rascil_sensitivity
rascil_sensitivity is a command line app written using RASCIL. It allows calculation of point source sensitivity (pss) and surface brightness sensitivity (sbs). The analysis is based on Dan Briggs’s PhD thesis https://casa.nrao.edu/Documents/Briggs-PhD.pdf
rascil_sensitivity works by constructing a Visibility set and running invert to obtain the point spread function. The visibility weights in the Visibility are constructed to be equal to the time-bandwidth product each visibility sample. For natural weighting, these weights are used as the imaging weights. The sum of gridded weights therefore gives the total time-bandwidth of the observation. Given Tsys and efficiency it can then calculate the point source sensitivity. To obtain the surface brightness sensitivity, we calculate the solid angle of the clean beam fitted to the PSF, and divide the point source sensitivity by the solid angle.
Weighting schemes such as robust weighting and visibility tapering modify the imaging weights. The point source sensitivity always worsens compared to natural weighting but the surface brightness sensitivity may improve.
The robustness parameter and the visibility taper can be specified as single values or as a list of values to test.
The array configuration is specified by 2 parameters: configuration identifies a table with details of the available dishes, subarray names a json file listing the ids (i.e. row numbers in the configuration table) of the dishes to be used. If no subarray is specified then all dishes will be selected. The json format is:
{"ids": [64, 65, 66, 67, 68, 69, 70, ....etc.]}
The principal output is a CSV file, written by pandas in which all values of robustness and taper are tested, along with natural weighting.
The processing is distributed using Dask over all frequency channels specified.
Example script
The following:
python $RASCIL/rascil/apps/rascil_sensitivity.py --results range_0.5_int_20 --time_range -0.25 0.25 \
--integration_time 20 --msfile range_0.5_int_20.ms
produces the output:
Final results:
weighting robustness taper cleanbeam_bmaj cleanbeam_bmin cleanbeam_bpa ... pss_casa reltonat_casa sa sbs tb sbs_casa
0 uniform 0.0 0.0 0.000124 0.000106 0.348636 ... 5.055773e-08 4.214877 5.290084e-12 4.844478e+06 7.435200e+13 9557.074591
1 robust -2.0 0.0 0.000125 0.000107 0.346705 ... 4.907281e-08 4.091084 5.423607e-12 4.528158e+06 8.096404e+13 9048.003290
2 robust -1.5 0.0 0.000138 0.000119 0.366295 ... 4.237805e-08 3.532957 6.570541e-12 2.905383e+06 1.339994e+14 6449.703859
3 robust -1.0 0.0 0.000220 0.000209 19.006936 ... 3.168845e-08 2.641790 1.669975e-11 6.384441e+05 4.295821e+14 1897.540277
4 robust -0.5 0.0 0.000328 0.000316 40.826795 ... 2.208990e-08 1.841582 3.703912e-11 1.701715e+05 1.229183e+15 596.393758
5 robust 0.0 0.0 0.000454 0.000437 33.235117 ... 1.618849e-08 1.349596 7.111900e-11 5.956637e+04 2.721061e+15 227.625391
6 robust 0.5 0.0 0.000600 0.000577 30.284717 ... 1.360183e-08 1.133952 1.242658e-10 2.643972e+04 4.523710e+15 109.457521
7 robust 1.0 0.0 0.000729 0.000702 -149.373492 ... 1.228866e-08 1.024476 1.836020e-10 1.549264e+04 6.035397e+15 66.930950
8 robust 1.5 0.0 0.000791 0.000761 30.715780 ... 1.200501e-08 1.000829 2.160325e-10 1.241103e+04 6.792939e+15 55.570408
9 robust 2.0 0.0 0.000802 0.000772 -149.271796 ... 1.199519e-08 1.000010 2.221125e-10 1.194877e+04 6.932970e+15 54.005008
10 natural 0.0 0.0 0.000804 0.000773 -149.270574 ... 1.199506e-08 1.000000 2.228600e-10 1.189396e+04 6.950160e+15 53.823312
[11 rows x 24 columns]
Command line arguments
Calculate relative sensitivity for MID observations
usage: rascil_sensitivity [-h] [--use_dask USE_DASK]
[--imaging_npixel IMAGING_NPIXEL] [--msfile MSFILE]
[--imaging_cellsize IMAGING_CELLSIZE]
[--imaging_oversampling IMAGING_OVERSAMPLING]
[--imaging_weighting IMAGING_WEIGHTING]
[--imaging_robustness [IMAGING_ROBUSTNESS ...]]
[--imaging_taper [IMAGING_TAPER ...]] [--ra RA]
[--tsys TSYS] [--efficiency EFFICIENCY]
[--diameter DIAMETER] [--declination DECLINATION]
[--configuration CONFIGURATION]
[--subarray SUBARRAY] [--rmax RMAX]
[--frequency FREQUENCY]
[--integration_time INTEGRATION_TIME]
[--time_range TIME_RANGE TIME_RANGE] [--nchan NCHAN]
[--channel_width CHANNEL_WIDTH] [--verbose VERBOSE]
[--results RESULTS]
Named Arguments
- --use_dask
Use dask processing?
Default: “True”
- --imaging_npixel
Number of pixels in ra, dec: Should be a composite of 2, 3, 5
Default: 1024
- --msfile
Export Measurement file.
Default: “”
- --imaging_cellsize
Cellsize (radians). Default is to calculate.
- --imaging_oversampling
Oversampling of synthesised_beam (Default 3.0)
Default: 3.0
- --imaging_weighting
Type of weighting: uniform or robust or natural
- --imaging_robustness
Robustness for robust weighting,
Default: [-2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0]
- --imaging_taper
If set, use value for Gaussian taper, specified as radians in image plane
- --ra
Right ascension (degrees)
Default: 15.0
- --tsys
System temperature (K)
Default: 20.0
- --efficiency
Correlator efficiency
Default: 1.0
- --diameter
MID antenna diameter (m)
Default: 15.0
- --declination
Declination (degrees)
Default: -45.0
- --configuration
Name of configuration or path: MID(=MIDR5), MIDR5, MEERKAT+
Default: “MIDR5”
- --subarray
Name of json file describing subarray to be used, default is all antennas
Default: “”
- --rmax
Maximum distance of station from centre (m)
Default: 200000.0
- --frequency
Centre frequency (Hz)
Default: 1360000000.0
- --integration_time
Integration time (s)
Default: 600
- --time_range
Hour angle range in hours
Default: [-4.0, 4.0]
- --nchan
Number of channels
Default: 1
- --channel_width
Channel bandwidth (Hz)
Default: 100000000.0
- --verbose
Verbose output?
Default: “False”
- --results
Root name for output files
Default: “rascil_sensitivity”