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with rain are shown in Fig. 179. A strong emission peak is present around 60 GHz due to
oxygen absorption (emission), which dominates the contribution from all other constituents
except rain. The strong emission Tb(ν)at frequencies near 60 GHz (see Figure 180) depends
primarily on the concentration of molecular oxygen and layer’s temperature. Since oxygen
is well-mixed for altitudes below 80 km, its concentration is constant and well known so
the only unknown associated with the high brightness emission near 60 GHz is atmospheric
thermodynamic temperature.
Figure 179: Atmospheric absorptionnormalized coefficient αν(h) as frequency function notice
the first narrow peaks at 60 Ghz
Figure 180: Spectral shape of the brightness temperature of atmospheric radio-emission,
measured using ground based radiometric observationalong the zenith direction in the oxygen
absorption band at 60 Ghz
A ground-based radiometer looking upward detects the integrated emissions up to an
heights which depends on the level of absorption associated to the observation frequency.
Frequencies in the immediate vicinity of the absorption peak (Figure 180) experience the
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