Correlation Between Atmospheric Noise Levels at Different Frequencies

Correlation between half-hourly atmospheric noise burst levels at 1.6 and 2.9 MHz at Bangalore was examined on a long-term seasonal basis. Good correlation was observed in all cases, and it was found that noise level at one frequency can be predicted from that at another with a standard error of estimate of about 3 dB. Extension of the analysis to the band 100 kHz-5.0 MHz showed that the correlation decreases as the frequency separation increases. Significance of this result for the presentation of noise data is discussed. The problem of the average spectrum of noise is also discussed. It is observed that if the spectrum characteristics are studied for a short period of time (as in the case of local thunderstorms), large variations in the results are to be expected as a matter of statistical fluctuation. Therefore, the problem needs to be studied on a long-term seasonal basis.