Making Dark data

Dark data is used to correct dark current in a CCD stored within any integration time, and is made from Dark raw data by subtracting an overscan and Bias data. In HSC pipeline, the mean value of an overscan is subtracted from Dark raw data of each [visit, CCD]. And then, Bias data is subtracted from this overscan-subtracted Dark data. It is final Dark data. This process will be done by HSC pipeline command of reduceDark.py

# Making Dark data
reduceDark.py $home/hsc --calib=$home/hsc/CALIB --rerun=calib_dith_16h_dark --id visit=6600 --detrendId calibVersion=all

# Usage：
#   reduceDark.py <a directory for data reduction> --calib=<a directory for detrend data> --rerun=<rerun name> --id visit=<visit ID of Dark raw data> --detrendId --detrendId calibVersion=<version for making detrend>

Note

General parameters of reduceDark.py are same as reduceBias.py.


Once reduceDark.py is done, you can find following data in your repository. Final Dark and intermediate data is produced in $home/hsc/CALIB and $home/hsc/rerun/[rerun], respectively

  • Dark data　　　　　　　　　　　　　　　　　　　　　　　　　　　：DARK-[ccd].fits in $home/hsc/CALIB/DARK/[dateObs]/[filter]/[calibVersion]/
  • A result of overscan subtraction for each [visit, ccd] Dark raw data：oss-[visit]-[ccd].png in $home/hsc/rerun/[rerun]/[pointing]/[filter]/thumbs/
  • A result of flattened by Flat data for each [visit, CCD] (※1)　　　　：flattened-[visit]-[ccd].png in $home/hsc/rerun/[rerun]/[pointing]/[filter]/thumbs/
  • Dark data for each [visit, CCD]　　　　　　　　　　　　　　　　　：c[ccd].fits in $home/hsc/rerun/[rerun]/postISRCCD/v[visit]-f[filter]/

Note

※1 Although Dark raw data does not flattened by Flat data during the process of reduceDark.py, flattened-[visit]-[ccd].png files are produced by default. If these files are unnecessary for you, they do not produced with –config doWriteFlattenedThumb=False parameter when you perform reduceDark.py.

We present Dark raw data (left) and Dark data produced by reduceDark.py (right) in Figure 2. Dark data is slightly smaller than Dark raw data as is the case with Bias data, because overscan and prescan regions are removed from Dark raw data. Pixel values in Dark data are almost exactly zero.

../_images/dark_raw_1.png

Fig 2: (Left) Dark raw data, and (right) Dark data produced in reduceDark.py.


After you confirm your Dark data, you must register the data to a registry

# Registering Dark data to calib-registry
genCalibRegistry.py --root=~/hsc/CALIB --camera=HSC --validity=1000

Note

You do not need add –create parameter when you perform genCalibRegistry.py, since you have already created a calib-registry when you register Bias data.