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The initial step of the analysis is represented by the definition of the GNSS capabilities and receiver requirements in the environment of interest. The service volume concept has been introduced to this aim, and recent studies pointed out the interest to define and include GNSS performance above the altitude of the constellation itself [1], [2]. It is well known that signals, even if primarily broadcast from GNSS sources in order to serve Earth surface and proximity (i.e. with a beam directed nadir), are available at a limited extent also above the constellation.

Biomass burning is a key Earth system process, a major element of the terrestrial carbon cycle and a globally highly significant source of certain atmospheric trace gases and (primarily fine mode) aerosols. Natural and anthropogenic biomass burning occurs on all continents except Antarctica, with an estimated average of 3.5 - 4.5 million km2 of vegetation burnt in global wildfires each year (though this does not include the very large numbers of "small" agricultural fires that are difficult to map using current coarse spatial resolution remote sensing datasets).

Ambient space plasma can induce electrostatic noise in a linear antenna onboard a spacecraft. The resulting quasi-thermal noise (QTN) intensity spectrum as a function of frequency depends on the plasma parameters. The phenomenon can be utilised for inferring the plasma parameters if one measures the induced noise by a sensitive radio receiver. This is called QTN spectroscopy and it has been demonstrated and validated in several space missions that the technique is able to uncover the correct plasma parameters.