Interaction between Electromagnetic Radiation and Matter

By: Abdullah Khan

Center For Integrated Mountain Research Punjab University

ElectromagnetismElectromagnetic RadiationEMR__ Foundation Of Remote SensingEMR__ Interaction with AtmosphereAtmospheric WindowsEMR__ Interaction with Earth Surface FeaturesTypes of ReflectionSpectral Reflectance Properties

Contents

It is the science of charge and of the forces and fields associated with charge. Electricity and magnetism are two aspects of electromagnetism.

It is the phenomena associated with electric and magnetic fields and their interactions with each other and with electric charges and currents.

Electromagnetism

is radiated by atomic particles at the source (the Sun)propagates through the vacuum of space at the speed

of light interacts with the Earth's atmosphereinteracts with the Earth's surface interacts with the Earth's atmosphere once again, and finally reaches the remote sensors where it interacts

with various optical systems and detectors

Electromagnetic Radiation

The foundation of remote sensing technology is based on the measurement and interpretation of the patterns of EMR.

necessary for remote sensing: energy source to illuminate the target consists of perpendicular fields travelling at the speed of light (c) electrical

field and magnetic field. The whole range of EMR is called spectrum. EMR is characterized by wavelength and frequency. Different wavelengths or

frequencies indicates different portion of EMR. EMR interact with atmosphere. The atmosphere causes significant absorption

and scattering of the wavelength. EMR also interact with the surface materials in the form of absorption,

reflection, and transmission.

EMR__Foundation of Remote Sensing Technology

As the energy travels through the Earth’s atmosphere it is either:-a) Scatteredb) Absorbed Scattering: causes EM radiation to be redirected from its original

path.

Rayleigh ScatteringMie ScatteringNon-selective Scattering

Absorption: molecules in the atmosphere absorb energy.

EMR__Interaction with the Atmosphere

Rayleigh Scatteringo interaction of particles smaller in diameter than the

wavelengths of the radiation.o preferential scattering of shorter wavelengths (e.g.

ultraviolet and blue).o caused by oxygen and nitrogen molecules in the upper

atmosphere.

EMR__ Interaction with the Atmosphere

Mie Scattering interaction of particles about the same diameter as the

wavelengths of the radiation. tends to affect longer wavelengths than Rayleigh

scatter. caused by water vapor and dust particles in the lower

atmosphere.

EMR__ Interaction with the Atmosphere

Non-Selective Scattering interaction of particles of larger diameter than the

wavelengths of the radiation scatters visible wavelengths equally caused by water droplets (in fog and clouds)

EMR__ Interaction with the Atmosphere

Ozone:-absorbs ultraviolet radiation from the sun. Carbon dioxide:-absorbs in the far infrared portion of the

spectrum. Water vapor:-absorbs long wave infrared and shortwave

microwave radiations. atmospheric absorption has maximum affect on shorter

wavelengths (gamma, x-ray, UV) atmospheric absorption has little to no affect on

microwave radiation (longer wavelengths).

Atmospheric absorption

Atmospheric Windows

those areas of the spectrum which are not severely influenced by atmospheric absorption and thus, are useful to remote sensors, are called atmospheric windows.

can pass through the atmosphere.

Atmospheric Blinds wavelengths which are blocked by the atmosphere.

EMR__Interaction with the Atmosphere

three forms of interaction take place where energy is incident upon the surface:

i. Absorption

ii. Transmission

iii. Reflection In remote sensing, are most interested in measuring the

radiation reflected from targets. The reflection of the energy depends on the degree of surface

roughness of the target relative to the wavelength of the energy incident on it.

EMR__ Interaction with Earth’s Surface

Spectral Reflectance: the proportion of incident energy (I) of a given

wavelength interval that is reflected (R) by a particular feature is referred to as the spectral reflectance (or albedo) of that object.

Spectral Signature: the range of spectral reflectance of a particular feature at

different wavelengths is called the spectral signature (or spectral reflectance curve) of the object.

EMR__Interaction with Earth Surface Features

We refer to two types of reflection, which represent the two extreme ends of the way in which energy is reflected from a target: specular reflection and diffuse reflection.

Whether a particular target reflects specularly or diffusely, or somewhere in between, depends on the surface roughness of the feature in comparison to the wavelength of the incoming radiation.

If the wavelengths are much smaller than the surface variations or the particle sizes that make up the surface, diffuse reflection will dominate.

For example, fine-grained sand would appear fairly smooth to long wavelength microwaves but would appear quite rough to the visible wavelengths.

Types of Reflection

Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection.

Spectral reflectance

Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection.

Diffused reflectance

How much of EMR will be reflected depends on the nature of the materials and which portion of the EMR is being measured.

The nature of this reflected component over a range of wavelengths is called spectral response patterns.

Spectral patterns are descriptions of the degree to which energy is reflected in different regions of the spectrum. Spectral Signature

Every natural and artificial object reflects and emits EMR over a range of wavelengths in its own chemical composition and physical state.

Within some limited wavelength region, a particular object will usually exhibit a diagnostic spectral response patterns that differs from other objects.

Spectral Reflectance Properties

beyond 1.3 μm energy incident upon vegetation is essentially absorbed or reflected with little to no transmittance of energy

dips in reflectance occur at 1.4, 1.9 and 2.7 μm because water in the leaf absorbs strongly at these wavelengths

reflectance peaks occur at about 1.6 μm and 2.2 μm, between the absorption bands

Spectral reflectance of Vegetation

• the factors that influence soil reflectance act over less specified spectral bands

• factors affecting soil reflectance are moisture content, soil texture (proportion of sand, silt and clay), surface roughness, presence of iron oxide and organic matter content

• the presence of moisture in soil will decrease its reflectance absorption bands at about 1.4, 1.9, 2.2 and 2.7 μm

Spectral reflectance of Soil

Water absorbs radiation at near-IR wavelengths and beyond (strong absorption bands at about 1.4, 1.9 and 2.7 μm)

Clear water absorbs relatively little energy with wavelengths < 0.6 μm, resulting in high transmittance in the blue-green portion of the spectrum •

• Increases in chlorophyll concentration tend to decrease reflectance in blue wavelengths and increase it in green wavelengths.

Spectral reflectance of Water

www.wikipedia.com support.esri.com www.oceanoptics.com www.colorado.edu oregonstate.edu www.ntd-ed.org resources.yesican-science

References