Remote Sensing
Remote
sensors can either be active or passive. The external stimuli are responded by passive sensors. They record natural energy, which is reflected or emitted from the surface of the Earth. Sunlight reflected is the most frequent source of radiation detected by passive sensors. Active
sensors collect data about the Earth using internal stimuli. Polar-orbiting satellites are in an orbital plane, inclined to the equatorial plane at almost 90 degrees. This inclination allows the satellite to sense the entire globe, including the polar regions, providing observations of hard-to - reach locations via the earth. Many polar-orbiting satellites are considered as sun-synchronous, meaning that at the same solar time each cycle, the satellite passes over the same location. Geostationary satellites follow the Earth's rotation and travel at the same rate of rotation; as a result, the satellites appear to be fixed in one place to an observer on Earth. Electromagnetic energy, which is produced by the vibration of charged particles, travels through the
atmosphere and space vacuum in the form of waves. These waves have different wavelengths and frequencies (the distance from the wave crest to the wave crest; a shorter wavelength means a higher frequency.
Sensors or instruments, on-board satellites and aircraft use the sun as an illumination source or provide their own illumination source, measuring the energy that is reflected backwards.
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