The term 'remote sensing' literally means observation and gathering data from a distance.
But in more specific terms it refers to the recording and analysis of electromagnetic radiation in the visible, infra-red, ultraviolet and microwave wavelength reflected, scattered or radiated from various objects on Earth.
In present day satellites-based remote sensing, 'multi-spectral imaging' is used that is simultaneous imaging of the Earth's surface in more than one color, or wavelength, both visible and invisible, to bring out a lot of latent information unavailable in ordinary photographs.
Unlike ordinary cameras which use photographic film to record images, multi-spectral cameras carried on board Remote-Sensing Satellites use solid-state electronic destroy known as Charge-Coupled Devices or CCDs to receive the images.
Remote sensing satellite's orbit is called a polar orbit because it passes over both the polar regions of the earth in a north-south direction.
It is called sun-synchronous because the orbit also keeps step with the Sun in that it passes over a specific location on the sun lit side of the Earth when the Sun is at the same height above the eastern horizon.
This helps in image interpretation because with the same Sun-angle, the shadows cast by different features are then only a function of their heights.
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