Near 60 GHz, many oxygen absorption lines merge together, at sea-level pressures, to form a single, broad absorption band, which is shown in more detail in Fig. 2. This figure also shows the oxygen attenuation at higher altitudes, with the individual lines becoming resolved at lower pressures. Some additional molecular species (e.g. oxygen isotopic species, oxygen vibrationally excited species, ozone, ozone isotopic species, and ozone vibrationally excited species, and other minor species) are not included in the line-by-line prediction method. These additional lines are insignificant for typical atmospheres, but may be important for a dry atmosphere. For quick and approximate estimates of specific attenuation at frequencies up to 350 GHz, in cases where high accuracy is not required, simplified algorithms are given in Annex 2 for restricted ranges of meteorological conditions. The specific gaseous attenuation is given by: (1) where and are the specific attenuations (dB/km) due to dry air (oxygen, pressure-induced o w nitrogen and non-resonant Debye attenuation) and water vapour, respectively, and where is the f frequency (GHz) and ( is the imaginary part of the frequency-dependent complex refractivity: N f  (2) is the strength of the line, is the line shape factor and the sum extends over all the lines (for Si i-th Fi frequencies, above 118.750343 GHz oxygen line, only the oxygen lines above 60 GHz complex f, should be included in the summation; the summation should begin at = 38 rather than at = 1); is i i the dry continuum due to pressure-induced nitrogen absorption and the Debye spectrum. The line strength is given by: (3) where: : dry air pressure (hPa) p : water vapour partial pressure in hPa (total barometric pressure   e ptot p e)  300/T : temperature (K). T FIGURE 1 Specific attenuation due to atmospheric gases, calculated at 1 GHz intervals, including line centres FIGURE 2 Specific attenuation in the range 50-70 GHz at the altitudes indicated Local values of and measured profiles (e.g. using radiosondes) should be used; however, in p, e T the absence of local information, the reference standard atmospheres described in Recommendation ITU-R P.835 should be used. (Note that where total atmospheric attenuation is
Near 60 GHz, many oxygen absorption lines merge together, at sea-level pressures, to form a single, broad absorption band, which is shown in more detail in Fig. 2. This figure also shows the oxygen attenuation at higher altitudes, with the individual lines becoming resolved at lower pressures. Some additional molecular species (e.g. oxygen isotopic species, oxygen vibrationally excited species, ozone, ozone isotopic species, and ozone vibrationally excited species, and other minor species) are not included in the line-by-line prediction method. These additional lines are insignificant for typical atmospheres, but may be important for a dry atmosphere. For quick and approximate estimates of specific attenuation at frequencies up to 350 GHz, in cases where high accuracy is not required, simplified algorithms are given in Annex 2 for restricted ranges of meteorological conditions. The specific gaseous attenuation is given by: (1) where o and w are the specific attenuations (dB/km) due to dry air (oxygen, pressure-induced nitrogen and non-resonant Debye attenuation) and water vapour, respectively, and where f is the frequency (GHz) and N ( f  is the imaginary part of the frequency-dependent complex refractivity: (2) Si is the strength of the i-th line, Fi is the line shape factor and the sum extends over all the lines (for frequencies, f, above 118.750343 GHz oxygen line, only the oxygen lines above 60 GHz complex should be included in the summation; the summation should begin at i = 38 rather than at i = 1); is the dry continuum due to pressure-induced nitrogen absorption and the Debye spectrum. The line strength is given by: (3) where: p : dry air pressure (hPa) e : water vapour partial pressure in hPa (total barometric pressure ptot  p  e)  300/T T : temperature (K). FIGURE 1 Specific attenuation due to atmospheric gases, calculated at 1 GHz intervals, including line centres FIGURE 2 Specific attenuation in the range 50-70 GHz at the altitudes indicated Local values of p, e and T measured profiles (e.g. using radiosondes) should be used; however, in the absence of local information, the reference standard atmospheres described in Recommendation ITU-R P.835 should be used. (Note that where total atmospheric attenuation is