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9.1 Simulating ALMA with simobserve and simanalyze
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The simobserve inputs are (submenus expand slightly differently for thermalnoise=manual and single dish observing):
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:
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.
More information about CASA may be found at the
CASA web page
Copyright © 2010 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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