Date: Wed, 2 Dec 2009 10:39:49 -0500 (EST)
From: Jun-Hui Zhao 
To: melvyn wright 
Cc: Peter Teuben 
Subject: Re: smauvplt.for

Hi Mel,
     I interleave my thoughts in your comments below.
     Jun-Hui

On Tue, 1 Dec 2009, melvyn wright wrote:

> Hi Jun-Hui,
>
> OK. thanks.  In principle, setting MAXWIN=98 should
> work, but I would not be suprised if some format and plotting
> tasks need to be modified to handle that.
      I agree with you. So far, I just implemented the smalod for
load the 4GHz x 2sb data into Miriad. I will look into calibration
and other programs in Miriad for handling SMA DB data.

>
> 2)  SMAMFCAL -- A separate question.
>
> What is the procedure that  SMA uses for
>  low SNR narrow bandpass determination.
>
> Is there an SMA recipe for deriving bandpass and gains
> for narrow spectral lines.
> Do you have a favored combination of  weight= xxx
> and  options=interpolate ?

      I don't have a particular procedure for a low S/N source.
But the default setup in SMAMFCAL with options=msmooth, i.e.
weight=2 and smooth=3,1,0.9,  gives a good solution
for most of the cases in handling SMA low S/N data.
weight=2 is always good for resolved planets and
high-angular-resolution data of QSOs with poor coherent long-baselines.

If one chooses the moving smooth (options=msmooth) to improve S/N, the
first parameter k in smooth (2k+1 is the number of channels involved in
the moving smooth window) is sensitive, which depends upon the actual
spectral resolution and S/N of each channel, i.e. for a very high spectral
resolution and poor S/N, one has to try a large k.

If one chooses orthogonal polynomial LSQ fitting to improve S/N,
I found polyfit=3 (cubic), default selection, appears to be good.
I haven't tested the high orders yet.

The brief descriptions in choosing these parameters are given in the
inline document along with SMAMFCAL.  In the SMA data reduction guide,
several cases in handling bandpass based on the procedures used by students,
postDr. and scientists in the past are given
http://www.cfa.harvard.edu/sma/miriad/manuals/SMAuguide/smauserhtml/node84.html
I just went back to read them and found that these cases are helpful but
didn't explain clearly why choose the particular setups. I would like to
improve the recipes based on experiements with a low S/N high angular
resolution observation at a high frequency.

                Jun-Hui



>
>
> cheers,
>
> Mel.
>