National Weather Service
JetStream - Online School for Weather
Introduction
Remote sensing is the science of obtaining information about a subject or object without actually being in contact with that subject or object. In the National Weather Service remote sensing equipment is used in the detection and measurement of weather phenomena with devices sensitive to electromagnetic energy such as...
- Light (satellite)
- Heat (infrared scanners on satellites)
- Radio Waves (Doppler radar)
Remote sensing provides a unique perspective from which to observe large regions. These sensors can measure energy at wavelengths which are beyond the range of human vision. In this section we will discover the various methods the National Weather Service uses to help us derive forecasts, weather watches, and warnings.
Electromagnetic waves
Electromagnetic waves are invisible forms of energy that travel though the universe. However, you can "see" some of the results of this energy. The light that our eyes can see is actually part of the electromagnetic spectrum. This visible part of the electromagnetic spectrum consists of the colors that we see in a rainbow - from reds and oranges, through blues and purples. Each of these colors actually corresponds to a different wavelength of light.
The sound we hear is a result of waves which we cannot see. Sound waves need something to travel through in order for it to move from one place to the next. Sound can travel through air because air is made of molecules. These molecules carry the sound waves by bumping into each other, like dominoes knocking each other over. Sound can travel through anything made of molecules - even water! There is no sound in space because there are no molecules there to transmit the sound waves.
Electromagnetic waves are not like sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air, solid objects and even space. This is how astronauts on spacewalks use radios to communicate. Radio waves are a type of electromagnetic wave.
Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.
Electromagnetic waves are formed when an electric field (which is shown in red arrows) couples with a magnetic field (which is shown in blue arrows). Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.
When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.
Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
