The Electromagnetic The Electromagnetic SpectrumSpectrum

EG5503EG5503

(GIS & Earth Observation)(GIS & Earth Observation)

Lecture TopicsLecture Topics

What is the Electromagnetic Spectrum?What is the Electromagnetic Spectrum?The concept of wavelengthThe concept of wavelengthProperties of EMR wavesProperties of EMR wavesEMR and the Sun-Atmosphere systemEMR and the Sun-Atmosphere systemHow does remote sensing exploit EMRHow does remote sensing exploit EMR

What is the Electromagnetic Spectrum?What is the Electromagnetic Spectrum?

The term The term radiationradiation covers a wide variety covers a wide variety of natural phenomenaof natural phenomena

All radiation involves the All radiation involves the exchange of exchange of energyenergy

The energy associated with The energy associated with electromagnetic radiation is called electromagnetic radiation is called radiant energyradiant energy

Radiant energy may exist in the Radiant energy may exist in the absence of matterabsence of matter

What is the Electromagnetic Spectrum?What is the Electromagnetic Spectrum?

All types of EMR are transmitted, or All types of EMR are transmitted, or propagated, as propagated, as waveswaves

In common with all waves, the two most In common with all waves, the two most fundamental properties of fundamental properties of electromagnetic waves are electromagnetic waves are lengthlength and and frequencyfrequency

The longer the wavelength the lower the The longer the wavelength the lower the frequency and vice versafrequency and vice versa

The concept of wavelengthThe concept of wavelength

Wavelength is usually measured in Wavelength is usually measured in metresmetres (the SI unit of length), (the SI unit of length), micrometres (1µm=10micrometres (1µm=10-6-6m) and m) and nanometres (1nm=10nanometres (1nm=10-9-9m)m)

The SI unit of frequency is The SI unit of frequency is hertzhertz (cycles (cycles per second)per second)

The electromagnetic spectrum may be The electromagnetic spectrum may be defined as the entire range of radiation defined as the entire range of radiation wavelengthswavelengths

Electromagnetic spectrum with

enhanced detail for visible region of the

spectrum

Note the large range of wavelengths

encompassed in the spectrum - it is over

twenty orders of magnitude!

Properties of EMR radiationProperties of EMR radiation

Transfer energy from place to placeTransfer energy from place to place Can be emitted and absorbed by matterCan be emitted and absorbed by matter Do not need a material medium to travel throughDo not need a material medium to travel through Travel at 3 X 10Travel at 3 X 1088 metres per second in a vacuum metres per second in a vacuum Can be polarised (made to vibrate in a plane)Can be polarised (made to vibrate in a plane) Can be reflected and refractedCan be reflected and refracted Can be diffracted (e.g. using a prism)Can be diffracted (e.g. using a prism) Carry no electric chargeCarry no electric charge

EMR and the Sun-atmosphere systemEMR and the Sun-atmosphere system

In order to understand how we can In order to understand how we can measure the physical environment with measure the physical environment with remote sensing, we must first understand remote sensing, we must first understand solar radiationsolar radiation

The amount of energy received by a The amount of energy received by a surface perpendicular to the Sun’s rays at surface perpendicular to the Sun’s rays at the Earth’s outer atmosphere is called the the Earth’s outer atmosphere is called the solar constantsolar constant (about 1370 J m (about 1370 J m-2-2 s s-1-1 average)average)

EMR and the Sun-atmosphere systemEMR and the Sun-atmosphere system

About 50% of incoming solar radiation is About 50% of incoming solar radiation is lost by the atmosphere: scattered (30%) lost by the atmosphere: scattered (30%) and absorbed (20%)and absorbed (20%)

ScatteringScattering involves the absorption and re- involves the absorption and re-emission of energy by particlesemission of energy by particles

AbsorptionAbsorption (unlike scattering) involves (unlike scattering) involves energy exchangeenergy exchange

EMR and the Sun-atmosphere systemEMR and the Sun-atmosphere system

Wavelengths Wavelengths less thanless than and and greater thangreater than 0.8µm (800nm) are often referred to as 0.8µm (800nm) are often referred to as shortwaveshortwave and and longwavelongwave radiation radiation respectivelyrespectively

The shortwave solar radiation consists of The shortwave solar radiation consists of ultravioletultraviolet and and visiblevisible

The terrestrial longwave component is The terrestrial longwave component is known as known as infraredinfrared

EMR and the Sun-atmosphere systemEMR and the Sun-atmosphere system Just under 50% of the radiation reaching Just under 50% of the radiation reaching

the Earth’s surface is in the visible rangethe Earth’s surface is in the visible range Components of visible light are referred to Components of visible light are referred to

as as colourscolours Each colour behaves differently and white Each colour behaves differently and white

light can be separated out by use of a light can be separated out by use of a prismprism

Colour separation occurs because of Colour separation occurs because of differential differential refractionrefraction

EMR and the Sun-atmosphere systemEMR and the Sun-atmosphere system

The human eye cannot see infrared The human eye cannot see infrared radiationradiation

Infrared radiation is absorbed by water Infrared radiation is absorbed by water vapour and carbon dioxide in the vapour and carbon dioxide in the tropospheretroposphere

The atmosphere’s relative transparency to The atmosphere’s relative transparency to incoming solar (SW) radiation, and ability incoming solar (SW) radiation, and ability to absorb/re-emit outgoing infrared (LW) to absorb/re-emit outgoing infrared (LW) radiation is the natural greenhouse effectradiation is the natural greenhouse effect

Remote Sensing and EMRRemote Sensing and EMR

Remote sensing exploits the different Remote sensing exploits the different characteristics of the electromagnetic characteristics of the electromagnetic spectrumspectrum

Satellites use Satellites use channelschannels - a channel - a channel corresponds to a specific waveband, or corresponds to a specific waveband, or portion of the electromagnetic spectrumportion of the electromagnetic spectrum

The European geostationary weather The European geostationary weather satellite METEOSAT for example has 3 satellite METEOSAT for example has 3 channelschannels

CHANNEL SPECTRAL RANGE USEVisible 0.45 to 1µm Daytime imagingInfrared 10.5 to 12.5 µm Temperature estimation and ImagingWater Vapour 5.7 to 7.1 µm Tropospheric humidity estimation

AnyAnyQuestions ?Questions ?