# NavList:

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

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Re: Refraction
From: Marcel Tschudin
Date: 2005 Aug 26, 00:53 +0300

```Frank

The calculation of refraction really gripped you! Thank you for the (fast)
transfer functions you provided. Before looking at them in detail, here some
remarks and questions

> There is  no sense in which these
> modern refraction integrations are superior to earlier  ones. They are
> somewhat
> more flexible and they converge faster, but they can  cover the same
> atmospheric complexity as earlier integrations.

Thanks to Andrew Young (and to our postman), I have a copy of the paper
"Sunset Science IV, Low-Altitude Refraction". One chapter of this paper
deals with explanations of errors made previously, e.g. using Lambert's
series expansion which is only semi convergent.

The Auer Standish procedure is the prefered procedure; he indicates that
this was already proposed by Bios in 1836 and then got forgotten. He
therefore refers to it as the BAS procedure.

> The difference  between the present
> Nautical Almanac refraction table and the earlier one  apparently comes
> down to a
> rather slight difference in temperature structure in  the atmosphere.

Does the Nautical Almanac have a different table than the previously
mentioned table 6 from Pub. No. 249? If so, which title, page number etc.?
Or, is there an other possibility to obtain it, instead of ordering it from

> The pre-2004 refraction table can be derived (using the Standish
> integration) from
> an atmosphere model with a temperature lapse rate of 7.25  degrees C per
> kilometer up to 11km and constant temperature above that. The  post-2004
> refraction
> table can be derived from an atmosphere model with a lapse  rate of 9.0
> deg
> C/km up to 2km and 6.5 deg C/km up to 13km and constant temp  above that
> level.
> These are both reasonable temperature curves which occur  somewhere on the
> Earth every day. They are both "right" in that sense.

Wouldn't it be possible to find the authors of the table and ask them which
model they used und why? Or, are there some clarifying comments in the
Almanac?

Marcel

```
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