BIMA Simulations with UVGEN

  The MIRIAD program uvgen  can indirectly be invoked by checker and used to create model visibility datasets. The way to activate your observe script to run UVGEN is by creating a setup with the name uvgen  , e.g.

  setup name=uvgen \
      source=$MIRCAT/point.source \
      ant=$MIRCAT/bima9_c.ant \
      corr=0,1 \
      gnoise=0 pnoise=0 systemp=0,0,0 tpower=0,0 jyperk=150

The presence of this setup will cause mint to automatically invoke the standard MIRIAD task uvgen  and create model visibility files. A few of the UVGEN specific keywords must be added to the uvgen setup, although most of them are computed by checker's version of MINT (see table below). Also note that those keywords which are filenames must be with their full pathname, since the observe script is not necessarely run where you expect it. Another problem which needs to be looked into is the random number generator used in MIRIAD: it causes uvgen to generate the same series of random numbers each time.

Also note that the presence of the uvgen setup has no meaning during observations, and does not have to be commented out.

required:
    source          a file with gaussian source(s), see $MIRCAT/*source
    ant             a file with antenna postitions, see $MIRCAT/*ant
    corr            tricky (TODO: INHERIT?)

    freq            ignored (TODO: INHERIT)
    itime           

optional:           (with some random number generator limitations)
    gnoise
         Antenna based gain noise, given as a percentage. This gives the
         multiplicative gain variations, specified by the rms amplitude to be
         added to the gain of each antenna at each sample interval. The
         gain error stays constant over the period given by the ``cycle(1)''
         parameter (see above). Thus ``cycle(1)'' can be varied to give
         different atmosphere/instrument stabilities. Note that the default
         of the ``cycle'' parameter means that the gain changes every
         integration. 

         A gain error can also be used to mimic random pointing errors
         provided the source is a point source.
         The default is 0 (i.e. no gain error).

    pnoise
         Antenna based phase noise, in degrees. This gives the phase
         noise, specified by the rms phase noise to be added to each
         antenna. Up to 4 values can be given to compute the phase noise
           pnoise(1) + pnoise(2)*(baseline)**pnoise(3)*sinel**pnoise(4)
         where ``baseline'' is the baseline length in km. Typical values
         for pnoise(2) are 1mm rms pathlength (e.g. 2 radians at 100 GHz),
         For Kolmogorov turbulence pnoise(3)=5/6 for baseline < 100m
         and 0.33 for baseline > 100m (outer scale of turbulence).
         pnoise(4)=-0.5 for a thick turbulent screen, and -1 for a thin layer.
         See also the ``gnoise'' parameter. Default is 0,0,0,0 (i.e.
         no phase error).

    systemp
         System temperature used to compute additive random noise and
         total power. One or 3 values can be given; either the average
         single sideband systemp including the atmosphere (TELEPAR gives
         typical values), or the double sideband receiver temperature, 
         sky temperature, and zenith opacity, when systemp is computed as:
           systemp = 2.*(Trx + Tsky*(1-exp(-tau/sinel)))*exp(tau/sinel)
         where systemp, Trx and Tsky are in Kelvin. Typical values for Hat Ck
         Trx, Tsky, and tau are 75,290,0.15. (OBSTAU gives values for tau).
         systemp is used to generate random Gaussian noise to add to each 
         data point. Default is 0,0,0 (i.e. no additive noise).

    tpower

         Two values can be given to represent the total power variations
         due to receiver instability (Trms), and atmospheric noise (Tatm). 
                  tpower = Trms * systemp +  Tatm * pnoise
         The receiver instablity is modeled as multiplicative Gaussian noise.
         The atmospheric noise is modeled to be correlated with the antenna
         phase noise. Typical values at 3 millimeter wavelength
         are Trms=10-3 and Tatm=0.2 K/radian (280 degrees/K).
         Default is tpower=0,0

    jyperk

         The system sensitivity, in Jy/K. Its value is given by 2*k/(eta * A)
         where k is Boltzmans constant (1.38e3 Jy m**2 / K), A is the physical
         area of each antenna (pi/4 * D**2), and eta is an efficiency.
         For the ATCA, D is 22 meters, and eta is composed of a correlator
         efficiency (0.88) and an antenna efficiency (0.65 at 6 cm). The
         overall result is jyperk=12.7. The default jyperk=150, a typical
         value for the Hat Creek 6.1 m antennas.

    options
	 (Not of any use for BIMA data yet, mostly for ATNF simulations)
    
internally derived:
    out             DO NOT USE (vis=)
    time            DO NOT USE (computed)
    radec           DO NOT USE 
    harange         DO NOT USE    
    elev            DO NOT USE    
    stokes          ???(not used for now)
    polar           ???(not used for now)
    lat             DO NOT USE    
    cycle           DO NOT USE    
    center

Limitations/Bugs:

• no source name in the visibility dataset, just UVGEN.
• corbw is wrong (listobs will complain)
• no polarization or channel