16cm CABB flagging strategy

[and460]

Hi guys,

I'm using the sumthreshold algorithm in PGFLAG to flag 16cm CABB data. I wanted to know if anyone has developed a fairly robust approach to flagging full stokes I, Q, U and V data in this band with PGFLAG in terms of settings for the sumthreshold parameters and the automated command sequence that can be fed to it? By 'robust', I mean getting most of the RFI while not decimating real flux or source structure by over-flagging. For example, by trial and error I have found the following to work quite effectively at getting rid of RFI, but it seems to perhaps be a bit heavy handed with typically up around 35% of the data being flagged for the data set on average afterwards:

pgflag vis=blah.2100 stokes=i,q,u,v flagpar=8,5,5,3,6,3 device=/xs command="=<b="
pgflag vis=blah.2100 stokes=v,q,u,i flagpar=10,2,2,3,7,3 device=/xs command="=<<b="
pgflag vis=blah.2100 stokes=v,q,u flagpar=8,2,2,3,6,3 device=/xs command="=<b="
pgflag vis=blah.2100 stokes=u,v,q flagpar=8,2,2,3,6,3 device=/xs command="=<b="

Basically it is intended to flag very bad RFI present in all Stokes products based on that present in Stokes V, then to mop up residual RFI based on that present in Stokes I, and then flag residual RFI in the polarised flux products based on that present in Stokes Q and U.

I am looking at source flux densities in 16MHz channel images across the full CABB band, which seem to be fairly sensitive to both the presence of RFI and over-flagging. The routine above is basically the best I have been able to do thus far, but I'm keen to hear if anyone has developed an approach that works well for 16cm CABB data in general. Any ideas?

[ste616]

Hi Craig,

Thankyou very much for this information. We're always very happy to see people share their techniques here on the ATCA forum.

As to your first paragraph though: I don't think 35% of the data being flagged in 16cm is particularly heavy-handed, unfortunately. I often find that I have to flag the range between 1.1 and 1.3 GHz (already 10%) entirely before any of the other ranges are looked at.