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[IGSSTATION-3163]: C2 data versus P2 data

IGS Station Mail          29 Jun 05:43:55 PDT 2009      Message Number 3163

Author: Jim Ray

Dear Station Colleagues,

There seems to be some confusion about the relative
importance of collecting and reporting observational
data for codeless L2P(Y) = P2 versus the new open signal
available on IIR-M satellites L2C = C2.  (Recall that
in the RINEX 2.?? format, the respective carrier phase
observable, L2, corresponds to whichever code signal is
tracked by the receiver.)

From the perspective of operational IGS products, the
P2 data is *required*.  The IGS products follows the
conventions of the GPS operational system as described in
IS-GPS-200, in particular to realize GPS Time, which is
based purely on P1 and P2 observations.  As we do not
yet track or apply code bias offsets for the hardware
delay differences between P2 and C2, it is not possible
to mix these code observables without degrading certain
IGS products (mainly the clocks and phase ambiguity fixing).

In addition, current GPS receivers do not follow a uniform
policy on the relative phases of the C2 and P2 signals so
use of mixed phases is problematic, especially in double-
differenced solutions.  This dilemma has been addressed in
updates of the RINEX standards (to versions 2.12 and 3.01)
which eliminate this ambiguity; see under "File Formats"
at  But these updates have not yet been

Therefore station operators are kindly asked to ensure that
their stations always report P2 observations.  Ideally, any
C2-tracking receivers should be enabled to report both P2
and C2.  If this is not possible, then please disable the
C2 option in favor of P2.  The C2 data are needed for study
of its proper utilization, determination of the code biases,
and other research interests.

Many thanks,