Worksheet 5b - Extracting slot window data to a structure (eis_readslot)#

As in the case of the narrow slit, sometimes it is useful to extract window data to a structure. This can be done as described in the narrow slit Worksheet 5.

The output structure in the case of slot data may be inconvenient and therefore there is a wrapper that is able to interpret whether the data is in scanning or sit-and-stare mode and provide a more manageable data structure.

One example of slot data that can be used is this slot raster part of the full Sun scan taken on November 1, 2011.

IDL> filename=’eis_l1_20111101_111043.fits’

To extract the window data:

IDL> eis_readslot,filename,wd,win=195.12,/estimate

where filename is that of the calibrated (level-1) data file. Note that the routine automatically looks in the same directory for the error file and reads this too.

Specifying 195.12 means the routine will find the window that contains the wavelength 195.12 Å (the strong Fe XII line).

One common use of the slot data is to build large field-of-view images by taking multiple exposures at adjacent solar positions (scanning mode). Often the observation includes an overlap of these exposures to prevent data gaps. The routine is able to deal with that overlap by estimating it from the header information. To take advantage of this option use the ESTIMATE keyword.

The returned structure contains an intensity array and error array, as well as a lot of useful auxiliary information. To see the structure tags do:

IDL> help,wd,/str 

note that the HDR tag contains the complete header structure for the data-set.

And the image can be displayed using standard software:

IDL> plot_image,