[ntp:questions] Accuracy of NTP - Advice Needed

unruh unruh at invalid.ca
Sun Dec 25 00:44:11 UTC 2011


On 2011-12-24, jimp at specsol.spam.sux.com <jimp at specsol.spam.sux.com> wrote:
> unruh <unruh at invalid.ca> wrote:
>> On 2011-12-24, jimp at specsol.spam.sux.com <jimp at specsol.spam.sux.com> wrote:
>>> John Hasler <jhasler at newsguy.com> wrote:
>>>> unruh writes:
>>>>> They require ns accuracy in the timing and m accuracy in the
>>>>> distance. And the timing is not simply gps ( although they could have
>>>>> gotten that wrong) but then that timing has to be brought down into
>>>>> the mine a km or so below ground and horizontally and that also has to
>>>>> be surveyed for the distance.
>>>> 
>>>> The NOvA detector is not in a mine so it should be possible to site the
>>>> GPS receiver directly above it and drop a cable straight down.  The same
>>>> should be possible at the Fermi end.  You could set up both timing
>>>> chains at Fermilab (using indentical components including cable lengths
>>>> if you want to be fanatical), calibrate them against each other for
>>>> delay from antenna to output, and then pack one up and ship it up north
>>>> (of course there may be good reasons not to do it this way).  The
>>>> surveying should be easier than in Europe: there's no mountain range in
>>>> the way.
>>>
>>> That's the common misconception of the geology.
>>>
>>> Basically the lab is in a tunnel in the side of a mountain and is no more
>>> a km underground than is the lobby of a 20 story hotel 20 stories
>>> underground.
>> 
>> But it is a few km inside the mountain. Is a mine in Denver not
>> underground just because Denver is 1600 m above sea level? 
>
> The issue is that most people don't seem to be able to understand how
> to get an accurate position of a location that is vertically under a km
> or so of dirt, yet horizontally feet from wide open sky and GPS signals.

A few feet? I assume that was a misprint for a few km.

>
>
>



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