The third category of data that you might wish to image is a band of channels. That is, you wish to make a multi-frequency synthesis image and grid together all the channels in the (u,v) plane making use of the variation of u and v across the band to improve the sampling of the (u,v) plane. The output is still one image.
Both MX and HORUS can do this kind of imaging. Therefore, once again, you can either image directly from the multi-source file with HORUS or you can use SPLIT (§ 12) (you may have already done this if you have combined data from different observing runs). If you want to make a very large image you may need to sort the data into XY order with UVSRT (§ 15.2), but generally the internal sorting that HORUS and MX can do allows big enough images.
In the adverb box below, I give a simple example of gridding IFs 1 and 2 and all channels in the range 8-28 together to make one output image.
MX | |
bif=1 | Select desired IFs |
eif=2 | |
bchan=8 | First channel to grid |
echan=28 | Last channel to grid |
chinc=1 | Channel increment |
npoints=21 | Number of channels to grid together |
channel=0 | No CLEAN restart |
HORUS | |
bif=1 | Select desired IFs |
eif=2 | |
bchan=8 | First channel to grid |
echan=28 | Last channel to grid |
chinc=1 | Not relevant |
optype='sum' | Grid all selected channels and IFs |
It would be interesting to compare the multi-frequency synthesis image with the channel 0 image, if you believe there is some (u,v) coverage benefit to be gained in the former.