Calibrating an EVLA OSRO HI data set
Overview
Currently, this describes the reduction of the Leo Ring dataset collected with WIDAR0. This page will need to be revised when "real" OSRO data is acquired.
Importing Data
importing data will probably be quirky; let's not discuss the details of this yet.
Get Some Basic Information on Your Data
Use listobs (roughly equivalent to LISTR in AIPS) to list information about your scans, correlator setup, and antenna positions.
# listobs :: List data set summary in the logger
vis = 'leotest.ms' # Name of input visibility file (MS)
verbose = True
async = False # If true the taskname must be started using
# listobs(...)
will produce output that looks like this:
2010-02-11 18:11:34 INFO listobs ########################################## 2010-02-11 18:11:34 INFO listobs ##### Begin Task: listobs ##### 2010-02-11 18:11:34 INFO listobs::::casa 2010-02-11 18:11:34 INFO listobs ================================================================================ 2010-02-11 18:11:34 INFO listobs MeasurementSet Name: /export/home/rso-lchomiuk/test/Leo/leotest.ms MS Version 2 2010-02-11 18:11:34 INFO listobs ================================================================================ 2010-02-11 18:11:34 INFO listobs Observer: leo2pt Project: T.B.D. 2010-02-11 18:11:34 INFO listobs Observation: VLA 2010-02-11 18:11:34 INFO listobs Data records: 70290 Total integration time = 11264.5 seconds 2010-02-11 18:11:34 INFO listobs Observed from 18-Dec-2009/10:52:17.0 to 18-Dec-2009/14:00:01.5 (UTC) 2010-02-11 18:11:35 INFO listobs::ms::summary 2010-02-11 18:11:35 INFO listobs ObservationID = 0 ArrayID = 0 2010-02-11 18:11:35 INFO listobs Date Timerange (UTC) Scan FldId FieldName nVis Int(s) SpwIds 2010-02-11 18:11:35 INFO listobs 18-Dec-2009/10:52:17.0 - 10:53:45.0 1 0 J1042+1203 660 9.6 [0] 2010-02-11 18:11:35 INFO listobs 10:54:14.0 - 10:56:51.5 2 1 J1042+1203 1122 9.71 [0] 2010-02-11 18:11:35 INFO listobs 10:57:20.0 - 11:06:57.5 3 2 Leo-1 3894 9.92 [0] 2010-02-11 18:11:35 INFO listobs 11:07:25.0 - 11:17:03.0 4 3 Leo-2 3894 9.93 [0] 2010-02-11 18:11:35 INFO listobs 11:17:32.0 - 11:22:10.0 5 2 Leo-1 1914 9.86 [0] 2010-02-11 18:11:35 INFO listobs 11:22:39.0 - 11:27:16.5 6 3 Leo-2 1914 9.83 [0] 2010-02-11 18:11:35 INFO listobs 11:27:45.0 - 11:30:23.5 7 1 J1042+1203 1122 9.82 [0] 2010-02-11 18:11:35 INFO listobs 11:30:52.0 - 11:40:30.0 8 2 Leo-1 3894 9.93 [0] 2010-02-11 18:11:35 INFO listobs 11:40:59.0 - 11:50:36.5 9 3 Leo-2 3894 9.92 [0] 2010-02-11 18:11:35 INFO listobs 11:51:05.0 - 11:55:42.5 10 2 Leo-1 1914 9.83 [0] 2010-02-11 18:11:35 INFO listobs 11:56:11.0 - 12:00:49.0 11 3 Leo-2 1914 9.86 [0] 2010-02-11 18:11:35 INFO listobs 12:01:18.0 - 12:03:56.0 12 1 J1042+1203 1122 9.76 [0] 2010-02-11 18:11:35 INFO listobs 12:04:25.0 - 12:14:03.0 13 2 Leo-1 3894 9.93 [0] 2010-02-11 18:11:35 INFO listobs 12:14:32.0 - 12:24:09.0 14 3 Leo-2 3894 9.9 [0] 2010-02-11 18:11:35 INFO listobs 12:24:37.0 - 12:29:15.0 15 2 Leo-1 1914 9.86 [0] 2010-02-11 18:11:35 INFO listobs 12:29:44.0 - 12:34:21.5 16 3 Leo-2 1914 9.83 [0] 2010-02-11 18:11:35 INFO listobs 12:34:49.0 - 12:37:28.0 17 1 J1042+1203 1122 9.88 [0] 2010-02-11 18:11:35 INFO listobs 12:37:57.0 - 12:47:35.0 18 2 Leo-1 3894 9.93 [0] 2010-02-11 18:11:35 INFO listobs 12:48:04.0 - 12:57:41.5 19 3 Leo-2 3894 9.92 [0] 2010-02-11 18:11:35 INFO listobs 12:58:10.0 - 13:02:48.0 20 2 Leo-1 1914 9.86 [0] 2010-02-11 