Mapping Planets using Radar
- Several planetary surfaces in the Solar System are obscured from view.
- Venus is completely covered with thick clouds.
- Earth's dry land is covered with vegetation.
- Titan, the largest moon of Saturn, has an atmosphere filled
with thick haze.
- In all of the examples above, visible light cannot reach us from
the planet's surface, but radio light can penetrate the clouds or
- In practice we transmit a short pulse of radio light either
from an Earth-based transmitter or from an orbiting spacecraft
and then record the reflected signal.
- This activity is similar in many ways to taking a flash
picture with a camera in a dark room.
- Instead of recording an image directly onto film one must
carefully analyze the strength, time delay, and doppler shift of
the returning signal to reconstruct a picture.
- The strength of the signal measures how well the surface
material reflects the radio light.
In general the efficiency of the reflection is a measure
of the roughness of the surface.
- The time delay measures the distance to various surface
features and to various regions of the planet.
- The reflection from a mountain peak will arrive
before the reflection from the plains below.
- Since the pulse of radio light illuminates a large area
the doppler shift differentiates between different locations
on the rotating planet.
- Combining all of this information, one can reconstruct a realistic view of the surface structure.
Created November 10, 2000