Measurements over Seattle 6 using horizontally and vertically polarized 

 antennas indicate that Airborne :nan-made radio noise ^oes not have a predom- 

 ii.ant polarization. When viewed from above, the radiation field propagating 

 from a two-dimensional ourface distribution of independent noise sources 

 should be unpolarized. Airborne measurements using downward-directed isotro- 

 pic antennas do not show significantly greater radio noise than linearly 

 polarized antennas. 



Calculation of man-made radio noise power, p. ( a t altitude h, depends 

 upon the knowledge ofj (1) the losses *nd pattern function of the measuring 

 antenna; (2) the distribution of the man-made surface noise sources as a func- 

 tion of position and frequency; (3) transmission path looses; and (4) the 

 degree of correlation beLween noise sources of adjacent surface areas. 



Given the above information, p h may be represented as an integral, which 

 in the general case, requires numerical evaluation. The degree of difficulty 

 in evaluating the integral varies with the power pattern of the receiving 

 antenna, the function representing the surface noise distribution and the 

 surface area covered by the antenna pattern. For an isotropic antenna posi- 

 tioned above the center of a symmetrical surface noise distribution, evalua- 

 tion of the integral is much simpler. In addition, transmission path absorp- 

 tion can be assuned to be zero for frequencies less than 3 GHz and observation 

 altitudes of less than 10 miles. 



Correlation between man-made noise sources is not well known. Limited 

 data suggest that for altitudes above a few thousand feet there is no correla- 

 tion. This allows the treatment of man-made noise power from single sources as 

 additive quantities. All man-made noise sources can be considered to be dis- 

 tributed two-dimensionally on a plane that is parallel to and near the 

 surfacr. Also, the noise power emission from any unit a.-ea on the two-dimen- 

 sional distribution may be assumed to be uniform. Thii - assumption implies 

 that the earth and physical surroundings are either good noise-absorbing or 

 noiee-scattering media o- Nath. 



Based on the above assumptions and limitations the integral representa- 

 tion of airborne man-made noise power p^ in watts per unit bandwidth b taken 

 from reference 2 is 



p (f,d) F(Y ,Y ) 

 *h-»rJ - —2 2 «■ 



4TTR 



As shown in figure 5 the observing antenna is positioned above a business area 

 at height h, with a separation R between the anten.ia and differential element 

 d\ containing the noise sources. A r is the antenna aperture area and F(Y t ,Y2) 

 is the normalized (to unity) power pattern of the receiving antenna in terms 

 of angle variables (Y|',Ya)« 



When the airborne antenna is a dipole, its effective area becomes identi- 

 cally equal to the area of antennas used for most surface noise measurements. 

 The normalized power pattern may be written for a vertical dipole or monopole 

 antenna in terms of angle variables from figure 5 as: 



cos 2 1V2 * sin6) 



F(Y,.Y,) - r* . (9) 



1 2 cos2 9 



