Chapter 5 - Les Irregularites de la Couche D et Leur Effet Sur la Forme D'Onde Des Atmospheriques

Abstract

Observation of the waveforms of atmospherics with two loops spaced a very small fraction of a wavelength apart very often shows differences in induced signals which cannot be attributed to the equipment. The main characteristic of the phenomenon is its variability in form and time. At a frequency of 5500 c/s, one observes on occasion amplitude ratios as large as ½ or ½ with no phase effect, or phase differences which can reach 0⋅3 rad without amplitude effect. Combined effects are also frequently recorded. The time scale of the events although being very variable is of the order of seconds. The use of an array of several loops shows that the effects are in general different for each loop. Simultaneous measurements conducted at sites 15 km apart showed no correlation in form or time of occurrence. When such anomalies are observed, the directions of arrival given by a crossed loop direction finder do not agree with the data obtained from two perpendicular 15 km long bases. The patterns given by the crossed loops are then elliptical, and in many cases the long base equipment gives imaginary directions of arrival. These phenomena are attributed to D-layer irregularities producing focusing effects and interference patterns on the ground.