SUBROUTINE DISTANCE(rlat1,rlat2,rlon1,rlon2,x)

C     DISTANCE CALCULATES THE DISTANCE BETWEEN TWO 
C     LATITUDE,LONGITUDE POINTS

c*****************************************************
c
c      rlat1,rlon1 - first position
c      rlat2,rlon2 - second position
c      x - distance between points
c
c*****************************************************

c*****************************************************
c
c    Parameters:
c
c     req - radius of the earth at the equator
c     pi - pi
c
c*****************************************************

      parameter (req=6378.137D00, pi=3.141592653D00)

      double precision ang,x1,rlat1a,rlat2a,rlon1a,rlon2a

c*****************************************************
c
c    Convert lats and lons to radians
c
c*****************************************************

      rlat1a=((rlat1*pi)/180.)+0.D00
      rlat2a=((rlat2*pi)/180.)+0.D00

      rlon1a=((rlon1*pi)/180.)+0.D00
      rlon2a=((rlon2*pi)/180.)+0.D00

c*****************************************************
c
c     Figure distance
c
c*****************************************************

      ang=(dsin(rlat1a)*dsin(rlat2a)) +
     *             (dcos(rlat1a)*dcos(rlat2a) *
     *             dcos((rlon1a-rlon2a)))
      if ( ang .ge. 1.0D00 ) then
       x=0.
      else
       x1=req* dacos(ang) 
       x=x1
      endif

      return
      end