[time-nuts] Precise Time transfer and relative position over a short baseline

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Apr 11 16:48:36 EDT 2016


Its an intensity interferometer, there are no fringes.
The SNR is such that 	several hours of integration are required.
If this method is at all feasible each telescope would likely need a hydrogen 
maser or equivalent for such a technique to be useful.
More frequent phase comparisons allow drift to be tracked without requiring 
such an expensive flywheel.

Bruce

On Monday, April 11, 2016 01:26:52 PM djl wrote:
> I have not followed this closely. Why not use the data itself? The
> theoretical pattern for the telescope pair can be calculated. Even
> though the signals are not i.i.d, from phototubes, the data can be slid
> along and the delay pattern established and compared to the theoretical
> pattern?  Timing is then important for "pointing". Certainly the
> compared signals can be used in any case to correct timestamps.
> Sorry if this has been mentioned before, in that case, great minds run
> in the same track :-) :-)
> Don
> 
> On 2016-04-11 00:58, Ilia Platone wrote:
> > As alternative to independent clocks and single photon tagging, we
> > considered to use TDCs: a possible solution would be radio cross links
> > between the telescopes that drive the start/stop signals of the TDCs,
> > then we'd tag only the lapses between photon detection from each
> > telescope. In this way a single clock would be used on a receiving and
> > recording station.
> > 
> > Is this a good solution?
> > Regards,
> > Ilia.
> > 
> > Il 11/04/2016 07:00, Bruce Griffiths ha scritto:
> >> There is a proposal to use multiple light bucket style optical
> >> telescopes to do Intensity stellar Interferometry over short baselines
> >> (up to perhaps 1km  or so) by using independent clocks to time tag
> >> photon  arrivals. store the time tags and process the data off line.
> >> Depending on the time tag resolution there is a need to measure the
> >> time differences between the independent clocks to an accuracy in the
> >> 1ns to 100ps range. Is there a better way of doing this other than
> >> using geodetic grade GPS receivers capable of GPS carrier phase
> >> measurements?Since the local clock flywheel oscillators will need to
> >> not deviate by more than 100ps or so over the several minutes required
> >> to perform the carrier phase averaging what sort of clock will be
> >> suitable apart from a good rubidium standard with a cleanup
> >> oscillator?
> >> NB Running fibres or coax between the telescopes isnt an option.
> >> 
> >> The relative positions of the telescopes has to be known to within a
> >> cm or so for this to work.
> >> Bruce
> >> 
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