importvla

importvla(archivefiles, vis='', bandname='', frequencytol='150000.0Hz', project='', starttime='', stoptime='', applytsys=True, autocorr=False, antnamescheme='new', keepblanks=False, evlabands=False)[source]

Import VLA archive file(s) to a measurement set

[Description] [Examples] [Development] [Details]

Parameters

  • archivefiles (pathVec) - Name of input VLA archive file(s)

  • vis (string=’’) - Name of output visibility file

  • bandname (string=’’) - VLA frequency band name:''=>obtain all bands in the archive file

  • frequencytol (string=’150000.0Hz’) - Frequency shift to define a unique spectra window (Hz)

  • project (string=’’) - Project name: '' => all projects in files

  • starttime (string=’’) - Start time to search for data

  • stoptime (string=’’) - End time to search for data

  • applytsys (bool=True) - Apply nominal sensitivity scaling to data and weights

  • autocorr (bool=False) - Import autocorrelations to MS, if set to True

  • antnamescheme (string=’new’) - 'old' or 'new'; 'VA04' or '04' for VLA ant 4

  • keepblanks (bool=False) - Fill scans with blank (empty) source names (e.g. tipping scans)

  • evlabands (bool=False) - Use updated eVLA frequencies and bandwidths for bands and wavelengths

Description

The task importvla reads in VLA data in archive format, as downloaded from the VLA data archive. It will handle archival VLA data in both old style (before July 2007) and new style (after July 2007). It can apply the system temperature (Tsys) to the data and to the weights. If more than one band is present, each band will be put in the same MeasurementSet but in a separate spectral window.

Note

NOTE: importvla will import the on-line flags (from the VLA system) along with the data. Shadowed antennas will also be flagged. The flags will be put in the MAIN table and thus available to subsequent tasks and tools. If you wish to revert to unflagged data, use flagmanager to save the flags (if you wish), and then use flagdata with mode=’manualflag’ and unflag=True to toggle off the flags.

Parameter descriptions

archivefiles

The parameter archivefiles is used to specify the input VLA Archive format file names, as can be found in the NRAO Archive. Note that archivefiles takes a string or list of strings, as there are often multiple files for a project in the archive. If the data are located in a different directory on disk, then use the full path name to specify each archive file. The scaling of VLA data both before and after the June 2007 Modcomp-turnoff is fully supported, based on the value of applytsys.

vis

Name of output visibility file.

bandname

The importvla task allows selection on the frequency band. The bandname indicates the VLA Frequency band(s) to load, using the traditional bandname codes. These are:

  • ’4’ = 48-96 MHz

  • ’P’ = 298-345 MHz

  • ’L’ = 1.15-1.75 GHz

  • ’C’ = 4.2-5.1 GHz

  • ’X’ = 6.8-9.6 GHz

  • ’U’ = 13.5-16.3 GHz

  • ’K’ = 20.8-25.8 GHz

  • ’Q’ = 38-51 GHz

  • ’’ = all bands (default)

Note

NOTE: After the transition from the VLA to JVLA, the actual frequency ranges covered by the bands have changed, and additional bands have been added (namely ’S’ from 1-2 GHz and ’Ka’ from 26.4-40 GHz). See the frequency ranges of the JVLA bands for details.

frequencytol

The frequencytol parameter specifies the frequency separation tolerated when assigning data to spectral windows. The default is frequencytol=’150000.0Hz’. For Doppler tracked data, where the sky frequency changes with time, a frequencytol < 10000 Hz may produce too many unnecessary spectral windows.

project

You can specify a specific project name to import from archive files. The default ’’ will import data from all projects in file(s) archivefiles. For example for VLA Project AL519:

  • project = ‘AL519’ # this will work

  • project = ‘al519’ # this will also work

Note

NOTE: project=’AL0519’ will NOT work (even though that is what queries to the VLA Archive will print it as).

starttime and stoptime

You can specify start and stop times for the data, e.g., starttime=’1970/1/31/00:00:00’ and stoptime=’2199/1/31/23:59:59’. The blank defaults will load all data fitting other criteria.

