Effect of Multiple GNSS Integration on the Number and Spatiotemporal Coverage of Radio Occultation Events

Abstract

The development of global navigation satellite systems (GNSSs) and multi-system compatible radio occultation (RO) techniques provides favorable conditions and opportunities for increasing the number of occultation events and improving their spatiotemporal coverage. The performance of the multiple GNSS RO event number, spatiotemporal coverage, and uniformity need assessments by robust and functional approaches. Firstly, a simulation system of RO events, which took the orbit perturbations into account, was established, and the concepts of global coverage fraction and uniformity of RO events were defined. Secondly, numerical experiments were designed to analyze the GNSS RO performances of a single-receiving satellite and satellite constellations under the condition of using current multiple GNSSs as transmitting satellite systems, in which the Earth was divided into 400 × 400 km2 grids. Finally, the number, timeliness, global coverage fraction, and uniformity of GNSS RO events for a single-receiving satellite and receiving satellite constellations were numerically calculated and analyzed. The results showed that ➀ multiple GNSS integration improved the number of GNSS RO events and their global coverage for a single polar-orbit satellite significantly, e.g., the 24 h multiple GNSS RO event number was about 7.8 times that of the single GNSS system, BeiDou navigation satellite system-3, while the corresponding 24 h global coverage fraction increased nearly 3 times. ➁ In the multiple GNSS integration scenario, the constellation composed of 12 polar-orbit low-Earth-orbit satellites achieved 100% RO event global coverage fraction within 24 h, of which the RO detection capability was comparable to the 100 Spire weather satellites and global positioning system (GPS) RO system. ➂ More GNSS RO events of the polar-orbit constellations were distributed in the middle- and high-latitude zones. Therefore, multiple GNSS integration could increase the RO event number and global coverage significantly to benefit the global climate monitoring and global numerical weather prediction, and the polar-orbit constellations were more favorable to atmospheric detection in middle- and high-latitude regions.

Global Stratospheric Properties of Gravity Waves From 1 Year of Radio Occultations

“…We obtained respectively sampling errors of 34% and 26%. How many more retrievals per day would be needed to obtain two and three times the number of quartets is not a simple question to answer as it depends specifically among other factors on LEO satellite distribution regarding inclinations and their local time coverage (Liu et al., 2022). So the sampling error may be reduced with more quartets (i.e., RO), but from Figure 1 it is also clear that a more homogeneous distribution is necessary, which may be only achieved with some orbital trajectory planning in future missions.…”

“…A further significant increase of retrievals in the future may even allow results on a monthly or some rough longitudinal basis. Studies are already being developed on the possible coming performance of multiple GNSS systems regarding the amount of RO retrievals and their spatiotemporal coverage and uniformity (e.g., Liu et al., 2022).…”