Measurement of Geomagnetic and Atmospheric Noise at a Remote Site

A magnetic field observatory has been established at Fisher's Island, NY, where the geomagnetic and atmospheric noise in the frequency band from 0.6 to 30 Hz is measured continuously. The primary sensors are an orthogonal pair of 2-m air-core loops, whose sensitivity makes them among the world's quietest at 70 fT/gamma Hz. These loops are free of mechanical interference from natural forces (such as wind and waves), having been designed so that their electrical band is below the first mechanical resonance at 37 Hz. After transmission directly over an existing microwave link to a laboratory in New London, CT, the data are plotted on a frequency-versus-time spectrograph for quick-look analysis while they are simultaneously digitized, Fourier transformed, averaged, and stored on magnetic disk. Averaged plots of magnetic field strength over various time cycles have been made. General observations show that the atmospheric noise is highest in the summer, corresponding to increased electrical activity in the tropics. Averaged Schumann resonances have also been plotted over a 1.year timeframe to show characteristic seasonal effects.