applytsys

The applytsys parameter controls whether the nominal sensitivity scaling (based on the measured TSYS, with the weights scaled accordingly using the integration time) is applied to the visibility amplitudes or not. If True, then it will be scaled so as to be the same as AIPS FILLM (i.e., approximately in deciJanskys). Note that post-Modcomp data is in raw correlation coefficient and will be scaled using the TSYS values, while Modcomp-era data had this applied online. In all cases, importvla will do the correct thing to data and weights based on an internal flag in the VLA Archive file, either scaling it or unscaling based on your choice for applytsys.

Note

NOTE: If applytsys=True and you see strange behavior in data amplitudes, it may be due to erroneous TSYS values from the online system. You might want to then fill with applytsys=False and look at the correlation coefficients to see if the behavior is as expected.

autocorr

Autocorrelations are written to the MeasurementSet if autocorr=True. Generally for the VLA, autocorrelation data is not useful, and furthermore the imaging routine will try to image the autocorrelation data (it assumes it is single dish data) which will swamp any real signal. Thus, if you do fill the autocorrelations, you will have to flag them before imaging.

antnamescheme

The antnamescheme parameter controls whether importvla will try to use a naming scheme where JVLA antennas are prefixed with EA (e.g., ’EA16’) and old VLA antennas have names prefixed with VA (e.g., ’VA11’).

keepblanks

Turns on or off whether importvla fills the scans with blank (empty) source names (e.g., tipping scans).

evlabands

The evlabands=True option is provided to allow users to access JVLA frequencies outside the standard VLA tunings (e.g., the extended C-band above 6 GHz).

Warning

WARNING: Use of this option for standard VLA data will cause unexpected associations, such as X-band data below 8 GHz being extracted to C-band (as the JVLA C-band is 4–8 GHz). Use with care.

Notes

If the output vis parameter (MeasurementSet) already exists or is an illegal name, the following SEVERE warning is shown. (<archivefiles> and <vis> are those parameter values):

SEVERE \*\* Error importing <*archivefiles*> to <*vis*>
SEVERE Need valid visibility file name (bad name or already exists)
SEVERE An error occurred running task importvla.

When importvla finishes without writing any rows to the output MeasurementSet (because of the data selection resulting from the parameter settings or because of problems with the data as described below) then this SEVERE error message is shown (”<vis>” is the value of the vis parameter).

SEVERE \*\* visibility file is empty: <*vis*>
SEVERE An error occurred running task importvla.

This task has not been tested on VLA archive data with revisions less than 23. Using importvla to import older revisions results in the following warning message (the revision level of the archive data is shown):

WARN This function has not been tested on VLA archive data with revisions less
WARN than 23 & the data in this record has a revision level of 5
WARN It is very likely that the correlation data will be scaled incorrectly

The epoch value is set to zero in archive data for revsions less than 10. importvla assumes a value of 1950 in that case, resuting in the code using a value of B1950_VLA where necessary in the output MeasurementSet (mean epoch [1979.9] and ecliptic at B1950.0). This warning message is given when that assumption is made:

WARN epoch is 0, assuming B1950_VLA

Records involving unsupported observing modes are skipped by importvla. If only unsupported observing modes are found no rows will be written and the output MeasurementSet will be empty. A warning message similar to the following is shown when an unsupported observing mode is seen, indicating the mode and a short description of that mode.

WARN Unsupported observing mode: IA interferometer pointing
mode A (IF)

The polarization information is sometimes impossible for importvla to determine for some old (early) correlator modes. In that case, the task will skip that record. If no other correlator modes are found in the data the resulting output MeasurementSet will be empty. This is a SEVERE error and may indicate that there are other problems with any data that was written to the MeasurementSet.

SEVERE Unable to determine polarization information for some
or all correlator modes.
SEVERE That data can not be filled and the resulting
visibility file may be empty.

