[LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Hi Tony,

Getting the solar time currently means looking at your watch or the upper right-hand corner of the monitor. Would anybody else’s summary of the notion of “easy access” include phrases like: “8.23 bits two’s complement fixed point” or “NMEA sentences that contain anything like UT1 or DUT1 or delta-T”?

I have been presuming tenth-second DUT1 values are slated for demolition with leap seconds. Can anybody confirm differently? I applaud the goal of ensuring understanding and usage of whatever infrastructure will exist. Few systems currently use DUT1. One of the issues is that many more will need to start.

UT1 itself is only known retroactively. If your use of the word “stunt” wasn’t a typo, it seems to me that NIST rather needs robust and easy-to-use infrastructure. I was never able to get reliable access to the UT1 NTP server, and generally, our group doesn’t build reliance on third-party NTP pools into our operational systems.

We should all welcome GNSS support for access to UT1 (or a coherent variation known in advance), but as you suggest this will require new infrastructure and standards. Perhaps I’m off the mark, but that most definitely doesn’t imply anybody else has yet found the mark themselves.

Rob


Seaman, Robert Lewis - (rseaman) <rseaman at arizona.edu> wrote:

> The plan, rather, is to cease easy access to solar time.

The resolution says the GCPM

: encourages the BIPM to work with relevant organizations to identify the
: need for updates in the different services that disseminate the value of
: the difference (UT1-UTC) and to ensure the correct understanding and use
: of the new maximum value.

So I think your summary is a bit off the mark.

I guess the ITU is going to revise TF.460 to allow larger values of DUT1
in time signals, and MSF etc. will accommodate the change too. (Do any of
the national broadcast signals actually follow the ITU spec?)

GPS L5 signals provide UT1 as an 8.23 bits two's complement fixed point
difference from GPS time. This is enough to cope with the changes in the
CGPM resolution. See IS-GPS-705 p. 87 at https://www.gps.gov/technical/icwg/

I have not been able to find any specs for NMEA sentences that contain
anything like UT1 or DUT1 or delta-T, but I expect they will be created
before too long, as more GPS receivers support L5 signals.

And there are other sources of UT1 like NIST's stunt NTP servers.

--
Tony Finch  <dot at dotat.at>  https://dotat.at/

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