medium fog (visibility of the order of 0.05 300 m) thick fog (visibility of the order of 0.5 50 m) A mathematical model based on Rayleigh scattering, which uses a double-Debye model for the dielectric permittivity ( ) of water, can be used to calculate the value of for frequencies up to f Kl 1 000 GHz: (dB/km)/(g/m3) (13) where is the frequency (GHz), and: f (14) The complex dielectric permittivity of is given by: (4) (15) = 77.66 + 103.3 ( 1) (16) – 0 = 0.0671 (17) 1 = 3.52 (18) 2 = 300 / (19) T with the temperature (K). T The principal and secondary relaxation frequencies are: = 20.20 146 ( 1) + 316 ( 1)2 GHz (20) fp – – – = 39.8fp GHz (21) fs In [6.6] some values for the average liquid water content of clouds are given, see table 6.5 Table 6.5: Liquid water content of cloud types [6.6] Cloud type Average water content in g/cm3 large cumulus 2.5 fair weather cumulus 0.5 Stratocumulus 0.2 Stratus 0.2-0.3 Altostratus 0.2
medium fog (visibility of the order of 300 m) 0.05 thick fog (visibility of the order of 50 m) 0.5 A mathematical model based on Rayleigh scattering, which uses a double-Debye model for the dielectric permittivity ( f ) of water, can be used to calculate the value of Kl for frequencies up to 1 000 GHz: (dB/km)/(g/m3) (13) where f is the frequency (GHz), and: (14) The complex dielectric permittivity of is given by: (4) (15) 0 = 77.66 + 103.3 ( – 1) (16) 1 = 0.0671 (17) 2 = 3.52 (18) = 300 / T (19) with T the temperature (K). The principal and secondary relaxation frequencies are: fp = 20.20 – 146 ( – 1) + 316 ( – 1)2 GHz (20) fs = 39.8fp GHz (21) In [6.6] some values for the average liquid water content of clouds are given, see table 6.5 Table 6.5: Liquid water content of cloud types [6.6] Cloud type Average water content in g/cm3 large cumulus 2.5 fair weather cumulus 0.5 Stratocumulus 0.2 Stratus 0.2-0.3 Altostratus 0.2