Great Wall of China:
     POLICE USE RADAR TO ZAP A SPEEDING CAR--BY SENDING THE RADAR OUT AND
MEASURING THE TIME IT TAKES TO BOUNCE BACK YOU CAN FIND OUT HOW FAR AWAY THE
CAR IS AND HOW FAST IT'S GOING.  THE SPACE SHUTTLE HAS BEEN DOING THE SAME THING
TO THE EARTH. NOT TO SEE HOW FAST THE GLOBE IS SPEEDING ALONG, BUT TO MAP IT. 
GEOLOGIST DIANE EVANS RUNS THIS PROJECT, CALLED SIR-C, FOR NASA. 

     Evans: "When we fly a radar system. . . It actually extends our ability to see beyond
what we normally can see with just our normal vision. "

     WHEN THE RADAR HITS THE EARTH IT GOES IN FARTHER IF THE SOIL IS DRY, LESS IF THE
EARTH IS WET.  AND IT REBOUNDS IMMEDIATELY IF IT HITS SOMETHING HARD LIKE A ROCK
OR AS EVANS FOUND OUT, IF IT HITS SOMETHING MAN MADE. 

     Evans: "One day I was asking my secretary what she thought would be an
interesting thing to find in the Sir-C data and she said I wonder  if you saw the great wall
of china, and so we looked at the survey images and amazingly enough we saw the
great wall of china so we processed the data to its full resolution and when we did that
and looked we actually saw not just one wall but two."
     
     THE SHUTTLE'S RADAR HAD PICKED UP NOT JUST RUINS OF A PREVIOUS WALL, BUT
SUBTLE CHANGES IN THE GROUND WHERE THE PREVIOUS WALL HAD BEEN.  EVANS SAYS
THAT WHEN A CHINESE COLLEAGUE WENT OUT TO EXAMINE THE WALL FROM THE
GROUND,

     Evans: "he could see more in the radar image than he could actually see in the
field."

     EVANS SAYS THAT THE OLDER WALL WAS BUILT BY THE SUI DYNASTY ABOUT 15,000
YEARS AGO, AS COMPARED TO THE WALL STILL STANDING WHICH WAS BUILT BY THE MING
DYNASTY 600 YEARS AGO.  NOW ARCHAEOLOGISTS HAVE ASKED HER TO USE THE
SHUTTLE'S RADAR TO SEARCH FOR OTHER THINGS, TOO, LIKE TEMPLES HIDDEN FROM VIEW
IN OVERGROWN JUNGLES.