Lecture 2 - Electromagnetic Radiation

Remote Sensing Principles

• Lecture 2: Electromagnetic Radiation

• Instructor: Gregory A. Carter, Ph.D.

• Institution: The University of Southern Mississippi

Electromagnetic Radiation Overview

• Altered when it interacts with objects, carrying information about them.

• Requires understanding of radiation and its interaction with materials.

Nature of Electromagnetic Radiation

• Comprised of electromagnetic waves exhibiting wave-particle duality:

  • Wave properties

  • Particle properties (photons)

• Generated by accelerated electric charge.

Types of Electromagnetic Radiation

• Varies based on production mechanisms:

  • Gamma radiation: atomic nucleus decay

  • Light, UV, X-rays: electron orbit transitions

  • Infrared radiation: molecular vibrations/rotations

  • Radio waves: oscillations of electric currents in antennas.

Conceptualization by James Clerk Maxwell

• In the 1860s, EMR was conceptualized as a wave traveling at speed of light (c = 3 x 10^8 m/s).

• Composed of two fluctuating fields: electric and magnetic, at right angles to each other.

• Plane polarized: when the electric field is in a fixed plane.

Properties of Electromagnetic Waves

• Characteristics depend on:

  • Wavelength (λ): distance between points on a wave; varies from long AC waves to short gamma waves.

  • Frequency (ν): number of oscillation cycles per unit time.

• All travel at speed of light in a vacuum (c = 3 x 10^8 m/s); no theoretical limits on λ or ν.

• Relationship: c = λν.

Electromagnetic Spectrum

• Wavelengths and Frequencies:

  • Vary from gamma rays (10^-12 m) to radio waves (kilometers long).

• Visible Spectrum: λ = 400 nm to 700 nm.

Quantum Theory of Electromagnetic Radiation

• Proposed by Niels Bohr and Max Planck.

• Energy transferred in discrete packets (quanta or photons).

• Energy equation: E = hν; E is higher at higher frequencies and shorter wavelengths.

• Planck constant (h = 6.626 x 10^-34 J·s).

Measurement Units

• Radiant Energy: Joule (J).

  • Examples of photon energy:

    • UV (λ = 254 nm): 471 kJ/mol

    • Blue (λ = 460 nm): 260 kJ/mol

    • Red (λ = 700 nm): 176 kJ/mol.

• Radiant Flux: Watt (W) = Js^-1.

International System of Units (SI Units)

• Base Quantities:

  • Length: meter (m)

  • Mass: kilogram (kg)

  • Time: second (s)

• Derived Quantities:

  • Area: m²

  • Volume: m³

  • Frequency: Hertz (Hz)

  • Energy: Joules (J).

References

• Jensen, J. R. (2007). Remote Sensing of the Environment.

• National Institute of Standards and Technology.

• Rees, W.G. (2013). Physical Principles of Remote Sensing.

• Rossotti, H. (1983). Colour: Why the World Isn’t Grey.