Identifier sws_flatfield
Purpose Flatfield all separate det scans per AOT band and line
with respect to eachother or a Reference spectrum.
Synopsis struct_out = sws_flatfield( struct [, degree]
[, /fitmethod]
[, aot_band=aotband]
[, det=det]
[, lines=lines]
[, scans=scans]
[, ref_spec=ref_spec]
[, /offset]
[, /scaling]
[, clip=clip]
[, minfit=minfit]
[, /noupdown]
[, /select]
[, /noplot]
[, logfile=logfile]
Arguments name I/O type description
-------------------------------------------------------------
struct_out O struct Output struct of the same size
as the input struct.
struct I struct Input struct AAR or SPD
degree I int Degree of polynomial
[default: 0]
fitmethod I keyword Method to use for the fits.
'POLY'nomial
'ORTHO'normal polynomial
[default: 'ORTHO']
aot_band I strarr AOT bands (e.g '1a','1b'...)
[default: all aot_bands]
det I intarr Detectors to flatfield.
Only these detectors are flatfielded.
Note however that the reference
is still the data of all detectors
or the reference spectrum
[Default: all detectors]
lines I intarr Individual lines. LINES = 0 will
results in all lines being treated
as one and the flatfielding is
done over the whole AOT-band.
[default: all]
scans I intarr Scans, as defined in the AAR
scnt tag, to use.
SCANS=0 combines all scans.
[Default: all]
ref_spec I struct Reference spectrum to which the data
will be aligned (as an AAR struct).
offset I keyword Treat the differences as offset errors.
[default]
scaling I keyword Treat the differences as scaling errors.
clip I float Clip all the data above or below the
spectrum before doing the fit.
Can be useful in the presence of lines.
[default: 5]
minfit I integer Minimum number of distinct wavelength
points required to make a 'proper' fit.
If there are not enough points in a
scan, this is removed from the data.
[default: 10]
noupdown I keyword Do not fit the up and down scans
separately
select I keyword Select a xrange in the plot which
is to be used in flatfielding.
The selection is done by drawing
a box in the plot covering the
desired wavelength range.
noplot I keyword Do not plot the data and fits
logfile I string Log some diagnostic messages
[Default: 'sws_flatfield.log']
Returns SPD or AAR structure depending on input structure
Description FLATFIELD_SWS will will flatfield the data in an AAR or SPD.
It will do so by fitting a median, line or an orthonormal
polynomial of the same order to:
1. - all grating down data (or all data if NOUPDOWN
is specified) of the same AOT-band, line and scan
as the scans in 2 over the same wavelength region.
or
- a reference spectrum (specified with REF) over
a wavelength range similar to the scans in 2.
If in the reference AAR the status and flag are
filled with AOT-band information, this will
be used to select the reference data of the
same AOT-band (but NOT LINE of SCNT) as the data.
2. all separate detector scans (all up and down scans (unless
NOUPDOWN is specified) for all specified detectors in
each specified AOT-band, line and scan).
These two fits are then used to correct the scans as either
an offset or a scaling correction (/OFFSET or /SCALING)
When not using a reference spectrum (i.e. using the
data itself as a reference) one extra correction is
applied to the data after all detectors have been
corrected. The total flux in both the up and the down
scan (in the selected range) will be made equal
to that of the reference data, being either the down
data or all data.
It is possible to do a one step sigma clipping procedure
in the polynomial fitting (keyword CLIP). Note that this
has only impacts on the fit, no data will be removed.
This is done by first making a fit of the specified
order, determining the rms with respect to this and then
replacing the data CLIP*rms above or below the fit by the
values of the fit before doing a second fit.
All data will be corrected, so also the data poits which
are flagged as NODATA.
In an SPD all scans separated by a DARK current block
are treated as separate lines.
Scans which are shorter than MINFIT will be flagged as
NODATA.
Examples
To align all detectors within the separate AOT bands.
flat_aar = sws_flatfield( aar )
To align all the data onto a reference spectrum, e.g.
to the model spectrum of HR6705 by Cohen.
HR6705_M_COHEN = read_faar('IAS_SED:HR6705_M_COHEN.FITS')
flat_aar = sws_flatfield( aar, ref=HR6705_M_COHEN )
Default all lines in e.g. an AOT2 spectrum will be handled
separately. This means that all scans in each separate
line is FLATFIELDED TO THE DOWN SCAN OF THAT LINE.
To flatfield all lines covering the same wavelength
range so the same level one can supply a reference
spectrum. This can be e.g. the data itself, a rebinned
spectrum or a model. So e.g.
ref = sws_rebin(aar,aot_band='3d')
flat_aar = sws_flatfield(aar,ref=ref,aot_band='3d')
Comments
V2.9 Also in the reference spectrum (when provided)
a selection is done on AOT-band. This means that
e.g. the aar itself or a fully rebinnen AAR
can be provided without problems.
V4.0 option SCANS and DET added.
Category UTIL
Filename sws_flatfield.pro (module: sws_flatfield)
Dependencies calls: ORTHO_POLY, CHK_MULTIX
Version 4.3
History 1.0 06-02-1996 FL document created
1.1 25-02-1996 FL mask removed, data clipping added
1.2 26-02-1996 FL minfit added
01-04-1996 BV variable 'wave' replaced by 'waves'
1.3 06-05-1996 FL error with 0th order fit
also sigma clipping of ref. spectrum
doc. improved.
1.4 15-05-1996 FL default degree of fit set to 0
1.5 10-07-1996 FL optional flatfielding per line
OFFSET as default correction
1.6 20-08-1996 FL rewritten, no interpolation errors,
improved fitting and speed
1.7 11-09-1996 FL SPR_S0058, tried to 'really' improve speed
Per default lines are treated separately.
proper colors and plot titles
/SELECT added as option
1.8 15-09-1996 FL SPR_S0060 define xrange_fit
1.9 26-06-1996 FL SPR_S0071 proper plot of fit with /SELECT
another heroic attempt to make it faster
2.0 28-11-1996 FL SPR_S0131 new interface to CHK_MULTIX
2.1 24-01-1997 FL SPR_S0170, occasional strange fits
improved efficiency
2.2 24-01-1997 FL SPR_S0175, option LINE=0 did not work
2.3 24-01-1997 FL SPR_S0176, scalar/array(1) conflict
2.4 18-02-1997 FL SPR_S0187, better higher order fits
2.5 25-02-1997 FL SPR_S0190, better check validity ref scan,
plot only VALID data
2.6 05-03-1997 FL SPR_S0197, undefined variable, no of ref pts
2.7 15-04-1997 FL SPR_S0218, Shifts in flux level
2.8 22-04-1997 FL SPR_S0226, High order fits using ref spectrum
2.9 19-05-1997 FL SPR_S0231, interpolation error for order 0
slow array initialization
3.0 23-05-1997 FL SPR_S0232, Incorrect offsets with /SELECT
3.1 12-06-1997 FL SPR_S0238, Not use VER, non-standard IA
SPR_S0239, Check on width of REF SCAN
4.0 05-09-1997 FL SPR_S0267, use scnt, add DETS option
4.1 25-09-1997 FL SPR_S0281, more efficient selection of data
SPR_S0282, use rgb colors
4.2 21-10-1997 FL SPR_S0283, occasionaly wrong reference fits
4.3 19-01-1998 FL SPR_S0310, fits in double precision
SPR_S0311, replaced orthopoly by ortho_poly