EUVI analysis guide

Updated 20-May-2025.

This guide gives some basic information for getting started with EUVI data. For more detailed information, check the SECCHI data user guide. There is also useful information in the COR1 User Guide that is applicable to EUVI.

Downloading data

Setup

Firstly create a directory where you plan to store the EUVI data, and then add the following line to your IDL startup file:

setenv,'SECCHI_LZ=/data/stereo'

where /data/stereo is the directory where you'll be keeping the data.

Downloading from the VSO

I recommend obtaining data from the VSO through the IDL command line. For example:

IDL> list=vso_search('17-jul-2014 07:00','17-jul-2014 11:00',inst='euvi',wave=304,source='stereo_a')
IDL> a=vso_get(list)

This downloads to your local directory all of the STEREO-A 304 channel FITS files for a four hour period on 17-Jul-2014.

Ingesting the data

It is best to store your downloaded data in the SECCHI directory structure, so you should ingest your newly-downloaded files by doing:

IDL> sccingest,'.'

This moves the files into the directory defined by $SECCHI_LZ (see above).

Filename format

The COR1 User Guide explains the filename format. In particular, there is a five-letter code in the filename such as "n4euA". The first letter will always be 'n' (normal) for EUVI, the second character will usually be 4 for a synoptic image, 5 for a special sequence (e.g., a CME is detected so extra images are obtained), or 7 for a low-resolution beacon image. The 3rd and 4th characters are 'eu' for EUVI, and the 5th character gives the spacecraft (A or B).

Selecting files

To select files from your local SECCHI data repository, you can run the GUI-based routine scclister:

IDL> list_struct=scclister()

which allows you to see which files you have for a specified day or time range. The output structure list_struct contains details on these files and can be used as an input to secchi_prep.

If you prefer to filter the image set on the command line, then try, e.g.,

IDL> list_struct=scclister('20090113..20090114', 'EUVI', sc='b', size='2048', filt='S1',dest='SSR1', polar=171, sort_type='ascending',sort_by='DateObs')

Note that the keyword 'polar' is used to select wavelength, and dest takes 'SSR1' for synoptic images and 'SSR2' for special event sequences (e.g., CMEs).

Prepping your data

With your file list from scclister, you can then prep your data by doing:

IDL> secchi_prep, list_struct.sc_a, hdr, im, rotate=1, /smask, /interp

(For the case where the files correspond to spacecraft A.) If you want to shrink the images down to 1024 pixels, then set outsize=1024.

Use the keyword /write_fts to write the prepped data as FITS files to your local directory. Note that the filenames will be identical to the original filenames, except "n4euA" (for example) will be written as "14euA", i.e., the "n" is changed to "1".

To run secchi_prep on a local file rather the scclister structure, do:

IDL> secchi_prep, filename, hdr, im, rotate=1, /smask, /interp

Converting to IDL maps

The outputs "hdr" and "im" can be converted to IDL maps by doing:

IDL> index2map, hdr, im

Spacecraft separation angle

To determine the separation angle between the either of the STEREO spacecraft and Earth, do, e.g.,

IDL> angle=get_stereo_sep_angle('2009-11-22 02:14','B','Earth',/degrees)

Page maintained by Dr Peter R Young.