;*********************************************
;  Calculate the distance in meters from two points on earth
;
;  Point 1
;  lat1 = latitude of point 1
;  lon1 = longitude of point 1
;
;  Point(s) 2
;  lat2 = latitude of point 2 OR array
;  lon2 = longitude of point 2 OR array
;
;  Returned value
;  dm = distance in meters
;**********************************************

pro great_circle_distance,lat1,lon1,lat2,lon2,dm

;  Convert from degrees to radians
rlat1=double(lat1*(!dpi/180.0)) 
rlon1=double(lon1*(!dpi/180.0)) 
rlat2=double(lat2*(!dpi/180.0)) 
rlon2=double(lon2*(!dpi/180.0))

;  Earth radius - km converted to meters
re=double(6378.0*1000.0)

;  Calculate the great circle distance in meters
;  dm = distance in meters
dm=re*acos(sin(rlat1)*sin(rlat2)+$
    cos(rlat1)*cos(rlat2)*cos(rlon2-rlon1))

return
end