Neutral Atmosphere

The neutral atmosphere refers to the part of the Earth’s atmosphere where the gases are electrically neutral, meaning free electrons and ions are negligible. It includes the troposphere, stratosphere, mesosphere, and lower thermosphere, below the ionosphere. In geodesy and satellite navigation, the neutral atmosphere affects radio signal propagation through refraction, causing delays that must be corrected for precise positioning.

More Info: https://geodesy.science/item/lower-neutral-atmosphere/