MSDP data processing

- Different data levels: advantages and limitations

- How to solve problems:

- when the code stops (channel geometry…)

- when the results are distorted spatially (scanning problems…)

- when clouds disturb the observations

- when the results exhibit periodic fluctuations (profile interpolations)

- improvement of telescope pointing in X-scans, signal/noise ratio. …

- A few problems in more details:

- Channel geometry and grid geometry

- Cospatiality adjustment (2D)

- Parameter files for THEMIS and other instruments over the years

Pierre Mein, MSDP whorkshop, Tarbes 2006

THEMIS / MSDP

Different data levels

Raw data fits 3 files t…

1) sequence.par + msdpauto (idl)

1 file for 1 window and 1 time fits 1 files b……

creates new directory + ms.par

2) new directory + ms.par + ms1 (f90)

a) Calibrations (geometry, photometry)

Superposable calibrated channels msdp files c….

b) Results with preliminary wavelength calibration

Bisector for each observing time msdp msdp files d….

Bisector for full scan msdp files q….

c) Results with internal wavelength calibration

Line profiles for each time msdp files r….

Line profiles for full scan msdp files p….

I+VI-V

Raw dataSimultaneous 2D spectro-polarimetry

- Example of 16 channels (alternate wavelengths)- Grid at first focus in front of polarization analyser

Focus F1Focus Sp1 Focus Sp2

Files t… raw data fits 3

Files b… 1 file for 1 window and 1 time fits 1

t….b…. b….b…. Scan files

t….x…. b….x…. Dark current

t….y…. b….y…. Flat field

t….z…. b….z…. Field stop

Line profile restoration

(9 channels,

without polar. analysis, VTT)

For each time, series of identical rectangles, at different

Might be used for direct line profile inversion

to specify parameters of a solar model

without profile interpolations

This would avoid interpolations and loss of accuracy

(see corrections of periodic fluctuations…)

Superposable calibrated channels files c….

- In case of series of exposures (bursts), allow seeing effects correction by destretching (Pic du Midi)

- Provide the full data for 1 observing time without loss of field-of-view (overlaps mix successive observations in q- and p- files).

- Can be used to investigate far line wings near the edges of channels (one wing near one edge)

Results for each time

Files d… preliminary wavelength calibration

(mainly bisector computations)

Files r… calibrated wavelengths

(mainly line profiles)

Full scan results

Files q…. (bisector) Not corrected 0

Files p…. (profiles) Corrected 0

-The standard processing provides

Without polarization With Zeeman circular

analysis analysis

Additional arrays

- q-files with intensity near line centre Stokes V near line centre

sum of intensities +/- Int. differences (cospatiality test)

difference of intensities +/- Stokes V at +/-

intensity from bisector +/- velocity from bisector +/-

velocity from bisector +/- B// from bisector +/-

- p-files with intensity line profile Stokes V line profile

In case of Q,U,V observations, separate files for +Q,-Q,+U,-U,+V,-V

noted (param nqseul) 1 2 3 4 5 6

and beam-exchange results 7 8 9

1) If the IDL interface « msdpauto » stops ?

(the  b- files are not created)

- Check the directory name of data in

msdpauto, ’…..directory….’

- Check the number bs of channels in « sequence.par »

(the code divides the frames in 2 windows of 8 channels

in the case of 16 channels beam-shifters)

How to solve problems

How to solve problems

2) in all cases when the Fortran code « ms1 » stops ?

- The most simple way to modify the parameters of « ms1 »

is to edit and modify « ms.par », and to run again « ms1 »

- To modify parameters automatically for a full campaign,

it is necessary to modify « tyear.par »

if the parameters are present in that file

(t for Themis,year = 2002, 2003, …

« pyear.par » for Pic du Midi, « myear.par » for Meudon,…)

In that case, run again the IDL interface « msdpauto »

If the code stops before channel geometry determination ?

(before any message including « milgeo »)

Either the code does not read files with the good format:

Check sundec and iswap in ms.par, or sd in sequence.par

Or the code does not find the data files:

Check that files y,z are present

and also x if parameter idc=1

Check also that the directory name is correct in ms.par

If the code stops and asks for an « increase of milgeo » ?

The code cannot determine the edges of channels.

-1) If the geo.ps file is available

-display it by

ggv geo.ps

And modify in ms.par the parameters after headers « bmg »

such as thresholds si,sj,sgi,sgj,… (see param.txt for details)

If the code stops and asks for an « increase of milgeo » ?

-2) If the geo.ps file is not available,

- display the average field-stop file by

IDL

image = readmsdp(‘z………’)

tvscl,im

and check the location of channels (parameters i1, i2m),

the sharpness (intvi,intvj)…

i2m=250

How to solve problems

if the resulting q- and p-files exhibit strong spatial distortions ?

Something is wrong in the parameters specifying symetries and scanning directions, or grid location.

- Small rectangles:

Some of the following parameters must be modified: inveri, inverj, xfirst

Note also that

invi, invj determine the final symetries of the maps

invern, inverl, invers determine signs and orders of

wavelengths and Stokes parameters

Xfirst = 0

Xfirst = 1

Xfirst = 1, norma = 0199

NaD1, intensity +/-40mA, 16 oct 2002

How to solve problems

if the resulting q- and p-files exhibit strong spatial distortions ?

- Lines parallel to the X-scanning direction:

Display grid.ps and modify caldeb,ideb, igri, itgri (see param.txt)

Automatic correction with caldeb = 1

How to correct cloud effects ?

