1. Propagation through the troposphere

The troposphere is the region of the atmosphere, between the ground and around 12 km above sea level, where meteorological phenomena occur. Dry air, whose density decreases almost exponentially with altitude, and the presence of water vapour in varying quantities give this medium a refractive index slightly greater than unity, resulting in the absorption of electromagnetic waves. Hydrometeors (rain, snow, hail, clouds, fog) cause additional absorption, depending on local weather conditions.

The troposphere induces significant propagation effects on Earth-satellite links at frequencies above 5 GHz. For frequencies between 1 GHz and 1,000 GHz, these tropospheric effects can be classified into four main categories: attenuation (§ 1.1