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subroutine siem_interpolate(frequency,discriminator,emissivity,seaice_type) 4
!
!$$$ subprogram documentation block
! . . . .
! subprogram:
!
! prgmmr:Banghua Yan org: nesdis date: 2004-03-01
!
! abstract:
! (1) Find one snow emissivity spectrum to mimic the emission property of the
! realistic snow condition using a set of discrminators
! (2) Interpolate/extrapolate emissivity at a required frequency
!
! program history log:
!
! input argument list:
!
! frequency - frequency in GHz
! discriminators - emissivity discriminators at five AMSU-A & B window channels
! discriminator[1] : emissivity discriminator at 23.8 GHz
! discriminator[2] : emissivity discriminator at 31.4 GHz
! discriminator[3] : emissivity discriminator at 50.3 GHz
! discriminator[4] : emissivity discriminator at 89 GHz
! discriminator[5] : emissivity discriminator at 150 GHz
!
! Note: discriminator(1) and discriminator(3) are missing value in
! 'AMSU-B & Ts','AMUS-B' and 'MODL' options., which are defined to as -999.9,
! output argument list:
!
! em_vector[1] and [2] - emissivity at two polarizations.
! seaice_type - snow type (reference [2])
!
! remarks:
!
! attributes:
! language: f90
! machine: ibm rs/6000 sp
!
!$$$
! use kinds, only: r_kind,i_kind
implicit none
integer(i_kind),parameter:: ncand = 16,nch =5
integer(i_kind):: ich,ichmin,ichmax,i,j,k,s,seaice_type
real(r_kind) :: dem,demmin0
real(r_kind) :: em(ncand,nch)
real(r_kind) :: frequency,freq(nch),emissivity,discriminator(*)
real(r_kind) :: cor_factor,adjust_check,kratio, bconst
data freq/23.8_r_kind, 31.4_r_kind, 50.3_r_kind,89.0_r_kind, 150.0_r_kind/
! Estimate sea ice emissivity at a required frequency
seaice_type = -999 ! temporal assumption
do i = 2, nch
if(frequency < freq(1)) exit
if(frequency >= freq(nch)) exit
if(frequency < freq(i)) then
emissivity = discriminator(i-1) + (discriminator(i)-discriminator(i-1))* &
(frequency - freq(i-1))/(freq(i) - freq(i-1))
exit
end if
end do
if(frequency < freq(1)) emissivity = discriminator(1)
! Assume emissivity = constant at frequencies >= 150 GHz
if (frequency >= freq(nch)) emissivity = discriminator(nch)
end subroutine siem_interpolate