On 10/16/2011 01:59 AM, iov...@inwind.it wrote:
From mi...@flatsurface.com, Oct 16,2011, 01.50
At 05:46 PM 10/15/2011, Jim Palfreyman wrote...
http://nbcu.mo2do.net/s/18488/29?itemId=tag:dvice.com,2011://3.
83661&fullPageURL=/archives/2011/10/speedy-neutrino.php
Comments please!
What an annoying website.
Here's a better source, without all the unnecessary pagination and
pablum. http://arxiv.org/abs/1110.2685
Well, the title of the paper is "Times of Flight between a Source and a
Detector observed from a GPS satelite". From a single GPS satellite? Does this
make any sense?
Therein lies the prime weakness of that paper. It assumes that a single
GPS bird was used, while in fact many was being used. It is an expansion
of the statement:
The Cs4000 oscillator provides the reference frequency to the PolaRx2e
receiver, which is
able to time-tag its “One Pulse Per Second” output (1PPS) with respect to the
individual GPS
satellite observations.
However, more usefull information follows:
The latter are processed offline by using the CGGTTS format [19]. The
two systems feature a technology commonly used for high-accuracy time transfer
applications
[20]. They were calibrated by the Swiss Metrology Institute (METAS) [21] and
established a
permanent time link between two reference points (tCERN and tLNGS) of the
timing chains of
CERN and OPERA at the nanosecond level. This time link between CERN and OPERA
was
independently verified by the German Metrology Institute PTB
(Physikalisch-Technische
Bundesanstalt) [22] by taking data at CERN and LNGS with a portable
time-transfer device [23].
The difference between the time base of the CERN and OPERA PolaRx2e receivers
was
measured to be (2.3 ± 0.9) ns [22]. This correction was taken into account in
the application of
the time link.
(Both quotes is from page 9 in the OPERA paper)
For me, this reads out that they use common view for comparison of the
cesium clocks, in which case main part of the time sent from the
satelite would in fact cancel, and I also expect even more detailed
effects like ionspherics is being canceled, which was not even covered.
More details both of the processing actually done would assist, but I
assume it will cover many of the relative effects that GPS time
involves. However, this paper did not really provided a good insight
into that.
Cheers,
Magnus
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