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> They mention "low altitudes, btw". What does the irradiation
> phenomenon have to do with low altitudes?

In low altitude Sun sights, the lower limb is affected to a "substantially"
greater degree by refraction than the upper limb.  My best guess relates to
the art, rather than science, of cel nav.  In cases of low Sun altitude,
some practitioners seem willing to trade off the possible affects of
irradiation against what they perceive to be a greater risk of error from
refraction at low altitudes by using the lower limb.

I suspect that even if one could quantify the affect of the scope and its
optics, contrast ratio between the sun and sky, sea and sky, body altitude
etc., it still comes down to how each individual's sensors and brain parses
the input.  That seems, from what I have read, to be the fuzzy variable that
makes it impossible to quantify irradiation for the masses.

Good luck on nailing it down ;-)

Bill

   

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