Louis, Vicki, Craig

Today we revived the correlated noise budget code located at https://git.ligo.org/aligo_commissioning/correlated_noise, first made in June (alog 71333).
This code is a standalone singular script which grabs the raw DCPD data, grabs the DARM calibration OLG and sensing function info, does some math from Kiwamu's DCC T1700131, and produces a correlated noisebudget.

Formerly, I had used my own noise_recorder white noise injections to get the DARM calibration information.  But since I am gone, it would be better if we used a maintained piece of software to get the calibration.
Today, Louis helped me to use a pydarm .npz file to get the DARM OLG and sensing functions.  
The code we developed today is in /ligo/gitcommon/correlated_noise/code/plot_cross_correlation_pydarm_npz_calibration.py

Attached are the correlated noisebudget results for GPS start 1387130434, over 600 seconds of data.  
I posit that we don't really need a ton of time to integrate down, both because the shot noise floor is not that far away from the correlated noise floor, and we can use logbinning averaging to achieve a higher effect number of averages in a shorter amount of time.

Results
I've used the Dec 18 noisebudget traces made by Camilla in /ligo/gitcommon/NoiseBudget/aligoNB/out/H1/lho_darm_noisebudget/lho_darm_noisebudget.hdf5.
Overall, the correlated noise results seem decently sensible, especially at high frequency.
I note that the correlated noise limit we are hitting at 1 kHz seems to be laser frequency noise (third plot attached).

At 500 Hz, we are running into our "thermal noise floor".  
Whether or not this is really thermal noise is anyone's guess, since it is above our official estimate, but the story for O4a remains the same as from O3.

At 20 Hz, the correlated noise seems to overestimate what is actually in DARM, which cannot be correct.  
This is something Sheila has been concerned with in the past (alog 70978).  
This could be chalked up to a small change in the actual vs pydarm DARM OLG, unclear what else it could possibly be.

It is worth noting that the DARM OLG cannot really affect the correlated noise results massively above 500 Hz, just because the magnitude of the DARM OLG is around 0.1 there and falling quickly.  

Future Work
The next steps is for Vicki to import this code to the aligoNB, removing all calls to my nds2utils library (avoiding a dependency there).
Louis also wants to add some functionality to aligoNB so that the noisebudget can call pydarm at a GPS time and get the most recent calibration.  (Craig loves this).
Louis will clone the aligoNB env to verify everything still works before making a "pull request" to the actual aligoNB repo.