Impact of Tropospheric Anomalies on Ground-to-Air Radio Navigation Systems

Shrivathsan Narayanan, Axel von Engeln, Christoph Günther, Okuary Osechas

Peer Reviewed

Abstract:	The propagation of electromagnetic waves emitted from ground-based transmitters is influenced by the stratification of the atmosphere. In extreme superrefractive situations characterized by strong temperature inversions or strong vertical gradients of moisture, the ranging signals are deflected towards the ground (ducting) through large atmospheric bending, which often results in additional propagation delay. A global ducting climatology based on 10 years of ERA-5 re-analysis European Centre for Medium-Range Weather Forecast (ECMWF) [4] data is created, to investigate the tropospheric ducting properties. Ducting probability, altitude, thickness and magnitude for different seasons and times are calculated by analyzing the refractivity gradient with respect to altitude. High ducting probabilities (? 90 %) are found in several locations, especially in the tropics, indicating that the tropospheric ducts are not particularly rare. It is shown that tropospheric ducts can produce zenith delay error in the order of several centimeters. The tropospheric zenith errors are then used to generate a map of the worst case zenith duct error observed at each grid point. The maximum zenith error that was observed while screening for ducting occurrences within 5 km of the atmosphere is between 4 cm to 20 cm. This zenith delay error when mapped to elevation angles close to the horizon, results in a mismodeling of tropospheric delay in the order of meters. This additional bias in tropospheric delay, is not so significant in the context of state-of-the-art terrestrial ranging systems (e.g. DME). However, with recent developments in accurate terrestrial ranging systems like eDME, LDACS [10], the relative effect of tropospheric anomalies like ducting becomes more significant. In this paper we quantify the impact of tropospheric duct anomalies on the ranging error of ground-to-air radio navigation systems.
Published in:	Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019) September 16 - 20, 2019 Hyatt Regency Miami Miami, Florida
Pages:	3451 - 3460
Cite this article:	Narayanan, Shrivathsan, von Engeln, Axel, Günther, Christoph, Osechas, Okuary, "Impact of Tropospheric Anomalies on Ground-to-Air Radio Navigation Systems," Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019, pp. 3451-3460. https://doi.org/10.33012/2019.16892
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