SUBROUTINE SRTM_TAUMOL18 &
 & ( KLEV,&
 & P_FAC00   , P_FAC01  , P_FAC10   , P_FAC11,&
 & K_JP      , K_JT     , K_JT1     , P_ONEMINUS,&
 & P_COLH2O  , P_COLCH4 , P_COLMOL,&
 & K_LAYTROP , P_SELFFAC, P_SELFFRAC, K_INDSELF  , P_FORFAC, P_FORFRAC, K_INDFOR,&
 & P_SFLUXZEN, P_TAUG   , P_TAUR    &
 & )  

!     Written by Eli J. Mlawer, Atmospheric & Environmental Research.

!     BAND 18:  4000-4650 cm-1 (low - H2O,CH4; high - CH4)

USE PARKIND1  ,ONLY : JPIM     ,JPRB
USE YOMHOOK   ,ONLY : LHOOK,   DR_HOOK

USE PARSRTM  , ONLY : JPLAY, JPG, NG18
USE YOESRTA18, ONLY : ABSA, ABSB, FORREFC, SELFREFC &
 & , SFLUXREFC, RAYL &
 & , LAYREFFR, STRRAT  
USE YOESRTWN , ONLY : NSPA, NSPB

IMPLICIT NONE

!-- Output
INTEGER(KIND=JPIM),INTENT(IN)    :: KLEV 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FAC00(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FAC01(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FAC10(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FAC11(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_JP(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_JT(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_JT1(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_ONEMINUS 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_COLH2O(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_COLCH4(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_COLMOL(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_LAYTROP 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_SELFFAC(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_SELFFRAC(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_INDSELF(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FORFAC(JPLAY) 
REAL(KIND=JPRB)   ,INTENT(IN)    :: P_FORFRAC(JPLAY) 
INTEGER(KIND=JPIM),INTENT(IN)    :: K_INDFOR(JPLAY)
 
REAL(KIND=JPRB)   ,INTENT(OUT)   :: P_SFLUXZEN(JPG) 
REAL(KIND=JPRB)   ,INTENT(OUT)   :: P_TAUG(JPLAY,JPG) 
REAL(KIND=JPRB)   ,INTENT(OUT)   :: P_TAUR(JPLAY,JPG) 
!- from INTFAC      
!- from INTIND
!- from PRECISE             
!- from PROFDATA             
!- from SELF             
INTEGER(KIND=JPIM) :: IG, IND0, IND1, INDS, INDF, JS, I_LAY, I_LAYSOLFR, I_NLAYERS

REAL(KIND=JPRB) :: Z_FAC000, Z_FAC001, Z_FAC010, Z_FAC011, Z_FAC100, Z_FAC101,&
 & Z_FAC110, Z_FAC111, Z_FS, Z_SPECCOMB, Z_SPECMULT, Z_SPECPARM, &
 & Z_TAURAY  
REAL(KIND=JPRB) :: ZHOOK_HANDLE

IF (LHOOK) CALL DR_HOOK('SRTM_TAUMOL18',0,ZHOOK_HANDLE)
I_NLAYERS = KLEV

!     Compute the optical depth by interpolating in ln(pressure), 
!     temperature, and appropriate species.  Below LAYTROP, the water
!     vapor self-continuum is interpolated (in temperature) separately.  

I_LAYSOLFR = K_LAYTROP
      
DO I_LAY = 1, K_LAYTROP
  IF (K_JP(I_LAY) < LAYREFFR .AND. K_JP(I_LAY+1) >= LAYREFFR) &
   & I_LAYSOLFR = MIN(I_LAY+1,K_LAYTROP)  
  Z_SPECCOMB = P_COLH2O(I_LAY) + STRRAT*P_COLCH4(I_LAY)
  Z_SPECPARM = P_COLH2O(I_LAY)/Z_SPECCOMB 
  IF (Z_SPECPARM >= P_ONEMINUS) Z_SPECPARM = P_ONEMINUS
  Z_SPECMULT = 8.*(Z_SPECPARM)
  JS = 1 + INT(Z_SPECMULT)
  Z_FS = MOD(Z_SPECMULT, 1.0_JPRB )
! Z_FAC000 = (1. - Z_FS) * P_FAC00(I_LAY)
! Z_FAC010 = (1. - Z_FS) * P_FAC10(I_LAY)
! Z_FAC100 = Z_FS * P_FAC00(I_LAY)
! Z_FAC110 = Z_FS * P_FAC10(I_LAY)
! Z_FAC001 = (1. - Z_FS) * P_FAC01(I_LAY)
! Z_FAC011 = (1. - Z_FS) * P_FAC11(I_LAY)
! Z_FAC101 = Z_FS * P_FAC01(I_LAY)
! Z_FAC111 = Z_FS * P_FAC11(I_LAY)
  IND0 = ((K_JP(I_LAY)-1)*5+(K_JT(I_LAY)-1))*NSPA(18) + JS
  IND1 = (K_JP(I_LAY)*5+(K_JT1(I_LAY)-1))*NSPA(18) + JS
  INDS = K_INDSELF(I_LAY)
  INDF = K_INDFOR(I_LAY)
  Z_TAURAY = P_COLMOL(I_LAY) * RAYL

