When reading a RINEX observation file, you will find that the header contains a series of observation codes as highlighted in the example below.



Observation Codes
Each row of observation codes is associated with one GNSS constellation.
G: GPS
E: Galileo
S: SBAS
R: GLONASS
C: BeiDou
J: QZSS
I: NavIC (IRNSS)

The first character of each observation code denotes the type of measurement and can take one of the following 4 values.
C: Pseudorange
L: Carrier Phase
D: Doppler
S: Signal Strength

The second two characters of the observation code provide the specific GNSS signal from which the observation was obtained. The following table provides the last two characters of the RINEX observation code for each GNSS signal.

Table1: RINEX Observation Codes

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