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NRAO Home > CASA > CASA Task Reference Manual |
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0.1.119 simobserve
Requires:
Synopsis
visibility simulation task
Description
This task simulates interferometric or total power measurment sets It is
currently optimized for JVLA and ALMA, although many observatories are
included, and adding your own is simply a matter of providing an antenna
location file (see below).
simobserve is meant to work in conjunction with the simanalyze task - Calling simobserve one more times will produce simulated measurement set(s), which are then gridded, inverted and deconvolved into output simulated images using simanalyze.
ALMA users are encouraged to use the simalma task, which provides additional information on the multiple simobserve and simanalyze calls required to simulate an ALMA observation which may consist of 12m interferometric, 7m interferometric, and 12m total power data.
More information and examples are availible at http://casaguides.nrao.edu/index.php?title=Simulating_Observations_in_CASA Please contact CASA experts with any questions.
Arguments
Inputs |
| ||
project |
| root prefix for output file names
| |
| allowed: | string |
|
| Default: | sim |
|
skymodel |
| * simobserve uses 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.
* simobserve 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 that setting those parameters simply changes the header values, ignoring any values already in the image. No regridding is performed. * You can also manipulate an image header manually with the ”imhead” task. * If you have a proper Coordinate System, simobserve will do its best to generate visibilities from that. | |
| allowed: | string |
|
| Default: |
| |
inbright |
| scale surface brightness of brightest pixel e.g.
”1.2Jy/pixel”
| |
| allowed: | string |
|
| Default: |
| |
indirection |
| set new direction e.g. ”J2000 19h00m00 -40d00m00”
| |
| allowed: | string |
|
| Default: |
|
|
incell |
| set new cell/pixel size e.g. ”0.1arcsec”
| |
| allowed: | string |
|
| Default: |
| |
incenter |
| set new frequency of center channel e.g. ”89GHz”
(required even for 2D model)
| |
| allowed: | string |
|
| Default: |
|
|
inwidth |
| set new channel width e.g. ”10MHz” (required even for
2D model)
| |
| allowed: | string |
|
| Default: |
| |
complist |
| componentlist to observe
| |
| allowed: | string |
|
| Default: |
| |
compwidth |
| bandwidth of components
| |
| allowed: | string |
|
| Default: | ”8GHz” | |
setpointings |
| ||
| allowed: | bool | |
| Default: | True |
|
ptgfile |
| list of pointing positions
| |
| allowed: | string |
|
| Default: | $project.ptg.txt |
|
integration |
| integration (sampling) time
| |
| allowed: | string |
|
| Default: | 10s | |
direction |
| ”J2000 19h00m00 -40d00m00” or ”” to center on model
| |
| allowed: | stringArray |
|
| Default: |
| |
mapsize |
| angular size of map or ”” to cover model
| |
| allowed: | stringArray |
|
| Default: |
|
|
maptype |
| hexagonal, square (raster), ALMA, etc
| |
| allowed: | string |
|
| Default: | hexagonal |
|
pointingspacing |
| spacing in
between pointings or ”0.25PB” or ”” for ALMA default
INT=lambda/D/sqrt(3), SD=lambda/D/3
| |
| allowed: | string |
|
| Default: |
|
|
caldirection |
| pt source calibrator [experimental]
| |
| allowed: | string |
|
| Default: |
|
|
calflux |
| ||
| allowed: | string |
|
| Default: | 1Jy |
|
obsmode |
| observation mode to simulate
[int(interferometer)—sd(singledish)—””(none)]
| |
| allowed: | string |
|
| Default: | int |
|
refdate |
| date of observation - not critical unless concatting
simulations
| |
| allowed: | string |
|
| Default: | 2014/01/01 |
|
hourangle |
| hour angle of observation center e.g. ”-3:00:00”, ”5h”,
”-4.5” (a number without units will be interpreted as
hours), or ”transit”
| |
| allowed: | string |
|
| Default: | transit |
|
totaltime |
| total time of observation or number of repetitions
| |
| allowed: | string |
|
| Default: | 7200s |
|
antennalist |
| interferometer antenna position file
| |
| allowed: | string |
|
| Default: |
|
|
sdantlist |
| single dish antenna position file
| |
| allowed: | string |
|
| Default: | aca.tp.cfg |
|
sdant |
| single dish antenna index in file
| |
| allowed: | int |
|
| Default: | 0 |
|
outframe |
| spectral frame of MS to create
| |
| allowed: | string |
|
| Default: | LSRK |
|
thermalnoise |
| add thermal noise: [tsys-atm—tsys-manual—””]
| |
| allowed: | string |
|
| Default: | tsys-atm |
|
user_pwv |
| Precipitable Water Vapor in mm
| |
| allowed: | double |
|
| Default: | 0.5 |
|
t_ground |
| ambient temperature
| |
| allowed: | double |
|
| Default: | 270. |
|
t_sky |
| atmospheric temperature
| |
| allowed: | double |
|
| Default: | 260. |
|
tau0 |
| zenith opacity
| |
| allowed: | double |
|
| Default: | 0.1 |
|
seed |
| random number seed
| |
| allowed: | int |
|
| Default: | 11111 |
|
leakage |
| cross polarization (interferometer only)
| |
| allowed: | double |
|
| Default: | 0.0 |
|
graphics |
| display graphics at each stage to
[screen—file—both—none]
| |
| allowed: | string |
|
| Default: | both |
|
verbose |
| ||
| allowed: | bool |
|
| Default: | False |
|
overwrite |
| overwrite files starting with $project
| |
| allowed: | bool |
|
| Default: | True |
|
bool
Example
-------------------------------
project -- the root filename for all output files.
