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Electromagnetic Radiation in Remote Sensing - Lesson Summary

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Rudiments of Remote Sensing

Remote Sensing is the technology of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy. The Components of Remote Sensing are: Energy sources, Radiation and atmosphere, Interaction with the target
Recording of energy by the sensor, Transmission, reception, and processing
Interpretation and analysis, Applications. Historical Development of Remote Sensing The first Remote Sensing started in 1858. In 1947, the first space base photo was taken. This was taken through an automatic K-12 camera using black and white images by the Viking sounding rocket. Electromagnetic Spectrum in Remote Sensing The first requirement for any remote sensing instrument or sensor is an energy source. Passive remote sensing requires an energy source to work but active remote sensing doesn’t require an energy source because the sensor generates its own energy in form of pulses. There are no satellites in the ultraviolet portion of the spectrum. Satellites only work using the nearly ultraviolet portion of the spectrum. Our eyes can only detect the visible spectrum. Other radiations that are invisible to our eyes can be detected using remote sensing instruments. The infrared (IR) region of the electromagnetic spectrum can be divided into two categories, based on their radiation properties – Reflected IR and Emitted or thermal IR. Electromagnetic Radiation’s Interaction with Atmosphere Before radiation (used for remote sensing) reaches the earth’s surface, it has to travel through some distance from the earth’s atmosphere. The particles and gases in the earth’s atmosphere affect the incoming or outgoing radiation, through scattering and absorption Scattering occurs when large gas molecules or particles present in the atmosphere interact with the electromagnetic radiation, causing the electromagnetic radiation to be redirected from its original path. In contrast to scattering, absorption causes molecules in the atmosphere to absorb energy at various wavelengths. Interaction Mechanism of Electromagnetic Radiation There are three forms of interaction that occur when energy is incident upon a surface. They are: Reflection | absorption | transmission. A spectral response for an object can be built by measuring the energy that is reflected by targets on the earth’s surface over a variety of different wavelengths. Radiation Laws in Remote Sensing The four laws that govern electromagnetic radiation from an object are. Planck’s Law: Every object emits radiation at all times and at all wavelengths. Stefan-Boltzmann’s law: The total energy emitted by a black body is proportional to the fourth power of its absolute temperature. Wien’s Displacement law: At any particular temperature, a blackbody emits radiation within a range of wavelengths. However, the balckbody's absolute temperature determines which wavelength transmits the maximum amount of energy. Kirchhoff’s Law: The absorptivity of a substance for radiation of a specific wavelength is equal to its emissivity for the same wavelength.