HIS.DOC     Version 1.0                 ROK     10-28-90

    The High-resolution Interferometer Sounder (HIS) is a Fourier Transform
Spectrometer (FTS) which uses laser controlled sampling and on-board
blackbodies to achieve highly accurate wavelength and spectral radiance
absolute calibration.  The HIS data described below was collected under 
United States and State of Wisconsin funded projects lead by Principal 
Investigator William L. Smith, Professor of Meteorology, and
Director of the Cooperative Institute for Meterological Satellite Studies at
the University of Wisconsin -- Madison.  This file contains a description of 
the HIS instrument function and a recommended procedure for simulating the HIS
radiances.

    The instrument function of the HIS can be characterized in the following
way.  The HIS makes measurements directly in the Fourier or interferogram
domain.  The measurements range from zero path difference to a maximum delay
that depends on the way the data was processed.  The recommended method
of matching the HIS measurements is to first calculate the high resolution
atmospheric radiance over the free spectral range (FSR) given below for each
band, then to interpolate the calculation to an interval which is a sub-
multiple of the HIS spacing (given as DV below for each band) starting at
exactly V1 (the beginning of the FSR for each band).  This interpolated 
spectrum should be taken smoothly to zero outside the optical filter range
given below for each band but before the ends of the free spectral range
(given as V1 and V2 below for each band).  The spectrum
(which should have a number of points equal to a power of 2) should then
be Fourier transformed using a standard FFT routine.  The resulting 
interferogram must be truncated (i.e., set to zero) beyond the maximum
delay given for each band.  The truncated interferogram is then inverse
transformed by the FFT routine, but with a reduced number of points consistent
with the DV of the HIS data listed with each band.  The resulting spectrum
can then be compared directly with the HIS data.
    The HIS data are unapodized and the interferometer finite field of view
effect has been removed.  All wavenumbers listed in the following tables
are in reciprocal centimeters (cm-1).  Only the data within the optical filter
bandpass has been included in the data files.
    IMPORTANT NOTE:  The HIS calibration is undefined in the narrow spectral
range 667.016 to 669.771 cm-1.  An arbitrary constant value has been
inserted in each of the band 1 files for plotting purposes only.  This
region should *not* be used for spectroscopic comparisons.


 For  HIS data files  GPXO3120.B1 & .B2  AND  GPXN0111.B1 & .B2 :
       (groundbased measurements of downwelling radiance)

                FREE SPECTRAL RANGE                   OPTICAL FILTER RANGE
   Band          V1             V2        DV

    1          564.250      1128.50    .2755127           600.      1080.     
    2          987.4375     1974.875   .9642944          1080.      1800.     


   Band    Max. Delay(cm.)    Unapodized Spectral Resolution (cm^-1)

     1         1.37350                   0.36403
     2         0.51851                   0.96429


 For  HIS data files  HIS86104.B1 & .B2 :
       (NASA U2 measurements of upwelling radiance)

                FREE SPECTRAL RANGE                   OPTICAL FILTER RANGE
   Band          V1             V2         DV

    1          564.250      1128.50    .2755127            600.      1080.     
    2          987.4375     1974.875   .4821472           1080.      1800.     


   Band    Max. Delay(cm.)    Unapodized Spectral Resolution (cm^-1)
 
    1         1.37350                   0.36403
    2         0.78486                   0.63706

 

  Please refer questions about HIS data to:
       Robert O. Knuteson
       Cooperative Institute for Meterological Satellite Studies
       University of Wisconsin -- Madison
       1225 W. Dayton
       Madison, WI  53706  USA
       phone (608-263-4085)
       fax   (608-262-5974)