18:11:35 INFO listobs 13:03:17.0 - 13:07:54.5 21 3 Leo-2 1914 9.83 [0] 2010-02-11 18:11:35 INFO listobs 13:08:23.0 - 13:11:01.5 22 1 J1042+1203 1122 9.82 [0] 2010-02-11 18:11:35 INFO listobs 13:11:31.0 - 13:21:08.5 23 2 Leo-1 3894 9.92 [0] 2010-02-11 18:11:35 INFO listobs 13:21:37.0 - 13:31:14.5 24 3 Leo-2 3894 9.92 [0] 2010-02-11 18:11:35 INFO listobs 13:31:43.0 - 13:36:21.0 25 2 Leo-1 1914 9.86 [0] 2010-02-11 18:11:35 INFO listobs 13:36:50.0 - 13:41:27.5 26 3 Leo-2 1914 9.83 [0] 2010-02-11 18:11:35 INFO listobs 13:41:56.0 - 13:44:34.5 27 1 J1042+1203 1122 9.82 [0] 2010-02-11 18:11:35 INFO listobs 13:48:02.0 - 14:00:01.5 28 4 1331+305 4818 9.99 [0] 2010-02-11 18:11:35 INFO listobs (nVis = Total number of time/baseline visibilities per scan) 2010-02-11 18:11:35 INFO listobs Fields: 5 2010-02-11 18:11:35 INFO listobs ID Code Name RA Decl Epoch SrcId nVis 2010-02-11 18:11:35 INFO listobs 0 NONE J1042+1203 10:42:44.6052 +12.03.31.2641 J2000 0 660 2010-02-11 18:11:35 INFO listobs 1 D J1042+1203 10:42:44.6052 +12.03.31.2641 J2000 1 6732 2010-02-11 18:11:35 INFO listobs 2 NONE Leo-1 10:47:22.0000 +12.16.38.0000 J2000 2 29040 2010-02-11 18:11:35 INFO listobs 3 NONE Leo-2 10:46:45.0000 +11.50.38.0000 J2000 3 29040 2010-02-11 18:11:35 INFO listobs 4 K 1331+305 13:31:08.2880 +30.30.32.9589 J2000 4 4818 2010-02-11 18:11:35 INFO listobs (nVis = Total number of time/baseline visibilities per field) 2010-02-11 18:11:35 INFO listobs Spectral Windows: (1 unique spectral windows and 1 unique polarization setups) 2010-02-11 18:11:35 INFO listobs SpwID #Chans Frame Ch1(MHz) ChanWid(kHz)TotBW(kHz) Ref(MHz) Corrs 2010-02-11 18:11:35 INFO listobs 0 256 TOPO 1415.3756 7.8125 2000 1415.3756 RR LL 2010-02-11 18:11:35 INFO listobs Sources: 6 2010-02-11 18:11:35 INFO listobs ID Name SpwId RestFreq(MHz) SysVel(km/s) 2010-02-11 18:11:35 INFO listobs 0 J1042+1203 0 - - 2010-02-11 18:11:35 INFO listobs 1 J1042+1203 0 - - 2010-02-11 18:11:35 INFO listobs 2 Leo-1 0 - - 2010-02-11 18:11:35 INFO listobs 3 Leo-2 0 - - 2010-02-11 18:11:35 INFO listobs 4 J1331+3030 0 - - 2010-02-11 18:11:35 INFO listobs 5 J1331+3030 0 - - 2010-02-11 18:11:35 INFO listobs Antennas: 12: 2010-02-11 18:11:35 INFO listobs ID Name Station Diam. Long. Lat. 2010-02-11 18:11:35 INFO listobs 0 ea02 E02 25.0 m -107.37.04.4 +33.54.01.1 2010-02-11 18:11:35 INFO listobs 1 ea03 E09 25.0 m -107.36.45.1 +33.53.53.6 2010-02-11 18:11:35 INFO listobs 2 ea04 W01 25.0 m -107.37.05.9 +33.54.00.5 2010-02-11 18:11:35 INFO listobs 3 ea05 W08 25.0 m -107.37.21.6 +33.53.53.0 2010-02-11 18:11:35 INFO listobs 4 ea08 N01 25.0 m -107.37.06.0 +33.54.01.8 2010-02-11 18:11:35 INFO listobs 5 ea09 E06 25.0 m -107.36.55.6 +33.53.57.7 2010-02-11 18:11:35 INFO listobs 6 ea15 W06 25.0 m -107.37.15.6 +33.53.56.4 2010-02-11 18:11:35 INFO listobs 7 ea19 W04 25.0 m -107.37.10.8 +33.53.59.1 2010-02-11 18:11:35 INFO listobs 8 ea24 W05 25.0 m -107.37.13.0 +33.53.57.8 2010-02-11 18:11:35 INFO listobs 9 ea25 N02 25.0 m -107.37.06.2 +33.54.03.5 2010-02-11 18:11:35 INFO listobs 10 ea27 E03 25.0 m -107.37.02.8 +33.54.00.5 2010-02-11 18:11:35 INFO listobs 11 ea28 N08 25.0 m -107.37.07.5 +33.54.15.8 2010-02-11 18:11:35 INFO listobs::::casa 2010-02-11 18:11:35 INFO listobs ##### End Task: listobs ##### 2010-02-11 18:11:35 INFO listobs ##########################################
