An experimental investigation of the reflection and absorption of radiation of 9-cm. wave-length

The paper, which was circulated as a confidential report to the Radio Research Board in October 1944, describes measurements on the reflecting power of various surfaces at a wave-length of 9 cm and angles of incidence ranging from 80° to 45°; these included level and uneven bare ground, vegetation-covered ground, tap water and a 4% salt solution approximating to sea water. Specular reflection was found to occur only from very level surfaces; the absorptions of these surface media were measured, and from the combined measurements of reflection and absorption their electrical constants were derived. Rough surfaces, either of bare ground or vegetation-covered ground, gave values of reflection coefficient in general agreement with the optical rule that regular reflection is only observed from an uneven surface if the product of the depth of the surface irregularities and the cosine of the angle of incidence is a small fraction of the wave-length. If this fraction exceeded ½λ, the values of reflection coefficient measured were about 0.1. The calculated values of reflection coefficient corresponding to dry soil, wet soil and sea water for angles of incidence varying from 0° to 85° are given in an appendix to the paper.