VIRCAM: Quality of dome flats
|
HC PLOTS |
RMS of master flat |
|
RMS of ratio flat |
|
counts avg |
|
counts range |
|
QC1 database (advanced users):
browse |
plot
|
VIRCAM dome flats are technical calibrations, to monitor flat field cosmetics.
Dome flats are acquired by illuminating the screen inside the telescope building with several halogen lamps.
They can serve as a substitute for twilight flats in case
twilight flats cannot be acquired for a longer times.
RMS of master dome flat
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.FLATRMS | vircam_dome..qc_dome_rms | | ENG | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The rms of the master dome flat is monitored for all filters: NB118, NB980, Y, Z, J, H ,K separately.
The K-band is monitored
here.
Scoring&thresholds RMS of master dome flat
Not scored
History
No remarks.
Algorithm RMS of master dome flat
The QC.DOMERMS is a measure of RMS in ADU obtained from master dome flat products. It is the median of the absolute deviations from the median ( = MAD ) times 1.48 derived from the master dome flat.
RMS of ratio flat
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.FLATRATIO_RMS | vircam_dome..qc_ratiodome_rms | | ENG | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
The vircam dome flat pipeline recipe allows to specify a reference flat, which can be any
master dome flat. The pipeline divides the master flat by the submitted reference flat and extracts some QC parameters
of which the RMS of the ratio flat is the most important. The pixel-to-pixel relative response
differences (= the fixed pattern noise), which dominate the RMS of the master flat, are canceled out in the ratio flat.
The RMS of the ratio flat is therefore sensitive to other changes in the master flat, like:
- changes in the relative gain of the 16 read-out channels (16 vertical stripes each one 128 pixel wide).
In addition to the qc_ratiodome_rms we monitor qc_dome_chanRMS.
wich divides the ratio dome flat in 16 junks (the 16 read-out channels),
takes the average signal of each of the 16 detector areas and determines
the rms over these 16 channel means. By this QC1 parameter it is possible
to disentangle the channel gain contributions from other contributions
to the overall qc_ratiodome_rms. This becomes important for the period
starting in early 2020 (after a detector controller intervention),
when the channel gain variations increased and became the dominating
contribution to the qc_ratiodome_rms, in particular for detectors #6 and
#10, #12 and #14. In this period the values of qc_ratiodome_rms
are dominated by channel gain variations and are no longer sensitive
to the detector characteristics originally intended to be monitored,
in particular for detectors #6 and #10, #12 and #14.
- new dust grains
- new bad pixel (e.g. 2013-03--01 on chip #3)
- controller issues
Trending
The RMS of the ratio dome flat is monitored here.
Scoring&thresholds RMS of ratio flat
The values are not scored
History
The maintenance of the reference flat means it has to
be updated from time to time, typically twice a year and after interventions. The dome flat QC1
DB contains the name of the reference twilight flat
(qc_dome_refname) and the time stamp of the reference
dome flat (qc_dome_refdate).
Algorithm RMS of ratio flat
The master flat is divided by the reference flat, the RMS is taken.
For reasons of demonstration we have performed the
following exercise: We have processed the H-band dome
flat from 2022-10-01 using the linearity calibration
products CHANNEL_TABLE and BadPixelMap also from
2022-10-01. We have registered this MASTER_DOME_FLAT
as REFERENCE_DOME_FLAT for the subsequent analysis. In
a first sequence, we have processed some other H-band
dome flats of 2022-10 and 2022-11 using the same
REFERENCE_DOME_FLAT and the same CHANNEL_TABLE and
BadPixelMap from 2022-10-01.
|
QC report of MASTER_DOME_FLAT from 2022-10-01. REFERENCE_DOME_FLAT is the MASTER_DOME_FLAT, hence the RATIO_DOME_FLAT is 1.0.
|
|
QC report of MASTER_DOME_FLAT from 2022-11-09. The same CHANNEL_TABLE and the REFERENCE_DOME_FLAT from 2022-10-01 is used.
There are no channel gain variation in this particular RATIO_DOME_FLAT, as they are introduced by the same CHANNEL_TABLE product.
|
In a second sequence we have processed the 2022-10-01 dome flat a second time using the CHANNEL_TABLE from 2022-11-05.
|
QC report of MASTER_DOME_FLAT from 2022-10-01 calibrated with the CHANNEL_TABLE from 2022-11-05.
The channel gains have changed and become apparent in the RATIO_DOME_FLAT.
|
|
H-band dome flat of chip #12. raw frame.
|
The channel gain variations of the order of 2\% become visible only in the RATIO_DOME_FLATs where all other spatial large scale illumination
are canceld out.
Counts in dome flats
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
average counts | vircam_dome..qc_dome_medavg | | ENG | | [docuSys coming] |
range | vircam_dome..qc_dome_medrng | | ENG | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
While twilight flats are affected by the
decreasing sky brightness during dawn, dome
flats are illuminated by a set of stable lamps.
The average counts in dome flats is monitored here
.
The stability of the lamp within the series of five raw frames is monitored via the
counts range
parameter.
While the dome flat field lamps, both the ones used for the H and K band as well as those used for the bluer bands Z, Y, J, NB118, NB980,
are stable over a longer period, the K-band dome flat counts show a correlation with the ambient temperature (see Fig. below).
Scoring&thresholds Counts in dome flats
The values are not scored.
History
On 2018-08-07, M1 and entrance window was washed. Counts of dome flats (which pass M1 and entrance window) increased from 6500 ADU to 7200 ADU for the Y-band e.g., a value with was registered the least time in late 2011.
Algorithm Counts in dome flats
The counts, the average over five raw frames is taken.
|
Relation between the average counts in K-band dome flats and the ambient temperature.
Data cover the period 2015 - 2023.
|
|