Summary of ELF propagation validation system field strength measurements, 1976 to 1978

From August 1976 through December 1978, extremely low frequency (ELF) field strength and effective noise measurements were taken continuously in Connecticut and sporadically aboard operational submarines. This article summarizes the field strength measurements taken at both land (Connecticut) and sea (North Atlantic, Western Pacific) locations during January, March, April, and October 1977 and January/ February 1978. The main conclusion is that the average field strengths measured aboard the submarines (which were located at distances of 4-12 Mm from the Wisconsin Test Facility) are in excellent agreement with previous ELF measurements taken over similar paths. Anomalous ELF field strength variations were also correlated with geomagnetic activity. Interference between the direct and "round-the-world" paths was probably observed during the Western Pacific area daytime propagation period in early October 1977. ELF propagation effects were also observed during the February 13, 1978, significant solar particle event.