Microwave remote sensing is a technique that uses microwave radiation, typically in the wavelength range of about 1 mm to 1 m, to acquire information about the Earth’s surface and atmosphere. Unlike optical remote sensing, microwave remote sensing has the advantage of being largely independent of solar illumination and atmospheric conditions such as clouds, haze, and rain. This makes it especially valuable for all-weather, day-and-night observations, which is critical for continuous environmental monitoring. Microwave remote sensing systems are broadly classified into passive and active systems. Passive microwave remote sensing measures the natural microwave energy emitted by the Earth’s surface and atmosphere. This emitted energy, known as brightness temperature, depends on the physical temperature and emissivity of the target. Sensors such as microwave radiometers record this radiation and are widely used to study atmospheric water vapour, cloud liquid water, soil moisture, and sea surface temperature. Passive systems are particularly useful for large-scale and global observations, although they generally have lower spatial resolution compared to active systems. Active microwave remote sensing involves the transmission of microwave signals from the sensor towards the target and the measurement of the reflected or backscattered energy. Radar is the most important active microwave remote sensing system.