[daip] Re: comments on Phase Referencing: A Short Guide

[Leonia Kogan]

Ed,

You wrote:

>to finish an
>AIPS task which is similar to DELZN, but works on phase
>rather than delay.  This will be more useful to the average
>phase referencing radio astronomer.  DELZN is a pretty
>specialized program and is not really too useful for most
>normal applications.  You have to measure group delays which most
>astronomers don't understand and normally measure.

This statement is not correct. Both DELZN and ATMCA have both options
group delay and phase. The difference DELZN and ATMCA is not here!!!!

DELZN requires the observation of many calibrators at large range of
the elevations. DELZN fits the polynomials to the the zenith atmosphere
as a function of time for each antenna.
Having known the zenith atmosphere as a function of time, DELZN
recalculates it to the target source elevation using the given mapping
function.
So, DELZN does not pay attention to the possible azimuth dependence of the atmosphere and does not pay attention on the local 'features' of the atmosphere.

ATMCA requires the observation of several calibrators at the vicinity of the 
target source(s) and fits the atmosphere delay at the vicinity of the target 
source as the following linear combination of the two sky 
coordinates and time:
                

    DELAY = PH0 + SLRA*DRA + SLDEC*DDEC + SLT*DT
         where   PHO is delay at the point DRA=0, DDEC=0, DT=0
                 SLRA  is  slope of the delay at RA direction
                 SLDEC is slope of the delay at DEC direction
                 SLT   is slope of the delay at time direction
                 DRA is deviation of the reference point at RA
                 DDEC is deviation of the reference point at DEC
                 DT is deviation of the reference point at time
                 The deviations are considered relatively the target
                 (reference) source in sky and in time.

ATMCA can solve the problem of the local 'features' of the atmosphere!!!!!

Leonia


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>From efomalon at nrao.edu Fri May 28 08:22 MDT 2004
Date: Fri, 28 May 2004 10:22:19 -0400
From: Ed Fomalont <efomalon at nrao.edu>
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To: Amy Mioduszewski <amiodusz at zia.aoc.nrao.edu>
CC: Leonia Kogan <lkogan at zia.aoc.nrao.edu>, gtaylor <gtaylor at zia.aoc.nrao.edu>
Subject: Re: comments on Phase Referencing: A Short Guide
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Hi Amy,

    I've just arrived back in town.

    As you may know, I am working with Kogan to finish an
AIPS task which is similar to DELZN, but works on phase
rather than delay.  This will be more useful to the average
phase referencing radio astronomer.  DELZN is a pretty
specialized program and is not really too useful for most
normal applications.  You have to measure group delays which most
astronomers don't understand and normally measure.

    Here is what I think we should do.  First, apologies for
not sending the draft to you.  I should have.  Second, I think
both DELZN and ATMCO (the phase version) drafts should be
coordinated in some way since they both use observations of
more than one calibrator to obtain better results.  The explain
files for each also need information to help in the optimum
observing, as well as reduction strategies.  I am waiting to
finish my phase reference draft in order to incorporate these
two tasks.

    I suggest that when I am at the AOC for ten days which overlap
the summer school, we (a more general we than just you and I) should
try to finalize these write-ups and the tasks.

    Cheers,  Ed





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