IGS positioning on phase aligment for GPS L2 data

The members of the Infrastructure Committee have prepared the following statement which was distributed to the receiver manufacturers late in 2010 by the IGS Governing Board:

The IGS urges all GNSS receiver manufacturers to adopt a

standardized phase alignment practice for all GNSS signal

modulations common to a given carrier frequency, in order

to minimize user confusion and to remain consistent with

the long standing and universal practice established for the

GPS L1C/A and L1P(Y) signals.

The issue of phase changes associated with some GPS flex

power modes is a much less pressing concern considering GPS

assurances not to exercise such modes till after 2020 and

considering that the GPS navigation message will be updated

to flag such events when they occur.

We have come to this consensus at the IGS to speak with one voice and to send a clear message that the manufacturers need to provide phase measurements on all frequencies that are aligned so that users of the measurements do not have to second guess what they are using.

It is hoped that this statement and that the IGS relationship within the RTCM sc104 will help to resolve this issue for the benefit of all dual frequency GNSS users. In the end we anticipate that either an agreement will be reached for all manufacturers to provide aligned phases on L2 as they already do for L1 and to provide the amount they align them by so that the original measurement can be reconstructed should anyone need to.

To provide the alignment information the RINEX format has had a compulsory line added to the header as follows:

" The applied corrections are to be reported in a new SYS / PHASE SHIFT header record to allow the reconstruction of the original values, if needed. The uncorrected group of observations is not reported in the SYS / PHASE SHIFT records.

In case the reported phase correction of an observation type does not affect all satellites of the same system, the header record allows to also indicate a list of the respective satellites.

The SYS / PHASE SHIFT header record is mandatory. If the file does not contain any observation pairs affected by phase shifts or if (exceptionally) the applied corrections are not known, the observation code field and the rest of the SYS / PHASE SHIFT header record field of the respective satellite system(s) are left blank.

This has been added to the latest RINEX format versions:

Rinex 2.12

Rinex 3.01

… more on those versions in an upcoming post!! :)

Best regards!

Nacho

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