Date: Mon, 29 Jun 2009 08:43:34 -0400 From: "Jim.Ray" Subject: [IGSSTATION-3163]: C2 data versus P2 data To: IGSStation Reply-to: jim.ray@noaa.gov Message-id: <4A48B6F6.2040305@noaa.gov> Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit User-Agent: Thunderbird 2.0.0.21 (Windows/20090302) Sender: owner-igsstation Precedence: bulk ****************************************************************************** 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 acc.igs.org. But these updates have not yet been implemented. 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, --Jim