> > Then let's improve the infrastructure for communicating the best > > estimation of earth orientation parameters. Then in a world of > > ubiquitous computing anyone who wants to estimate the current > > rubber-second-time is free to evaluate the splines or polynomials > > (or whatever is used) and come up with output devices to display that. > > This is fine, but leaves open the question of when 9:00am is here in > Seattle. And why not transmit rubber-second-time as well, where > technically feasible (such as over the internet)?
The technical problem is that many timing systems aren't connected to the internet. They are at secure installations and they only have GPS almanac data at their disposal. And, no, they aren't likely to ever be on the internet. Any changes would have to be announced a long time in advance, and GPS almanac would have to be updated to include more information. The second technical problem is that the length of a second is implicitly encoded in the carrier for many of the longwave time distribution stations. 10MHz is at SI seconds. For rubber seconds, the broadcast would drift into adjacent bands reserved for other things. Also, GPS would have to remain in SI seconds. The error in GPS time translates directly to an error in position. Approximately 1m/ns of error (give of take a factor of 3). Rubber seconds would require that the rubber timescale be off by as much as .5s. So GPS has to remain in GPS time (UTC w/o leap seconds, basically). That means that the rubberness of the seconds would need to be broadcast in the datastream. Many GPS receivers put out a PPS. This needs to be in SI seconds, or a number of other applications break. However, if one defined UTC in terms of these rubber seconds, then the top of UTC second would be out of phase with this PPS. That breaks a lot of assumptiosn that rightly assume that PPS is phase aligned to top of second. The interval math in UTC that's hard today would be significantly harder with rubber seconds. But it is just software, eh? In short, it is an interestingly naive idea that was tried in the 1960's and failed when there were only dozens of high precision time users rather than the hundreds of thousands there are today. The earth does not define the second any more. At most, it defines the day and the year. > What is a good source of earth orientation parameters, btw? usno publishes several. Warner