Some things to note here are: The phase calibrator is called J1042+1203, the flux calibrator is 1331+305, and there are two science pointings, Leo-1 and Leo-2. The correlator is set up in such a way to have one spectral window (or IF). This window is sampled with 256 channels each 7.8 kHz wide. There are no cross-polarization data (note that 'Corrs' is set to only 'RR LL').
Choose a Reference Antenna
You'd like your reference antenna to be near the center of the array, and the easiest way to envision the array layout is with plotants.
# plotants :: Plot the antenna distribution in the local reference frame:
vis = 'leotest.ms' # Name of input visibility file (MS)
figfile = '' # Save the plotted figure to this file
async = False # If true the taskname must be started using
# plotants(...)
will produce a plot that looks like this:
You can zoom and pan if you click on this icon: 
. Then, holding down your left mouse button and fiddling with the mouse will let you pan; holding down the right mouse button and fiddling with the mouse enables zooming in and out. Make note of an antenna near the center of the array, and check the observing logs to make sure nothing fishy happened to it during the observations. You can also take a quick look at the antenna in plotms to make sure it looks reasonably steady (we'll talk more about plotms below).
First Round of Data Flagging
Oftentimes, the first few integrations of each scan are bad, and you'd like to flag them. This is called 'quack' a la AIPS, and is implemented using flagdata. This is what the default flagdata parameters look like in your CASA window:
Tip: You'll notice that some parameters are colored differently than others. Standard parameters (familiar from AIPS) are simple black text (like 'vis' above). Parameters which are shaded grey (like 'selectdata') are expandable, and once they have been expanded (like 'mode'), green sub-parameters (like 'autocorr') will appear. Note that if you were to change 'mode' from 'manualflag' to, say, 'quack', a different menu of green sub-parameters would appear.
To quack the first 10 seconds of each scan, set the flagdata parameters to:
# flagdata :: All purpose flagging task based on selections
vis = 'leotest.ms' # Name of file to flag
flagbackup = True # Automatically back up the current flags?
mode = 'quack' # Mode (manualflag,shadow,quack,summary,autoflag,rfi)
autocorr = False # Flag autocorrelations
unflag = False # Unflag the data specified
quackinterval = 10 # Quack n seconds from scan beginning/end
quackmode = 'beg' # Quack mode. 'beg' ==> beginning of scan. 'endb' ==> end of
# scan. 'end' ==> all but end of scan. 'tail' ==> all but
# beginning of scan
quackincrement = False # Flag incrementally in time?
spw = '' # spectral-window/frequency/channel
field = '' # Field names or field index numbers: ''==>all,
# field='0~2,3C286'
selectdata = False # More data selection parameters (antenna, timerange etc)
async = False # If true the taskname must be started using flagdata(...)
Now is also the time to flag any obviously aberrant data in your calibrators. You might choose to flag with viewer, which displays a raster image of your uv data and is similar to SPFLG and TVFLG in AIPS (click here for an introduction to viewer). Alternatively, you can flag using a 2-dimensional interactive plot with plotms click here for an introduction to plotms). The plotting capabilities are similar to UVPLT in AIPS, and plotted points can be flagged (like WIPER in AIPS).
