Ionosphere Monitoring and Prediction Center


France 43.6°N / 1.5°E / 214 m

S4 index (GPS CA)

σΦ index (GPS L1)

Trans-ionospheric radio signals of global navigation satellite systems (GNSS) like GPS, GLONASS, and GALILEO may suffer from rapid and intensive fluctuations of their amplitude and phase caused by small-scale irregularities of the ionospheric plasma. This phenomenon, which is called radio scintillation, can strongly disturb or disrupt the signal transmission. For technical applications it is useful to derive and to provide the well accepted S4 and σΦ indices describing the amplitude/ intensity and the phase fluctuation of a received signal, respectively. For that purpose the DLR operates several GNSS high-rate receivers in Europe providing the necessary receiver-satellite-link specific amplitude and phase information, cf.

Location and coordinates of Toulouse GNSS high-rate receiver operated within DLR’s Experimentation and Verification Network (EVnet)

Station locationAbbreviation in filenameEvnet IDLatitude / Longitude / Height
Toulouse/Francetomsto0143.6°N / 1.5°E / 214 m

Product Specification

External partiesThe GNSS receiver stations are hosted by Swedish Institute of Space Physics, SUPAERO Laboratory of Electronics and Physics, the Universidad de La Laguna, and the German Aerospace Center.
Data providersGNSS stations are part of DLR’s experimentation and verification network (EVnet)
Input data50 Hz GPS phase and amplitude measurements
Input sampling rates50 Hz
Reliability of data sourceCycle slip detection is conducted as preprocessing step for σΦ
Region of sensorsEurope
Spatial resolutionComputation of scintillation indices at the location of the GNSS stations
Temporal resolution1 min
Time informationUTC Time
Reference coordinate systemECEF coordinate system with WGS84 reference ellipsoid
AlgorithmsThe S4 index is the coefficient of variation of the squared amplitude. The σΦindex describes the standard deviation of the phase measurements.
File formatASCII
ASCII file format

1 > "GPS Week,"

2  > "GPS TOW - End of epoch," 

3  > "GPS PRN"

4  > S4 based on L1/CA

5 > σΦ in radian

Terms and Conditions of Use

In any case you plan to use IMPC material please consider the IMPC terms and conditions of use.