simalma(project='sim', dryrun=True, skymodel='', inbright='', indirection='', incell='', incenter='', inwidth='', complist='', compwidth='"8GHz"', setpointings=True, ptgfile='$project.ptg.txt', integration='10s', direction='', mapsize=['', ''], antennalist=['alma.cycle1.1.cfg', 'aca.cycle1.cfg'], hourangle='transit', totaltime=['20min', '1h'], tpnant=0, tptime='0s', pwv=0.5, image=True, imsize=[128, 128], imdirection='', cell='', niter=0, threshold='0.1mJy', graphics='both', verbose=False, overwrite=False)¶
Simulation task for ALMA
project (string=’sim’) - root prefix for output file names
dryrun (bool=True) - dryrun=True will only produce the informative report, not run simobserve/analyze
skymodel (string=’’) - model image to observe
skymodel != ''
inbright (string=’’) - scale surface brightness of brightest pixel e.g. “1.2Jy/pixel”
indirection (string=’’) - set new direction e.g. “J2000 19h00m00 -40d00m00”
incell (string=’’) - set new cell/pixel size e.g. “0.1arcsec”
incenter (string=’’) - set new frequency of center channel e.g. “89GHz” (required even for 2D model)
inwidth (string=’’) - set new channel width e.g. “10MHz” (required even for 2D model)
complist (string=’’) - componentlist to observe
complist != ''
compwidth (string=‘“8GHz”’) - bandwidth of components
setpointings = True
antennalist (stringArray=[‘alma.cycle1.1.cfg’, ‘aca.cycle1.cfg’]) - antenna position files of ALMA 12m and 7m arrays
hourangle (string=’transit’) - hour angle of observation center e.g. -3:00:00, or “transit”
totaltime (stringArray=[‘20min’, ‘1h’]) - total time of observation; vector corresponding to antennalist
tpnant (int=0) - Number of total power antennas to use (0-4)
tpnant != 0
tptime (string=’0s’) - total observation time for total power
pwv (double=0.5) - Precipitable Water Vapor in mm. 0 for noise-free simulation
image (bool=True) - image simulated data
image = True
imsize (intArray=[128, 128]) - output image size in pixels (x,y) or 0 to match model
imdirection (string=’’) - set output image direction, (otherwise center on the model)
cell (string=’’) - cell size with units or “” to equal model
niter (int=0) - maximum number of iterations (0 for dirty image)
threshold (string=’0.1mJy’) - flux level (+units) to stop cleaning
graphics (string=’both’) - display graphics at each stage to [screen|file|both|none]
overwrite (bool=False) - overwrite files starting with $project
This task simulates ALMA observation including 12-m, ACA 7-m and total power arrays, and images and analyzes simulated data.
This task makes multiple calls to simobserve (to calculate visibilities and total power spectra), followed by gridding of total power spectra (if total power is requested), concatenation of the simulated visibilities, calls to the simanalyze task for visibility inversion, deconvolution, and calculation of difference, and fidelity images, and feathering of single dish and interferometric data.
These steps may not all be familiar to new users, so the simalma task runs by default in a “dryrun” mode, in which it assesses the user’s input parameters and sky model, and prints an informational report including the required calls to other CASA tasks, both to the screen and to a text file in the project directory (defined below).
The user can modify their parameters based on the information, then either run with dryrun=False to actually call the other tasks to create the simulated data, or run the other tasks individually one at a time to better understand and control the process. More information on running simalma can be found here.
NOTE: The ALMA project is refining the optimal method of combining the three types of data. If that best practice is changed after this release of CASA, the user can control the process by modifying the calls to the other CASA tasks.
The root filename for all output files. A subdirectory will be created, and all created files will be placed in that subdirectory including the informational report.
An input image used as a model of the sky. simalma 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 image (ia) tool to create an image and insert the data. simalma does NOT require a coordinate system in the header. If the coordinate information is incomplete, missing, or you would like to override it, set the appropriate “in” parameters.
NOTE: Setting those parameters simply changes the header values, ignoring any values already in the image. No regridding is performed.
If you have a proper Coordinate System, simalma will do its best to generate visibilities from that, and then create a synthesis image according to the specified user parameters. You can manipulate an image header manually with the imhead task.
The peak brightness to scale the image to in Jy/pixel, or ” ” to keep it 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.
The central direction to place the sky model image, or ” ” to use whatever is in the image already.
The spatial pixel size to scale the skymodel image, or ” ” to use whatever is in the image already.
The frequency to use for the center channel (or only channel, if the skymodel is 2D). E.g., “89GHz”, or ” ” to use what is in the header. Required even for a 2D model.
The width of channels to use, or ” ” to use what is in the image. Should be a string representing a quantity with units e.g., “10MHz”.
NOTE: Only works reliably with frequencies, not velocities. 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.
A component list model of the sky, added to or instead of skymodel. Click here for more information.
The bandwidth of components. If simulating from components only, this defines the bandwidth of the MS and output images.
If True, calculate a map of pointings and write ptgfile. If graphics are on, display the pointings shown on the model image. Observations with the ALMA 12m and ACA 7m arrays will observe a region of size “mapsize” using the same hexagonal algorithm as the ALMA OT, with Nyquist sampling. The total power array maps a slightly (+1 primary beam) larger area than the 12m array does, to improve later image combination. It samples the region with lattice grids of spacing 0.33 lambda/D. If setpointings=False, read pointings from 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. simalma will observe these until totaltime is used up.
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 increase the time at each point to be larger than the parameter integration time.
Mosaic center direction. e.g., ‘J2000 19h00m00 -40d00m00’. If unset, will use the center of the skymodel image. Can optionally be a list of pointings, otherwise simobserve will cover a region of size mapsize according to maptype.
