CASA Measurement Sets

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2.1 CASA Measurement Sets

Data is handled in CASA via the table system. In particular, visibility data are stored in a CASA table known as a Measurement Set (MS). Details of the physical and logical MS structure are given below, but for our purposes here an MS is just a construct that contains the data. An MS can also store single dish data (essentially a set of auto-correlations of a 1-element interferometer), though there are also data formats more suitable for single-dish spectra (see § 8).

Inside the Toolkit:

Measurement sets are handled in the ms tool. Import and export methods include ms.fromfits and ms.tofits.

Note that images are handled through special image tables, although standard FITS I/O is also supported. Images and image data are described in a separate chapter.

The headers of any FITS files can be displayed in the logger with the listfits task:

#  listfits :: List the HDU and typical data rows of a fits file:
fitsfile            =         ’’        #  Name of input fits file
async               =      False        #  If true the taskname must be started using
                                        #   listfits(...)

Unless your data was previously processed by CASA or software based upon its predecessor aips++, you will need to import it into CASA as an MS. Supported formats include some “standard” flavors of UVFITS, the VLA “Export” archive format, and most recently, the ALMA Science Data Model (ASDM) format. These are described below in § 2.2.

Once in Measurement Set form, your data can be accessed through various tools and tasks with a common interface. The most important of these is the data selection interface (§ 2.3) which allows you to specify the subset of the data on which the tasks and tools will operate.

2.1.1 Under the Hood: Structure of the Measurement Set

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