]

I would assume that refers to running a survey line down either side of a passage (i.e. you can't see both walls at once).

[Kelly Jessop]

What is the dual baseline method used to survey low viz caves? It was mentioned in the first chapter of the Heinerth & Oigarden cave diving book.

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If I recall correctly from my research this was used at Lafayette Blue. I have been involved over the last couple years,when conditions allow,to bring the survey up to higher grade,and add some passages missing off the original map. Interestingly I found Sheck's map to be very accurate. I hope you are enjoying the history section,this was a true labor of love between Bill and myself,and involved 100s of hours of research,interview etc.

[Kelly Jessop]

I recall that this method was developed because the viz is poor and the sidewalls can be 60 feet apart. Although interestingly some sidewalls are marked in dashed lines which indicates that they weren't measured,and if you have the NSS guidebook from the Lake City convention you'll see the story to that. One procedure we put in place when measuring side walls,is don't reel the tape in quickly. When my buddy was measuring a sidewall 50' away in 10' viz,I reeled the tape spool in quickly,and he suddenly didn't have a guide line back to me :-( uh-oh!

[skip]

Yes, the history is interesting - I hope you plan a book dedicated just to the history, with the details!

If I understand correctly, the double baseline, is as Marbry suggested two survey lines? You then measure from survey line 1 to the sidewall, floor, ceiling (and azimuth), then do the same from survey line 2, but to the opposite wall. Then you also must measure distance between the two lines. It might be easier if the stations were the same location on both lines, but probably not necessary - or depends on level of the survey?

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[Webmaster]

Yes, the history is interesting - I hope you plan a book dedicated just to the history, with the details!

If I understand correctly, the double baseline, is as Marbry suggested two survey lines? You then measure from survey line 1 to the sidewall, floor, ceiling (and azimuth), then do the same from survey line 2, but to the opposite wall. Then you also must measure distance between the two lines. It might be easier if the stations were the same location on both lines, but probably not necessary - or depends on level of the survey?

-skip

I think you're trying to make it too complicated Skip. The whole point of doing that is so that you don't have to constantly measure over to the other survey/wall. Except periodically, and at junctions to tie the two together and aid in error detection. Otherwise you might as well just run a single survey line. You would probably also want to start both from a common point.

In that context you can think of it like surveying a large room in an air filled cave. Often you will have a central breakdown pile that limits visibility from anywhere on the perimeter. The primary survey would then typically be to survey around the perimeter of the room, tieing-in on either side. Incidentally the Sarawak Chamber in Borneo, which is the largest cave room in the world; I understand it took them around 18 hours to survey the perimeter.

By following both walls, you have at the very least delimited the extents of the passage, and hopefully detected any side leads in the process.

Marbry