NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip by sextant and systematic error
From: Marcel Tschudin
Date: 2013 Apr 2, 23:32 +0300
My intention would not be to arrive at some measured "real time terrestrial refraction" (or dip); I would rather aim at improving its estimate based on some (general) environmental data.
You mentioned also:
"By the nature of the experiments, every set of data would unfortunately be limited to a particular locale."
Yes, indeed, unfortunately. I think Freiesleben and/or Hasse mentioned already that when performing measurements on a ship the environmental conditions are already disturbed by the presence of the ship itself. In a similar way will measurements made from the coast in some way be influenced by the land / sea transition. At one time I was hoping to account for this influence to a certain extend by using the Diurnal Temperature Range (DTR) which tends to be large far from surface waters, smaller at the coast and minimal at some narrow headland. However, my Hs observations show unfortunately no (direct) correlation with the DTR ...
Marcel
From: Marcel Tschudin
Date: 2013 Apr 2, 23:32 +0300
Frank, you wrote:
"Certainly today we can do highly detailed numerical simulations based on much finer resolution models of atmospheric temperature variations. The environmental data, though, is not really suited to our task. To predict refraction between an observer 25 feet high and the ocean horizon "zone" centered some five miles away, we would need access to detailed temperature and pressure data for that path."
"Certainly today we can do highly detailed numerical simulations based on much finer resolution models of atmospheric temperature variations. The environmental data, though, is not really suited to our task. To predict refraction between an observer 25 feet high and the ocean horizon "zone" centered some five miles away, we would need access to detailed temperature and pressure data for that path."
My intention would not be to arrive at some measured "real time terrestrial refraction" (or dip); I would rather aim at improving its estimate based on some (general) environmental data.
"By the nature of the experiments, every set of data would unfortunately be limited to a particular locale."
