# How are Raw Observations Processed to Obtain Pure CMB Data?

I'm confused about how they identify and subtract radiation from unwanted astronomical sources while measuring the Cosmic Microwave Background Radiation.

Here's what I initially guessed:

1. The dipole anisotropy is found out by measuring anisotropies $A$, $B$ and $C$ in arbitrary $x,y,z$ directions and then adding them up like a vector to get the direction and magnitude of earth's relative velocity to the CMB. Once this is cancelled the anisotropy drops from $10^{-3}$ to $10^{-5}$.
2. We already have data about many known astronomic bodies and can calculate their radiation in the relevant microwave range (if any) and directly subtract it.
3. Some special types of entities may be known in astrophysics to emit radiation in a very specific pattern so that we can immediately recognize and subtract it.
4. Microwave noise from our galaxy's dust and other astronomic bodies is also significant and that part is sometimes just ignored in CMB calculations while in others it is cancelled out by using known data.

The problem is this: in point 1. we already assume isotropy (which is one of the things we want to prove) and we don't know whether what we've subtracted includes a component of CMB as well.

Also since we don't know the exact location of each and every galaxy, dust cloud, etc. in the observable universe we can't rely on point 2. We may always think we are looking at the CMB but may be looking at some faint, red-shifted radiation from some astrophysical entity.

Because of this, I know my guesses 1 and 2 (and maybe even 3) above are wrong. My lack of knowledge about the nature of radiation from specific astrophysical bodies makes it even harder for me to draw conclusions. So I was wondering if somebody could explain how it is actually done.

P.S. I have read the question How do we tell the CMB apart from other radiation? but the discussion there is limited to a very specific construed case and I'm interested in a slightly more detailed, but qualitative description of the actual procedures used currently by experimentalists which I know are much more complicated.

• What do the Planck data reduction papers say? – Rob Jeffries Jun 13 '17 at 20:58
• @RobJeffries I had read plancks hfi amd lfi data processing papers since I thought they are the ones relevant to what i was looking for but were too technical and went totally over my head. I was hoping for a undergrad level answer.... – alex Jun 14 '17 at 7:15
• Ok then - useful to know. – Rob Jeffries Jun 14 '17 at 7:17
• – SRS Jul 1 '18 at 8:54