S4 Index

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The $S 4$ Index is a standard index used to measure ionospheric disturbances.

[edit] Description

The $S 4$ is defined as $S_4=\sqrt{\frac{\langle I^2\rangle-\langle I\rangle^2}{\langle I \rangle ^2}}$ where $I$ is the received signal intensity and $\langle I \rangle$ is the ensanble average of the signal power over a one-minute window. This is often sampled on a 50Hz sampling rate of the L1 (1.5754GHz) GPS channel.^[1]

[edit] Real Time data

This parameter is displayed in real time by many institutions

[edit] References

^ Yeh, K. C. and C. H. Liu , Radio wave scintillations in the ionosphere, Proc. IEEE, 70(4), 324-360, 1982.

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