NavList:

Frank,

In this very interesting recent post of yours summarizing all "your" Refraction Formulae, my attention got caught by the following one :

[Quote]" Correction for height above sea level. htObs is the observer's height above sea level in km:

  refx = refx * exp(-htObs / 9.5) " [Unquote]

Since I never - so far ... - had to deal with refractions applicable to high elevated spots on the Earth, I never studied the subject in close detail.

(1) - Let's start on an example :

From a spot at 25,000' AMSL in standard atmosphere :

htObs = 7.620 km , OAT = -34.5 °C , QNH = 1013 mb , "onsite" pressure (QFE) = 376 mb

(1.1) - I would compute Standard Astronomic Refraction as follows :

Temperature correction factor : Tcf = ( 273.15 + 10 ) / (273.15 - 34.5) = 1.1865

Pressure correction factor : Pcf = QFE / 1010 = 376 / 1010 = 0.3723

"T & P" combined  correction factor : "Ctp" = Tcf * Pcf = 0.4417

(1.2) - On the other hand : " exp(-htObs / 9.5) " = 0.4484, quite close from the previous line value ... so , instead of being an additional correction factor - i.e. on top of "Ctp" - as I first understood it upon reading your initial post, this exponential correction factor is probably the fully integrated correction factor designed to entirely replace the former traditional "T & P" calculation, no ?

Thanks for this interesting piece of information.

Then, from which AMSL htObs - and above - do you think we can validly start using it ?

Please advise,

Kermit