ESO
SINFONI Pipeline User Manual
Doc:
VLT-MAN-ESO-19500-3600
Issue:
Issue 1.0
Date:
Date 2005-10-19
Page:
71 of 88
10.1.5
Detector gain computation
The gain is computed as part of the recipe si_rec_detlin.
Pairs of consecutive off-flats (be those frm_off1 and frm_off2) and pairs of consecutive on-flats (be those
'2-
8
and
'2-
8
) are selected from the input data frames and their difference is computed (
'
_
'2-
8
$
'2-
8
4
'2-
8
and
'
_
'2-
$
'2-
4
'2-
). Then the mean of each frame (
'2-
8
,
'2-
8
,
'2-
"
,
'2-
) and the standard deviation of the difference
'
_
'2-
8
!
and
'
_
'2-
!
are computed.
Finally the gain is given by:
$
'2-
8
'2-
8
!
4
'2-
'2-
!
'
_
'2-
8
!
4
'
_
'2-
!
!
10.1.6
Read Out Noise computation
All possible consecutive pairs having the same DIT are extracted from the input set of frames. For each pair
the second frame is subtracted from the first one. Then the noise is computed in a region defined by parameters
xmin, xmax, ymin, ymax, over nsamp samples each of size hsize taken randomly in the given region. The
noise multiplied by
, where NDIT the number of DIT repetitions, gives the read out noise.
10.1.7
Fixed Pattern Noise computation
The FPN is computed in the same way as the RON but it is applied to a master dark/flat. The factor
does not apply.
10.1.8
Line position determination
The locations of the arc lamp lines are determined on an arc lamp frame, input of the recipe si_rec_wavecal or
si_rec_distortion.
For each detector column, an initial guess wavelength is assigned to each detector row pixel by using the
pixel row value and the input initial guess value for the starting wavelength, (begin_wave), the linear and
quadratic terms of the dispersion (guess_disp1 and guess_disp2) at the given instrument setting. Then
the detector rows corresponding to each entry of the reference line list are identified. Line positions and
intensities given by the reference line table are assigned to those columns. A delta-shaped spectrum is
obtained in this way. This spectrum is convolved with a Gaussian profile of given sigma. A pixel shift
is obtained by correlating this artificial line spectrum with the arc lamp frame spectrum. The correlation
takes into account only those lines whose intensity is greater than a threshold set by parameter min_diff.
Thus one obtains accurate values for the position and the wavelength assigned to each image position.
To determine the dispersion relation (see 10.1.9) more accurately the recipe selects and uses only line
identifications whose distance from the nearest neighbour is greater than half_width pixels.
