ÜDS-Fen 2002-1 Soru=62

We understand from the passage that radar signals ----.

Post war radar has been developed for an enormous
range of uses from police radar speed traps to the
ballistic missile early warning systems. At sea it is
used on ships of all sizes from the super tankers
down to pleasure craft, and the air it guards military
and civilian aircraft against collisions. It is even used
to keep track of the orbital junkyard created by
innumerable space launches. Radar found an
unexpected use in astronomy and space navigation.
Radar signals were bounced off the moon in 1946
and reflections were obtained from Venus and the
sun in the late 1950s. Subsequently, radar maps
were made of the moon and Venus - not that such
long ranges are essential for radar maps to prove
themselves useful. For example, satellite-borne radar
aimed at the earth has actually led to the discovery of
previously unknown remnants of a Mayan canal
drainage system in Central America.