GNSS: The blooming

(Image: Artist's impression of GIOVE-A. Courtesy of ESA).

TRANSIT, GPS, GLONASS, Galileo, Compass... Since 1964, various different satellite-based navigation systems with global coverage have been deployed. The TRANSIT system, by USA, started its operational phase in 1964 (only for military purposes) and has been working until 1996. In 1993, the US GPS system began operations while the Russian GLONASS reached its completeness in 1995 (although nowadays, only 10 satellites are fully operational). The European Galileo and the Chinese COMPASS navigation satellite systems are under development.

On top of these global systems, various regional systems have been deployed and others have already been announced: the north american WAAS, the european EGNOS, the japanese MSAS, the Indian IRNSS.

We’re talking of tens and tens of satellites that will be operational, emitting precise L‑band spread spectrum signals, and that will remain in operation for several decades.

Although these signals are thought for providing position to the final user, already in 1993 [1] it has been proposed that such signals might be used for Earth observation purposes, given that they all reflects on the surface of our planet. 

To have a closer look to the capabilities of GNSS signals in some of these areas, you can have a look to Starlab Library.

[1] Martín-Neira.M. “A passive reflectometry and interferometry system (PARIS): application to ocean altimetry”. ESA Journal, 17: 331–355, 1993