Integral equation approach to the propagation of lowfrequency groundwaves over irregular terrain. 2: Twodimensional terrain features and elevated receivers
Abstract
This report presents solutions of the one and twodimensional integral equations that describe groundwave propagation. Considered are the effects of: (1) terrain irregularities that are narrower than a Fresnel zone, and (2) receiver elevations. The results define the condition under which the simpler onedimensional equation can be used, as well as those that demand the more complicated twodimensional form. A frequency of 100 kHz is assumed throughout, although certain results are easily scaled to other frequencies. It is well known that the onedimensional equation is invalid unless the terrain is nearly uniform across a Fresnel zone. It has been found that for obstacles narrower than about 10 km and typical pathlengths the onedimensional equation erroneously predicts propagation anomalies that (1) are independent of width, and therefore too large, and (2) diminish too slowly at long distances. Considerable error can be incurred by applying the onedimension equation to moderately sized terrain features. For example, for a pathlength of 500 km, that equation overstates by a factor of four unless the diameter approaches a Fresnel zone widthwhich exceeds 10 km for long propagation paths. Even for wide obstacles, the onedimensional formulation neglects reflection and interference phenomena.
 Publication:

Final Technical Report
 Pub Date:
 October 1981
 Bibcode:
 1981psrc.rept.....F
 Keywords:

 Ground Wave Propagation;
 Integral Equations;
 Radio Receivers;
 Fresnel Region;
 Low Frequencies;
 Terrain Analysis;
 Communications and Radar