mkspsf: Telescope PSF Simulator
Python package to simulate the PSF for an antenna array using the casacore tools, makems and wsclean:
- if a configuration file with antenna positions are provided, a CASA antenna table is created,
- to build a dummy measurement set, the configuration information is given to makems followed by
-
wsclean to simulate the observations
Reference: WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
The tool required antenna positions and a basic pointing direction. Antenna positions can either be in the form of a config file, or a CASA antenna table. MeerKAT antenna positions are assumed by default.
Output will always be to the current working directory.
- The antenna positions provided are in ENU or ITRF coordinates provided as config information
- A default makems.cfg file that can be used as configuration information for
makems
> cat makems.cfg
AntennaTableName=ANTENNAS
NTimes=300
StepTime=86400.
StartFreq=856.0e+06
StepFreq=1671872.0
NFrequencies=512
NBands=1
Declination=-60d00m00.0s
RightAscension=00h00m00.0s
StartTime=2014/01/01/15:00
MSName=makems.MS
MSDesPath=.
NParts=1
WriteImagingColumns=True
WriteAutoCorr=True
Display available optional parameters:
> mkspsf --help
Usage: mkspsf [options] --cfg <makems.cfg> <ant_pos_file>
Options:
--version show program's version number and exit
-h, --help show this help message and exit
--cfg=CFG Config file for makems
--table Create a CASA antenna table
--ant_list=ANT_LIST Comma separated list of antenna names
Telescope Geographic Coordinates:
--array=ARRAY Name of telescope / array (default array='mkat')
--lat=LAT Latitude (default MeerKAT lat='-30:42:47.4')
--lon=LON Longitude (default MeerKAT lon='21:26:38.0')
--alt=ALT Altitude (default MeerKAT alt='1060.0')
Coordinate Classification:
--enu Antenna position file giving ENU coordinates using format: E N U dish_diam
station mount Default if not specified is ITRF coordinates using format: X Y
Z diameter station mount
Output Options:
-o, --output Save graphs to PNG format
-v, --verbose Display results and all graphs
--debug Display additional debug results
MAKEMS Simulation Options:
--ant=TBLNAME Antenna table name, else ANTENNA table will be generated
--ms=MSNAME Name of the measurement set to create
--stime=STIME Observation start time YYYY/MM/DD/hh:mm:ss.
--synthesis=SYNTHESIS Total synthesis / integration time in seconds (default snapshot of 5
minutes).
--dt=DT Accumulation time given as nr seconds per dump (default rate 4 seconds per
dump)
--dtime=DTIME Regular separation of simulated integration series (default is a scan every
12 hours.)
--dec=DECLINATION J2000 declination for simulation default -60d00m00.0s
--ra=RIGHTASCENSION J2000 right ascension for simulation default 00h00m00.0s
--nparts=NPARTS Nr of parts into which the measurement set is to be split
--nbands=NBANDS Nr of subbands to use, default=1 and max=4.
--nfreqs=NFREQS Total number of frequencies
--sfreq=SFREQ Comma separated list of length NBands with start frequency per band
--stepfreq=STEPFREQ Comma separated list of length NBands with step frequency per band
WSCLEAN Simulation Options:
--weight=WEIGHT Weightmode can be: natural, uniform, briggs (default=uniform). When using
Briggs' weighting, add the robustness parameter
--robust=ROBUST Robustness parameter for briggs weighting (-2 <= x <= 2)
--superweight=SUPERWEIGHT Increase the weight gridding box size, similar to Casa's superuniform
weighting scheme (default 1.0). The factor can be rational and can be less
than one for subpixel weighting.
--taper-gaussian=TAPER_GAUSSIAN Taper the weights with a Gaussian function ('--taper-gaussian <beamsize>').
This will reduce the contribution of long baselines. The beamsize is by
default in asec, but a unit can be specified ('2amin').
--taper-tukey=TAPER_TUKEY Taper the outer weights with a Tukey transition ('--taper-tukey <lambda>').
Lambda specifies the size of the transition; use in combination with option
'maxuv-l'.
--taper-inner-tukey=TAPER_INNER_TUKEY Taper the weights with a Tukey transition ('--taper-inner-tukey <lambda>').
Lambda specifies the size of the transition; use in combination with option
'minuv-l'.
--taper-edge=TAPER_EDGE Taper the weights with a rectangle, to keep a space of lambda between the
edge and gridded visibilities.
--taper-edge-tukey=TAPER_EDGE_TUKEY Taper the edge weights with a Tukey window ('--taper-edge-tukey <lambda>').
Lambda is the size of the Tukey transition. When option 'taper-edge' is also
specified, the Tukey transition starts inside the inner rectangle.
--maxuv-l=MAXUV_L Set the min/max uv distance in lambda (--maxuv-l <lambda>).
--minuv-l=MINUV_L Set the min/max uv distance in lambda (--minuv-l <lambda>).
--make-psf-only Only make the psf, no images are made.
