On the Graphical Method of Drawing APD's for Atmospheric Radio Noise

It has been found that an amplitude probability distribution (APD) of a defined form factor cannot be drawn on a Rayleigh graph by the well-known graphical method using the three statistical moments for a significant part of a large number of samples of atmospheric radio noise in VLF-LF bands. An attempt has been made to approximate an individually measured APD for a sample of atmospheric radio noise using the concept of the form factor. It has been found that the great majority of measured APD's for the noise at a few frequencies can be approximated with reasonable accuracy. Based upon a large number of pairs of APD's, measured and approximated, each pair being obtained for a single noise sample, various parameter relations are obtained for the purpose of comparison with the original parameter relations associated with the graphical method. The results of the comparison show that some agreements as well as some disagreements exist between the two groups of the parameter relations. It is worthy of note that the agreements and disagreements are due to two types of atmospheric radio noise with different characteristics.