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.

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