[IGSMAIL-4379]: data smoothing in IGS RINEX

[Angelyn W. Moore]

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IGS Electronic Mail      15 May 16:52:28 PDT 2003      Message Number 4379
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Author: Angelyn Moore

Dear IGS Colleagues,

You probably noticed quite a few messages from station operators
regarding data smoothing earlier this spring.  This message is
intended to explain further and make a general announcement
about it.

The IGS CB was made aware that Ashtech RINEX data, when the
available Ashtech smoothing corrections are applied, may contain
incorrect P1 and P2 values.  One detectable manifestation of this
is that the L1 multipath figure has a drift with respect to time,
within a given satellite arc.

We attempted to detect which IGS sites may be applying this smoothing
by looking at the L1 multipath.  In most cases the answer was clearly
'yes' or 'no' but some sites' data was inconclusive.  Due to this
uncertainty as well as an incomplete understanding of what the impact
of the smoothing corrections was, we began by contacting the operators
of Ashtech sites identified as probably smoothing.  We asked that
they check whether it was true and if possible, set smoothing to off.

As usual, many site operators were quickly responsive, and confirmed
that smoothing had been set 'on' but would afterward be set to 'off'.
It's now clear that this action did have a noticeable effect and
the drift of L1 with respect to time was removed.

Some operators of Ashtech sites might not have received the original
message, due to the L1 slope tests being initially inconclusive.
Therefore, this message now serves as a general request to operators,
and a reminder to those who could not quickly respond to earlier
emails.  Procedures for turning off smoothing appear below.

Please note that the -general- question of whether data should or
may be smoothed is separate from this issue, which is specific to
Ashtech receivers.  If you have any opinions or evidence on
the general question of smoothing, please forward them to me or
igscb at igscb.jpl.nasa.gov for consideration in upcoming revised
station operating guidelines.

Otherwise, if you operate an Ashtech receiver, please consider turning
off smoothing in the RINEX creation step as follows:

- For teqc: not using the +smooth option.  teqc defaults to not applying
the smoothing, but if you received teqc from Ashtech, it may have
+smooth turned on.

- For ASRINEXO: set "L2 FIT / PR SMOOTH FLAG" to 0

- For Micro-Z's with firmware > CN00: avoid "Data Mode 7" with the
smoothing option.  In this case the unsmoothed data is not saved for
possible use at the RINEX conversion step.

You're invited to let me know of any of the following (if you have
not already):

- If you cannot make this change at your station

- If you use another RINEX translator and cannot identify how smoothing
would be switched off.

Finally, please feel free to let me know if you have any other questions!

Best regards,
Angie
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Angelyn W. Moore, Ph.D.            Deputy Director, IGS Central Bureau
  JPL/Caltech                               Angelyn.W.Moore at jpl.nasa.gov
  4800 Oak Grove Dr. MS 238-540                   voice: +1 818 354 5434
  Pasadena CA 91109 USA  http://igscb.jpl.nasa.gov  fax: +1 818 393 6686