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9.1 Simulating ALMA with simobserve and simanalyze

The simobserve inputs are (submenus expand slightly differently for thermalnoise=manual and single dish observing):

project             =      ’sim’        #  root prefix for output file names  
skymodel            =         ’’        #  model image to observe  
     inbright       =         ’’        #  scale surface brightness of brightest pixel e.g. "1.2Jy/pixel"  
     indirection    =         ’’        #  set new direction e.g. "J2000 19h00m00 -40d00m00"  
     incell         =         ’’        #  set new cell/pixel size e.g. "0.1arcsec"  
     incenter       =         ’’        #  set new frequency of center channel e.g. "89GHz" (required even for 2D model)  
     inwidth        =         ’’        #  set new channel width e.g. "10MHz" (required even for 2D model)  
 
complist            =         ’’        #  componentlist to observe  
     compwidth      =     ’8GHz’        #  bandwidth of components  
 
setpointings        =       True  
     integration    =      ’10s’        #  integration (sampling) time  
     direction      =         ’’        #  "J2000 19h00m00 -40d00m00" or "" to center on model  
     mapsize        =   [’’, ’’]        #  angular size of map or "" to cover model  
     maptype        =     ’ALMA’        #  hexagonal, square, etc  
     pointingspacing =         ’’       #  spacing in between pointings or "0.25PB" or "" for 0.5 PB  
 
obsmode             =      ’int’        #  observation mode to simulate  
                                        #   [int(interferometer)|sd(singledish)|""(none)]  
     antennalist    = ’alma.out10.cfg’  #  interferometer antenna position file  
     refdate        = ’2012/05/21’      #  date of observation - not critical unless concatting  
                                        #   simulations  
     hourangle      =  ’transit’        #  hour angle of observation center e.g. -3:00:00, or "transit"  
     totaltime      =    ’7200s’        #  total time of observation or number of repetitions  
     caldirection   =         ’’        #  pt source calibrator [experimental]  
     calflux        =      ’1Jy’  
 
thermalnoise        = ’tsys-atm’        #  add thermal noise: [tsys-atm|tsys-manual|""]  
     user_pwv       =        1.0        #  Precipitable Water Vapor in mm  
     t_ground       =      269.0        #  ambient temperature  
     seed           =      11111        #  random number seed  
 
leakage             =        0.0        #  cross polarization (interferometer only)  
graphics            =     ’both’        #  display graphics at each stage to [screen|file|both|none]  
verbose             =      False  
overwrite           =       True        #  overwrite files starting with $project  
async               =      False        #  If true the taskname must be started using simobserve(...)

This task takes an input model image or list of components, plus a list of antennas (locations and sizes), and simulates a particular observation (specifies by mosaic setup and observing cycles and times). The output is a measurement set suitable for further analysis in CASA.

The simanalyze inputs are:

project             =      ’sim’        #  root prefix for output file names  
image               =       True        #  (re)image $project.*.ms to $project.image  
     vis            =  ’default’        #  Measurement Set(s) to image  
     modelimage     =         ’’        #  prior image to use in clean e.g. existing single dish image  
     imsize         =          0        #  output image size in pixels (x,y) or 0 to match model  
     imdirection    =         ’’        #  set output image direction, (otherwise center on the model)  
     cell           =         ’’        #  cell size with units or "" to equal model  
     niter          =        500        #  maximum number of iterations (0 for dirty image)  
     threshold      =   ’0.1mJy’        #  flux level (+units) to stop cleaning  
     weighting      =  ’natural’        #  weighting to apply to visibilities  
     mask           =         []        #  Cleanbox(es), mask image(s), region(s), or a level  
     outertaper     =         []        #  uv-taper on outer baselines in uv-plane  
     stokes         =        ’I’        #  Stokes params to image  
 
analyze             =       True        #  (only first 6 selected outputs will be displayed)  
     showuv         =       True        #  display uv coverage  
     showpsf        =       True        #  display synthesized (dirty) beam (ignored in single dish simulation)  
     showmodel      =       True        #  display sky model at original resolution  
     showconvolved  =      False        #  display sky model convolved with output beam  
     showclean      =       True        #  display the synthesized image  
     showresidual   =      False        #  display the clean residual image (ignored in single dish simulation)  
     showdifference =       True        #  display difference image  
     showfidelity   =       True        #  display fidelity  
 
graphics            =     ’both’        #  display graphics at each stage to [screen|file|both|none]  
verbose             =      False  
overwrite           =       True        #  overwrite files starting with $project  
async               =      False        #  If true the taskname must be started using simanalyze(...)

This task analyzses one more more measurement sets - interferometric and/or single dish. The output is a synthesized image created from those visibilities, a difference image between the synthesized image and your sky model convolved with the output synthesized beam, and a fidelity image. (see ALMA memo 398 for description of fidelity, which is approximately the output image divided by the difference between input and output)

The combined task simdata is modular: one can modify one’s sky model, predict visibilities, corrupt the Measurement Set, re-image, and analyze the result all separately, provided in a few cases the filenames are set correctly.


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