Limb Correction Procedure for Window Channel IR

     Subroutines are provided to read in limb correction
models, determine satellite zenith angle for a pixel, and
finally to apply a limb correction to window channel IR
pixels.  To obtain necessary subroutines:

 ftp ftp.ncep.noaa.gov
 use anonymous as userid, use email address as password
 cd pub/precip/sza-corr
 get SZA_CORRECTION_README
 get error_regrid
 get latitudinal-error_annual-cycle-model
 get sza-Tb-lat+seas_models.f
 get sza.f
 get sza-Tb-lat+seas_correct.f
 get sza-Tb-lat+seas_models+corr_example.f
 
  error_regrid: IR correction model derived at the Tropics, 
                should be read in once at the beginning of
                the IR correction software.

  latitudinal-error_annual-cycle-model: This model adjusts
                the original correction model (derived in
                the Tropics) for seasonal and latitudinal
                dependency.

  sza-Tb-lat+seas_models.f: This subroutine reads in the
                two models above and should be called only 
                once at the beginning of the zenith angle
                correction program.  The call to this
                subroutine is: 

              call szamodels(error,errorlat,itype)
  
                where error and errorlat are the output IR
                correction model (derived at the Tropics)
                and the seasonal and latitudinal adjustment 
                model respectively, itype is the input binary
                parameter which should be set to zero(0) for
                LINUX or PCs or one(1) for SGI or HPs.

  sza.f: This subroutine computes geostationary satellite
                zenith angle for a pixel providing the
                earth location of both the satellite and
                the target are known.  The call to this
                subroutine is:

              call satang(XLAT,XLON,SUBLON,ANGZEN,ANGNDR)

                where XLAT and XLON are latitude and
                longitude of the target pixel respectively,
                SUBLON is longitude of the geostationary
                satellite located on the equator, ANGZEN 
                and ANGNDR are output satellite zenith
                angle and nadir angle respectively.

  sza-Tb-lat+seas_correct.f: This subroutine corrects
                IR window channel brightness temperature
                for the effects of satellite zenith angle
                for zenith angles greater than 26 degrees,
                providing original pixel brightness
                temperature, satellite zenith angle, Julian
                day and target pixel latitude are known.
                The call to this subroutine is:
 
    call szacorr(error,errorlat,Tb,sza,xjday,xlat,Tbcorr)

                where error and errorlat are previously
                read models, Tb and sza are original 
                target pixel brightness temperature and
                satellite zenith angle respectively, xjday
                and xlat are Julian day and target pixel
                longitude respectively, Tbcorr is the
                output limb corrected brightness
                temperature.

  sza-Tb-lat+seas_models+corr_example.f:  This is an
                example program that uses all of the above
                subroutines to correct a sample pixel of
                original Tb = 235K, for each day of a
                leap year.  Here the example satellite is
                GOES 8 with a subsat = 285, the sample
                pixel is located at latitude = 41.2 and
                longitude = 228.0  I ran this on a LINUX
                so I set itype = 0