Let's assume we have multi-epoch observations on a particular field of interest with measurement sets vis_1.ms, vis_2.ms, ... vis_n.ms. The task msuvbin needs to be executed n times, one for each input data set with all the other parameters that define the output data set intact. For instance, for the 1st execution of msuvbin, one may set the following parameters:

vis = 'vis_1.ms'
field = '0'
spw = ''
taql = ''
outvis = "uvgrid.ms'
phasecenter = ''
nx = 2048
ny = 2048
cell = '2.0arcsec'
ncorr = 2
nchan = 320
fstart = "1025.00MHz"
fstep = "62.5kHz"
wproject = False
memfrac = 0.9

Here we note the following:

  • Field '0' was selected from the input data, and its position will define the phase center of the output uv grid. If another position is desired for the phase center, then the parameter phasecenter needs to be specified.
  • nx and ny define the number of the pixels along the x and y axes of the grid, respectively. The size of each pixel is defined by the parameter cell. These would be the same values that one would use in the task clean/tclean for imsize and cell to image the output uv grid, and therefore need to be set by taking into account the image that one will eventually be making.
  • ncorr defines the number of the correlations in the output uv grid. If the input data set has the correlations RR and LL, and ncorr is set to 1, then the output uv grid will be written as Stokes I. If ncorr is set to 2, then the output grid will have both the RR and LL correlations.
  • nchan determines the number of channels in the output uv grid with a frequency width per channel set by the parameter fstep. The lowest frequency of the output data is set by the parameter fstart. Note that msuvbin will perform on the fly Doppler correction; the resulting grid will be in the LSRK frame. The fstart value is the starting frequency in the LSRK frame. The above example will produce a uv grid with 320 channels starting at 1025 MHz in LSRK, with each channel having a width of 62.5 kHz.
  • memfrac may be used to set how much memory the task should use. In the above example 90% of the available memory will be utilized by the task.

After gridding the 1st data set, the task msuvbin will need to be executed on the other data sets one at a time by changing the vis parameter only (i.e., vis='vis_2.ms', then vis='vis_3.ms', etc...) and keeping the other parameters intact. The task msuvbin will perform the proper averaging when gridding the data sets on the same uv grid. The volume of the output data set stays the same regardless of how many measurement sets are added onto the same grid.