Microwaves
| Microwaves have
wavelengths that can be measured
in centimeters! The longer
microwaves, those closer to a
foot in length, are the waves
which heat our food in a
microwave oven. |
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|
Microwaves are good for
transmitting information from
one place to another because
microwave energy can penetrate
haze, light rain and snow,
clouds, and smoke.
Shorter microwaves are used
in remote sensing. These
microwaves are used for radar
like the doppler radar used in
weather forecasts. Microwaves,
used for radar, are just a few
inches long. |
|
This microwave tower can transmit
information like telephone calls and
computer data from one city to
another.
How do we "see" using Microwaves?
Radar is an acronym for "radio
detection and ranging". Radar was
developed to detect objects and
determine their range (or position) by
transmitting short bursts of microwaves.
The strength and origin of "echoes"
received from objects that were hit by
the microwaves is then recorded.
| Because radar
senses electromagnetic waves
that are a reflection of an
active transmission, radar is
considered an active remote
sensing system. Passive remote
sensing refers to the sensing of
electromagnetic waves which did
not originate from the satellite
or sensor itself. The sensor is
just a passive observer. |
 |
What do Microwaves show us?
 
|
This is a radar
image acquired from the Space
Shuttle. It also used a
wavelength in the L-band of the
microwave spectrum. Here we see
a computer enhanced radar image
of some mountains on the edge of
Salt Lake City, Utah. |
In the 1960's a
startling discovery was made quite by
accident. A pair of scientists at Bell
Laboratories detected background noise
using a special low noise antenna. The
strange thing about the noise was that
it was coming from every direction and
did not seem to vary in intensity much
at all. If this static were from
something on our world, like radio
transmissions from a nearby airport
control tower, it would only come from
one direction, not everywhere. The
scientists soon realized they had
discovered the cosmic microwave
background radiation. This radiation,
which fills the entire Universe, is
believed to be a clue to it's beginning,
something known as the Big Bang.
The image above is a Cosmic
Background Explorer (COBE) image of the
cosmic microwave background, the pink
and blue colors showing the tiny
fluctuations in it.
| Did you
know that if you had a sensitive
microwave telescope in your
house that you would detect a
faint signal leaking out of your
microwave oven, and from various
other man-made sources, but also
a faint signal coming from all
directions that you pointed it?
This is the Cosmic Microwave
Background! |
