Handling ALMA data

NRAO Home > CASA > CASA Cookbook and User Reference Manual

[next] [prev] [prev-tail] [tail] [up]

8.3.2.2 Handling ALMA data

Using importasdm task, ASDM data can be imported to ASAP directly. To do that, you should set singledish=True and specify id or name of the antenna by the antenna parameter (see § 2.2.1). This functionality is still under testing. You can use previous two step process (import ASDM as MS using importasdm task first, then import MS as ASAP format) to import ASDM as ASAP format if you have any problem during direct import.
If the MS data contain data from multiple single dish antennas you need either, to specify the antenna parameter when importing data (sd.scantable) or, to split the data by antenna using sd.splitant for further processing in ASAP since ASAP scantable cannot properly store the data from multiple antennas. The method sd.splitant splits a Measurement Set by antenna ID and save the tables as scantables containing data from each antenna. The names of output scantables are defined as prefix specified by users (with parameter outprefix) + ’.’ + antenna name. For example, if you split Measurement Set, foo.ms, which contains data from antA and antB, with outprefix=’splitted’, i.e., sd.splitant(’foo.ms’, outprefix=’splitted’), the names of scantables are ’splitted.antA’ and ’splitted.antB’. The returned value of the method is a list of scantable names.
It is possible to read the 2-element interferometric data taken by the ALMA telescopes as a single dish data to further examine it using ASAP Toolkit and the SDtasks. The usage is the same as importing single dish data. For example, to load the ALMA interferometry data, myOSFint.ms
s=sd.scantable(’myOSFint.ms’, ’False’)

It is still experimental and limited to data obtained with a two-element array.
In ALMA, Tsys measurement is done in a specific spectral window for calibration so that it is necessary to transfer Tsys to the spectral window for target scan. This will be done using filltsys module. Usage is as follows:
import filltsys
filltsys.fillTsys( filename=’mydata.asap’, specif=5, tsysif=1, mode=’linear’ )

The parameter filename specifies a name of the data to be processed. Data must be in ASAP format. The spectral windows (=IFs) for target scan and calibration scan should be set using specif and tsysif, respectively. You can identify those informations using sdlist task. The mode is an interpolation mode along frequency axis. Available options are ’linear’, ’nearest’, ’zero’, ’slinear’, ’quadratic’, ’cubic’, and any integer specifiying an order of the spline interpolation. Note that filltsys will overwrite the data specified by filename.

[next] [prev] [prev-tail] [front] [up]

More information about CASA may be found at the CASA web page

This code is available under the terms of the GNU General Public Lincense