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    Re: Dip uncertainty
    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

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