This page (revision-13) was last changed on 07-Dec-2016 14:14 by Peter Young

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NarrowWorksheet2
NarrowWorksheet2

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At line 1 changed one line
!!!Worksheet 2 - Reading and browsing data
!!!Worksheet 2 - Calibrating EIS data (eis_prep)
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The EIS FITS file to be used in all the worksheets is from 9-Dec-2007, 11:30 UT:
Generally it is recommended that you calibrate your data file before you begin taking a look at it. This is because EIS data are affected by warm pixels on the CCD which make it difficult to study the images.
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filename=’eis_l0_20061209_113031.fits’
To calibrate your data, do the standard call to eis_prep is
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(NOTE: you may need to add the path name, depending on where the file is located.)
IDL> eis_prep,filename,/default,/save,/retain,/quiet
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To read an EIS FITS file from the command line, type:
To see what these keywords do (and see other options), go to the wiki section on eis_prep keywords.
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IDL> data=obj_new(‘eis_data’,filename)
The keyword /default makes the routine use the default processing options, and the keyword /save makes eis_prep create two files in your current working directory. These are the level-1 FITS file, and the error FITS file.
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data is an IDL object. You can extract information from the object using various methods. E.g.,
TIP: it is a good idea to compress these files with gzip and move them to a directory called /level1.
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IDL> exp=data->getexp()\\
IDL> xpos=data->getxpos()\\
IDL> wd0=data->getvar(0)\\
NOTE: “bad” data (referred to as missing) are flagged with a value of -100 in the error FITS file arrays (not the level-1 arrays). The missing data in the level-1 arrays are replaced with the median value of the surrounding pixels. This is useful for display purposes, but for scientific analysis you should not use any pixels flagged as missing.
With the /default option, eis_prep does the following things:
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wd0 is a 3D array containing the window data for the specified window (0 in this case). You can get a list of all methods by doing:
* Flag any saturated data as missing (saturated data have a DN value of 16383)
* Remove the CCD pedestal and dark current
* Flag hot pixels as missing
* Flag warm pixels as missing (not implemented at present)
* Flag cosmic rays as missing
* Calibrate data, and create error arrays
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IDL> data->display_methods
To extract the header into a string array, do:
IDL> hdr_obj=data->gethdr()\\
IDL> text=hdr_obj->getbte_hdr()
A number of useful header tags can be sent to a structure by doing:
IDL> eis_get_hdr_struc,data,hdrstr
To find which wavelength windows are contained in data, do:
IDL> wininfo=eis_get_wininfo(filename,/list)
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#Using commands from Worksheet 2, how many pixels in the Fe XII 195 data array have been flagged as missing by eis_prep?
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#Using eis_get_wininfo and the getvar() object method, extract an image in Fe XII 195 by summing all wavelength pixels in the window. Plot the image. What do you have to do to the image to orient it correctly? (You may need to refer to XRT images from Day 1 of the workshop.)
#Using the following commands:
IDL> aux_data=data->getaux_data()\\
IDL> exptimes=data->sec_from_obs_start(*(aux_data.ti_1))\\
IDL> xpos=data->getxpos()\\
work out in which direction EIS rasters (east-west, or west-east).
This page (revision-13) was last changed on 07-Dec-2016 14:14 by Peter YoungTop