oi_kalman_gain.F90

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!SFX_LIC Copyright 1994-2014 CNRS, Meteo-France and Universite Paul Sabatier
!SFX_LIC This is part of the SURFEX software governed by the CeCILL-C licence
!SFX_LIC version 1. See LICENSE, CeCILL-C_V1-en.txt and CeCILL-C_V1-fr.txt  
!SFX_LIC for details. version 1.
SUBROUTINE oi_kalman_gain(PDWG_DWG,PDWG_DW2,PD2,PK1,PK2)
!
!****-------------------------------------------------------------------
!
USE modd_csts,  ONLY : xrholw 
USE modd_assim, ONLY : xrd1, xsigwgo, xsigwgb, xsigw2b
!
!
USE yomhook   ,ONLY : lhook,   dr_hook
USE parkind1  ,ONLY : jprb
!
IMPLICIT NONE
!
REAL ,INTENT(IN)  :: pdwg_dwg, pdwg_dw2, pd2
REAL ,INTENT(OUT) :: pk1, pk2
!
REAL :: zsig_wg,zsig_w2,zsig_wo,za,zb,zh1,zh2,zdenom
REAL(KIND=JPRB) :: zhook_handle
!
! Standard deviation of background and observation errors
!
IF (lhook) CALL dr_hook('OI_KALMAN_GAIN',0,zhook_handle)
zsig_wg = xsigwgb
zsig_w2 = xsigw2b
zsig_wo = xsigwgo
!
! Jacobians elements
!
zh1 = pdwg_dwg
zh2 = pdwg_dw2
!
! Elements of background covariance matrix
!
za = (zsig_wg*zh1)**2 + (zsig_w2*zh2)**2
zb =  zsig_w2**2
!
zdenom = (za + zsig_wo*zsig_wo)
!
! Kalman gain elements (m3/m3)
!
pk1 =  za    /zdenom !*RD1*XRHOLW
pk2 =  zb*zh2/zdenom !*PD2*XRHOLW
IF (lhook) CALL dr_hook('OI_KALMAN_GAIN',1,zhook_handle)
!
!**---------------------------------------------------------------------
END SUBROUTINE oi_kalman_gain