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| mosaic simulation task:
| | {{simdata}} |
| mosaic simulation task:
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| This task simulates interferometric observations (currently
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| only ALMA can be done easily). New functionality is actively
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| being added, so if you have changed versions of CASA, check
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| the inputs carefully.
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| Please contact CASA experts with any questions, especially
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| about features noted below as *experimental*
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| -------------------------------
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| project -- root filename for all output files.
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| -------------------------------
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| modifymodel -- change the coordinate system of the model sky image?
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| * if graphics selected, display the rescaled model image
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| skymodel -- if modifymodel=False, use this as the sky model.
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| * if modifyimage=True, use this as the starting point, modify it
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| write the output to a different image (default $project.skymodel)
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| and use that new image as the sky model
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| inbright -- peak brightness in Jy/pixel, or "" for unchanged
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| * NOTE: "unchanged" will take the numerical values in your image
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| and assume they are in Jy/pixel, even if it says some other unit
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| in the header.
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| indirection -- central direction, or "" for unchanged
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| incell -- spatial pixel size, or "" for unchanged
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| incenter -- frequency of center channel e.g. "89GHz", or "" for unchanged
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| inwidth -- width of channels, or "" for unchanged - this should be a
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| string representing a quantity with units e.g. "10MHz"
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| * NOTE: only works reliably with frequencies, not velocities
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| * NOTE: it is not possible to change the number of spectral planes
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| of the sky model, only to relabel them with different frequencies
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| That kind of regridding can be accomplished with the CASA toolkit.
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| -------------------------------
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| setpointings -- calculate a map of pointings, or if false, provide ptgfile
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| * if graphics selected, display the pointings shown on the model image
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| ptgfile -- a text file specifying directions in the same
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| format as the example, and optional integration times, e.g.
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| #Epoch RA DEC TIME(optional)
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| J2000 23h59m28.10 -019d52m12.35 10.0
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| * if the time column is not present in the file, it will use
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| "integration" for all pointings.
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| * NOTE: at this time the file should contain only science pointings:
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| simdata will observe these, then optionally the calibrator,
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| then the list of science pointings again, etc, until totaltime
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| is used up.
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| integration --- Time interval for each integration e.g '10s'
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| * NOTE: to simulate a "scan" longer than one integration, use
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| setpointings to generate a pointing file, and then edit the
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| file to repeat each pointing several times before moving to the
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| next point.
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| direction -- mosaic center direction e.g 'J2000 19h00m00 -40d00m00'
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| * can optionally be a list of pointings
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| * otherwise simdata will pack mapsize according to maptype
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| mapsize -- angular size of map
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| * set to "" to span the model image
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| maptype -- hexagonal or linear
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| pointingspacing -- spacing in between beams e.g '1arcsec'
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| or "0.25PB" to use 1/4 of the primary beam FWHM, or
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| "" will use the primary beam HWHM.
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| -------------------------------
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| predict -- calculate visibilities from skymodel (which may have been
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| modified above, (optionally) complist, and $ptgfile (which
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| may have been generated above)
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| * if graphics selected, display the array (like plotants), the uv
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| coverage, the synthesized (dirty) beam, and ephemeris information
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| * if simulating from component list only, you should specify
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| modifymodel=False, and set compwidth, the desired bandwidth -
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| there is not currently a way to specify the spectrum of a component,
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| so simulations from a componentlist only will be continuum (1 chan)
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| refdate -- central time of simulated observation eg: '2012/05/21/22:05:00'
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| * NOTE: observations are currently centered at the nearest transit *
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| totaltime --- total time of observation e.g '7200s'
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| antennalist -- ascii file containing antenna positions.
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| each row has x y z coordinates and antenna diameter;
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| header lines are required to specify the observatory name
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| and coordinate system e.g.
