[LEAPSECS] preprint about timekeeping for neutrino experiment

[Richard B. Langley]

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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| Richard B. Langley                            E-mail:  

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