|
|
| Line 1: |
Line 1: |
| == Help on polcal task: ==
| | {{polcal}} |
| <pre>
| |
| Determine instrumental polarization calibrations
| |
| | |
| The instrumental polarization factors (D-terms), the calibrator polarization,
| |
| and the R-L polarization angle can be determined using polcal. The solutions
| |
| can be obtained for each antenna/spwid and even individual channels, if desired.
| |
| Previous calibrations of the total intensity data should be applied on the fly
| |
| when running polcal, since polcal uses the 'data' column, not the 'corrected'
| |
| column.
| |
| | |
| After calibrating the total intensities, the simplest way to calibrate the
| |
| polarization data is:
| |
| | |
| a) Run polcal with poltype = 'D+QU' on the main 'calibrator' source. The D terms
| |
| and polarization (QU) of the calibrator will be determined. Relatively good
| |
| parallactic angle coverage is needed.
| |
| | |
| b) If there is little parallactic angle coverage, place the known calibration of
| |
| the main calibrator (or 0) using setjy with the appropriate fluxdensity. Then
| |
| run polcal with poltype = 'D'. Run plotcal with xaxis = 'real'; yaxis ='imag'
| |
| to view solutions.
| |
| | |
| c) To determine R-L polarization angle, use setjy to put the fluxdensity of the
| |
| polarization calibrator [I,Q,U,0.0] in the model column. For resolved sources
| |
| put in values associated with an appropriate u-v range. Polarized models are
| |
| not yet available for the major polarization standard sources, so very
| |
| resolved polarized sources should not be used.
| |
| | |
| d) Run polcal with poltype = 'X' and include polarization standard. Make sure to
| |
| include all previous calibrations, especially the D results. Run plotxy with
| |
| correlation = 'RL LR' and make sure polarization angles are as expected.
| |
| | |
| e) Run applycal with all calibration table, include the D and X tables. Make sure
| |
| that parang = T
| |
| | |
| NOTE: For very high dynamic range, add 'f' after D to determine D terms for each
| |
| channel.
| |
| | |
| Keyword arguments:
| |
| vis -- Name of input visibility file
| |
| default: none; example: vis='ngc5921.ms'
| |
| caltable -- Name of output gain calibration table
| |
| default: none; example: caltable='ngc5921.dcal'
| |
| | |
| --- Data Selection (see help par.selectdata for more detailed information)
| |
| | |
| field -- Select field using field id(s) or field name(s).
| |
| [run listobs to obtain the list id's or names]
| |
| default: ''=all fields.
| |
| Most likely, the main calibrator source should be picked.
| |
| If field string is a non-negative integer, it is assumed a field index
| |
| otherwise, it is assumed a field name
| |
| field='0~2'; field ids 0,1,2
| |
| field='0,4,5~7'; field ids 0,4,5,6,7
| |
| field='3C286,3C295'; field named 3C286 adn 3C295
| |
| field = '3,4C*'; field id 3, all names starting with 4C
| |
| spw -- Select spectral window/channels
| |
| type 'help par.selection' for more examples.
| |
| spw='0~2,4'; spectral windows 0,1,2,4 (all channels)
| |
| spw='<2'; spectral windows less than 2 (i.e. 0,1)
| |
| spw='0:5~61'; spw 0, channels 5 to 61, INCLUSIVE
| |
| spw='*:5~61'; all spw with channels 5 to 62
| |
| spw='0,10,3:3~45'; spw 0,10 all channels, spw 3, channels 3 to 45.
| |
| spw='0~2:2~6'; spw 0,1,2 with channels 2 through 6 in each.
| |
| spw='0:0~10;15~60'; spectral window 0 with channels 0-10,15-60
| |
| NOTE ';' to separate channel selections
| |
| spw='0:0~10^2,1:20~30^5'; spw 0, channels 0,2,4,6,8,10,
| |
| spw 1, channels 20,25,30
| |
| selectdata -- Other data selection parameters
| |
| default: True
| |
| timerange -- Select data based on time range:
| |
| default = '' (all); examples,
| |
| timerange = 'YYYY/MM/DD/hh:mm:ss~YYYY/MM/DD/hh:mm:ss'
| |
| Note: if YYYY/MM/DD is missing dat defaults to first day in data set
| |
| timerange='09:14:0~09:54:0' picks 40 min on first day
| |
| timerange= '25:00:00~27:30:00' picks 1 hr to 3 hr 30min on next day
| |
| timerange='09:44:00' data within one integration of time
| |
| timerange='>10:24:00' data after this time
| |
| uvrange -- Select data within uvrange (default units meters)
| |
| default: '' (all); example:
| |
| uvrange='0~1000'; uvrange from 0-1000 kilo-lamgda
| |
| uvrange='>4';uvranges greater than 4 kilo-lambda
| |
| antenna -- Select data based on antenna/baseline
| |
| default: '' (all)
| |
| If antenna string is a non-negative integer, it is assumed an antenna index
| |
| otherwise, it is assumed as an antenna name
| |
| antenna='5&6'; baseline between antenna index 5 and index 6.
| |
| antenna='VA05&VA06'; baseline between VLA antenna 5 and 6.
