!**********************************************************************c
      SUBROUTINE CALRH_GSD(P1,T1,Q1,RHB)

! Algorithm use at GSD for RUC and Rapid Refresh                           
!------------------------------------------------------------------
!

      use ctlblk_mod, only: jsta, jend, im, jm

      implicit none

      integer :: j, i
      real :: tx, pol, esx, es, e
      REAL P1(IM,JM),T1(IM,JM),Q1(IM,JM),RHB(IM,JM)


      DO J=JSTA,JEND
      DO I=1,IM

! - compute relative humidity
        Tx=T1(I,J)-273.15
        POL = 0.99999683       + TX*(-0.90826951E-02 +    &
           TX*(0.78736169E-04   + TX*(-0.61117958E-06 +   &
           TX*(0.43884187E-08   + TX*(-0.29883885E-10 +   &
           TX*(0.21874425E-12   + TX*(-0.17892321E-14 +   &
           TX*(0.11112018E-16   + TX*(-0.30994571E-19)))))))))
        esx = 6.1078/POL**8

          ES = esx
          E = P1(I,J)/100.*Q1(I,J)/(0.62197+Q1(I,J)*0.37803)
          RHB(I,J) = AMIN1(1.,E/ES)


      ENDDO
      ENDDO

      RETURN
      END