[LEAPSECS] multiple UTCs
dennis.c.ferguson at gmail.com
Wed Jan 18 10:47:19 EST 2012
On 18 Jan, 2012, at 22:45 , Zefram wrote:
> Tom Van Baak wrote:
>> Anyone specifically using such a "tracking" version of UTC
>> wants to track earth angle, rather than coordinate with civil
>> time, so why not just let them use UT1?
> Because access to UT1 requires frequent network access. I'm thinking
> about atomic clocks that sit on a shelf for years, or which will be used
> in isolated locations. We've discussed the use cases (for longer lead
> time on leap seconds) in previous threads.
By the time UTC might stop the GPS-III satellites should be up, as should
much of the Beidou and Galileo constellations, and you should be able to get
real time UT1 predictions from your satellite receiver. The data from
GPS includes both an offset and a rate, and I've seen promises that it
should be accurate to the low 10's of microseconds.
>> What these users want is a get_ut1_timeofday(),
> This certainly ought to be available too. It's on my Perl module
> todo list.
> Even here there are multiple tradeoffs available, when realising UT1 by
> atomic clock plus predicted offset. If you retrieve Bulletin A weekly
> then you get a tracking precision on the order of 1 ms. It looks like
> if you examined the daily data, making much shorter-range projections,
> you could get a tracking precision more like 100 us. How network-reliant
> are you willing to be, and how close to UT1 do you need to be?
Is there a use case where you would have the tracking version of UTC
available without also having either a network connection or a satellite
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