Flat
Overview
This file describes the data model for the Flat.
It is a series of images starting from
the combination of all input pixelflat frames.
The images are written to disk as a multi-extension FITS file
prefixed by Flat in the Calibrations/ folder.
See Calibration Frame Naming for the naming convention.
Inspecting
PypeIt provides the pypeit_chk_flats script to inspect
the key Flat outputs.
The script usage can be displayed by calling the script with the
-h option:
$ pypeit_chk_flats -h
usage: pypeit_chk_flats [-h] [--type TYPE] [--try_old] file
Display flat images in Ginga viewer
positional arguments:
file PypeIt Flat file [e.g. Flat_A_1_DET01.fits]
options:
-h, --help show this help message and exit
--type TYPE Which flats to display. Must be one of: pixel, illum, all
(default: all)
--try_old Attempt to load old datamodel versions. A crash may ensue..
(default: False)
pypeit_chk_flats
This script takes a Flat as input and displays
a series of images in a
ginga viewer, each in a separate tab.
Here is a typical call:
pypeit_chk_flats Calibrations/Flat_A_1_DET01.fits
Below we describe the standard products. There is enough variation from spectrograph to spectrograph that we have not included example screen-shots.
Raw Flat
This is the processed and combined pixelflat image.
Despite the name, it is not completely raw.
This image should look like any one of your input
pixelflat images.
Pixel Flat
This is the normalized to unity image which is used to correct for pixel-to-pixel variations across the detector.
It should look mainly like a salt-and-pepper, random-noise image fluctuating very close around values of 1.
For many detectors there may be ‘pock’ marks, columns, and even funny patterns.
It is also typical for the extreme spectral portions (top/bottom) to have more structure or pattern noise. This is especially true if there is limited flux at these ends (e.g. the data goes below the atmospheric cutoff).
Illumination Flat
This image should also have most values near unity, but there will be vertical coherence. And the edges (left/right) may fall off well below unity.
Flat Model
This image should largely resemble the Raw Flat.
Troubleshooting
If one or more of your image appears to be in err, here are the things to consider:
Is one or more of your flat frames junk?
Is one or more of your input flat frames mis-labeled?
Did you saturate portions of the flat?
Current FlatImages Data Model
Internally, the image is held in
FlatImages
which subclasses from pypeit.datamodel.DataContainer.
The datamodel written to disk is:
Version 1.1.2
HDU Name |
HDU Type |
Data Type |
Description |
|---|---|---|---|
|
… |
Empty data HDU. Contains basic header information. |
|
|
float64 |
Processed, combined pixel flats |
|
|
float64 |
Normalized pixel flat |
|
|
float64 |
Model flat |
|
|
… |
bspline model of the pixelflat for |
|
… |
… |
… |
… |
|
… |
2D polynomial fits to the fine correction of the spatial illumination profile of the pixelflat for |
|
… |
… |
… |
… |
|
int16 |
Mirrors SlitTraceSet mask for flat-specific flags |
|
|
float64 |
Relative spectral illumination |
|
|
float64 |
Waveimage for pixel flat |
|
|
float64 |
Processed, combined illum flats |
|
|
… |
bspline model of the illumflat for |
|
… |
… |
… |
… |
|
… |
2D polynomial fits to the fine correction of the spatial illumination profile of the illumflat for |
|
… |
… |
… |
… |
|
int16 |
Mirrors SlitTraceSet mask for flat-specific flags |
|
|
int64 |
Slit spat_id |