program maskreding
       implicit none
       integer idim,jdim,kdim,tdim
       parameter(idim=513,jdim=386,kdim=30,tdim=12)
       real*8 h8(idim,jdim),mask8(idim,jdim)
       real   h4(idim,jdim),srho(kdim),mask(idim,jdim)

       integer i,j,k,t

       open(11,file='mask.dat',form='unformatted')
       read(11)mask8
       close(11)

       do j=1,jdim
        do i=1,idim
           mask(i,j)=mask8(i,j)
        enddo
       enddo

       open(51,file='mask4.dat',form='unformatted')
       write(51)mask

      end