S4 Index

The $S\_4$ Index is a standard index used to measure ionospheric disturbances.

Description

The $S\_4$ is defined as $S\_4=sqrt\{frac\{langle\; I^2\; angle-langle\; I\; angle^2\}\{langle\; I\; angle\; ^2$ where $I$ is the received signal intensity and $langle\; I\; angle$ is the ensemble 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.Yeh, K. C. and C. H. Liu , "Radio wave scintillations in the ionosphere", Proc. IEEE, 70(4), 324-360, 1982.]

Real Time data

This parameter is displayed in real time by many institutions
* [http://gps.ece.cornell.edu/scintplot_aopr.html at Arecibo Observatory]
* [http://gps.ece.cornell.edu/scintplot.html at Cornell University]
* [http://200.241.80.42/gps/scintplot.html at INPE's Sao Luis Observatory in Brasil]

References