Lecture 2

Question 1

what are the components of electromagnetic radiation

Answer 1

source / Atmospheric interaction / interaction with the earth’s surface / sensor

Question 2

What are the sources of electromagnetic radiation

Answer 2

Natural radiation(1) sun - only in the day (2) any object on the earths surface above 0 kelvin emits energy. day or night Artificial radiation(3) the instrument itself, it fires a pulse and measures its return. day and night as not reliant on the sun

Question 3

What is wavelength?

Answer 3

The distance between wave crests

Question 4

What wavelength is blue

Answer 4

0.4-0.5 micro metres 400-500 nm

Question 5

what wavelength is green

Answer 5

0.5 - 0.6 µm or 500 – 600 nm

Question 6

what wavelength is red

Answer 6

0.6 - 0.7 µm or 600 – 700 nm

Question 7

give examples of how The colour of objects is related to the way the reflect and absorb energy. Dark/light surface

Answer 7

A white surface reflects most of the light – reflect red/green and blue in equal parts ▪ A dark surface absorbs most of the light

Question 8

explain the infrared wavelengths

Answer 8

(0.7 µm) to the microwave spectrum (1mm)
Near infrared (NIR) 0.7 – 1.0 µm
Shortwave IR (SWIR) 1.0 - 3.0 µm
Mid infrared (MIR) 3.0 – 5.0 µm
Far infrared (FIR) 5 µm – 1 mm

Question 9

what is far infrared also known as

Answer 9

thermal infrared (radiation emitted from warm surfaces)

Question 10

microwaves - wavelength

Answer 10

Wavelengths longer than Infra red (>1mm)

Question 11

what are passive sensors (microwaves)

Answer 11

detect and respond to natural input from the physical environment-measure emitted energy ▪ related to the temperature and moisture properties of the surface

Question 12

What are active sensors (microwaves)

Answer 12

generate their own energy ▪ backscatter related to the surface roughness

Question 13

Why are microwaves useful

Answer 13

▪ All-weather capability ▪ can see through clouds ▪ not reliant on energy from the sun ▪ can operate at night – good for tropical regions as often cloudy.

Question 14

Give two types of Natural radiation

Answer 14

solar radiation and Terrestrial radiation

Question 15

Describe artificial radiation

Answer 15

• Send its own source of energy pulse
• Record the back scattered energy
  *Time taken by the pulse – can calculate height of objects on the surface.
• Strength of echo received from the object

Question 16

what are the two types of natural radiation and which wavelenfths are they

Answer 16

Reflected - visible, IR and MIR
Emitted - MIR and FIR

Question 17

All radiation used for remote sensing passes through the atmosphere before and after it has interacted with Earth surface. This alters the radiations…

Answer 17

▪ Speed
▪ Frequency
▪ Intensity
▪ Direction

Question 18

Give examples of Aerosols and gases in the atmosphere. what happens to them

Answer 18

dust, soot emitted from combustion processes or cars – concentration varies by time of day. some energy absorbed, some scattered and some passes through and measured by sensor.

Question 19

Amount of Atmospheric scattering depends on…

Answer 19

• Size of the particle
• Abundance of the particle – time of year for example
• Wavelength of EMR – longer the wavelength the less impacted by atmospheric scattering
• Depth of the atmosphere – elevation of sun in sky varies – energy passes through different depths of atmosphere.

Question 20

List 3 types of scattering

Answer 20

1. Rayleigh Scattering
2. Mie scattering
3. Non-selective scttering

Question 21

Raleigh scattering

Answer 21

1890’s caused by gas molecules in the upper atmosphere
smaller than radiation wavelength.
as wavelength gets shorter scattering increases
Graph – blue part is more effected by Raleigh scattering than the red
This is why the sky is blue - in the day where the observer sees the scattered radiation
▪ also causes the red sky at sunset where red wavelengths are scattered due to the angle of the sun in the sky

Question 22

Mie Scattering

Answer 22

Larger particles. Can be emitted from anthropogenic activities like combustion.
Caused by water vapour, pollen, smoke particles & dust in lower atmosphere (troposhphere) – larger particle cannot rise so high in the atmosphere.
Mie scattering occurs when the diameter of atmospheric particulates are similar to or larger than the wavelengths of the scattered light

Scattering influences the wavelengths from the blue to middle infrared
▪ has a greater effect on radiation of longer wavelengths than Rayleigh scattering
Haze/pollution in the atmosphere causes scattering = worse in urban environments

Question 23

Non-selective

Answer 23

Particles much larger than incident radiation (e.g. water droplets and large dust particles)
▪ Takes place in lower atmosphere
▪ Not wavelength dependent as all wavelengths scattered equally
▪ E.g. clouds contain water droplets which scatter all visible wavelengths equally
▪ therefore clouds appear white – always when above them.

Question 24

The type of scattering occurs because of? (2)

Answer 24

The wavelength of the incident radiant energy. The size of the gas molecule, dust particle and or water vapour droplet encountered.

Question 25

What’s the difference between scattering and absorption?

Answer 25

Absorption = loss of energy, scattering is just moved

Question 26

Describe absorption in the atmosphere

Answer 26

Due to gasses in the atmosphere. Affects wavelengths that are shorter or longer than visible light. Energy absorbed in the atmosphere emitted at longer wavelengths (greenhouse gases). there is a loss of energy

Question 27

Give three common examples of gasses absorbed int he atmosphere

Answer 27

1) Ozone - high in the atmosphere - absorbed by Ultra Violet
2) Carbon Dioxide - lower in the atmosphere - absorbed by Mid and far/thermal infrared)
3) Water vapour - lower in the atmosphere - absorbed by far infrared.

Question 28

What are atmospheric windows?

Answer 28

Areas that are not absorbed - appear white on the graph. satellites make measurements in these areas.

Question 29

What wavelength range does the sun emit the most energy?

Answer 29

Visible light – 0.4um to 0.7um

Question 30

Name 3 sources of EMR?

Answer 30

Natural 1)The sun – only in the day
2) Terrestrial (objects on the earth’s surface and the earths surface itself) because some energy is absorbed and then reemitted – causing urban heat islands.
Artificial: 3) Active sensor - from satellites etc.

Question 31

Name 3 types of atmospheric scattering?

Answer 31

Raleigh, Mie and non-selective
Scattering is removed from the data (atmospheric correction)