Electromagnetic Spectrum Flashcards
Objects also _____ that has been emitted by other objects.
Reflect radiation
All objects emit __? Except objects at __?
Electromagnetic Radiation, Absolute Zero
The most familiar form of Electromagnetic Radiation
Visible Light
Generated by several mechanisms, including changes in the energy levels of electrons, acceleration of electrical charges, decay of radioactive substances, and the thermal motion of atoms and molecules
Electromagnetic (EM) energy
As this radiation approaches the Earth, it passes through the atmosphere before reaching the Earth’s surface. What happens to it?
Some is reflected upward from the Earth’s surface, some is absorbed at the surface of the Earth and is then reradiated as thermal energy.
____ Radiation, such as that generated by imaging radars, is also used for remote sensing
Man-Made Radiation
Electromagnetic Radiation consists of ____ which varies in magnitude in a direction perpendicular to the direction of propagation, and ____ which is oriented at right angles to the electrical field and is propagated in phase with the electrical field.
Electrical field (E), Magnetic field (H)
The distance from one wave crest to the next
Wavelength
Measured as the number of crests passing a fixed point in a given period of time.
Frequency
Equivalent to the height of each peak. Often measured as energy levels (formally known as spectral irradiance), expressed as watts per square meter per micrometer (i.e., as energy level per wavelength interval).
Amplitude
Specifies the extent to which the peaks of one waveform align with those of another. Measured in angular units, such as degrees or radians.
Phase (of a waveform)
If two waves are aligned, they oscillate together and are said to be ____? (a phase shift of 0 degrees).
In Phase
If a pair of waves are aligned such that the crests match with the troughs, they are said to be ____?
Out of Phase
Which spectrum, from 0.30 to 15 µm, defines those wavelengths that can be reflected and refracted with lenses and mirrors.
Optical Spectrum
Which spectrum extends from about 0.38 to 3.0 µm; it defines that portion of the solar spectrum used directly for remote sensing.
Reflective Spectrum
Radiation of significance for remote sensing can be said to begin with the ____ region, a zone of short-wavelength radiation that lies between the X-ray region and the limit of human vision. Means “beyond the violet”. Since it’s easily scattered by the Earth’s atmosphere, it is not generally used for remote sensing of Earth materials.
Ultraviolet / Ultraviolet Radiation
The ____ of an object is defined by the color of the light that it reflects
Color
Limits of the ____are defined by the sensitivity of the human visual system
Visible Spectrum
Primary Colors (Answer based on wavelength): 0.4 to 0.5 µm, 0.5 to 0.6 µm, 0.6 to 0.7 µm
Blue, Green, Red
Equal proportions of the three additive primaries combine to form what?
White / White light
Each of the three subtractive primaries absorbs a third of the visible spectrum (Color Absence). Yellow absorbs ____, Cyan absorbs ____, and Magenta absorbs ____?
Blue, Red, Green
A mixture of equal proportions of pigments of the three subtractive primaries yields ___?
Black
Wavelengths longer than the red portion of the visible spectrum are designated as the ___? It extends from 0.72 to 15 µm—making it more than ____ times as wide as the visible light spectrum.
Infrared / Infrared Region, 40
Defined as those regions of the infrared spectrum closest to the visible. Can use films, filters, and cameras with designs similar to those intended for use with visible light. Essentially solar radiation reflected from the Earth’s surface
Near Infrared and Mid Infrared radiation
Consisting of wavelengths well beyond the visible, extending into regions that border the microwave region, emitted by the Earth. Consists of “heat,” or “thermal energy”.
Far Infrared / Far Infrared Region
In this region, the longest wavelengths commonly used in remote sensing are those from about 1 mm to 1 µm in wavelength. The shortest wavelengths in this range have much in common with the thermal energy of the far infrared. The longer wavelengths of this region merge into the radio wavelengths used for commercial broadcasts.
Microwave / Microwave Region
Planck discovered that electromagnetic energy is absorbed and emitted in discrete units called ____? The size of each unit is directly proportional to the ____ of the energy’s radiation.
Quanta or Photons, Frequency
The generation of electric currents by the exposure of certain substances to light, as the effect of the impact of these discrete units of energy (quanta) on surfaces of certain metals, causing the emission of electrons.
Photoelectric Effect
Made the wave model of electromagnetic radiation.
James Clerk Maxwell
Based on the assumption from classical (mechanical) physics that light and other forms of electromagnetic energy propagate as a series of waves. Best explains some aspects of the observed behavior of electromagnetic energy (e.g., refraction by lenses and prisms and diffraction), whereas quantum theory provides explanations of other phenomena (notably, the photoelectric effect).
Wave Model
The rate at which photons (quanta) strike a surface. Measured in Watts (W)
Radiant Flux (Fe)
____ measures radiation that strikes a surface, _____ defines the rate at which radiation is emitted from a unit area (also measured in watts per square meter)
Irradiance, Radiant Exitance
All objects with temperatures above absolute zero have _____ and ____ energy.
Temperature, Emit
The amount of energy and the wavelengths at which it is emitted depend on the ____ of the object.
Temperature
As the temperature of an object increases, the total amount of energy emitted also _____, and the wavelength of maximum (peak) emission becomes ______.
Increases, Shorter
A _____ is a hypothetical source of energy that behaves in an idealized manner. It absorbs all incident radiation; none is reflected. Emits energy with perfect efficiency. A hypothetical entity because in nature all objects reflect at least a small proportion of the radiation that strikes them and thus do not act as perfect reradiators of absorbed energy.
Blackbody
_____ states that the ratio of emitted radiation to absorbed radiation flux is the same for all blackbodies at the same temperature.
Kirchhoff’s Law
The emissivity of a true blackbody is __, and that of a perfect reflector (a whitebody) would be ___.
1, 0
_____ is a useful measure of their effectiveness as radiators of electromagnetic energy. Those objects that tend to absorb high proportions of incident radiation and then to reradiate this energy will have high ones and vice versa.
Emissivity
Defines the relationship between the total emitted radiation (W) (often expressed in watts · cm–2) and temperature (T) (absolute temperature, K).
Stefan–Boltzmann Law
S-B law states that ___ blackbodies emit more energy per unit area than do ___ blackbodies.
Hot, Cool
Specifies the relationship between the wavelength of radiation emitted and the temperature of a blackbody.
Wien’s Displacement Law
According to Wien’s Displacement Law, as blackbodies become ____, the wavelength of maximum emittance shifts to _____ wavelengths.
Hotter, Shorter
