Monday, June 22, 2009

Combining Data with Different Pointings

Here is a question from reader Korinne:

I have data from three VLA pointings in L band at the same frequency (with the same channel width) but with different pointing centres which cover an area of an object and partially overlap, unintentionally as the pointings don't overlap at the other frequency we observed that the observations were mostly set up for.

What is the best way to combine this data? I initially imaged and cleaned and then combined with flatn, but it seems like there might be some way to do it at the uv level, but from my readings of the cookbook I can't figure out how I would go about that, particularly in slightly more detail.

My answer below the fold...

I think you want DBCON, which can concatenate data in UV space. Try reading this post. The answer is basically that it depends on just how different your different data pointing are.

If you are actually talking about mosaicing a source, where your various pointings are offset by significant fractions of the primary beam, then FLATN might be your best bet. A bit more discussion of mosaicing here.

2 comments:

Korinne said...

Thank you. I'll be looking into it, to figure out whether it dbcon will do it whether I need to use something for mosaics.

Adrienne said...

I've only used miriad for imaging mosaics. steps:
- invert (in=(all your uv files), options=double,mosaic)
- mossdi (to clean)
- restor (to add your clean components back in to the residuals)