Specific Attenuation by Atmospheric Gases according to ITU-R P.676-10 Two methods are described in ITU-R P.676-10 [6.2]: A more detailed line calculation of gaseous attenuation –by-line A simplified method, based on curve-fitting of the line-by-line calculation agrees with the more accurate calculations to within an average of about 10% at frequencies removed from the centres of major absorption lines. The absolute difference between the results from these algorithms and the line-by-line calculation is generally less than 0.1 dB/km and reaches a maximum of 0.7 dB/km near 60 GHz. In the following the specific attenuation due to dry air and water vapour, is estimated using the simplified algorithms, valid for the frequency range 120 to 350 GHz: The specific attenuation due to dry air is calculated using the following equations: o (2) (3) (4) Where frequency (GHz) f = where represents total air pressure rp ptot/1013, ptot 288/(273 rt t) pressure (hPa) p t temperature (C) The specific attenuation w due to water vapor is calculated using the following equations: (5)
Specific Attenuation by Atmospheric Gases according to ITU-R P.676-10 Two methods are described in ITU-R P.676-10 [6.2]: A more detailed line –by-line calculation of gaseous attenuation A simplified method, based on curve-fitting of the line-by-line calculation agrees with the more accurate calculations to within an average of about 10% at frequencies removed from the centres of major absorption lines. The absolute difference between the results from these algorithms and the line-by-line calculation is generally less than 0.1 dB/km and reaches a maximum of 0.7 dB/km near 60 GHz. In the following the specific attenuation due to dry air and water vapour, is estimated using the simplified algorithms, valid for the frequency range 120 to 350 GHz: The specific attenuation o due to dry air is calculated using the following equations: (2) (3) (4) Where f frequency (GHz) rp = ptot/1013, where ptot represents total air pressure rt 288/(273 t) p pressure (hPa) t temperature (C) The specific attenuation w due to water vapor is calculated using the following equations: (5)