Date: Thu, 24 Apr 2003 12:00:04 +0200
From: Jean-Paul Berthias <jean-paul.berthias@cnes.fr>
To: Pascal Willis <Pascal.R.Willis@jpl.nasa.gov>
Cc: Alfred Piuzzi <Alfred.Piuzzi@cnes.fr>,
    Carey Noll <carey.noll@gsfc.nasa.gov>,
    Vincent Patrick <Patrick.Vincent@cnes.fr>,
    Martine Feissel <feissel@ensg.ign.fr>,
    Sabine HOURY <Sabine.Houry@cnes.fr>,
    "John C. Ries" <ries@csr.utexas.edu>,
    Nikita Zelensky <nzelensk@geodesy.gsfc.nasa.gov>,
    Bruce J Haines <bjh@cobra.jpl.nasa.gov>
Subject: Re: duplicated DORIS/ENVISAT data - and other DORIS satellites

Hello Pascal,

In your mail you talk about duplicated data. However, this is not the case: one
measurement has been performed on channel 1, the other one on channel 2. Most of
the time, when tracking the same beacon, both channels give the same result, and
we indicate this by using 3 as channel indicator in the file. However, there are
times when the two channels do not give the same result. Often this can be
linked to the fact that one of them at least is in error, and we have many
filters to remove those data. 

But there are also cases when we cannot discriminate between the measurements of
the two channels. In this case they both end up on the delivery file. This is
normal, as both measurements are valid in our sense.

The fact that you see it more on ENVISAT is certainly related to the screening
procedure which is not as extensive for this type of receiver. The filters on
simultaneous but different measurements were introduced after the "problem" was
discovered on Jason, and they might not work as well on ENVISAT which is a
receiver of a different technology. We will look into this.

Jean-Paul