Electromagnetic Radiation
1. Remote Sensing
   Definition
        Science and art of obtaining information about an object, area, or
        phenomenon through the analysis of data acquired by a device that is not
        in contact with object, area, or phenomenon.

   Processes (fig 1.1)
        Data acquisition:
        - energy sources
        - energy through the atmosphere
        - interaction with surface features
        - retransmission
        - sensor systems
        - sensor data

   Data analysis:
        - data processing
        - compilation
        - application
 

2. Electromagnetic radiation
   The sun produces a full spectrum of electromagnetic radiation

   Two components of EM radiation: (fig 1.2)

        - electrical field (E): varies in magnitude in a direction
            perpendicular to the direction of propagation

        - magnetic field (M): at right angle to the electrical field,
            is propagated in phase with the electrical field

   Three properties of EM energy: (fig 1.2)
        1 Wavelength (l): the distance from one wave crest to the next
          - measure units: micrometer (mm)
                           1m = 1,000 mm, 1mm = 1,000microm

        2 Frequency (n): the number of crests passing a fixed point
               in a given period of time
          - measure units: hertz (cycle per second)

        3 Amplitude: the height of each peak
          - measured as watts per square meter (energy level)

   The speed of EM energy  c  300,000km/second,   c = nl
        - among the three properties, wavelength is the most commonly
            used in the field of remote sensing
 

3. Electromagnetic spectrum

   Major divisions of EM spectrum
        Ultraviolet spectrum: 0.3 - 0.38microm, is easily scattered

        Visible spectrum:
        - blue  0.4 - 0.5microm
        - green 0.5 - 0.6microm
        - red   0.6 - 0.72microm

        Infrared spectrum:
        - near infrared: 0.72 - 1.3microm
        - mid infrared:  1.30 - 3.0microm
        - far infrared:  7.00 - 15microm, emitted from the earth

        Microwave spectrum: 1mm - 1m

4. Radiation laws
   The dual nature of light (Newton)
        - light is formed by a stream of quanta (photons) that
            travels in straight line. The size of each quantum is directly
            proportional to the frequency of the energy's radiation
                                        Q = hn
          The quantum model best explains the photoelectric effect

        - EM energy propagates as a series of waves
          The wave model best explains the refraction and diffraction

   Radiation laws
        - Some of the absorbed energy will be reradiated as emitted
            energy

        - the blackbody

        - Kirchhoff's law: the ratio of emitted radiation to absorbed
radiation flux is the same for all blackbodies at the same
temperature

        - emissivity (e): the ratio between the emittance of a given
object (M) and that of blackbody (Mb) at the same
temperature
                        e = M/Mb
           e (of a blackbody) = 1,  e (of a perfect reflector) = 0

        - The Stefan-Boltzmann law: the total emitted radiation (W
watts.cm-2) from a blackbody is proportional to the fourth
power of its absolute temperature (K, 0oK = -273.16oC)
                        W = s T4,                               s is a constant
          Hot blackbodies emit more energy than do cool blackbodies

        - Wien's displacement law: as temperature (T, measured in oK)
of objects increases, the wavelength (l) of peak emittance becomes
shorter (fig 1.4)
                        l = 2,897.8/T

5. Readings: Chpt 1
 
 

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