Change of phase with distance of a low-frequency ground wave propagated across a coast-line

Observations of the change of phase with distance have been made on a frequency of 127.5 kc/s along a number of paths radiating from a transmitter near Lewes and crossing the south coast between Pevensey and Littlehampton. The nature of the ground adjacent to the coast, the angle of crossing the coast-line and the lengths of the land and sea sections covered varied from path to path; the greatest distance covered out to sea was 22 km. Measurements were also made over paths at right angles to the radials, and the phase changes in the area off Worthing, where the paths were tangential to the coast, were examined in detail. The results confirm the existence of a phase-recovery effect which, as theoretical considerations have shown, should be experienced by a wave passing from low-conductivity ground to sea water and which was indicated by previous measurements over geological boundaries on land. The detail of the measurements at sea shows also that, in addition to this general behaviour of the phase, there are superimposed systematic variations whose magnitudes decay from about 4° of phase near the coast to a negligible amount at 6¿ out to sea and on some paths are comparable to the recovery. A very marked phase disturbance within ¿/2 of the coast on the landward side is also evident; it is similar to that previously observed over geological boundaries on land.