Electromagnetic energy and remote sensing Flashcards
What is the primary source of electromagnetic (EM) energy for remote sensing?
The sun.
What forms of EM energy does the sun provide?
Visible light, heat, and UV-light.
Name the two models of electromagnetic energy.
Wave model and photon model.
Describe the wave model of EM energy.
EM radiation consists of electric and magnetic fields that travel at the speed of light.
What is the relationship between wavelength and frequency?
They are inversely related; as wavelength increases, frequency decreases.
What radiates electromagnetic energy due to molecular agitation?
All matter above absolute zero.
What is a blackbody?
An object that absorbs and re-emits all EM energy.
State the Stefan-Boltzmann Law.
W=σT4W=σT4, where WW is total radiant emittance, σσ is a constant, and TT is absolute temperature.
What is the electromagnetic spectrum?
A range of all types of electromagnetic radiation based on wavelength.
List the visible spectrum colors in order of increasing wavelength.
Violet, blue, green, yellow, orange, red.
Differentiate between reflected and thermal IR.
Reflected IR is sunlight reflected off surfaces; thermal IR is heat emitted by objects.
What distinguishes active from passive sensors?
Active sensors emit their own energy; passive sensors rely on natural energy sources.
Give an example of an active sensor
Radar.
Why can passive sensors measuring long wavelengths operate at any time
They measure Earth’s temperature, not sunlight.
What are the two main mechanisms affecting EM radiation in the atmosphere?
Scattering and absorption
What factors influence scattering?
Wavelength, particle abundance, and travel distance.
What is Rayleigh scattering?
Scattering caused by particles smaller than the wavelength, dominating in the upper atmosphere.
What causes Mie scattering?
Particles similar in size to the wavelength, such as dust and water vapor.
What is nonselective scattering?
Scattering caused by particles much larger than the wavelength, affecting all wavelengths equally.
Why are clouds white?
Due to nonselective scattering of all visible wavelengths.
What are the three types of energy interactions with a target?
Reflection, absorption, and transmission.
Define specular reflection
Reflection where energy is directed in a single direction from a smooth surface.
Define diffuse reflection.
Reflection where energy is scattered uniformly in all directions from a rough surface
What is spectral reflectance?
The fraction of incident radiation reflected by a surface as a function of wavelength.
