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Re: Dip uncertainty
From: Trevor Kenchington
Date: 2004 Dec 6, 23:03 -0400
From: Trevor Kenchington
Date: 2004 Dec 6, 23:03 -0400
Alex wrote: > I think it does: if the anomalous refraction always decreases > with height of the observer, than the anomalous refraction from > the space ship would be smaller than that from a sailboat. > > And we all agree that it is probably not smaller. > > In view of these thought experiments I suppose that > anomalous refraction is not a monotone function of the height. Nobody suggested that it was, at least not over the range from sea level to the Space Station. The position that Bruce and I have been supporting is that anomalous dip is usually less pronounced for an observer on the bridge of a modern ship or in the top of a sailing ship than for one located near the waterline or aboard a small yacht. As I tried to point out before, in these cases, we are concerned with the anomalies caused by temperature variations within the one air mass in contact with the sea surface. Those anomalies are generally somewhat less at heights of a few tens of metres than they are within a metre or two of the surface. Observations at enormously-greater heights of eye are subject to additional anomalies caused by thermoclines that are not parallel and planar. We know from common observations of the setting Sun that the combined effects of all of those disruptions of the path of a light ray passing through the atmosphere (from the vacuum of space to the surface) at a low angle can be quite large, relative to the normal range of anomalies in dip observed by mariners. It would be the same for a ray passing from the surface to the Space Station but that has little to do with the issue at hand. Trevor Kenchington -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus