Measurement Set Contents

Overview

In order to fully understand your data and the way CASA operates on it, it's helpful to have a full picture of the way the data are stored, and what a "measurement set" really is. This CASA Guide describes the measurement set (MS) structure, and demonstrates some ways in which you can explore the information stored within an MS. This is particularly useful when exploring the lower-level CASA Toolkit functions, but is also good information to keep in mind when performing basic analysis.

Throughout this Guide, we will be using the same data as the EVLA 6cmWideband Tutorial SN2010FZ. You can use this as well if you would like identical result to what is presented here: the MS can be directly downloaded from http://casa.nrao.edu/Data/EVLA/SN2010FZ/SN2010FZ_10s.ms.tar.gz (dataset size: 2.9 GB).

Alternatively, you can get the data straight from the EVLA archive. Go to the NRAO Science Data Archive, and search for project AS1015. Then select the AS1015_sb1658169_1.55388.89474846065 dataset and choose to apply the online flags (check box "Apply flags generated during observing"); also, time-average to 10 seconds to reduce the MS size. Finally, be sure to select the tar option.

The measurement set directory structure and contents

A measurement set is actually a directory; the data and metadata are stored in tables and subdirectories within this directory. To see these components, open a terminal window, go into the MS directory, and type ls:

Inspecting MS contents in CASA

listobs, browsetable, etc.