ELF Nonlinear Noise Processing Experimental Measurements. Part 3. Synoptic Sample of Diurnal and Seasonal Noise Variation in Italy.

摘要

Using a suitable nonlinearity in the input stage of an extremely low frequency receiver can improve received signal-to-noise ratio (SNR) by whitening the nongaussian atmospheric noise at these frequencies. Previous studies indicate that performance of simple clippers, carefully adjusted on the basis of the raw noise amplitude statistics, is very nearly equal to that of the optimum clipper. A collection of ELF noise data for the summer, fall and spring seasons and nearly all times of day has been acquired at a reveiving site near Pisa, Italy. These data have been used to evaluate the improvement in SNR that can be expected from simple clipping under a variety of noise and propagation conditions. Under both quiet and noisy conditions little performance difference is observed among processing channels with clipping levels as far apart as 6 to 18 dB, in the vicinity of the optimum clipping level. The nonlinear processing method described in this report provides at least 6 dB of SNR improvement over the performance obtained without suitable processing. (Author)