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| # observatory=ALMA
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| # coordsys=UTM
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| # datum=WGS84
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| # zone=19
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| * standard arrays are found in your CASA data repository,
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| os.getenv("CASAPATH").split()[0]+"/data/alma/simmos/"
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| * if "", will not not produce an interferometric MS
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| * a string of the form "alma;0.5arcsec" will be parsed into a full 12m ALMA
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| configuration. This only works for full ALMA and may fail to find the
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| standard configuration files on some systems - see casaguides.nrao.edu
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| caldirection -- *NEW* an unresolved calibrator can be observed
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| interleaved with the science pointings. This feature is
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| experimental, so please contact us with any questions.
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| * The calibrator is implemented as a point source clean component
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| with this direction and flux=calflux
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| sdantlist -- antenna position file with antennas to be used for
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| single dish or total power simulation
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| * if "", will not produce a total power MS
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| sdant -- the index of the antenna in the list to use for total
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| power. defaults to the first antenna on the list.
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| -------------------------------
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| thermalnoise -- add thermal noise
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| * this parameter takes two possible values:
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| - tsys-atm: J. Pardo's ATM library will be used to construct an
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| atmospheric profile for the ALMA site:
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| altitude 5000m, ground pressure 650mbar, relhum=20%,
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| a water layer of user_pwv at altitude of 2km,
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| the sky brightness temperature returned by ATM,
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| and internally tabulated receiver temperatures
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| - tsys-manual: instead of using the ATM model, specify the zenith
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| sky brightness and opacity manually. Noise is added and then
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| the visibility flux scale is referenced above the atmosphere.
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| * In either mode, noise is calculated using an antenna spillover
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| efficiency of 0.96, taper of 0.86,
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| surface accuracy of 25 and 300 microns for ALMA and EVLA
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| respectively (using the Ruze formula for surface efficiency),
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| correlator efficiencies of 0.95 and 0.91 for ALMA and EVLA,
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| receiver temperatures for ALMA of
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| 17, 30, 37, 51, 65, 83,147,196,175,230 K interpolated between
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| 35, 75,110,145,185,230,345,409,675,867 GHz,
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| for EVLA of
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| 500, 70, 60, 55, 100, 130, 350 K interpolated between
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| 0.33,1.47,4.89,8.44,22.5,33.5,43.3 GHz,
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| for SMA of
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| 67, 116, 134, 500 K interpolated between
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| 212.,310.,383.,660. GHz
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| * These are only approximate numbers and do not take into account
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| performance at edges of receiver bands, neither are they guaranteed
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| to reflect the most recent measurements. Caveat emptor and use the
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| sm tool to add noise if you want more precise control.
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| t_ground -- ground/spillover temperature in K
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| user_pwv -- precipitable water vapor if constructing an atmospheric model
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| t_sky -- atmospheric temperature in K [for tsys-manual]
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| tau0 -- zenith opacity at observing frequency [for tsys-manual]
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| * see casaguides.nrao.edu for more information on noise,
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| in particular how to add a phase screen using the toolkit
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| -------------------------------
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| leakage -- add cross polarization corruption of this fractional magnitude
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| -------------------------------
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| image -- invert and deconvolve the measurement set(s)
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| * NOTE: interactive clean or more parameters than the subset visible
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| here are available by simply running the clean task directly,
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| then returning to simdata to run "analyze" if desired.
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| * NOTE: the channelization of the output image cube will be the
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| same as that in the simulated Measurement Set.
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| * if graphics selected, display the clean image and residual image
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| * uses Cotton-Schwab clean for single fields and Mosaic gridding
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| for multiple fields (with Clark PSF calculation in minor cycles).
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| vis -- the simulated interferometric MS, or total-power one, or both
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| ** use $project.noisy.ms if you have corrupted the MS
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| modelimage -- prior (e.g. SD) image to be used in clean
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| cell -- cell size e.g '10arcsec'. "" defaults to the skymodel cell
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| imsize -- image size in spatial pixels (x,y)
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| 0 or -1 will use the model image size; example: imsize=[500,500]
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| niter -- mumber of clean/deconvolution iterations, 0 for no cleaning
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| threshold -- flux level to stop cleaning
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| weighting -- weighting to apply to visibilities
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| options: 'natural','uniform','briggs' (robust=0.5)
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| outertaper -- apply additional uv outer taper of visibilities
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| stokes -- Stokes parameters to image; 'I','IV','IQU','IQUV'
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| -------------------------------
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| analyze -- compute and display difference between model and output,
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| fidelity, etc.
