Polarization measurements of low frequency echoes

Abstract

Observation of the state of polarization of a 160 kc pulse modulated signal reflected by the ionosphere at vertical incidence was begun at the Sterling, Virginia, station of the National Bureau of Standards on October 15, 1950. The emitted signal propagated upward was plane polarized. The polar pattern of the electric vector in the reflected wave groups is oscillographically recorded. The state of polarization of the echoes observed from October 15 to November 30, 1950, was characterized by a stable condition interspersed with short periods of instability of the polar pattern. The stable state elliptical pattern was oriented 60° to 70° east of magnetic north, with ratio of major to minor axis varying from 3 to 5, and left-hand sense of rotation of the polar vector. Unstable polarization occurred at sunrise and sunset, and at other irregular times. The echo usually increased in time duration or split into separate groups during unstable periods. Duration of the unstable periods varied from a few minutes to a half-hour.