1 SHORT_MODEL Simulate single-dish observations
        SHORT_MODEL

    This task simulates observations performed with single-dish antennas, to
    be used later on as short spacings information. The model image is  con-
    volved  by the antenna lobe (via Fourier Transform) and the intensity is
    then estimated at (i) the position of the mosaic fields, and (ii) on  an
    externally  defined  grid (see IMAGE_SAMPLING documentation). If the re-
    quired position does not coincide with a pixel center, a bilinear inter-
    polation from the neighbor pixels is performed.

    Pointing  errors  can  be  simulated  by  estimating  the intensity at a
    slightly wrong position. This task can generate simple kind of  pointing
    errors  but  it can also read an input pointing error table (enabling to
    simulate much more complex kind of pointing errors).

    Thermal noise can then be added  to  the  data,  and  the  corresponding
    weight is stored. Finally, a calibration error can be simulated: the ob-
    served intensities are multiplied by a random factor  whose  mean  value
    (different from 1 if a systematic error is present) and rms can be spec-
    ified. In this case, we obtain: results = cal_rr*(model+thermal0ise).

    The error on the amplitude gain is modeled as the sum of an offset and a
    drift  with time. The offset and drift values are randomly reset at each
    calibration for each antennas. In addition, an offset common to all  the
    antennas can also be added to the amplitude gain.

    Intensity unit of input image is supposed to be Kelvin. The output table
    has the following format: 4 columns x Number of antenna  x  (NFIELDS$  +
    Number  of observed positions). Column 1 is the X offset in radian, col-
    umn 2 the Y offset in radian, column 3 the weight and column 4 the  flux
    in  Jy.   The  first NFIELDS$ lines of the model are the position of the
    mosaic for use by UV_ZERO and all the other ones are the nod of the  ex-
    ternally  defined  grid  (by  IMAGE_SAMPLING) for use by UV_SINGLE. This
    complex line layout comes from historical reasons (as usual)...

    Limitation: only image can be processed (i.e. *no*  data  cube)  meaning
    that this task can not (yet) handle spectra cubes.

2 SKY$
        TASK\FILE "Name of Sky Image" SKY$

    Filename  of  input  image used as sky model. Its intensity unit is sup-
    posed to be Kelvin.

2 POINT$
        TASK\FILE "Table Name of Pointing Centers" POINT$

    Filename of the table where the sampling coordinates  are  stored  (e.g.
    output  of IMAGE_SAMPLING with NFIELDS$ additional lines at table begin-
    ning).

2 ERROR$
        TASK\FILE "Table Name of Pointing Errors (optional)" ERROR$

    Filename of the table where the pointing errors are stored. This parame-
    ter  is needed only when PEC$ = 5. You can use the "point_rror.map" pro-
    cedure to generate complex pointing error tables directly in the  format
    needed here.

2 MODEL$
        TASK\FILE "Output Table Name" MODEL$

    Filename  of  the  table which can then be used as input of UV_SHORT for
    computation of the missing short-spacings.

2 NFIELDS$
        TASK\INTE "Number of Mosaic Fields" NFIELDS$

    Number of lines at start of the input pointing center and  error  tables
    and  of  the output table which will give the fluxes at the positions of
    the mosaic field centers. If you are not interested  by  this  seemingly
    strange feature, just add one line at start of the input tables and dis-
    card one line at start of the output table and set this parameter to  1.
    It would be better to be able to set this parameter to 0 (perhaps in an-
    other life...).

2 DIAM$
        TASK\REAL "Antenna Diameter [m]" DIAM$

    Common diameter of the modeled single dish antennas.

2 FREQ$
        TASK\REAL "Observing Frequency [GHz]" FREQ$

    Frequency of modeled observation.

2 NOISE$
        TASK\REAL "Noise Level Required for Weighting [K] (optional)" NOISE$

    This the noise level obtained if all the spectra of the maps observed by
    all the available antennas were added. Needed only when ADDNOISE$ = YES.

2 CALOFF$
        TASK\REAL  "Mean  and  RMS  amplitude offset at each calibration [%]
    (optional)" CALOFF$[2]

    Needed only when ADDCALERR$ = YES.

2 CALDRIFT$
        TASK\REAL "RMS amplitude drift [%/hour] (optional)" CALDRIFT$

    Needed only when ADDCALERR$ = YES.

2 CALTIME$
        TASK\REAL "Time between 2  amplitude  calibrations  [s]  (optional)"
    CALTIME$

    The  random and drift amplitude factor will be reset every CALTIME$ sec-
    onds.  Needed only when ADDCALERR$ = YES.

2 INTTIME$
        TASK\REAL "Integration time [s] (optional)" INTTIME$

    Integration time on each nod of the externally defined grid. Needed only
    when ADDCALERR$ = YES.

2 SERR$
        TASK\REAL "Pointing Error Sigmas (Optional)" SERR$[2]

    RMS of lambda and beta pointing errors. Needed only when 1 < PEC$ < 5.

2 PEC$
        TASK\INTE "Pointing Error Model" PEC$

    Code  used  to  define  the pointing error model. 1 means "No errors", 2
    "Fixed error", 3 "Fully random error", 4 "Random for  each  antenna  but
    fixed  in  time"  and  5 "Use an outside table where pointing errors are
    stored". User can use the "point_rror.map" procedure to generate complex
    pointing error tables directly in the format needed here.

2 ADDNOISE$
        TASK\LOGI "Adds noise?" ADDNOISE$

    Logical switch deciding whether to add thermal noise.

2 ADDCALERR$
        TASK\LOGI "Adds calibration errors?" ADDCALERR$

    Logical switch deciding whether to add amplitude calibration errors.

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