ATMOSPHERIC ATTENUATION AT MILLIMETER WAVELENGTHS 915 



'6 1 1 1 1 1 1 1 1 1 1 rr — I 1 i 



1 1 r 



"I r 



._ SEA LEVEL 



_---8 KILOMETERS 



,--11 KILOMETERS 



.--32 KILOMETERS 



50 



52 



54 56 58 60 62 64 66 



FREQUENCY IN KILOMEGACYCLES PER SECOND 



68 



70 



Fig. 9 — Calculated curves of oxygen absorption at various altitudes for a 

 line-breadth constant of 600 megacycles and a temperature of 293° K. (Courtesy 

 of T. F. Rogers, Air Force Cambridge Research Center.) 



6.1 mm) the measurements were highly consistent, due mainly to the 

 longer path that was used. Errors in the absolute values of the absorption 

 are estimated not to exceed ±0.05 db/km in the 49 to 54.5 kmc region, 

 ±0.25 db/km in the 55.5 to 59 kmc region. The errors in absolute absorp- 

 tion are governed mainly by the structural and thermo-mechanical sta- 

 bility of the corner reflectors. 



-I 



o 



Q 



3:20 



3:30 



3:40 



3:50 4:00 



TIME OF DAY. P.M. 



4:10 



4:20 



4:30 



Fig. 10 — Attenuation of 6.0-mm radiation caused by a light rain. 

 Round-trip path length = 2.72 kilometers 



Average rainfall rate = 5 millimeters per hour 



