Propagation measurements at 500MHz over sea for varying meteorological parameters

500 MHz propagation measurements have been carried out on a 189 km path over the Baltic Sea over a period of three years. The field strengths were compared for different refractivity and meteorological conditions. For the monthly median field strength, a dependence on surface refractivity of 0.32dB per Nunit has been found. The correlation was somewhat better when using the gradient in the lower troposphere instead of surface refractivity. Comparisons were made with some other v.h.f. paths and a 500 MHz mixed land-sea path. The diurnal field-strength variation on the sea path was rather low. The mean diurnal amplitude of F50 was not more than 1.5dB. When the field strength exceeded 10% of the time the mean diurnal amplitude increased to 7dB, with a maximum in the late hours of the afternoon.