The folllowing warning appears to be limited to revisions 03 and 04 and it may indicate other problems wtih the output MeasurementSet. The check for this condition is always made against the first antenna encountered. All of the antennas that are different from that antenna will be shown in a warning message.

WARN The IF transfer switch for antenna VA04 is different
from the setting for antenna VA01.
WARN Correlations involving this antenna may have incorrect
polarization labelling.

Unsupported Observing Modes

  • “D ” : delay center determination mode

  • “IR” : interferometer reference pointing mode

  • “I*” : interferomter pointing mode * (IF). Where * is one of A, B, C, D.

  • “J*” : JPL mode * (IF). Where * is one of A, B, C, D.”

  • “P*” : single dish pointing mode * (IF). Where * is one of A, B, C, D

  • “TB” : test back-end and front-end

  • “TE” : tipping curve

  • “TF” : test front-end

  • “VS” : single dish VLBI

Examples

To import all K-band data from two archival VLA data-sets and write them out in a single MeasurementSet, taking into account all bands (and placing them in different spectral windows), applying the system temperatures and excluding the auto-correlations:

importvla(archivefiles=['inputfile1','inputfile2'],
          vis='output.ms', bandname='K', applytsys=True, autocorr=False)
Development

No additional development details

Parameter Details

Detailed descriptions of each function parameter

archivefiles (pathVec) - Name of input VLA archive file(s)
Default: none. Must be supplied
Examples:
archivefiles = ‘AP314_A959519.xp1’
archivefiles=[‘AP314_A950519.xp1’,
‘AP314_A950519.xp2’]
vis (string='') - Name of output visibility file
Default: none. Must be supplied
Example: vis=’NGC7538.ms’
NOTE: Will not over-write existing ms of same
name. A backup flag-file version ‘Original’ will
be made in vis.flagversions. See help
flagmanager.
bandname (string='') - VLA frequency band name:
Default: ‘’ (obtain all bands in the archive
file)
Options: ‘4’=48-96 MHz,’P’=298-345
MHz,’L’=1.15-1.75 GHz, ‘C’=4.2-5.1
GHz,’X’=6.8-9.6 GHz,’U’=13.5-16.3 GHz,
‘K’=20.8-25.8 GHz,’Q’=38-51 GHz
Example: bandname=’K’
frequencytol (string='150000.0Hz') - Tolerance in frequency shift in making spectral windows
Default: = 150000.0Hz’
Example: frequencytol = 1500000.0 (units = Hz)
For Doppler shifted data, less than 10000 Hz may
may produce too many unnecessary spectral
windows.
project (string='') - Project name to import from archive files
Default: ‘’ (all projects in file)
Example: project=’AL519’
Project = ‘al519’ or AL519 will work.
WARNING: Do not include leading zeros; project =
‘AL0519’ will not work.
starttime (string='') - Time after which data will be considered for importing
Default: ‘’ (all)
syntax: starttime = ‘2003/1/31/05:05:23’. Date
must be included!
stoptime (string='') - Time before which data will be considered for
importing
Default: ‘’ (all)
syntax: starttime = ‘2003/1/31/08:05:23’. Date
must be included!
applytsys (bool=True) - Apply data scaling and weight scaling by nominal
sensitivity (~Tsys)
Default: True (strongly recommended)
Options: True|False
autocorr (bool=False) - Import autocorrelations to MS
Default: False (no autocorrelations)
Options: False|True
antnamescheme (string='new') - ‘old’ or ‘new’ antenna names.
Default: ‘new’
Options: new|old
* ‘new’ gives antnenna names ‘VA04’ or ‘EA13 for
VLA telescopse 04 and 13 (EVLA)
* ‘old’ gives names ‘04’ or ‘13’
keepblanks (bool=False) - Should sources with blank names be filled into the data
base?
Default: False (do not fill)
Options: False|True
These scans are tipping scans (as of June 1,
2009) and should not be filled in the visibility
data set.
evlabands (bool=False) - Use the EVLA’s center frequency and bandwidths for
frequencies specified via wavelength or band.
Default: False
Options: False|True