Full-disk Mosaics
Once a month (when not in eclipse season), IRIS takes a full-disk mosaic in 6 spectral windows surrounding the strongest spectral lines (Mg II h and k, C II 1335 and 1334, and Si IV 1393 and 1403). The IRIS mosaics are built from a series of rasters taken at different pointings that cover the full disk, roughly as follows:
  • A total of ~185 pointings are commanded to cover the full disk; the total duration is approximately 18 hours
  • At each pointing, IRIS runs a 64-step raster with 2-arcsec steps, sampling an area roughly 180 arcsec (the height of the slit) by 128 arcesc (the width of the raster)
  • FUV and NUV spectra with 1-2 second exposure times are obtained at each raster step
The rasters are rearranged into 3-D data cubes (X, Y, lambda) covering the full disk in the neighborhood of the spectral lines. Data from selected AIA and HMI channels are used to construct "pseudo-mosaics" (or "FrankenMaps") showing the SDO signal at the time when IRIS was sampling each portion of the disk. The IRIS mosaics and SDO pseudo-mosaics are available as FITS files by clicking on the date links in the following table.

Si IV 1393 A
Si IV 1403 A
C II 1334 A
C II 1335 A

The FITS files for the IRIS mosaics can be read as follows:

IDL> dat = READFITS('IRISMosaic_20130930_MgIIh.fits', hdr)
IDL> HELP, dat
DAT       FLOAT    = Array[1002, 6011, 100]
IDL> header = FITSHEAD2STRUCT(hdr)
IDL> PLOT_IMAGE, dat[*,*,50], scale = [header.cdelt1, header.cdelt2], $
min = 0, max = 300, xtitle = 'X [arcsec]', ytitle = 'Y [arcsec]'

The standard WCS keywords for specifying the the linear coordinate system (CDELTn, CRPIXn, CRVALn) are used, where n is an integer specifying the dimension of the data (X, Y, lambda). Note that CDELT1 is typically larger than CDELT2 -- the X axis scale is set by the raster step size (generally 2 arcsec), while the Y axis scale is set by the spatial pixel size (generally 1/3 arcsec, for mosaics taken with 2x spatial summing).

In addition to the intensity data (in DN/s/pix), the files have two extensions containing 1) the integrated spectrum, and 2) a time tag for each pixel in the mosaic (in seconds from the start of the mosaic). They can be read as follows:

IDL> ispec = READFITS('IRISMosaic_20130930_MgIIh.fits', spechdr, exten=1)
IDL> help, ispec
ISPEC       FLOAT    = Array[100]
IDL> t_mask = READFITS('IRISMosaic_20130930_MgIIh.fits', thdr, exten=2)
IDL> pixel_tai = ANYTIM2TAI(header.date_obs) + t_mask
IDL> help, pixel_tai
PIXEL_TAI       DOUBLE    = Array[1002, 6011]

The SDO pseudo-mosaics can be read as follows:

IDL> READ_SDO, '20130930_AIA_0171.fits', sdo_hdr, sdo_dat
IDL> help, sdo_dat
SDO_DAT       FLOAT    = Array[4096, 4096]