Re: CaveXML>Range of Fields

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From: Ralph Hartley (hartley_at_aic.nrl.navy.mil)
Date: Mon Jan 29 2001 - 15:24:00 CET 

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Date: Mon, 29 Jan 2001 09:24:00 -0500
From: Ralph Hartley <hartley_at_aic.nrl.navy.mil>
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Subject: Re: CaveXML>Range of Fields
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Michael Lake wrote:

> Julian Todd wrote:
>
>> The time (incl date) is quite an interesting attribute because the water
>> level can change from year to year. Other measurements are more static.
>
> Thats interesting. I had not thought if that.

Also, the translation between depth and vertical position can vary from
place to place at the same time. In a cave with more than one sump, each
one will have it's own water level. I believe there are caves in which
the difference is hundreds of feet (with a perched sump, a drop, and a
terminal sump). For any depth measurement there needs to be a reference
level.

This is not a problem if a pair of depth readings are associated with a
shot, in that case the reference levels can be assumed to be the same.
That sort of reasoning can have ambiguous results though, especially if
divers occasionally use a clinometer. Do two sets of depth readings
separated by a clino shot have the same reference level? For proper
error analysis it matters.

The same sort of issue occurs with compasses as well. Declination, the
correction between magnetic and true north, varies from place to place
and from time to time. The variation is vary slow, however. The date of
the survey and some (approximate) geolocation of the cave should suffice.

Ralph Hartley

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