DIAMET and the Electromagnetic Spectrum

The Electromagnetic Spectrum

Energy can travel in waves in the form of changing electrical and magnetic fields. This is called electromagnetic radiation and the waves travel at the speed of light.

The Electromagnetic Spectrum contains a range of electromagnetic radiation. The waves all travel at the speed of light but occur in different parts of the spectrum depending on their wavelength and frequency.

Frequency is the term used in physics to describe how many waves are produced every second. If one complete wave is produced every second, then the frequency is one Hertz, or 1 Hz.

Wavelength is the length of one complete wave, and is usually measure in metres (m).

The Electromagnetic Spectrum contains waves of both high and low frequency.

Since the speed of the waves is constant, high frequencies correspond to short wavelengths, and low frequencies correspond to long wavelengths.

The complete list of the Electromagnetic Spectrum from lowest to highest frequency is Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-Rays and Gamma Rays.

The waves are grouped into bands and make up the Electromagnetic Spectrum below.

Visible light is made of different colours. Each colour has a different wavelength and frequency. The different bands of waves that make up the Electromagnetic Spectrum all have different properties. Scientists use the waves and their properties for different purposes.

Using the Electromagnetic Spectrum

Gamma waves have the highest frequency and the shortest wavelength. They are emitted by a number of radioactive materials and also some stars in space. They can pass through many objects including concrete, human body tissue and bone. This property makes them very useful for medical imaging.

X-Rays lie between ultraviolet radiation and gamma rays. They are also high frequency waves and can pass through human skin and tissue. X-Rays do not pass through bone, and detectors use this principle to build up a picture of bone outlines or shadows to reveal information for doctors.

Ultraviolet (UV) Radiation is found between visible light and X-Rays. UV rays are sometimes said to be found ‘beyond the visible’ in the spectrum. The Sun emits energy at all bands in the Electromagnetic Spectrum, but emits most strongly at visible, UV and Infrared frequencies. Our atmosphere stops 98% of all UV rays from the Sun and the remaining UV rays are used by our bodies to help produce Vitamin D. Too much UV also causes sunburn. UV radiation is also used in hospitals to sterilise equipment.

Visible Light is the part of the spectrum to which the human eye is the most sensitive, and also provides the mechanisms for plant photosynthesis.

Infrared (IR) Radiation lies between visible light and microwaves. It is just beyond the red end of the visible spectrum. Infrared radiation is absorbed by the skin and we feel it as heat. Thermal imaging cameras are used to detect heat and can find human bodies that have become buried after natural disasters. Hospitals also use thermal imaging to help detect cancerous tumours.

Microwaves are found in the low frequency part of the Electromagnetic Spectrum between IR Radiation and Radio Waves. Microwaves can be absorbed by water molecules and used for cooking. They can also be used to transmit mobile phone signals.

Radio Waves have the lowest frequency and longest wavelength of any waves in the Electromagnetic Spectrum. They are widely used for communications and also in astronomy as a way of ‘seeing’ into space. In medicine MRI (Magnetic Resonance Imaging) uses radio waves and a magnetic field to create images of the inside of the human body.

Weather and the Electromagnetic Spectrum

The UK’s Meteorological Office (Met Office) in Exeter is one of the world’s leading providers of weather forecasts. They use a technique called Numerical Weather Prediction to produce forecasts. This process uses a very large supercomputer which contains sophisticated computer programs to represent the science of the weather. The computer requires real weather observations as starting data. In order to create an accurate starting picture, forecasters use as many sources of weather observation as possible.

Electromagnetic waves can be transmitted (or emitted), absorbed, reflected (i.e. bounce off objects) or scattered (i.e. interact)

Instruments on board satellites measure how these waves behave when they interact with the Earth's surface, clouds or particles in the atmosphere.

Satellite instruments can record infrared energy emitted from the Earth's surface or measure visible radiation reflected by the surface of the Earth and clouds. These measurements produce infrared or visible satellite images, commonly seen in television forecasts.

Satellite instruments can also obtain information about the vertical structure of the atmosphere by measuring how much electromagnetic radiation is being absorbed at particular wavelengths.

Other instruments emit infrared radiation or microwaves toward the Earth’s surface. By measuring the amount of time it takes for the signal to return, scientists can work out the surface type and height.

Radar is an acronym for radio detection and ranging and uses the properties of Radio Waves or Microwaves to work out the position and intensity of rain bands. The radar instrument transmits a radio signal and then a receiver measures the reflected signals. The reflections reveal information about the distance to the rain, and the size of the rain drops.

Now complete the ‘EM Spectrum Factsheet’.

Diamet and the Electromagnetic Spectrum

The research aircraft used by the Diamet research scientists is equipped with many instruments that use properties of the electromagnetic spectrum to make measurements. Most of these instruments make use of ultraviolet, visible or infrared radiation.

Ultraviolet Radiation

Cloud top measurements are made by an instrument which uses laser radiation in the ultraviolet wave band to illuminate cloud tops and then analyse the backscattered light. This helps to identify the position of different atmospheric layers below the aircraft.

Ozone measurements are made by an instrument which examines how much ultraviolet radiation is being absorbed by the air.

Visible Radiation

Cloud particle size can be measured by focusing laser beams of visible light on a sampling area and detecting the particles’ shadows. The shadows are then magnified and the data examined.

Infrared Radiation

Carbon monoxide is measured by detecting how much infrared radiation is being absorbed by the air.

Relative Humidity can also be measured by instruments which look at how much water vapour is being absorbed in the infrared wave bands.

Now try the ‘EM Spectrum and Weather Challenge’.

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