An Improved Empirical Conversion Function between the Peak-to-peak Fluctuation and the S4 Index

The ionospheric scintillation fading must be taken in account in the attenuation margin design of the VHF/UHF satellite systems. Most of the studies on the scintillation observations are based on the S4 indices. Therefore, a conversion function from the S4 index to the peak-to-peak fluctuation is needed for the analysis of the scintillation fading in the VHF/UHF signals to be transimitted to/from the satetillite. Based on the relationship analysis of the peak-to-peak fluctuations of UHF/L-band signals and the corresponding S4 indices observed at three low-latitude stations in China, an improved empirical conversion function from the S4 index to the peak-to-peak fluctuation is put forward. The improved conversion function has a saturation trend in the strong scintillation regime, when the S4 indices are greater than 1.0, which may be helpful for the analysis of the scintillation fading in the VHF/UHF signals.