Polar ionospheric spread echoes and radio frequency properties of ice shelves

Records from three stations in the Antarctic and one Arctic drifting station show that downward radiation from an ionosonde aerial is reflected from sea water under the ice on which the station is built. As the ice is several wavelengths thick, an interference pattern is established which makes it possible to derive (a) the thickness and dielectric constant of the ice and (b) the direction from which ionospheric spread echoes arise. Spread F frequently occurs at vertical incidence in the polar regions.