Simdata CASA 3.1
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(Redirected from Simdata2)
mosaic simulation task:
mosaic simulation task (prototype):
This task simulates interfermetric observations (currently
only ALMA can be done easily). New functionality is actively
being added, so if you have changed versions of CASA, check
the inputs carefully.
Please contact CASA experts with any questions, especially
about features noted below as *experimental*
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project -- root filename for all output files.
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modifymodel -- change the coordinate system of the model sky image?
* if graphics selected, display the rescaled model image
skymodel -- if modifymodel=False, use this as the sky model.
* if modifyimage=True, use this as the starting point, modify it
write the output to a different image (default $project.skymodel)
and use that new image as the sky model
inbright -- peak brightness in Jy/pixel, or "" for unchanged
* NOTE: "unchanged" will take the numerical values in your image
and assume they are in Jy/pixel, even if it says some other unit
in the header.
indirection -- central direction, or "" for unchanged
incell -- spatial pixel size, or "" for unchanged
incenter -- frequency of center channel e.g. "89GHz", or "" for unchanged
inwidth -- width of channels, or "" for unchanged - this should be a
string representing a quantity with units e.g. "10MHz"
* NOTE: only works reliably with frequencies, not velocities
* NOTE: it is not possible to change the number of spectral planes
of the sky model, only to relabel them with different frequencies
That kind of regridding can be accomplished with the CASA toolkit.
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setpointings -- calculate a map of pointings, or if false, provide ptgfile
* if graphics selected, display the pointings shown on the model image
ptgfile -- a text file specifying directions in the same
format as the example, and optional integration times, e.g.
#Epoch RA DEC TIME(optional)
J2000 23h59m28.10 -019d52m12.35 10.0
* if the time column is not present in the file, it will use
"integration" for all pointings.
* NOTE: at this time the file should contain only science pointings:
simdata will observe these, then optionally the calibrator,
then the list of science pointings again, etc, until totaltime
is used up.
integration --- Time interval for each integration e.g '10s'
* NOTE: to simulate a "scan" longer than one integration, use
setpointings to generate a pointing file, and then edit the
file to repeat each pointing several times before moving to the
next point.
direction -- mosaic center direction e.g 'J2000 19h00m00 -40d00m00'
* can optionally be a list of pointings
* otherwise simdata will pack mapsize according to maptype
mapsize -- angular size of map
* set to "" to span the model image
maptype -- hexagonal or linear
pointingspacing -- spacing in between beams e.g '1arcsec'
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predict -- calculate visibilities from skymodel (which may have been
modified above, (optionally) complist, and $ptgfile (which
may have been generated above)
* if graphics selected, display the array (like plotants), the uv
coverage, the synthesized (dirty) beam, and ephemeris information
refdate -- central time of simulated observation eg: '2012/05/21/22:05:00'
* NOTE: observations are currently centered at the nearest transit *
totaltime --- total time of observation e.g '7200s'
antennalist -- ascii file containing antenna positions.
each row has x y z coordinates and antenna diameter;
header lines are required to specify the observatory name
and coordinate system e.g.
# observatory=ALMA
# coordsys=UTM
# datum=WGS84
# zone=19
* standard arrays are found in your CASA data repository,
os.getenv("CASAPATH").split()[0]+"/data/alma/simmos/"
* if "", will not not produce an interferometric MS
* NEW: a string of the form "alma;0.5arcsec" will be parsed into a full 12m ALMA
configuration. This only works for full ALMA and may fail to find the
standard configuration files on some systems - see casaguides.nrao.edu
caldirection -- *NEW* an unresolved calibrator can be observed
interleaved with the science pointings. This feature is
experimental, so please contact us with any questions.
* The calibrator is implemented as a point source clean component
with this direction and flux=calflux
sdantlist -- antenna position file with antennas to be used for
single dish or total power simulation
* if "", will not produce a total power MS
sdant -- the index of the antenna in the list to use for total
power. defaults to the first antenna on the list.
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thermalnoise -- add thermal noise
* NOTE: both the interferometric and single-dish MS will be
corrupted if they've been created above.
* currently only knows correct temps for ALMA and EVLA receivers
* this parameter takes two possible values:
tsys-atm: J. Pardo's ATM library will be used to construct an
atmospheric profile for the ALMA site and user_pwv.
noise is calculated from the specified ground temperature,
internally tabulated antenna spillover parameters, the sky brightness
temperature returned by ATM, and internally tabulated receiver
temperatures
tsys-manual: instead of using the ATM model, specify the zenith
sky brightness and opacity manually. Noise is added and then
the visibility flux scale is referenced above the atmosphere.
t_ground -- ground/spillover temperature in K
user_pwv -- precipitable water vapor if constructing an atmospheric model
t_sky -- atmospheric temperature in K [for tsys-manual]
tau0 -- zenith opacity at observing frequency [for tsys-manual]
* see casaguides.nrao.edu for more information on noise,
in particular how to add a phase screen using the toolkit
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leakage -- add cross polarization corruption of this fractional magnitude
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image -- invert and deconvolve the measurement set(s)
* NOTE: interactive clean or more parameters than the subset visible
here are available by simply running the clean task directly,
then returning to simdata to run "analyze" if desired.
