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0.1.118 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

model image to observe

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

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

Returns
bool

Example

 
    -------------------------------  
    project -- the root filename for all output files.  
    -------------------------------  
    skymodel -- 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 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 that 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.  
 
    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.  
    -------------------------------  
    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 -- calculate a map of pointings, or if false, provide 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’  
       * can optionally be a list of pointings  
       * otherwise simobserve will pack mapsize according to maptype  
    mapsize -- angular size of map  
       * set to "" to span the model image  
    maptype -- 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 beams e.g ’1arcsec’  
         "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 i)  
         - singledish (or s)  
       * 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 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 map  
    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.  This only works for full ALMA and may fail  
         to find the standard configuration files on some systems  
         - see casaguides.nrao.edu for more information.  
    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 and use the  
         sm tool to add noise if you want more precise control.  
    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  
    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  
 


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