[Difx-users] integration time
Hagatiana Andrianomena
handrianomena at ska.ac.za
Thu May 18 05:46:42 EDT 2017
Hi Mark,
I have used the clock values from SFXC for example:
# def BD;
# clock_early= 2017y059d13h00m00s : 216.030 usec : 2017y059d14h30m00s
: -2.20e-07 usec/sec;
# enddef;
My understanding is that DiFX expect the rates in usec/sec which is the
case here, so I have used
that value in the .v2d file, as for the clockEpoch I used
2017y059d14h30m00s here (converted to mjd).
For sure I am having issues with some values I am using, reason I do not
find fringes at some baselines.
With regards to EOP, I used the values from NASA.
Thanks for your reply Richard.
Regards,
Sam
On Thu, May 18, 2017 at 1:08 AM, Richard Dodson <richard.dodson at uwa.edu.au>
wrote:
> Hi
>
> I agree with all the above that the most likely source of a high delay
> offset is either incorrect position for the antenna in VEX, or a
> mis-translated value for the initial delay offset. If there are no fringes
> to any station it is unlikely to be antenna positions (as one being wrong
> is possible, but some of the ones you are using are very well established),
> so I put my money on Mark's suggestion. But another possible thing to
> check, if the above are correct, are the Earth Orientation Parameters. If
> these are wrong you essentially have introduced an offset in all the
> antenna positions.
>
> happy hunting!
> Richard
>
> On Thu, May 18, 2017 at 12:33 AM, Hagatiana Andrianomena <
> handrianomena at ska.ac.za> wrote:
>
>> Hi Mark,
>>
>> Many thanks for that very useful information.
>> I will double-check the $CLOCK values I was
>> using.
>>
>> Cheers,
>> Sam
>>
>> On Wed, May 17, 2017 at 5:02 PM, Mark Kettenis <kettenis at jive.eu> wrote:
>>
>>> > From: Hagatiana Andrianomena <handrianomena at ska.ac.za>
>>> > Date: Mon, 15 May 2017 08:51:59 +0200
>>>
>>> Sam,
>>>
>>> Note that if you are using $CLOCK parameters from a correlation with
>>> SFXC, the rates may not be specified in a form that DiFX expects. If
>>> the "unit" isn't specified, SFXC will interpret the rate as usec/sec,
>>> whereas DiFX will interpret the rate as sec/sec.
>>>
>>> Cheers,
>>>
>>> Mark
>>>
>>> > Hi Cormac,
>>> >
>>> > Please see attached the vex. I am interested in EF-YS-NK-HH-O8.
>>> >
>>> > cheers,
>>> > Sam
>>> >
>>> > On Mon, May 15, 2017 at 7:45 AM, Cormac Reynolds
>>> <cormac.reynolds at csiro.au>
>>> > wrote:
>>> >
>>> > > hi Sam,
>>> > >
>>> > > just following up on Adam's point. The most common cause of a very
>>> high
>>> > > residual fringe rate (as yours appears to be) in an otherwise
>>> functioning
>>> > > array is an error in the station position(s). If you send the vex
>>> file you
>>> > > used, and the stations you are interested in, it should be
>>> straightforward
>>> > > to say if that is a likely cause or not.
>>> > >
>>> > > cheers,
>>> > > Cormac.
>>> > >
>>> > > On 13/05/17 19:57, Hagatiana Andrianomena wrote:
>>> > >
>>> > >> Hi Adam,
>>> > >>
>>> > >> Many thanks for your explanations.
>>> > >>
>>> > >> Cheers,
>>> > >> Sam
>>> > >>
>>> > >> On Sat, May 13, 2017 at 1:37 PM, Adam Deller <
>>> adeller at astro.swin.edu.au
>>> > >> <mailto:adeller at astro.swin.edu.au>> wrote:
>>> > >>
>>> > >> Hi Sam,
>>> > >>
>>> > >> Integration time will affect the maximum fringe rate you are
>>> > >> sensitive to. Shorter integrations = higher fringe rate before
>>> you
>>> > >> lose signal due to decorrelation. But normally this is not a
>>> > >> limitation. I would be fairly surprised if a 1 second
>>> integration
>>> > >> time was a problem (unless there is an issue with the observing
>>> > >> setup).
>>> > >>
>>> > >> Spectral resolution will affect the maximum residual delay you
>>> are
>>> > >> sensitive too. Finer spectral resolution = larger delay before
>>> you
>>> > >> lose signal due to decorrelation.
>>> > >>
>>> > >> These are not DiFX-specific things, but general to radio
>>> > >> interferometers / correlators. To know what values are
>>> reasonable,
>>> > >> you need to know your instrument and what the expected residual
>>> > >> fringe rate and delay are.
>>> > >>
>>> > >> Cheers,
>>> > >> Adam
>>> > >>
>>> > >> On 12 May 2017 at 23:59, Hagatiana Andrianomena
>>> > >> <handrianomena at ska.ac.za <mailto:handrianomena at ska.ac.za>>
>>> wrote:
>>> > >>
>>> > >> Hi DiFX users,
>>> > >>
>>> > >> I got a question regarding the integration time in the
>>> setup:
>>> > >> SETUP default
>>> > >> {
>>> > >> tInt = 1.000000
>>> > >> fftSpecRes = 0.12500000
>>> > >> specRes = 0.12500000
>>> > >> doPolar = True
>>> > >> maxNSBetweenACAvg = 2000000
>>> > >> }
>>> > >>
>>> > >> I got this default setup by running oms2v2d using the .oms
>>> file
>>> > >> from the experiment. When running the difx I got no fringe
>>> but
>>> > >> from changing the tInt to
>>> > >> 0.08 and both fftSpecRes and specRes the result seems to
>>> suggest
>>> > >> I got fringe (see plot attached).
>>> > >>
>>> > >> I am not quite sure whether it is a naive question but I
>>> wonder
>>> > >> if there is a simple rule of thumb to get the right values
>>> of
>>> > >> those parameters in order to get fringe. I do not have much
>>> > >> experience with DiFX I must say though.
>>> > >>
>>> > >> Regards,
>>> > >> Sam
>>> > >>
>>> > >> _______________________________________________
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>>> > >>
>>> > >>
>>> > >>
>>> > >>
>>> > >> --
>>> > >> !=============================================================!
>>> > >> Dr. Adam Deller
>>> > >> ARC Future Fellow, Senior Lecturer
>>> > >> Centre for Astrophysics & Supercomputing
>>> > >> Swinburne University of Technology
>>> > >> John St, Hawthorn VIC 3122 Australia
>>> > >> phone: +61 3 9214 5307 <tel:+61%203%209214%205307>
>>> > >> fax: +61 3 9214 8797 <tel:+61%203%209214%208797>
>>> > >>
>>> > >> office days (usually): Mon-Thu
>>> > >> !=============================================================!
>>> > >>
>>> > >>
>>> > >>
>>> > >>
>>> > >> _______________________________________________
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>>
>
>
> --
> -------------------------
> Dr Richard Dodson,
> International Centre for Radio Astronomy Research
> University of Western Australia
> P: +8 6488 7842 E: richard.dodson at icrar.org
>
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