-------------------------------
skymodel -- input image (used as a model of the sky)
* simobserve uses 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.
* simobserve 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 that setting
those parameters simply changes the header values, ignoring
any values already in the image. No regridding is performed.
* You can also manipulate an image header manually with the "imhead" task.
* If you have a proper Coordinate System, simobserve will do its best to
generate visibilities from that.
inbright -- peak brightness to scale the image to 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 to place the sky model image,
or "" to use whatever is in the image already
incell -- spatial pixel size to scale the skymodel image,
or "" to use whatever is in the image already.
incenter -- 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.
inwidth -- 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
* 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.
-------------------------------
complist -- component list model of the sky, added to or instead of skymodel
see http://casaguides.nrao.edu/index.php?title=Simulation_Guide_Component_Lists_%28CASA_4.1%29
compwidth -- bandwidth of components; if simulating from components only,
this defines the bandwidth of the MS and output images
-------------------------------
setpointings -- if true, calculate a map of pointings and write ptgfile.
if false, read pointings from ptgfile.
* if graphics are on, display the pointings shown on the model image
ptgfile -- a text file specifying directions in the following
format, with 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:
simobserve 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 increase the time at each point to be larger than
the parameter integration time.
direction -- 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
mapsize -- angular size of mosaic map to simulate.
* set to "" to cover the model image
maptype -- how to calculate the pointings for the mosaic observation.
hexagonal, square (rectangular raster),
"ALMA" for the same hex algorithm as the ALMA Cycle 1 OT
or "ALMA2012" for the algorithm used in the Cycle 0 OT
pointingspacing -- spacing in between primary beams e.g ’10arcsec’
"0.25PB" to use 1/4 of the primary beam FWHM,
"nyquist" will use lambda/d/2,
"" will use lambda/d/sqrt(3) for INT, lambda/d/3 for SD
-------------------------------
obsmode -- observation mode to calculate visibilities from a skymodel image
(which may have been modified above), an optional component list,
and a pointing file (which also may have been generated above)
* this parameter takes two possible values:
- interferometer (or int)
- singledish (or sd)
* if graphics are on, this observe step will display the array
(similar to plotants), the uv coverage, the synthesized (dirty) beam,
and ephemeris information
* if simulating from a component list, you should specify "compwidth",
the desired bandwidth. There is not currently a way to specify the
spectrum of a component, so simulations from a componentlist only
will be continuum (1 chan)
refdate -- date of simulated observation eg: ’2014/05/21’
hourangle -- hour angle of observation e.g. ’-3h’
* note that if you don’t add a unit, it will assume hours
totaltime --- total time of observation e.g ’7200s’ or if a number without
units, interpreted as the number of times to repeat the mosaic.
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 "", simobserve will not not produce an interferometric MS
* a string of the form "alma;0.5arcsec" will be parsed into a full
12m ALMA configuration.
caldirection -- an unresolved calibrator can be observed
interleaved with the science pointings.
* The calibrator is implemented as a point source clean component
with this specified direction and flux=calflux
sdant -- the index of the antenna in the list to use for total
power. defaults to the first antenna on the list.
-------------------------------
thermalnoise -- add thermal noise
* 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:
altitude 5000m, ground pressure 650mbar, relhum=20%,
a water layer of user_pwv at altitude of 2km,
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.
* In either mode, noise is calculated using an antenna spillover
efficiency of 0.96, taper of 0.86,
surface accuracy of 25 and 300 microns for ALMA and EVLA
respectively (using the Ruze formula for surface efficiency),
correlator efficiencies of 0.95 and 0.91 for ALMA and EVLA,
receiver temperatures for ALMA of
17, 30, 37, 51, 65, 83,147,196,175,230 K interpolated between
35, 75,110,145,185,230,345,409,675,867 GHz,
for EVLA of
500, 70, 60, 55, 100, 130, 350 K interpolated between
0.33,1.47,4.89,8.44,22.5,33.5,43.3 GHz,
for SMA of
67, 116, 134, 500 K interpolated between
212.,310.,383.,660. GHz
* These are only approximate numbers and do not take into account
performance at edges of receiver bands, neither are they guaranteed
to reflect the most recent measurements. Caveat emptor. Use the
sm tool to add noise if you want more precise control, and use
the ALMA exposure time calculator for sensitivity numbers in proposals.
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 https://casaguides.nrao.edu/index.php/Corrupt
for more information on noise,
in particular how to add a phase screen using the toolkit
seed -- random number seed for noise generation
-------------------------------
leakage -- add cross polarization corruption of this fractional magnitude
graphics -- view plots on the screen, saved to file, both, or neither
verbose -- print extra information to the logger and terminal
overwrite -- overwrite existing files in the project subdirectory
-------------------------------
-------------------------------
Output produced: (not all will always exist, depending on input parameters)
To support different runs with different arrays, the names have the
configuration name from antennalist appended.
-------------------------------
project.[cfg].skymodel = 4d input sky model image (optionally) scaled
project.[cfg].skymodel.flat.regrid.conv = input sky regridded to match the
output image, and convolved with the output clean beam
project.[cfg].skymodel.png = diagnostic figure of sky model with pointings
project.[cfg].ptg.txt = list of mosaic pointings
project.[cfg].quick.psf = psf calculated from uv coverage
project.[cfg].ms = noise-free measurement set
project.[cfg].noisy.ms = corrupted measurement set
project.[cfg].observe.png = diagnostic figure of uv coverage and
visibilities
project.[cfg].simobserve.last = saved input parameters for simobserve task
More information about CASA may be found at the
CASA web page
Copyright © 2016 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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