A17.5.4 Equivalent Earth radius

The equivalent Earth radius a_e is considered to be dependent on the time percentage according to :

a_e  (p) = 6375 k (p)

with the Earth radius factor  k (p) expressed as:

                                                   for p < 50%

                                                                                           for p> 50%

and        

where:

     is the mean gradient of the radio refraction profile over a 1 km layer of the atmosphere from the surface. The default value is 40 unit/km for Europe (standard atmosphere). This yields   and a_e= 8500 km.

Note :   The mean gradient is positive.

       is the existence probability (in %) of the super-refractive layer (  > 100 unit/km) in the low atmosphere. Default value: 1 % for Europe.

Note :   The probabilities p and  are denoted in %, i.e. a range of variety: 0...100 %.

Note :   p is set to  50%, i.e. the median with respect to time is computed. Later versions may allow to choose a certain time percentage.