Worksheet 2 - Calibrating EIS data (eis_prep)#
In general the user should calibrate EIS data before he/she attempts to look it. This is because EIS data are affected by warm pixels on the CCD which make it difficult to study the images. The EIS calibration routine is called 'eis_prep'.
For the present worksheets we will analyze a data-set taken on 2006 December 9 at 11:30. Worksheet 1 described how to download this file. If it's still in your working directory, then do:
If you defined the $HINODE_DATA directory and moved the file there, then you can do:
IDL> filename=eis_find_file('9-dec-2006 11:30')
The standard call to eis_prep is:
IDL> eis_prep, filename, /default, /save, /retain, /quiet
The /save keyword results in two files being created in the user's directory which have the names:
TIP: it is a good idea to compress these files with gzip.
(If you defined the $HINODE_DATA environment variable in Worksheet 1, then use the eis_ingest.pro routine to transfer the files into your data directory.)
The first file is the level-1 EIS FITS file containing calibrated intensity arrays. The second file is the error file which contains the corresponding 1-sigma intensity errors for the arrays stored in the level-1 file.
Full details of the various keyword inputs to eis_prep are given in EIS Software Note #1, where detailed descriptions of the various steps performed by eis_prep are given.
One feature of eis_prep is that bad pixels in the data are flagged as 'missing'. These bad pixels can be due to cosmic ray hits, saturated pixels, dust particles on the detector, hot pixels and warm pixels. The latter are by far the most numerous, and are described in more detail in EIS Software Note #6. Bad pixels are flagged only in the error file and are assigned a value of -100. The bad pixels in the level-1 file are replaced by a value interpolated from neighbouring pixels. More details about the effect of missing data on EIS data analysis and interpolation methods are given in EIS Software Note #13.