# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Refraction and dip
From: Marcel Tschudin
Date: 2005 Oct 7, 11:50 +0300

```> Marcel, you still here? Do we have any open  issues on this topic? (sorry
> to
> be away so long)

Yes, I am still here and I am still working on it.

latitudes, I calculated in a first test run refraction and dip for latitude
60N. The results showed that the refraction and the dip vary with the
seasons and that the values are generally higher than the published values
which seem to have been calculated on the basis of a standard atmosphere.
The lowest (unrealistic?) values are those new ones published by USNO. The
results showed also that the Bowditch formula for calculating the dip (the
factor 1.76 in the metric version) should be at 60N during January around
1.65 and during July around 1.73 (the other months can be interpolated using
a cosine function). This might also be (one of) the reason(s) why Bill
encounters these differences with the Chicago buildings or for Asbjorn's
differences who is living somewhere around 60N. Andy Young wrote to me that
he deled this subject already in his dip-diagram paper: A.T.Young,
G.W.Kattawar, Sunset science.  II. A useful diagram,
Appl.Opt.37,3785-3792(1998). Unfortunately I do not have a copy of it.

What I calculated so far is not yet good enough. It turned out that doing it
right ends up in an enormous work... Under the very kind guidance of Andy
Young, I advance step by step. A main problem arose by realising that the
lapse rate distributions within a height layer are distributed
asymmetrically, meaning that taking the average or the median of these
values is not good enough. At the moment I try to derive a calculation
procedure in order to find an estimate for the most likely value (mode) of
lapse rate within a height layer. I have the impression that the calculation
with the most likely lapse rate values (mode) has not been done before...
So, there is still a lot, a lot of work to be done.

Marcel

```
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