Dear Colleagues,

One of the hottest areas in GNSS is now the added value of GNSS-augmented constellations for positioning of course, but also for studies of the atmosphere, and especially atmospheric water vapor.

These augmented constellations, still under phase A development, are based on a flotilla of numerous LEO (low Earth orbit) satellites that will retransmit reference signals (pseudo-range, carrier, clock drifts) from GPS-like high-altitude satellites, with highly precise clocks and orbits, to ground receivers.

These LEO satellites will typically have a ground visibility of the order of a few tens on minutes, while GNSS satellites have a ground visibility of typically several hours.

These LEO constellations will allow a scan of the atmosphere, in terms of radio propagation delays, with a sky coverage (line-of-sight geometries) and time resolution by at least one, or even two orders of magnitude improvement with respect to GNSS-only constellations. Unlike COSMIC satellites, scans will probe the entire atmospheric column, from the ground (boundary layer) to the atmosphere limit (120 km).

GPS satellites revolutionized the way to do positioning in the 1990s, and one of the byproducts of this revolution is now called GNSS meteorology, but this application is still hampered by the low number and slow motion of GNSS satellites. LEO constellations will introduce time-and-space high-resolution GNSS meteorology.

The main topics of interest of this Special Issue include but are not limited to:

- How to obtain post-processed or real-time accurate orbits of these LEO satellites, with the same accuracy that is now attained by PPP products for GNSS satellites, including LEO specialized ionosphere corrections;

- How to improve the mapping functions/gradient approach (VMF3 is the up-to-date family of mapping functions) in order to fully grasp the variability of the atmosphere. Ideally, the separation between the “dry” and wet components of the atmospheric refractivity should be done as the level of the modeling of the carrier phase in GNSS software (such as the Bernese or Gamit software) and not by using external a priori “dry” models, such as the Saastamoinen model acting of the total delays (“dry” + wet);

- How to precisely define and assimilate LEO-augmented meteorology products in numerical weather models (NWM).

Prof. Dr. Jean-Pierre Barriot
Guest Editor

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• GNSS-augmented constellations with LEO sub-satellites
• Precise orbits for LEO-augmented constellations
• Time and space dense GNSS-meteorology from LEO-augmented constellations
• Assimilation of dense GNSS-meteorology products in numerical weather models