[mmaimcal]Comment in ALMA memo 489

[MORITA, Koh-Ichiro]

Dear Mark,

Thank you for your critical comments on our memo, which
argues some problems in the memo regarding imaging
simulations.  Here is our brief answers to your comments.

Take care,
Koh-Ichiro

===========================================================
2004-03-29: Counter-comments on ALMA memo 489

     Koh-Ichiro Morita and Takahiro Tsutsumi
                      NAOJ


1. Use of OTF only for ACA+SD and not for ALMA+SD case
Mosaic:
The 19-field pointing observations is performed in hexagonal
pattern with a spacing between pointings, of a half beam size of
the 12-m antenna for both SD and interferometric observations
with ALMA 64 element array and ACA interferometric observations.
(i.e. the pointing positions are the same for the two mosaics).

OTF:
The OTF is performed twice as large as the mosaic field
and sampling is every 1/3 beam.

For the 64-element array, we assume that the total power data
is taken simultaneously with an interferometric observation,
thus mapping wide region with OTF is not considered.


2. Effect of a guard band (Blank sky data)
 >From the experience of the simulation using SDE by Morita,
need of the guard band concerns both homogenous array and
heterogeneous array.  We guess this is a specific problem to the
joint deconvolution using MEM.  It is not clear that the same
problem applies for the cases using CLEAN.

If we need more mapping area for the 64-element array, we need
more observing time and it is a disadvantage to the homogeneous
array, isn't it?


3. A problem on declination range
It is possible that the simulated observations for the homogeneous
array is the worst case. However, the configuration of the ALMA
64-array used in our simulations is the most compact one. As the
64-array configurations will be continuously reconfigured and not
all projects for wide field imagings will not be scheduled for
this compact configuration, the uv gap in this simulation will
be minimum.  As we stated in the memo, it will be a subject of
future simulations to study the effects of different source
declinations


4. Simultaneous observations
It is certainly desirable to make all observations nearly
the same time.  Thus, more careful calibration will be required
to combine the ACA and the 64-element array data.
Documentation on the specific calibration plan is in preparation.

We are also expecting to optimize the design of the ACA 12-m
to realize high precision total power observations.


5. Mosaicing with the 64-element array

Our memo is, by no means, not intended to deny mosaicing by the
64-element array.  As seen from our simulations including errors,
the addition of ACA is effective for targets with high dynamic
range.  For low intensity sources, the ACA is probably not so
effective.  (This needs to be confirmed by simulations with noise.)
For observations of such sources,  it will be made with the
64-element array.