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| * it is recommended to have graphics turned on for this subtask
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| showarray -- like plotants (ignored in single dish simulation)
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| showuv -- display uv coverage
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| showpsf -- display synthesized (dirty) beam (ignored in single dish simulation)
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| showmodel -- display sky model at original resolution
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| showconvolved -- display sky model convolved with output beam
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| showclean -- display the synthesized image
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| showresidual -- display the clean residual image (ignored in single dish simulation)
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| showdifference -- display difference between output cleaned image and
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| input model sky image convolved with output synthesized beam
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| showfidelity -- display fidelity image
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| fidelity = input/max( abs(input-output), 0.7*rms(output) )
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| -------------------------------
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| How to specify a model image:
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| -------------------------------
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| * simdata requires a CASA or fits image. If you merely have a grid of
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| numbers, you will need to write them out as fits or write a CASA script to
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| read them in and use the ia tool to create an image and insert the data.
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| * simdata does NOT require a coordinate system in the header. If the
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| coordinate information is incomplete, missing, or you would like to
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| override it, set "modifymodel=True". simdata will then assume that the
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| axes of your input correspond to RA, Dec, and (optionally) frequency and
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| (optionally) Stokes parameter.
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| * If you have a proper Coordinate System, simdata will so its best to
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| generate visibilities from that, and then create a synthesis image
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| according to the specified user parameters. Regridding the
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| spectral dimension may not have complete flexibility yet.
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| * You can manipulate an image header with the "imhead" task, or you can
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| delve deeper with the ia and cs tools. If you use the tools, you should
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| be aware that a CoordinateSystem in CASA can exist independently of an
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| Image. Once the CoordinateSystem is detached from the image, it is the
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| users responsibility to do any manipulation e.g. axis reordering on
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| both. Example:
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| ia.open("myimage_filename")
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| ia.summary() # see header as attached to the image
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| csys=ia.coordsys() # detach the CoordinateSystem
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| csys.summary() # examine it
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| csys.setreferencepixel([100,100])
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| arr=ia.getchunk() # get the data from the Image
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| ia.done()
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| csys.reorder([0,2,1]) # reorder the CoordinateSystem
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| arr=arr.reorder([0,2,1]) # reorder the data
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| ia.fromshape(outfile="mynewimage_file",shape=[32,32,256],csys=csys.torecord(),overwrite=True)
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| # make a new image, with the right shape and CoordinateSystem
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| ia.putchunk(arr) # put the data into the new image.
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| csys.done()
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| ia.done()
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| -------------------------------
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| Output produced: (not all will always exist, depending on input parameters)
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| -------------------------------
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| project.skymodel = 4d input sky model image (optionally) scaled
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| project.skymodel.flat.regrid.conv = input sky regridded to match the output
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| image, and convolved with the output synthesized beam
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| project.skymodel.png = diagnostic figure of sky model with pointings
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| project.ptg.txt = list of mosaic pointings
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| project.quick.psf = psf calculated from uv coverage
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| project.ms = noise-free measurement set
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| project.noisy.ms = corrupted measurement set
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| project.predict.png = diagnostic figure of uv coverage and visibilities
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| project.image = synthesized image
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| project.flux.pbcoverage = promary beam correction for mosaic image
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| project.residual = residual image after cleaning
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| project.clean.last = parameter file of what parameters were used in the
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| clean task
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| project.psf = synthesized beam calculated from weighted uv distribution
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| project.image.png = diagnostic figure of clean image and residual
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| project.fidelity = fidelity image
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| project.analysis.png = diagnostic figure of difference and fidelity
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| project.simdata.last = saved input parameters for simdata task
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