[daip] Re: Question about DELZN

[Richard Dodson]

Leonid,

  I am, we are, trying to extend DELZN into new modes of use. Please
be patient.

 You said many messages ago:

> Lets note that VAL_IANT -VAL_RANT are the values picked up from the SN
> table as a function of time.

   I.e. which was exactly as I expected. I.e. that Value in the SN
table is the difference. Now you have made a little clearer what you
meant. I.e. (if I have understood your latest mail) that VAL is that
which is found in the SN table. Not VAL_i-VAL_ref.

   As you have hinted there have been many people unable to interpret
the plots. I am just more stubborn and demanding than most, for which
I apologize -- but I am unable to change and will continue to ask
questions.

  I would be able to understand better if I could see the plots of the
calculated atmosphere -- for a dataset we are sure works (i.e. the
test one you have been using) -- under various changes of parameters.
If it is too much work to make the plots I asked for could I run the
tests myself? I would be happy to and it would be less work for you.

 So. Are we making progress? I believe so. You have demonstrated to
yourself that the VLBA can solve for the atmosphere on a single source
tracked for a day, which is exactly what we need for the VERA case. We
have a VERA experiment on the 22nd of March and we plan to combine the
usual operation with a more normal DELZN strategy. Then we will be
able to compare the results. This is why we need to sort out these
questions.

 Perhaps it would be useful to list the outstanding questions?

 I would like to see the similar plot that you sent, but with a lower
order polynomial fitted. I know I am asking for more work -- but it
should be quick to run. Alternatively I can run these tests on the
test data myself. This I think would be the more profitable.

>From your mail of March 3rd.
-----------------------------
>>If one alters the number
>>of parameters fitted for ATM one gets wildly different answers.

>Of cource. You can fit the linear polynomial to these data with
different >parameters.
>The fitting will be a little bit worse but still reasonable. So your
following >statement isong.
-----------------------------

With the clearer explanation of what the DELZN plots of the Zenith
delay are really showing I have a better understanding. However I
still would like to see the linear polynomial fit to the data file.


> I have looked at your plots and see that the elevation differences are
> less than 15 degrees. May be it is too small.

  Why is the elevation difference important to the solutions? Or do
you mean that the atmosphere over the antennae will be the same
therefore solutions derived from the differences will be degenerate?

  For the code: For the phase referenced experiment (I.e. VERA image
of the target and the similar program on Sgr A). Do you agree that a
new mapping function is required? Really we need to also fit for
position at the same time, but that can be added later once we are
sure that the new mapping function is really required.

                Richard