A number of interactions are possible when electromagnetic energy encounters matter, whether solid, liquid or gas. In Earth Observation there are two main interactions: atmospheric and with target. Atmospheric interaction: In radar remote sensing, atmospheric interactions are limited due to the long wavelengths compared to the size of the atmospheric particles. Water clouds can interfere with the radars operating below 2 cm in wavelength. The effects of rain can be generally ignored at wavelengths above 4 cm. For longer wavelengths (above 20 cm), an effect called Faraday rotation caused by the ionosphere, i.e., free charges (electrons) and the Earth’s magnetic field, can lead to a rotation of the polarization plane. Target interaction: The radar interaction with the object is a result of both radar system parameters (frequency, polarization, acquisition geometry) and the object physical properties (dielectric constant, i.e., water content; geometrical properties, i.e., the roughness, shape and orientation of the scatterer).
Discuss and compare different types of interactions of microwaves with matter
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