Intensities disturbed by clouds

Velocities and B// not disturbed

Correction norma (norma=0289)

Intensities corrected

How to solve problems

if q- and p-files exhibit spatial periodic fluctuations ?

The limited spectral resolution leads to slight periodic errors due to line profile interpolations,

which produce kinds of fringes parallel to the longer edge of field-stop.

Several ways can be used to correct them.

How to correct grooves due to interpolation between channels ? Themis, 16 channels, without correction

I_0 I_120

v_120 B_120

P= y

P

y

x

Themis: 16 channels P ~ 1.4 arcsec

9 channels P ~ 4.1 arcsec

n y * (y)

Channel step

For corrections, we assume that, locally, does not depend ony

(we neglect the inclination and curvature of lines = ct)

Spatial wavelength P of fluctuations versus y

1) Profile curvature deduced from neighbouring points

curvd = 4 (curvr = 4)

I’(3)

I(3)

I ’’(3)

ZI’

I

I’’

P/2

-P/2

Z(3)=I(3)

Z(4)=I(4)

Z(5)=I(5)

Z(6)=I(6)

Z(3.5)+Z(5.5)-2*Z(4.5) = (I’(4)+I’’(3)+I’(6)+I’’(5)-2*(I’(5)+I’’(4)))/2

Themis 16 channels 0.7 ’’

9 channels 2’’

Interval 4-5: Z = polynomial degree 4

x

y

2) Fourier filtering Crecd (w1d) w2d (w3d)Crecr (w1r) w2r (w3r)

0/1 0/1 0/1L = 2P P P/2

M

y

xj

i

Correction = - Ct* <<I(x,y)*apod(x)>-crecd,+crecd *cos(2y/L)*apod(y)>-P,+P

P

crecd

Themis, 16 channels, Curvature curvd = 4, Fourier crecd = 2000, w2d = 1

I_0 I_120

v_120 B_120

Corrections without any loss of spatial resolution

Power functions I’=(I-Iz)**a a= milalp / 1000

Iz=Imin * milzero / 1000

Interpolation

I = Iz + I’**(1/a)

1)

smoothing channels n-1, n, n+1

weights ¼, ½, ¼ nlisd = 2

nlisr = 2

(effect similar to Fourier filtering w1 = 1 (w1r = 1)

which degrades slightly the spatial resolution instead of

the spectral one)

2)

3) Mean departures between successive scan steps

lcrecq

My

x

Field of view of a d-file (1 t-value)

Each quantity (I, v, Stokes..) of all files d (or r) from the same scan defines a function F(x,y,t)

1) Computation of the mean A of F over x,y,t after rejection

( departures > sigma * milsigq /1000 )

2) For each pixel x,y, computation of the average D(x,y) of departures from A for all times t

3) Smoothing D' of D(x,y) versus x over –L,+L around M (L = lcrecq / 1000 arcsec)

4) The correction is - D' if crecq = 2 (folding with period P if crecq = 1)

The correction depends only on x and y. It does not degrade the spatial resolution.

VTT, 23 oct 2002 Hwithout correction

I_0

460 * 180 arcsec

I_290

Without correction

v_290

Without correction

quick.ps

P

Mean departures2D correlations and pointing corrections

VTT H 2D Correlations lcorq = 2 icormq = 4000 copasq = 2000 milcoq = 300

( 2d array) (4’’) (2’’) (0.3)

Corrections by mean departures

crecq = 2 lcrecq = 10000 milsigq = 2000

(10’’) (2 * )

I_0

I_290

v_290

Disc centre

Some additional improvements

Signal/noise ratio: can be improved by smoothing

versus wavelength nlisd,nlisr

versus x ilisdr

versus y jlisdr

Scattered light rate = scatter /1000

(computed over each line at constant

Very large scans increase the pixel = milsec /1000 arcsec

Cospatiality adjustment

0.5 arcsec error introduced manually (itana+500)

Cospatiality

test

Correction calana (calana=1, quadratic interpol.)

between dx = +/-1’’ et dy = +/-0.5’’)

Cospatiality

test

Channel geometry

Field stop

(8 channels)

Flat field

Because of a shift between field-stop and flat-field, due to misadjustment of grating angles, too large to be corrected by the code, the flat-field must be used instead of the field-stop

(calfs = -1)

But channel edges are more difficult to determine because of the presence of lines in some channels.

nleft, nright allow to locate some edges by similarity with neighbouring channels

calfs = -1 flat field used as field stop

nright = 3 right edge of channel 3deduced from left edge +size of channel 4

Steps Corrections Files Output results

geom calib

Power fctsScattered lightNormalizationSmoothing Profile curvatureFourier filteringCospatiality

2D - correlAverage departures

geoflatbmc

cmd

b

c

d

q

r

p

Aligned and calibrated channelsPossible direct inversionavoiding interpolation corrections

Individual maps I, v, B//Possible destretching

Large maps I, v, B//

Individual maps Profiles I, Q, U, V with calibrated central wavelength

Large spectrohéliog. I,Q,U,V Inversions with constant

quick

cmr

prof

Like cmd except cospatiality

Like quick except 2D - correl

Parameter files which specify MSDP instruments

THEMIS t2000.par, t2001.par,…t2005.par

LJR at Pic du Midi p2001.par,p2002.par,…p2005.par

Meudon Solar Tower m2003.par,m2004.par,m2005.par

processing msdpauto + ms1

VTT / DALSA cameras example of ms.par

processing dalsa + ms1

Wroclaw Large Coronagraph examples of ms.par (?)

processing similar to ms1