A study of the ground illumination footprint of meteor scatter communication
An examination is made of the ground illumination footprint of meteor trails and its effect on the simultaneous reception of meteor scatter transmissions by multiple receivers. A technique for calculating the ground illumination footprint of individual trails which provides added insight into the physical mechanisms is presented. The probability of adjacent station reception as a function of location on the ground is calculated by computing the ground illumination footprint of individual trails at different locations and orientations within the common volume and weighting each footprint by the number of trails at that location and orientation. Two different models for the spatial arrival pattern of meteor trails are considered: the first model assumes that trails arrive uniformly over the common volume, and the second calculates the number of arrivals from the spatial distribution of meteor orbits, antenna patterns, time of day, and season. The effect of antenna patterns on the ground illumination footprint of meteor scatter communication is examined. >
CHAPTER VIII – ELEMENTS OF THE THEORY OF DIFFRACTION
Introduction IN carrying out the transition from the general electromagnetic field to the optical field, which is characterized by very high frequencies (short wavelengths), we found that in certain regions the simple geometrical model of energy propagation was inadequate. In particular, we saw that deviations from this model must be expected in the immediate neighbourhood of the boundaries of shadows and in regions where a large number of rays meet. These deviations are manifested by the appearance of dark and bright bands, the diffraction fringes. Diffraction theory is mainly concerned with the field in these special regions; such regions are of great practical interest as they include the part of the image space in which the optical image is situated (region of focus). The first reference to diffraction phenomena appears in the work of Leonardo da Vinci (1452–1519). Such phenomena were, however, first accurately described by Grimaldi in a book, published in 1665, two years after his death. The corpuscular theory, which, at the time, was widely believed to describe correctly the propagation of light, could not explain diffraction. Huygens, the first proponent of the wave theory, seems to have been unaware of Grimaldi's discoveries; otherwise he would have undoubtedly quoted them in support of his views. The possibility of explaining diffraction effects on the basis of a wave theory was not noticed until about 1818. In that year there appeared the celebrated memoir of Fresnel (see Historical introduction) in which he showed that diffraction can be explained by the application of Huygens’ construction (see §3.3.3) together with the principle of interference. Fresnel's analysis was later put on a sound mathematical basis by Kirchhoff (1882), and the subject has since then been extensively discussed by many writers.
Radio Communication by Scattering from Meteoric Ionization
By a consideration of the amplitude and duration of echoes forward-scattered from individual meteor ionization trails, and of the probability of detecting randomly oriented trails over an oblique radio propagation path, an estimate of the contribution of meteoric ionization to extended range hf and vhf radio transmission has been obtained. It has been concluded that meteoric ionization alone would give a virtually continuous signal for a transmission path of about 1,000 km at frequencies near 15 mc. For the very high frequencies, scattering from meteor trails has been found to be at least an important contributing factor to the propagation of a signal over an oblique path. A precise evaluation of the role of this process must await a better determination of the number of trails as a function of their ionization density.