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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction and dip
From: Marcel Tschudin
Date: 2005 Oct 7, 11:50 +0300
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. After downloading millions of balloon data of stations at different 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