Angular size of mosaic map to simulate. Set to ” ” to cover the model image.
A vector of ASCII files containing antenna positions, one for each configuration of 7m or 12m dishes.In this task, it should be an ALMA configuration. Standard arrays are found in your CASA data repository, os.getenv(“CASAPATH”).split()+”/data/alma/simmos/”. A string of the form “alma;0.5arcsec” will be parsed into a 12m ALMA configuration. Examples: [‘alma.cycle2.5.cfg’,’aca.cycle2.i.cfg’], [‘alma.cycle1;0.3arcsec’,’alma.cycle1.1.cfg’,’aca.i.cfg’]
Hour angle of observation e.g., ‘-3h’.
The total time of observations. This should either be a scalar time quantity expressed as a string e.g., ‘1h’, ‘3600sec’, ‘10min’, or a vector of such quantities, corresponding to the elements of the antennalist vector, e.g., [‘5min’,’20min’,’3h’]. If you specify a scalar, that will be used for the highest resolution 12m configuration in antennalist, and any lower resolution 12m configurations, any 7m configurations, and any TP configurations will have observing times relative to totaltime of 0.5, 2,and 4, respectively.
The number of total power antennas to use in simulation.
If tpnant>0, the user must specify the observing time for total power as a CASA quantity e.g., ‘4h’.
NOTE: This is not broken up among multiple days - a 20h track will include observations below the horizon, which is probably not what is desired.
Precipitable water vapor. If constructing an atmospheric model, set 0 for noise-free simulation. When pwv>0, thermal noise is applied to the simulated data. J. Pardo’s ATM library will be used to construct anatmospheric profile for the ALMA site: altitude 5000m, ground pressure 650mbar, relhum=20%, a water layer of pwv at altitude of 2km, the sky brightness temperature returned by ATM, and internally tabulated receiver temperatures. See the documentation of simobserve for more details.
An option to invert and deconvolve the simulated MeasurementSet(s)
NOTE: Interactive clean or more parameters than the subset visible here are available by simply running either clean or tclean tasks directly.
If graphics turned on, 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).
The image size in spatial pixels (x,y). 0 or -1 will use the model image size. Examples: imsize=[500,500]
The phase center for synthesized image. Default is to center on the sky model.
Cell size e.g., “10arcsec”. cell = ” “ defaults to the skymodel cell.
The number of clean/deconvolution iterations, 0 for no cleaning.
The flux level at which to stop cleaning.
View plots on the screen, saved to file, both, or neither.
Print extra information to the logger and terminal.
Overwrite existing files in the project subdirectory. Please see the documents of simobserve and simanalyze for the list of outputs produced.
Example of a simalma routine. More information on this can be seen here.
# Set simalma to default parameters default("simalma") # Our project name will be "m51", and all simulation products will be placed in a subdirectory "m51/" project="m51" overwrite=True # Model sky = H_alpha image of M51 os.system('curl https://casaguides.nrao.edu/images/3/3f/M51ha.fits.txt -f -o M51ha.fits') skymodel="M51ha.fits" # Set model image parameters: indirection="J2000 23h59m59.96s -34d59m59.50s" incell="0.1arcsec" inbright="0.004" incenter="330.076GHz" inwidth="50MHz" antennalist=["alma.cycle5.3.cfg","aca.cycle5.cfg"] totaltime="1800s" tpnant = 2 tptime="7200s" pwv=0.6 mapsize="1arcmin" dryrun = False simalma()
No additional development details
- Parameter Details
Detailed descriptions of each function parameter
project (string='sim')- root prefix for output file names
dryrun (bool=True)- dryrun=True will only produce the informative report, not run simobserve/analyze
skymodel (string='')- model image to observe
inbright (string='')- scale surface brightness of brightest pixel e.g. “1.2Jy/pixel”
indirection (string='')- set new direction e.g. “J2000 19h00m00 -40d00m00”
incell (string='')- set new cell/pixel size e.g. “0.1arcsec”
incenter (string='')- set new frequency of center channel e.g. “89GHz” (required even for 2D model)
inwidth (string='')- set new channel width e.g. “10MHz” (required even for 2D model)
complist (string='')- componentlist to observe
compwidth (string='"8GHz"')- bandwidth of components
ptgfile (string='$project.ptg.txt')- list of pointing positions
integration (string='10s')- integration (sampling) time
direction (stringArray='')- “J2000 19h00m00 -40d00m00” or “” to center on model
mapsize (stringArray=['', ''])- angular size of map or “” to cover model
antennalist (stringArray=['alma.cycle1.1.cfg', 'aca.cycle1.cfg'])- antenna position files of ALMA 12m and 7m arrays
hourangle (string='transit')- hour angle of observation center e.g. -3:00:00, or “transit”
totaltime (stringArray=['20min', '1h'])- total time of observation; vector corresponding to antennalist
tpnant (int=0)- Number of total power antennas to use (0-4)
tptime (string='0s')- total observation time for total power
pwv (double=0.5)- Precipitable Water Vapor in mm. 0 for noise-free simulation
image (bool=True)- image simulated data
imsize (intArray=[128, 128])- output image size in pixels (x,y) or 0 to match model
imdirection (string='')- set output image direction, (otherwise center on the model)
cell (string='')- cell size with units or “” to equal model
niter (int=0)- maximum number of iterations (0 for dirty image)
threshold (string='0.1mJy')- flux level (+units) to stop cleaning
graphics (string='both')- display graphics at each stage to [screen|file|both|none]
overwrite (bool=False)- overwrite files starting with $project