The equivalent Earth radius a
e is considered to be dependent on the time percentage according to :
ae
with the Earth radius factor k
expressed as: 
Image Removed for p < 50%
Image Removed for p> 50%
and 
Image Removed
expressed as:
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| body | $k(p)={{k}_{50}}+(5-{{k}_{50}})\frac{(1.7-\log p)}{(1.7-\log {{\beta }_{0}})}$ |
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for p < 50%
for p> 50%and
| Mathinline |
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| body | ${{k}_{50}}=\frac{157}{157-\Delta N}$ |
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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 ae= 8500 km.
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