Abstract:
The total atmospheric absorption due to oxygen and water vapour in the frequency
range, 1O-350GHz was evaluated employing Liebe's empirical model. The basic
data include monthly mean meteorological parameters of pressure, temperature and
relative humidity obtained from four tropical sites, namely Akure
(Lat.07°1TN,Long.05°14'E),Kano(Lat.03°12'N, Long.08° 32'E), Lagos (Lat. 06°
N, Long.03° 21 'E) and Minna (Lat. 09° 5TN, Long.06° 32'E). All the four stations
are in Nigeria.
The specific attenuations by oxygen and water vapour are presented together with
the graphical illustrations of the results for the two principal seasons in Nigeria,
dry and wet seasons The wet season has a greater attenuation than the dry season.
An exception to this takes place at Akure site in 1991 when the attenuation during
the dry season exceeds that of wet season. In addition to this seasonal variation, the
specific attenuation also exhibits geographical variations. Lagos, a coastal station,
has the highest attenuation; Kano a far inland station, has the least attenuation
value. The water vapour three resonant absorption lines are obtained at 22,184 and
326GHz. The weakest spectrum line being at 22GHz,while the strongest is at
326GHz. Oxygen has an isolated resonant absorption at 118GHz and a series of
close lines at 54-66GHz, the peak of this is at 60GHz.
Using typical International Telecommunication Union (lTU) temperate climatic
parameters of pressure, temperature and water vapour pressure, the specific
attenuation for a temperate region is computed which, in turn, is compared with
those from tropical sites. Attenuation is higher in the tropical sites than in the
temperate zone. The tropical sites attenuation at 326GHz for wet season is about
two times the attenuation for the temperate region.
