CRIRES: Reference frames

CRIRES reference frames

The CRIRES reference frames pages offer:

• example frames for the daily health check settings (plus selected additional settings)
• an atlas of ThAr and N2O wavelength calibration exposures
• S/N in flat fields.

S/N per pixel in flat fields

This page offers an overview of the signal-to-noise ratio per pixel that can be achieved with flat fields as they are regularly measured during daytime operations. The presented data have been taken from 18 to 24 June 2009.

The plots show the average S/N per pixel for each column in dispersion direction (x direction on the detector). Grey-shaded regions indicate area that is affected by contamination from adjacent orders. Raw data come in stacks of three exposures. S/N has been determined with the following steps:

1. Each raw frame is normalized by the mean
2. For each column, the average noise is estimated from the difference of the first two images:
   phn = 1 / sqrt(2) * stddev(norm2-norm1)[x,y=100..400]
3. The average S/N per column is then:
   sn = sqrt(3) * median(norm1,norm2,norm3)[x,y=100..400] / phn