Integral Equation Approach to the Propagation of Low-Frequency Groundwaves over Irregular Terrains: II. Two-Dimensional Terrain Features and Elevated Receivers.
Abstract
This report presents solutions of the one- and two-dimensional integral equations that describe groundware propagation. Considered are the effects of: (1) terrain irregularities that are narrower than a Fresnel zone, and (2) receiver elevations. The results define the conditions under which the simpler one-dimensional equation can be used, as well as those that demand the more complicated two-dimensional form. A frequency of 100 kHz is assumed throughout, although certain results are easily scaled to other frequencies. It is well known that the one-dimensional 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 path-lengths the one-dimensional 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 one-dimension equation to moderately sized terrain features. For examples, for a path-length of 500 km, that equation overstates by a factor of four the effect of an obstacle 6 km in diameter. It cannot give accurate results unless the diameter approaches a Fresnel zone width-which exceeds 10 km for long propagation paths. Even for wide obstacles, the one-dimensional formulation neglects reflection and interference phenomena.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1981
- Accession Number
- ADA108578
Entities
People
- B. D'ambrosio
- E. C. Field Jr.
- S. Gayer