Sea-surface properties from the 100 kHz ground wave delay

In this study, we investigate effect of sea surface conductivity over a long all-seawater path, using the propagation delay in a 100 kHz radio signal. The change in delay, over such paths, is caused by changes in sea surface conductivity (due to changes in temperature and salinity) as well as atmospheric properties (temperature and pressure) that determine the refractive index of the atmosphere. In particular, we consider data of 17 months of propagation delay (at 100 kHz) on a 560 km all sea water path across the North Sea between Sylt in Germany and Harwich in the UK. We present the experimental results and compare with those from a basic model pertaining to both the atmospheric and sea surface contributions to the measured delay, with the aim to extract sea surface properties, including conductivity.