NavList:

Alex,

Comparing artificial horizon observations with natural horizon observations would have confirmed the discrepancies as dip anomalies or instrument error. Another way to check for dip anomaly is to compare calculated dip short with observed dip short measured by sextant. Height of eye and distance to short horizon must to be measured exactly.

Useful NGA web sight:

http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_portal_page_145&calcCode=03

Greg Rudzinski

[NavList] Re: Extremely poor conditions??
From: Alexandre Eremenko
Date: 20 Mar 2012 09:31
Franks,
Thank you very much.

1. Let me bring to your attention that it is the end of March today,
and all messages in our archive for 2012 are still listed under January.

2. The surface water temperature 3 days later was 40 F (I don't know where
to find the temperature for March 17. We were observing from the part of
the jetty which is adjacent to the shore. Bill walked to the end of the
jetty, (it protrudes from the shore to the lake) and says it was chilly
on the lake end.

So you mean that the layer of cold air near the water surface acts
like a sort of mirror, and the ray can be bent in the opposite direction
to the usual one by as much as 7'.
Most CelNav books do not warn about this.
Is there a way for a navigator who does not know his exact
position to figure out that such thing is happening?

Well, I sort of remember some discussion of this on the "old list"
under "Anomalous refraction", let me try to find it.

We should have tried the artificial horizon which we had with us!

Alex.

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