NavList:

   

Reply

Geoffrey Kolbe  wrote:
>   I grabbed an old Nautical Almanac, opened it randomly and lo and behold,
>
>   d = 0.0293*h^0.5 where d is in degrees and h is height of eye above
>   the horizon (sea level) in metres.

If you work out the geometry, you find

    d = sqrt(2*h/Re)

where Re is the radius of the earth.

In radar analyses, it's usual to use the "four-thirds earth model", i.e.

    d = sqrt(2*h/(1.33*Re))

which corrects for refraction.
See for example: http://twister.ou.edu/papers/Gao_Xue_Brewster_AAS2006.pdf

The NA formula above works out to

    d = sqrt(2*h/(1.2*Re))

which is a "six-fifths earth model", i.e. less refraction.  I wonder
whether that's because of the different wavelength, or different
typical heights (so different temperature and pressure profiles), or
what?

               - Jim Van Zandt

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply