[daip] estimate the coherence time in AIPS (coher)

[Leonia Kogan]

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>From zshen at vsop.isas.ac.jp Mon Apr  8 18:27 MDT 2002
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Date: Tue, 9 Apr 2002 09:27:39 +0900
To: Leonia Kogan <lkogan at zia.aoc.NRAO.EDU>
From: "Z.-Q. Shen" <zshen at vsop.isas.ac.jp>
Subject: Re: [daip] estimate the coherence time in AIPS (coher)
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Status: RO

Hi Leonia,

Thanks for the explanation to COHER. This is helpful.

May I ask you another question in AIPS? This is about the accuracy of the
printout data. For example, UVPRT can only print out amplitude as small
as 0.001. In some cases, this is not enough. For example, the correlation
coefficients are usually much smaller than 0.001. I am sure the real data
won't lose the accuracy. This is only about the format of the printout. Do
you happen to know about this problem?

You may direct this question to anyone who can help. Thanks.

Cheers,
Zhiqiang

> Hi Zhiqiang,
>
>The coherence time may not depend on the ratio of scalar and vector
>averaging aparm(3), if
>
>1. The number of visibilities for the given baseline and for the selected
>   source is less than 6. In this case the coherence time will be equal the
>   scan time.
>
>2. You have big noise, and so when you select aparm(2)=5 you cut off too
>   many points, and the rest numper of point can be less than 6 or even 2.
>
>   Try aparm(2) =100 taking all point into account and look if the coherence
>   time depends on aparm(3).
>
>You can examine your data with UVPRT selecting only one baseline for
>simplicity.
>
>Leonia
>
>
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>From: "Z.-Q. Shen" <zshen at vsop.isas.ac.jp>
>Subject: [daip] estimate the coherence time in AIPS (coher)
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>Date: Wed, 3 Apr 2002 16:54:48 +0900
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>To Whom it may concern,
>
>I tried to estimate the coherence time using AIPS task COHER.
>I set the parameters as follows:
>
>aparm(1)=3 (calibrator scan length)
>aparm(2)=5 ------(I'm quite confused with this cutoff)
>aparm(3)=0.9
>aparm(4)=0 (for a detailed debug)
>aparm(5)=0 (only use one 3 min scan)
>aparm(6)=1 (FRING done earlier)
>aparm(7)=0
>aparm(8)=1 (for 43 GHz).
>
>But I found the results are only affected by the selection of
>aparm(8) and could be very different when aparm(8) are
>picked up differently.  No matter what value I chose for
>aparm(3), it always gave the same results (if aparm(8) is
>not changed). This seems wrong to me.
>
>I'd like to have your suggestions.
>
>Regards,
>Zhiqiang Shen
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