| |
| antenna='5&6;7&8'; baseline 5-6 and 7-8
| |
| antenna='5'; all baselines with antenna index 5
| |
| antenna='05'; all baselines with antenna name 05, i.e. VLA ant 5
| |
| antenna='5,6,10'; all baselines with antennas 5, 6 and 10
| |
| scan -- Scan number range
| |
| msselect -- Optional complex data selection (ignore for now)
| |
| | |
| --- Solution parameters
| |
| poltype -- Type of instrumental polarization solution
| |
| 'D+QU' (or 'Df+QU') solve also for apparent source polarization (channelized D)
| |
| Need relatively good parallactic angle coverage for this
| |
| 'D' (or 'Df') solve only for instrumental polarization (channelized). The
| |
| I, Q, U flux density of the source can be placed in the model column using
| |
| setjy. Use for poor parallactic angle coverage.
| |
| 'X' = solve only for position angle correction. The source must have its
| |
| I, Q, U flux density in the model column. If the source is resolved, use
| |
| a uvrange that is appropriate.
| |
| 'D+X' (or 'Df+X') = solve also for position angle offset (channelized D) as
| |
| well as the D-term. Not normally done.
| |
| default: 'D+QU'
| |
| The solution used the traditional linear approximation. Non-linearized options
| |
| will be avaible soon.
| |
| solint -- Solution interval (units optional)
| |
| default: 'inf' (~infinite, up to boundaries controlled by combine);
| |
| Options: 'inf' (~infinite), 'int' (per integration), any float
| |
| or integer value with or without units
| |
| examples: solint='1m'; solint='60s', solint=60 --> 1 minute
| |
| solint='0s'; solint=0; solint='int' --> per integration
| |
| solint-'-1s'; solint='inf' --> ~infinite, up to boundaries
| |
| enforced by combine
| |
| combine -- Data axes to combine for solving
| |
| default: 'scan' --> solutions will break at field and spw boundaries,
| |
| but may extend over multiple scans (per field and spw) up
| |
| to solint.
| |
| Options: '','scan','spw',field', or any comma-separated combination
| |
| example: combine='scan,spw' --> extend solutions over scan boundaries
| |
| (up to the solint), and combine spws for solving
| |
| preavg -- Pre-averaging interval (sec)
| |
| default=300
| |
| Interval to apply parallactic angle.
| |
| refant -- Reference antenna name
| |
| default: '' => refant = '0'
| |
| example: refant='13' (antenna with index 13)
| |
| refant='VA04' (VLA antenna #4)
| |
| Use 'go listobs' for antenna listing.
| |
| USE SAME REFERENCE ANTENNA AS USED FOR I CALIBRATION.
| |
| minblperant -- Minimum number of baselines required per antenna for each solve
| |
| Antennas with fewer baaselines are excluded from solutions. Amplitude
| |
| solutions with fewer than 4 baselines, and phase solutions with fewer
| |
| than 3 baselines are only trivially constrained, and are no better
| |
| than baseline-based solutions.
| |
| default: 4
| |
| example: minblperant=10 => Antennas participating on 10 or more
| |
| baselines are included in the solve
| |
| minsnr -- Reject solutions below this SNR
| |
| default: 0.0 (accept all attempted solutions)
| |
| append -- Append solutions to the (existing) table
| |
| default: False; overwrite existing table or make new table
| |
| | |
| --- Other calibrations to apply on the fly before determining gaincal solution
| |
| | |
| gaintable -- Gain calibration table(s) to apply
| |
| default: '' (none); BUT I CALIBRATION TABLES SHOULD GENERALLY BE INCLUDED
| |
| examples: gaintable='ngc5921.gcal'
| |
| gaintable=['ngc5921.ampcal','ngc5921.phcal']
| |
| gainfield -- Select a subset of calibrators from gaintable(s)
| |
| default:'' ==> all sources in table;
| |
| same syntax as field
| |
| example: gainfield='0~3'
| |
| gainfield=['0~3','4~6'] means use field 0 through 3
| |
| from first gain file, field 4 through 6 for second.
| |
| interp -- Interpolation mode (in time) to use for each gaintable
| |
| default: '' --> 'linear' for all gaintable(s)
| |
| example: interp='nearest'
| |
| interp=['nearest','linear']
| |
| Options: 'nearest', 'linear', 'aipslin'
| |
| spwmap -- Spectral windows combinations to form for gaintable(s)
| |
| default: [] (apply solutions from each spw to that spw only)
| |
| Example: spwmap=[0,0,1,1] means apply the caltable solutions
| |
| from spw = 0 to the spw 0,1 and spw 1 to spw 2,3.
| |
| spwmap=[[0,0,1,1],[0,1,0,1]]
| |
| gaincurve -- Apply internal VLA antenna gain curve correction (True/False)
| |
| default: False;
| |
| Use gaincurve=True ONLY for VLA data
| |
| opacity -- Opacity correction to apply (nepers)
| |
| default: 0.0 (no opacity correction)
| |
| example: opacity=0.051
| |
| Typical VLA values are: 5 GHz - 0.013, 8 GHz - 0.013
| |
| 15 GHz - 0.016, 23 GHz - 0.051, 43 GHz - 0.07
| |
| async -- Run asynchronously
| |
| default = False; do not run asychronously
| |
| </pre>
| |
