1.4 Wavelength Regions of Electro-magnetic Radiation

Wavelength regions of electro-magnetic radiation have different names ranging from ray, Xray, ultraviolet (UV), visible light, infrared (IR) to radio wave, in order from the shorter wavelengths. The shorter the wavelength is, the more the electro-magnetic radiation is characterized as particle motion with more linearity and directivity. (see 1.2).

Table 1.4.1 shows the names and wavelength region of electro-magnetic radiation. One has to note that classification of infrared and radio radiation may vary according to the scientific discipline. The table shows an example which is generally used in remote sensing.

The electro-magnetic radiation regions used in remote sensing are near UV(ultra-violet) (0.3-0.4 m), visible light(0.4-0.7 m), near shortwave and thermal infrared (0.7-14 m) and micro wave (1 mm - 1 m).

Figure 1.4.1 shows the spectral bands used in remote sensing. The spectral range of near IR and short wave infrared is sometimes called the reflective infrared (0.7-3 m) because the range is more influenced by solar reflection rather than the emission from the ground surface (see 1.5). In the thermal infrared region, emission from the ground's surface dominates the radiant energy with little influence from solar reflection (see 1.5 and 1.7).

Visible light corresponds to the spectral colors. They are, in order from the longer wavelengths in the visible region, the so called rainbow colors; red, orange, yellow, green, blue, indigo and violet are located with respect to the wavelength.

Short wave infrared has more recently been used for geological classification of rock types. Thermal infrared is primarily used for temperature measurement (see 1.7), while micro wave is utilized for radar and micro wave radiometry. A special naming of k band, X band, C band, L band etc. is given to the micro wave region as shown in Figure 1.4.1.


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