Electromagnetic Energy

Electromagnetic energy is the energy source required to transmit information from the target to the sensor. It is a crucial medium that is described as an
electromagnetic spectrum. On this spectrum, many forms exist that describe energy in a specific region of the electromagnetic spectrum. These are visible light, radiowaves, microwaves, heat, uv rays, x-rays and gamma rays.

This spectrum is an overview of the continuum of electromagnetic energy from extremely short wavelengths (cosmic gamma rays) to extremely long wavelengths (radio and television waves). These divisions are not absolute and definate; overlapping may occur.


Regions of Electromagnetic Spectrum:

Gamma Ray <0.03 nanometers
X - Ray 0.03 - 3.0 nanometers
Ultraviolet 3.0 nanometers - 0.4 micrometers
Visible 0.4 - 0.7 micrometers
Near Infrared 0.7 - 1.3 micrometers
Mid-Infrared 1.3 - 3.0 micrometers
Thermal Infrared 3.0 - 5.0 mm + 8.0 - 14.0 mm
Microwave 0.3 - 300.0 cm


Most energy in the visible and infrared portions of the electromagnetic spectrum are measured in micrometers (10-6m). Millimeters may be used for longer wavelengths (blue - 0.4 - 0.5 mm). (the basic unit in wavelengths are measured in meters (m)). Depending on the wavelength and the nominal spectral location, principal applications can be matched with suitable satellite bands for classification.

 Band Wavelength

Nominal Spectral Location

Principal Applications

1 0.45-0.52 Blue Designed for water body penetration, making it useful for coastal water mapping. Also useful for soil/vegetation discrimination, forest type mapping, and cultural feature identification.
2 0.52-0.60 Green Designed to measure green reflectance peak of vegetation for vegetation discrimination and vigor assessment. Also useful for cultural feature identification.
3 0.63-0.69 Red Designed to sense in a chlorophyll absorption region aiding in plant species differentiation. Also useful for cultural feature identification.
4 0.76-0.90 Near infrared Useful for determining vegetation types, vigor, and biomass content, for delineating water bodies, and for soil moisture discrimination.
5 155.-1.75 Mid-infrared Indicative of vegetation moisture content and soil moisture discriminations, and thermal mapping applications.
6 10.4-12.5 Thermal infrared Useful in vegetation stress analysis, soil moisture discrimination, and thermal mapping applications.
7 2.08-2.35 Mid-infrared useful for discrimination of mineral and rock types. Also sensitive to vegetation moisture content.


Visible
wavelengths (including U.V., visible, and near infrared) are referred to in units, rather than micrometer. The unit angstrom may be used in older government documents (1 micrometer = 10 000 angstroms). Other measurements include 1 micron = 1micrometer.

Typical Unit of Measurement

Radio

meter (m)

 

cm ( cm) = 0.1 m

Microwave (Radar)

 

millimeter (mm) = 0.001 m

Infrared

micrometer (um) = 10 (-6m)

Visible

 

nanometer (nm) = 10 (-9)m, 10 (-3) um

Ultra Violet

 

angstrom (A) = 10 (-10)m

 

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