Correlated oscillations due to similar multi-path effects seen in two widely separated radio telescopes

TL;DR

This paper demonstrates that ground reflection-induced multipath interference causes correlated oscillations in radio signals observed by two distant telescopes, explaining previously unexplained correlations.

Contribution

It introduces a model showing ground reflection as the cause of correlated oscillations in widely separated radio telescopes at 1.4 GHz.

Findings

Ground reflection explains observed oscillations.

Correlations are due to multipath interference.

Simple specular reflection model fits data well.

Abstract

A multipath mechanism similar to that used in Australia sixty years ago by the Sea-cliff Interferometer is shown to generate correlations between the periods of oscillations observed by two distant radio telescopes pointed to the Sun. The oscillations are the result of interferences between the direct wave detected in the main antenna lobe and its reflection on ground detected in a side lobe. A model is made of such oscillations in the case of two observatories located at equal longitudes and opposite tropical latitudes, respectively in Ha Noi (Viet Nam) and Learmonth (Australia), where similar radio telescopes are operated at 1.4 GHz. Simple specular reflection from ground is found to give a good description of the observed oscillations and to explain correlations that had been previously observed and for which no satisfactory interpretation, instrumental or other, had been found.