[LEAPSECS] preprint about timekeeping for neutrino experiment

Richard B. Langley lang at unb.ca
Fri Sep 30 12:25:38 EDT 2011

Commercial civil dual-frequency receivers exist that do not need to
know the Y-code and that provide both L1 and L2 measurements and thus
removal of almost all of the ionospheric effect. Scan the GPS World
website for up-to-date information on GPS and GPS receivers.
-- Richard Langley

On 30-Sep-11, at 1:08 PM, Ian Batten wrote:


> On 30 Sep 2011, at 1532, Peter Vince wrote:


>> If they were using stand-alone caesium clocks, then yes - gravity and

>> altitude would make big difference. But they locked their clocks

>> to a

>> single common-view GPS satellite - surely, then, they were both

>> ticking at the same rate, and in sync?


> If you don't have access to the encrypted L2 frequency, what is the

> lower bound on clock precision for two separated stations observing

> some common-view satellites? I would have thought that propagation

> in the ionosphere would introduce enough uncertainty to make 60ns

> precision unlikely. It's difficult for the non-specialist to know

> which errors were reduced by the removal of SA and which errors are

> inherent to the technology, but one paper I found [1] says that use

> of the ionospheric model that is transmitted on L1 isn't anything

> like perfect:


>> Using the broadcast model under normal conditions removes about

>> half of the error (Fees and Stephens 1987) leaving a residual error

>> of around 60-90 nanoseconds during the day and 10 to 20 nanoseconds

>> at night (Knight and Rhoades 1987).


> I presume that some of these errors can be corrected if you know

> your location accurately, but what is the real state of the art?


> ian


> [1] Dana, P. H. Global Positioning System (GPS) time dissemination

> for real-time applications. Real-Time Systems 12, 9-40 (1997).




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