Hi John,
On 2018-03-19 01:12 AM, John Sauter wrote:
On Sat, 2018-03-17 at 22:52 +0000, Michael.Deckers via LEAPSECS wrote:
So, the likely future is that the limit on |UT1 - UTC| will be
dropped,
leap seconds will no longer be applied, and UTC will become a
fixed
translate of TAI (so that dissemination of TAI - UTC becomes
unnecessary).
I think you are reading too much into the recommendation. There is no
mention made of letting UT1 - UTC become unbounded, but only to
"consider the present limitation on the maximum magnitude of UT1 - UTC"
and to "improve further the accuracy of the prediction of UT1 - UTC".
Allowing UT1 - UTC to increase from plus or minus 0.9 seconds to plus
or minus 1.9 seconds would require changes in the protocols used to
disseminate UT1 - UTC, but it is definitely possible. Improving the
accuracy of the prediction of UT1 - UTC is a good idea but may not be
possible, since predicting the rotation of the Earth is like predicting
the weather.
In my opinion, the intended future is that the frequency of Bulletin C
is decreased from twice a year to once a year, or once every two years.
John Sauter ([email protected])
I'm afraid that phrase "consider the present limitation on the maximum
magnitude of UT1 - UTC" is a subtle rhetorical loophole to accommodate
those with the idea of eliminating Leap Seconds without actually using
those words. But I don't believe there is any consensus or plan to
change UTC, Leap Seconds, or the contents of Bulletins A, B, C, or D, at
least not yet.
There would be many consequences to allowing UT1-UTC to grow. It clearly
*breaks* the radio time broadcast protocols because their DUT1 variable
size won't accommodate larger values and there is little or no room in
the protocol to extend its range. Radio broadcasts have been operating
for decades and there is a large number of applications that rely on it,
including the so-called "atomic clock" industry, and its used as an
alternate time source as backup for GPS and NTP. It seems unlikely to me
a disruption of those services would be seen as acceptable.
Another consequence of eliminating Leap Seconds or allowing UT1-UTC to
grow would be its impact on the procedures used by BIPM and IERS in
maintaining TAI and UTC. There is a very large and complex
infrastructure of cooperating organizations, observation technologies,
and established data processing procedures that leads to UTC and DUT1,
amongst other things. The procedures for maintaining the reference
clocks and the EOP are complex and sophisticated, relying on software
development that stretches back decades, much of it written in Fortran.
These are vast and complex software packages, with each institution
running systems appropriate to their technology and responsibility to
each other and the system. Any substantial change to UTC, DUT1, or
UT1-UTC could have unknown impact on any part of those systems and their
interaction with each other.
While there have been many opinions advanced why Leap Seconds should be
retained I don't believe any formal analysis of the impact of a change
on the procedures and software used by BIPM, IERS, and contributing
organizations has been undertaken. Its not clear to me such an analysis
is even feasible but it seems pretty clear it would be a difficult. How
would this be funded? If a substantial change were made, how long would
it take to make appropriate modifications to the software and
procedures? Any change would not only effect the internal calculations
but also the database schemas and interchange formats and protocols used
to exchange information amongst the many contributing systems and
organizations. How long would it take to make these changes and verify
the results? Any bug anywhere could upset the whole system. I'm not a
expert in this but it appears to me the scale and complexity is very
significant and a major change would be very expansive and take years to
implement.
While the idea of eliminating Leap Seconds seems simple on the surface
it has important ramifications that could upset any number of systems
including the BIPM and IERS themselves. SDO's are inherently
conservative because reverse compatibility and continuity with existing
practice must always be honored. It is very difficult to make changes to
any widely adopted standard, and UTC must be one of the most widely used
standards of all time, except maybe the Gregorian calendar itself.
My opinion about Leap Seconds has changed from "what a neat solution!"
to "its probably impossible to change it because its just way too
expensive and dangerous". I think we're going to have to find a
different solution to the UTC (with Leap Seconds) v.s. Gregorian
calendar/compute timekeeping dilemma.
-Brooks
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