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Alex,

The problem with an experimental approach would be that we are dealing
with a stochastic system. No two places or days will have quite the same
anomalies. Indeed, different regions will likely have different patterns
of anomaly, while the height affected will change through the day at one
place. (Some may see an initial low anomaly grow as the effects of,
e.g., a cold surface extend up through the air mass. Others may see the
reverse for a time, as solar heating intensifies through the day.) It
would need a huge amount of data to produce global statistics on the
phenomenon.

Then there is the problem of how to measure the amount of anomalous
refraction (with a dipmeter?). Or would you rather measure the
temperature gradient and calculate the refractive index?

Finally: Maybe somebody has studied this but who would have sponsored
research relating to the heights of eye typical on small boats? I would
suspect that any research would have focused on whether to take
observations from the main deck, the bridge or the masthead of a
sizeable ship. But if the issue really is the first few feet of the
atmosphere versus the next layer above, there may not be much of a
gradient in frequency and severity of anomalies between deck and
masthead and hence nothing to study.

Scholar.google shows only 158 journal citations for "anomalous dip" and
none of the ones on the first page have anything to do with "dip" as we
understand it here nor with navigation of any kind. (Combining
"anomalous dip" with "horizon" produced only two hits, neither dealing
with our problem.) But perhaps that search engine doesn't recognize
journals of navigation as sufficiently academic for its purposes.


Trevor Kenchington


You wrote:

> Trevor:
>
>
>>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.
>>
>
> The opinions seem to be split on this subject,
> and I don't see how to settle it without experimental
> data on the anomalous refraction.
>
> If the whole "anomalous part" of the anomalous refraction happens
> within few meters from the sea surface, then you and Bruce are
> right. Surely someone studied this question, but I don't know
> how to find these results.
>
> Alex.
>
>


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Trevor J. Kenchington PhD                         Gadus@iStar.ca
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