EIS data analysis manual**

EIS data files used in this Tutorial

All data files are stored on NAOJ internal computer system. Here are the directories:

  • Raster data
  • Slot data

0. Using Xfiles quick look tool

 Xfiles  (in solarsoft EIS-tree) is convenient for a quick look of the data.

IDL> xfiles

For more information about how to use  Xfiles  tool, please click  here! 

1. Reading the EIS Level-0 data

1.1 Creation of object

    The EIS fits file normally is read to an 'Object'. EIS software then manipulates this Object to extract data contained in the fits file.
    To create an EIS object, use:

IDL> obj = obj_new ('eis_data', filename)

    Here filename should be a single file name, ie. this command does not supports file lists.

1.2 Process the CCD bias/dark/flat-field

    Before starting to analyse the data, revision processing of CCD bias, dark-current, and flat-field is necessary.
    Currently, only a simple program which removes CCD bias is offered.

IDL> eis_cal_dcql, obj

    'obj' now is renewed and CCD bias has been removed from the data

2. Extract spectrum data

2.1 get data for different 'Line-window'

    Each EIS fits file can include maximum 25 line-windows, ie. window 0, 1, ...,24.
    The following example shows how data for the 6th window is acquired from the data Object.

IDL> iwin=5
IDL> obj->getwin, iwin, data, pos

2.2 Despike line-window data

IDL> eis_despike, data

2.3 Get line-window size

    Line-window data has the dimension of data[xsize, ysize, nexp], ie. [X-direction, Y-direction, exposures].
    Each window may have different xsize, ysize.
    To get xsize, ysize and nexp, use:

IDL> xsize=obj->getxw( )
IDL> ysize=obj->getyw( )
IDL> nexp=obj->getnexp( )

2.4 Showing spectrum data

    The dimensions of raster cube are: data[lambda, y, x]
    To view the movie of the spectrum, do the following:

IDL> window,0,xs=xsize[ iwin ],ys=ysize[ iwin ]
IDL> stepper,data

2.5 Display slot picture

    When a lot is used, do as follows to display the picture.
    Note, it is necessary to reverse left-right (ie. east-west) direction. to display the slot picture in the correct direction.

IDL> window,0,xs=xsize[ iwin ],ys=ysize[ iwin ]
IDL> tvscl,rotate (data[ *, *, 0 ], 5 )

EIS slot

EIS slot picture

3. Display raster picture

    For raster scanning data, integrating the spectrum along wavelength direction gives the picture of the scan area on the Sun.

IDL> intensity = rotate (total (data, 1), 1)
IDL> window,0,xs=nexp,ys=ysize[ iwin ]
IDL> tvscl,intensity

EIS raster

EIS slit rastering picture

4. Fitting spectrum

4.1 Execution of GUI fitting tool 'xcfit'

IDL> objm = obj_new('eis_moment', obj, iwin=iwin, fit='gauss')

    Define one gauss function from menu, then 'xcfit' will executes spectrum fitting.
  1. [Add component..] -> [..showing absolute position]
  2. [Redo fit] So verifying that the fitting succeeds
  3. [Use as initial state] -> (value -> initial)
  4. [Exit] -> [Save changes]


    Extract the result from spectrum fitting.

IDL> moments=objm->getvar( iwin )
IDL> amplitude = rotate (moments [*, *, 0], 1)

4.2 Doppler shift

To get Doppler shift, you need to obtain central coordinate of the acquired gauss-fitting (in pixel unit).
Then using pixel scale 0.0223 (A/pixel) to convert it to wavelength

IDL> doppler = rotate (moments [*, *, 1], 1)
IDL> window,0,xs=nexp,ys=ysize [ iwin ]
IDL> tvscl,doppler

EIS Doppler shift map

4.3 Line width

Half breadth of the acquired gauss-fitting (in pixel unit)

IDL> width = rotate (moments [*, *, 2], 1)
IDL> tvscl,width

EIS line width map

5. Release of object

    When object is no longer needed it should be released, otherwise the
    system will fall due to lack of memory.

IDL> obj_destroy,obj
IDL> obj_destroy,objm

Appendix. Acquisition of FITS header

Full FITS headers are obtained like below.

IDL> hdr=obj->gethdr( )
IDL> header=hdr->getbte_hdr( )
IDL> print,header

To get information for a specific FITS keyword, eg. to get the observation starting day and time from keyword (DATE_OBS), one can use:

IDL> date=obj->getinfo('DATE_OBS')

** This page is based on EIS Analysis Tutorial webpage on NAOJ
All original materials are belong to NAOJ.
(Feedback to: js2 (MSSL))

Last Revised: Monday, 24-Jul-2006
Feedback and comments: webmaster

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