Propagation frequency shifts and impact on time and frequency transfer and gravity wave detection

Abstract

We further investigate previously announced unexpected frequency shifts and multipath splitting of short-wave Standard Frequency Signals between ∼1MHz and 25MHz over paths of 500km to 11000km. into components with appoximately diurnally variable frequency shifts of up to a Hertz or more, using SDR receivers with millihertz resolution. The theory so far for the observed effects is based on extending and modifying second order ‘Landau damping’ as in plasmas (such as the ionosphere) to the very weak electron plasma assumed in free-space to explain pulsar dispersion. By extrapolation of observed ionospheric and surface wave effects to GHz frequencies we find that any likely effects on existing satellite navigation systems are small enough to be negligible. Small short term, diurnal and seasonal frequency variations do seem to be indicators of local gravity potentials and gravity waves. Two new gravity wave detection methods are therefore proposed. A Rubidium source is now installed for more accurate absolute measurements of frequency shifts of observed trans-Atlantic sea or ionospheric sub-layer surface waves between 1 and 5MHz.