* NOTE: the channelization of the output image cube will be the
same as that in the simulated Measurement Set.
* if graphics selected, display the clean image and residual image
* uses Cotton-Schwab clean for single fields and Mosaic gridding
for multiple fields (with Clark PSF calculation in minor cycles).
ms -- the simulated interferometric MS, or total-power one, or both
modelimage -- prior (e.g. SD) image to be used in clean
cell -- cell size e.g '10arcsec'. "" defaults to the skymodel cell
imsize -- image size in spatial pixels (x,y)
0 or -1 will use the model image size; example: imsize=[500,500]
niter -- mumber of clean/deconvolution iterations, 0 for no cleaning
threshold -- flux level to stop cleaning
weighting -- weighting to apply to visibilities
options: 'natural','uniform','briggs' (robust=0.5)
outertaper -- apply additional uv outer taper of visibilities
stokes -- Stokes parameters to image; 'I','IV','IQU','IQUV'
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analyze -- compute and display difference between model and output,
fidelity, etc.
* it is recommended to have graphics turned on for this subtask
showarray -- like plotants
showuv -- display uv coverage
showpsf -- display synthesized (dirty) beam
showmodel -- display sky model at original resolution
showconvolved -- display sky model convolved with output beam
showclean -- display the synthesized image
showresidual -- display the clean residual image
showdifference -- display difference image
showfidelity -- display fidelity image
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How to specify a model image:
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* simdata requires a CASA or fits image. If you merely have a grid of
numbers, you will need to write them out as fits or write a CASA script to
read them in and use the ia tool to create an image and insert the data.
* simdata does NOT require a coordinate system in the header. If the
coordinate information is incomplete, missing, or you would like to
override it, set "modifymodel=True". simdata will then assume that the
axes of your input correspond to RA, Dec, and (optionally) frequency and
(optionally) Stokes parameter.
* If you have a proper Coordinate System, simdata will so its best to
generate visibilities from that, and then create a synthesis image
according to the specified user parameters. Regridding the
spectral dimension may not have complete flexibility yet.
* You can manipulate an image header with the "imhead" task, or you can
delve deeper with the ia and cs tools. If you use the tools, you should
be aware that a CoordinateSystem in CASA can exist independently of an
Image. Once the CoordinateSystem is detached from the image, it is the
users responsibility to do any manipulation e.g. axis reordering on
both. Example:
ia.open("myimage_filename")
ia.summary() # see header as attached to the image
csys=ia.coordsys() # detach the CoordinateSystem
csys.summary() # examine it
csys.setreferencepixel([100,100])
arr=ia.getchunk() # get the data from the Image
ia.done()
csys.reorder([0,2,1]) # reorder the CoordinateSystem
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How to specify a model image:
-------------------------------
* simdata requires a CASA or fits image. If you merely have a grid of
numbers, you will need to write them out as fits or write a CASA script to
read them in and use the ia tool to create an image and insert the data.
* simdata does NOT require a coordinate system in the header. If the
coordinate information is incomplete, missing, or you would like to
override it, set "modifymodel=True". simdata will then assume that the
axes of your input correspond to RA, Dec, and (optionally) frequency and
(optionally) Stokes parameter.
* If you have a proper Coordinate System, simdata will so its best to
generate visibilities from that, and then create a synthesis image
according to the specified user parameters. Regridding the
spectral dimension may not have complete flexibility yet.
* You can manipulate an image header with the "imhead" task, or you can
delve deeper with the ia and cs tools. If you use the tools, you should
be aware that a CoordinateSystem in CASA can exist independently of an
Image. Once the CoordinateSystem is detached from the image, it is the
users responsibility to do any manipulation e.g. axis reordering on
both. Example:
ia.open("myimage_filename")
ia.summary() # see header as attached to the image
csys=ia.coordsys() # detach the CoordinateSystem
csys.summary() # examine it
csys.setreferencepixel([100,100])
arr=ia.getchunk() # get the data from the Image
ia.done()
csys.reorder([0,2,1]) # reorder the CoordinateSystem
arr=arr.reorder([0,2,1]) # reorder the data
ia.fromshape(outfile="mynewimage_file",shape=[32,32,256],csys=csys.torecord(),overwrite=True)
# make a new image, with the right shape and CoordinateSystem
ia.putchunk(arr) # put the data into the new image.
csys.done()
ia.done()
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Output produced:
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Needs rewriting...