!  DO IG = 1, NG(18)
  DO IG = 1, NG18
    P_TAUG(I_LAY,IG) = Z_SPECCOMB * &
!    & (Z_FAC000 * ABSA(IND0,IG) + &
!    & Z_FAC100 * ABSA(IND0+1,IG) + &
!    & Z_FAC010 * ABSA(IND0+9,IG) + &
!    & Z_FAC110 * ABSA(IND0+10,IG) + &
!    & Z_FAC001 * ABSA(IND1,IG) + &
!    & Z_FAC101 * ABSA(IND1+1,IG) + &
!    & Z_FAC011 * ABSA(IND1+9,IG) + &
!    & Z_FAC111 * ABSA(IND1+10,IG)) + &
     & (&
     & (1. - Z_FS) * ( ABSA(IND0,IG) * P_FAC00(I_LAY) + &
     &                 ABSA(IND0+9,IG) * P_FAC10(I_LAY) + &
     &                 ABSA(IND1,IG) * P_FAC01(I_LAY) + &
     &                 ABSA(IND1+9,IG) * P_FAC11(I_LAY) ) + &
     & Z_FS        * ( ABSA(IND0+1,IG) * P_FAC00(I_LAY) + &
     &                 ABSA(IND0+10,IG) * P_FAC10(I_LAY) + &
     &                 ABSA(IND1+1,IG) * P_FAC01(I_LAY) + &
     &                 ABSA(IND1+10,IG) * P_FAC11(I_LAY) ) &
     & ) + &
     & P_COLH2O(I_LAY) * &
     & (P_SELFFAC(I_LAY) * (SELFREFC(INDS,IG) + &
     & P_SELFFRAC(I_LAY) * &
     & (SELFREFC(INDS+1,IG) - SELFREFC(INDS,IG))) + &
     & P_FORFAC(I_LAY) * (FORREFC(INDF,IG) + &
     & P_FORFRAC(I_LAY) * &
     & (FORREFC(INDF+1,IG) - FORREFC(INDF,IG))))   
!     &           + TAURAY
!    SSA(LAY,IG) = TAURAY/TAUG(LAY,IG)
    IF (I_LAY == I_LAYSOLFR) P_SFLUXZEN(IG) = SFLUXREFC(IG,JS)  &
     & + Z_FS * (SFLUXREFC(IG,JS+1) - SFLUXREFC(IG,JS))  
    P_TAUR(I_LAY,IG) = Z_TAURAY
  ENDDO
ENDDO

DO I_LAY = K_LAYTROP+1, I_NLAYERS
  IND0 = ((K_JP(I_LAY)-13)*5+(K_JT(I_LAY)-1))*NSPB(18) + 1
  IND1 = ((K_JP(I_LAY)-12)*5+(K_JT1(I_LAY)-1))*NSPB(18) + 1
  Z_TAURAY = P_COLMOL(I_LAY) * RAYL

!  DO IG = 1, NG(18)
  DO IG = 1, NG18
    P_TAUG(I_LAY,IG) = P_COLCH4(I_LAY) * &
     & (P_FAC00(I_LAY) * ABSB(IND0,IG) + &
     & P_FAC10(I_LAY) * ABSB(IND0+1,IG) + &
     & P_FAC01(I_LAY) * ABSB(IND1,IG) +       &
     & P_FAC11(I_LAY) * ABSB(IND1+1,IG))   
!     &           + TAURAY
!    SSA(LAY,IG) = TAURAY/TAUG(LAY,IG)
    P_TAUR(I_LAY,IG) = Z_TAURAY
  ENDDO
ENDDO

!-----------------------------------------------------------------------
IF (LHOOK) CALL DR_HOOK('SRTM_TAUMOL18',1,ZHOOK_HANDLE)
END SUBROUTINE SRTM_TAUMOL18

