The Fourier transform is not just limited to simple lab examples. When
used in real situations it can have far reaching implications about the
world around us.
Take for example the field of astronomy. Some times it isn't possible
to get all the information you need from a normal telescope and you need
to use radio waves or radar instead of light. These radar signals are treated
just like any other ordinary time varying voltage signal and can be processed
One recent example of this technique was the NASA Magellan
satellite which was released from the space shuttle Atlantis on 4th May
1989 and sent to Venus on a 15 month journey that took it one and a half
times around the sun.
Venus is Earth's closest planetary companion, and is comparable in its
size and diameter. It is difficult to study the surface of Venus because
it is perpetually covered with a cloud layer which normal optical telescopes
can't penetrate, so Magellan had radar and advanced Digital Signal
Processing that was designed to see through this cloud layer. It's mission
was map the planet with radar and to reveal surface features as small as
250 meters across.
The black and white pictures that it sent back were strips of the planets
surface, about 20 km wide, from the north pole to the south pole. One example
image of a surface feature called "Pandora Corona" is shown next. If you
look at the image, you will see a two black lines through the picture.
This is just a mismatch between the strips sent back by Magellan. It also
gives you an idea of the scale of the image as each strip is 20 km wide.
From the radar signal received from the planet Magellan was also
able to gather other information about the planets surface. The next image
is a global map of venus showing emissitivity of the Venus's surface.
By the end of the mission Magellan had far exceeded the mission
objectives by mapping 99% of the planet's surface, and by giving unpresidented
detail. By piecing all the information together from this mission and from
earlier Pioneer-Venus orbiter data, as well as the Soviet Venera 13 and
14 spacecraft, they were able to produce the following mosaic image which
is a global view of Venus using simulated color to enhance small scale
Microwave emissitivity of Venus.
Magellan was also carrying another smaller antenna that pointed
straight down and measured the time taken for a signal to reflect off the
surface. This was used to build up a topographic map of the surface beneath
the spacecraft. Combining this data with the earlier radar images they
were able to construct a 3D model of the surface of Venus. The model was
animated to provide an MPEG movie that flies you across the Maxwell Mountains
on Venus. Any of this would have been impossible if it had not been for
Digital Signal Processing and the Fast Fourier Transform.
Global view of Venus.
MPEG movie constructed from venus radar data.
Back to List of other applications