is in m/% of relative humidity a is in C–1. b Parameters and are given in Table 2 according to the geographical location. a b 2 a b Location (m/%) (C–1) Coastal areas (islands, or locations less than 10 km away 5.5 10−4 2.91 10−2   from sea shore) Non-coastal equatorial areas 6.5 10−4 2.73 10−2   All other areas 7.3  10−4 2.35  10−2 To compute the corrective factor of equation (16), an exponential variation with height of the k h atmospheric refractivity is assumed: N exp (– / (19) N(h)  Ns h h0) where is the average value of refractivity at the Earth surface (see Recommendation Ns ITUR P.453) and is given by: h0 (20) is then computed from the following expression: k (21) where and (h0) are the values of the refractive index at the Earth surface and at height (given ns n h0 by equation (20)) respectively, and and (h0) are the corresponding distances to the centre of the rs r Earth. For Earth- paths with elevation angle the tropospheric excess path length (m) can be expressed as the sum of and wet components. greater than °, : m (22) where: air total pressure and water vapour pressure at Earth surface (hPa) ps, es: mean temperature of the water vapour above the surface (K) Tms: vapour pressure decrease factor λ: : = 287.0 (J/kg K) Rd R/Md molar gas constant = 8.314 (J/mol K) R: dry air molar mass = 28.9644 (g/mol) Md:
a is in m/% of relative humidity b is in C–1. Parameters a and b are given in Table 2 according to the geographical location. 2 Location a (m/%) b (C–1) Coastal areas (islands, or locations less than 10 km away from sea shore) 5.5  10−4 2.91  10−2 Non-coastal equatorial areas 6.5  10−4 2.73  10−2 All other areas 7.3  10−4 2.35  10−2 To compute the corrective factor k of equation (16), an exponential variation with height h of the atmospheric refractivity N is assumed: N(h)  Ns exp (– h / h0) (19) where Ns is the average value of refractivity at the Earth surface (see Recommendation ITUR P.453) and h0 is given by: (20) k is then computed from the following expression: (21) where ns and n (h0) are the values of the refractive index at the Earth surface and at height h0 (given by equation (20)) respectively, and rs and r (h0) are the corresponding distances to the centre of the Earth. For Earth- paths with elevation angle the tropospheric excess path length (m) can be expressed as the sum of and wet components. greater than °, : m (22) where: ps, es: air total pressure and water vapour pressure at Earth surface (hPa) Tms: mean temperature of the water vapour above the surface (K) λ: vapour pressure decrease factor Rd : R/Md = 287.0 (J/kg K) R: molar gas constant = 8.314 (J/mol K) Md: dry air molar mass = 28.9644 (g/mol)
R12-SG03-RP-1005!!MSW-E.docx