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).The spatial binning is specified by the SUMSPAT keyword. When converting the data number into physical radiance units note that the slit width (1/3 arcsec) is the second factor in determining the steradian platescale. The spectral binning can differ between bandpasses. The spectral resolution of Level 2 data is determined by SUMSPTRN and SUMSPTRF for the NUV and FUV respectively. By default the mosaic processing code spectrally rebins the Level 2 data to a default value. Counts are conserved during this interpolation. The CDELT3 keyword in the mosaic FITS is determined from this ultimate spectral bin size. The keyword EXPTIME indicates the exposure time. The keyword OBSID indicates the observing program.

In addition to the intensity data, 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]