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subroutine ehv2pem( ehorz0,evert0,zlsat0,polar0, pems0) 3
!$$$ module documentation block
! . . . .
! module: ehv2pem combine V and H.pol emissivity
! prgmmr: okamoto org: np23 date: 2004-08-06
!
! abstract: combine vertical and horizontal polarized emissivity.
! effective for cross-track scan type sensor such as AMSU
! In contrast, for ssm/i, pems(V)=evert0, pems(H)=ehorz0,
! as they are
!
! program history log:
! 2004-08-06 okamoto
!
! input argument list:
! zlsat0 - satellite look angle in radians
! polar - channel polarization (0=vertical, 1=horizontal, or
! 0 to 1=mix of V and H)
! ehorz0 - emissivity at horizontal polarization
! evert0 - emissivity at vertical polarization
!
! output argument list:
! pems0 - surface emissivity at obs location
!
! attributes:
! language: cft77
! machine: IBM sp
!
!$$$
implicit none
real(r_kind):: ehorz0,evert0,zlsat0,polar0, pems0
real(r_kind):: pcl2,psl2,term1,term2
pcl2=cos(zlsat0)**2
psl2=sin(zlsat0)**2
term1 = evert0*pcl2 + ehorz0*psl2
term2 = evert0*psl2 + ehorz0*pcl2
pems0 = (one-polar0)*term1 + polar0*term2
return
end subroutine ehv2pem