Worksheet 3 - Reading and browsing data#

After calibrating the data with eis_prep we are now ready to read the data into IDL. First set the filename:

filename=’eis_l1_20061209_113031.fits’

(NOTE: you may need to add the path name, depending on where the file is located.)

Now to read the EIS FITS file from the command line, type:

IDL> data=obj_new(‘eis_data’,filename)

data is an IDL object. Information is extracted from the object through a large number of methods and some examples are given below.

To determine the coordinates of the center of the raster, do:

IDL> xcen=data->getxcen(/raster)
IDL> ycen=data->getxcen(/raster)

To find the exposure time for each exposure of the raster, do:

IDL> exp=data->getexp()

A single data window can be extracted by doing:

IDL> wd=data->getvar(195.12)

where the specified wavelength is used to pick out the data window containing that particular wavelength. The first dimension of WD is always wavelength, the second is always solar-Y, and the third can be either solar-X or time depending if the observation was a raster or a sit-and-stare observation.

A complete list of methods is obtained by doing

IDL> data->display_methods

while more detailed information on some methods is given elsewhere on the EIS wiki.

Exercise#

1. 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.)
2. 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).