GNSS Inter-satellite Ranging for Atmospheric Monitoring

Abstract

In this paper, a concept is presented which makes use of inter-satellite ranging (ISR) techniques for monitoring the atmospheric state. Thereby, for this study it is assumed that future GNSS satellites are equipped with an ISR payload and that each satellite is supposed to connect to other satellites in different orbital planes sequentially. For further analysis a Galileo constellation of 24 (27 and 30) MEO, four IGSO and one MEO spare satellite was simulated over a period of one year to reconstruct the paths of the ranging signals and to identify events when the signal is travelling through the atmosphere. Based on the detailed analysis of the transit events we identify inter-satellite ranging not only as complementing technique to improve the satellite orbit and clock accuracy of the GNSS constellation but also its large potential for monitoring the state of the neutral atmosphere and ionosphere. Thereby, due to the unique observation geometry between satellites in MEO, IGSO or in transfer orbit, range measurements can be obtained for specific observation arcs. Some of them show similarities to radio occultation profiles on long baselines, others allow e.g. to permanently scan down to specific layers in the atmosphere. Latter is possible if e.g. a spare satellite is placed in orbit so that a permanent link is installed to another MEO satellite in the same orbital plane. In addition to the geometric analysis, also a propagation analysis was carried out to identify atmospheric losses, which may harm signal reception. So far studies dealing with inter satellite ranging do not consider signal paths through the atmosphere. Thus, ISR link budgets were recalculated for various frequencies in the microwave band in order to get a first guess about the atmospheric losses and whether signal reception is possible after the inter-satellite link has passed the atmosphere. Considering frequencies at three bands (K, S and C), while for K-band signal reception is guaranteed only under specific atmospheric conditions, S- or C-band seems to be most promising when the entire atmosphere (ionosphere and neutral atmosphere) is monitored.