Polarization Changes of Radio Signals in Vertical Radio-Echo Sounding of Glaciers

Abstract

An electromagnetic linearly-polarized signal transmitted through the glacier in a vertical direction, reflected from the bedrock, and received with a receiving antenna, is found to be changed into one either partially or elliptically polarized. The polarization changes are believed to be due mainly to the crystal structure of the glacier and anisotropy caused by the pressure of the upper layers.

An analysis of the polarization diagrams obtained is up to the present the main method used for studies of the reflected signal polarization. Evidently using a simple dipole a partially-polarized signal is not distinguishable from one that is elliptically polarized, nor is a nonpolarized signal distinguished from circularly polarized. However, the data recently obtained are of great importance, particularly from studies of glacier crystal structure made in deep core drilling.

Possible reasons for the polarization changes of the signal have been analysed. Results of the analyses of the polarization diagrams obtained both at individual points and along extended traverses are discussed. It has been found that the signal reflected from a considerable ice thickness is polarized in such a way that the parallel orientation of the receiving and transmitting dipoles can be disregarded. En route recordings of the signal fluctuations obtained by parallel and orthogonally polarized dipoles are shown. The results of polarization studies are important for practical purposes. For example, bedrock relief sounding carried out with crossed dipoles makes it possible to get rid of interference signals occurring due to scattering from inhomogeneous structures of the upper part of the glacier.