Background
Updating the calibration for the IFO is done via a process that the Calibration group often refers to as "pushing a new calibration". This process entails the following discrete steps:


  
Based on a curated set of measurements, estimate the optical gain (Hc), coupled cavity pole frequency (Fcc), and [UIM, PUM, TST] actuation strengths as free parameters.*

  
Populate the pyDARM parameter model set (a.k.a. "the ini file") with the free parameters in the previous item. pyDARM uses these parameters to model IFO.

  
Calculate the values of various DARM model transfer functions evaluated at calibration line frequencies and caput them into their corresponding EPICS channels. The Calibration group often narrowly refers to these channels as the "TDCF EPICS records channels".

  
Encode the free parameters (Hc, Fcc, Q, Fs, H$$AUIM, H$$APUM, H$$ATST) as Foton ZPK design strings and install them in their respective CAL-CS filterbanks in /opt/rtcds/userapps/release/cal/[h,l]1/filterfiles/[H,L]1CALCS.txt. **

  
Manually export the sensing and actuation foton filters that need to be compensated for (removed) downstream as transfer function text files and update their paths in the pyDARM parameter model set. (LHO:47948) *** 

  
Generate FIR filters to be applied by GDS pipeline

  
Copy the now updated pyDARM parameter model set, GDS FIR filters, and "Foton exports" to a place where the GDS and uncertainty pipelines can access them and their associated files.****

  
Restart the GDS pipeline.

  
Point the hourly uncertainty calculation to the latest GPR fits.



pyDARM Report System
Over the past several months the Calibration group has been working on building and putting into place the infrastructure needed to purge the "pushing a new calibration" exercise of its manual and most time consuming processes. Working out of a pyDARM branch called "cmd-dev", we are in the final stages of getting everything into place for O4.

The new infrastructure is based upon a "report generation" system. pyDARM will now handle taking calibration measurements, processing them to estimate the free parameters, and everything (LHO:67594, LHO:69229, LHO:68267, LHO:67061) listed above except for the last two items. We are pending a full write-up that lists all of the new commands and their features.

You can view the latest pyDARM report directory for LHO at https://ldas-jobs.ligo-wa.caltech.edu/~cal/archive/H1/reports/20230510T062635Z/. The report itself, which members of the calibration and commissioning groups will use to determine whether to update the calibration, will be stored as [H,L]1_calibration_report_[report timestamp].pdf (e.g. H1_calibration_report_20230510T062635Z.pdf).

Update regarding foton exports
Most recently implemented is the capability to automatically call Foton and generate the "foton export" files as each report is generated. The resultant foton export file is now placed within each report directory as [H,L]1CALCS_InverseSensingFunction_Foton_tf.txt.




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* At present, we also estimate residual delays associated with the optical gain (H_c) and the actuation strengths (H_A). However, these delays are not currently used once they are estimated and are typically simply thrown away or stored and forgotten about.

** Of these, the most "critical" are often the sensing function parameters (Hc, Fcc, Q, Fs) because the sensing function changes on time scales that are much shorter than those of the actuation stages.

*** This is necessary because there are differences in how Foton and python generate transfer functions from zpk designs, especially at high frequencies. So in order to properly compensate for these filters as they are applied we export them as computed by Foton and carry these text files around for downstream processes to import and divide them out.

**** For O4, this will be at ldas-jobs.ligo-[wa,la].caltech.edu/~cal/archive/[H1,L1]/reports/.