2.01 Electromagnetic Radiation

Electromagnetic (EM) radiation helps us in making choices and enable us to deal with sensors of the future. This section will, therefore, clearly introduce you to the explanation of basic characteristic of EM radiation, it sources and the term EM spectrum, the influence of the atmosphere on EM radiation, interactions of EM Radiation with the Earth's surface (matter) and the basic principles of sensing EM Radiation.

The firt item that this learning path seeks to introduce you to is known as the EM radiation, which is modelled in two ways -- *by waves and or *by radiant particles called photons.

Question

What are the basic characteristics and sources of EM radiation?

Path

1. Electromagnetic radiation

This learning path now introduce you to these ways of modelling EM radiation--thus *Waves and *Photons

2. Waves and photons

This then leads us to the terms of wavelength and frequency; whereas the former is a differentiating property of the various types of EM radiation and measured in micrometres and the latter refers to the number of cycle of the wave that occur in one second and is usually measured in Hertz.

3. Wavelength and frequency

With the examination of all these elements together as in above, we will now look at EM spectrum which denotes the range of frequencies of EM radiation and their respective wavelengths and photon energies.

4. EM spectrum

The next subject in this learning path worth looking at is the sources of EM radiation. It is relevant to note here all matter with a temperature above absolute zero emits EM radiation because of molecular agitation.

5. Sources of EM radiation

In this learning path, we also consider the Planck's law of radiation, which is only applicable to black bodies.

6. Planck's law of radiation

In this breath we now look at blackbody objects, which are "idealized" objects with assumed extreme properties that aid in explaining EM radiation. These bodies which absorb 100% of incident EM radiation without reflecting anything and hence the appear perfectly black

7. Blackbody object radiance

Aside Blackbody objects, there are also Real objects which we will consider in this learning path as well. However, unlike the Blackbody object, Real object can re-emit some 80 to 90% of the radiation received.

8. Real object radiance

This then takes us to the term "Emissivity", which has values between 0 and 1.

9. Emissivity

It is important to note that before the radiation of the Sun reaches the Earth's surface, three(3) main interactions in the atmosphere have to occur: *Absorption; *Transmission; and *Scattering, hence the need to look at the concept of "Interactions of Atmosphere and EM" in this learning path.

10. Interaction of atmosphere and EM radiation

The next line of thought in this learning path is Atmospheric and transmission which are two elements that occur before the Sun's radiation reaches the Earth's surface.

11. Atmospheric absorption and transmission

In this learning path, we will also consider "Atmospheric scattering" which is one of the three (3) RS-relevant interactions in the atmosphere to occur before the Sun's radiation reaches the Earth's surface. Atmospheric scattering is divided into the following: *Rayleigh Scattering; *Mie Scattering; and *Non-selective scattering.

12. Atmospheric scattering

In this learning path,we now move on to look at 'Interaction of Electromagnetic Radiation with Matter (or the Earth's Surface)" as the next concept for our discussion. In this concept, it can be emphasized that EM radiation normally reaches an object interacts with it as a result of such interactions, the EM is absorbed, transmitted or reflected by the object. The Energy Conservation Law is applied to this concept, which states that all incident EM radiation (I) is absorbed, reflected (R), or transmitted (T).

13. Interaction of electromagnetic radiation with matter

Finally in this learning path you will introduce to Spectral Reflectance Curve or also known as just Spectral Signature.