PSF slice:
--beamwidth=BEAMWIDTH Beamwidth in arcseconds
--crop Crop the PSF to size
Basic usage to generate antenna table
mkspsf ../config/mkat_antennas.enu --enu --table
Snap shot image using default setting
mkspsf --cfg ../config/makems.cfg --enu ../config/mkat_antennas.enu --stime 2017/02/15/19:19:00 --crop
MeerKAT antenna positions are provided in ENU coordinates and require the --enu flag
Since the PSF will rotate with hour angle, --stime can be specified to get the shape at some user selected time, else the PSF at local time will be generated
Very narrow beam with the longest baselines, so the PSF output image is cropped, --crop, for better display
- A CASA ANTENNA table will be generated from the antenna positions provided in the ENU format config file
- A CASA measurement set will be simulated using default configuration
- PSF will be simulated and FITS image created
Snap shot image at a range of declinations, using a pre-existing ANTENNA table
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --dec -90d00m00s --stime 2017/02/15/19:25:00 --crop --weight briggs --robust -0.5 --synthesis 180 --dt 256
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --dec -60d00m00s --stime 2017/02/15/19:25:00 --crop --weight briggs --robust 0.0
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --dec -30d00m00s --stime 2017/02/15/19:25:00 --crop --weight briggs --robust -0.5
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --dec 10d00m00s --stime 2017/02/15/19:25:00 --crop --weight briggs --robust -0.5
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --dec 30d00m00s --stime 2017/02/15/19:25:00 --crop --weight briggs --robust -0.5
Single long integration
Single 12 hour synthesis scan, dumping every 256 seconds, starting at a specified date, pointing at declination -30 degrees
mkspsf --cfg ../config/makems.cfg --enu ../config/mkat_antennas.enu --synthesis 43200 --dt 256 --dec -30d00m00s --stime 2017/01/01/09:00:00
Concatenated measurement sets
4 hour scan (8 half hour scans 1.5 hours apart)
mkspsf --cfg ../config/makems.cfg --enu ../config/mkat_antennas.enu --synthesis 14400 --dtime 1.5 --dt 256 --stime 2014/01/01/09:00:00 --crop
2 hour scan (4 half hour scans 3 hours apart)
mkspsf --cfg ../config/makems.cfg --enu ../config/mkat_antennas.enu --synthesis 7200 --dtime 3 --dt 256 --stime 2014/01/01/09:00:00 --crop
15 minute scan (2 7.5 minute scans 6 hours apart)
mkspsf --cfg ../config/makems.cfg --enu ../config/mkat_antennas.enu --synthesis 900 --dtime 6 --dt 256 --stime 2014/01/01/09:00:00 --crop
Create a simulated PSF for the following observation setup
Beamformer observation to map the beam shape uses a 10 min drift scan over a target.
Observed: 2017-02-21: 15:27:58.654 SAST 15:37:58.400 SAST
Dump rate / period: 0.25011 Hz / 3.998 s
Antennas: m001,m006,m010,m014,m021,m025,m031,m034
Freq:
- Correlator: 1284.0, 856.0, 4096, 208.984
- Beamformer: 1284.0, 428.0, 2048, 208.984
Az: 155:10:19.4
El: 45:24:03.3
RA: 04:08:20.37884
Dec: -65:45:09.0806
Since output is to the current working directory, create a temporary work space
mkdir fbf_beamshape
cd fbf_beamshape
[Optional] To prevent accidental removal of work while trying out various options, create a file that will help you remove intermediate output safely:
Use a text editor to create a text file called Makefile
Paste the following:
clean:
rm -f *.pyc
rm -f *.log *.last *.loc
rm -rf *_p0
realclean: clean
rm -f *.png *.fits
clobber: realclean
rm -f *.enu *.cfg
rm -rf *ANTENNA*
Execute using: make [clean/realclean/clobber]
-
make cleanwill remove temporary files generated in the simulation process -
make realcleanwill remove temporary files as well as output images generated by the simulations -
make clobberwill also remove the generated antenna table and other generated configuration files
Simulating the PSF
Generate a custom antenna table (mkat_ANTENNA) for selected antennas in working directory
mkspsf ../config/mkat_antennas.enu --enu --table --ant_list='m001,m006,m010,m014,m021,m025,m031,m034'
Simulate PSF for observation
make realclean
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --weight uniform --dec -65d45m09.0806s --ra 04h08m20.37884s --stime 2017/02/21/13:27:58
display *.png
make realclean
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --weight briggs --dec -65d45m09.0806s --ra 04h08m20.37884s --stime 2017/02/21/13:27:58
display *.png
make realclean
mkspsf --cfg ../config/makems.cfg --ant mkat_ANTENNA/ --weight natural --dec -65d45m09.0806s --ra 04h08m20.37884s --stime 2017/02/21/13:27:58
display *.png
Save antenna locations to config file for reuse
make clobber
mksarray --enu ../config/mkat_antennas.enu --ant 'm001,m006,m010,m014,m021,m025,m031,m034' -s -o -v
mv subarray.itrf ../config/mkat_8ant_subarray.itrf