It has become clear that, as discussed in Astier, et.al., we need to correct the non-linearity of the ASPIC amplifiers. I created a linearizer with the current cubic polynomial fit using measurePhotonTransferCurve.py, then applied it using the ISR and re-ran measurePhotonTransferCurve.py. It did not correct the "bump" around 50,000 ADU, as shown in the attached NonLinearity_R22S11_C04_25Aug20.png. Astier, et.al. recommend using a spline fit to better capture the nature of the bump. I implemented this in a notebook at NCSA at:
and also uploaded it to git hub at:
It does a much better job at correcting the bump, although not as good as in Pierre's paper. You can see the improved correction in the attached NonLinearity_Correction_R22S11_C04_02Sep20.png. Both of these plots are analogous to Figure 3 in Astier, et.al.
Note that the expTime data in this notebook was generated by applying the MONDIODE correction. In order to do this, I modified ptc.py with the following lines. While I added "fudge factors" for three of the neutral density filters, I think this is not that critical since I ended up not using the low flux points in the spline fit. Please contact me if any of this is not clear. I think the next step is to implement the spline correction, which I think Chris Waters may already be working on. Then we can try correcting the flux in the ISR using the spline fit and re-do the PTC curves.