The review paper, given by E. L. Maxwell (USA), concentrated on recent developments in three areas: (a) prediction of atmospheric noise levels and characteristics, (b) calculation of system performance in the presence of atmospheric noise, and (c) measurement of atmospheric noise.
The development of a digital-computer model for predicting the characteristics of VLF atmospheric-noise characteristics was described. The model provides for the calculation of (a) mean values of vertical electric-field intensity which can be converted to mean noise power available from an ideal short vertical antenna, Fa, (b) the standard deviation from the mean values, (c) mean values of voltage deviation Vd) and (d) the direction of arrival of the noise energy. It uses both thunderstorm and lightning distributions derived from thunderstorm-day observations at more than 7000 locations and lightning characteristics to calculate the noise energy radiated per square kilometer over the entire earth surface. An earth-ionosphere waveguide model is used to calculate the noise energy propagated to any location. Statistical characteristics of noise are calculated from those of thunderstorms and lightning and from propagation parameters. It was emphasized that measured VLF noise data were not used to generate the model. The accuracy of the noise model was good when compared with atmospheric radio-noise (ARN-2) data but not better than that of the empirical model of CCIR Report 322  when compared with data from the 16 locations used for that model. For very high latitudes and other remote locations the results from the current model differ from those of CCIR Report 322 by up to 20 db. It seemed desirable to update the report for VLF by using the results from the noise-prediction model and all the noise data collected by the NBS/NOAA network. It was suggested that a separate map for VLF for three-month periods for the world might be preferable to the presentation in CCIR Report 322. Some continuing measurements with ARN-2 equipment were remommended.