Averaging data in plotms

You can average your measurement set on the fly with plotms. The averaging options can be found under the Data tab, and are mostly intuitive.

Have a first look at the data by hitting the (MS)Plot button. By default, the axes will be visibility amplitude vs. time. The y-axis amplitudes aren't yet calibrated, but for the sake of the discussion we'll refer to them as flux densities in Jy. The x-axis labeling is a little garbled in this development version of the software, but straightaway there appear some wildly discrepant data. For a typical decimeter-wave continuum data set, sources and calibrators are expected to show visibility amplitudes of a few Jy or less; visibilities with amplitudes in the 100s of Jy range are likely bogus. Here's how to flag them. Click to enlarge

Data with no time averaging. However, time averaging can be a little confusing, as it is controlled by three fields. If you click the checkbox next to Time under Averaging, a blank box with units of 'seconds' should become active, along with two checkboxes: Scan and Field. To the right, we've plotted two calibrator sources from a multi-source measurement set. There has been no averaging. One is a phase calibrator observed in six scans, while the other is a brighter flux calibrator observed in one scan at the end of the observations. Try setting the blank box to a very long time---let's say 50000 seconds---much longer than your total time observing. If we plot amplitude vs. time, you'll notice that not all of the data has been averaged together in time; in fact, only data within individual scans has been averaged together. If we click on the Scan checkbox and replot the data, we now see that the scans for the individual calibrators have been averaged together. Finally, if for some reason, we'd like to average the two sources together in time, we click to make a checkmark in the Fields box. Now we get a plot like the one to the right; all data from both calibrators has been averaged to a single point in time.