Wavelet-Transform-based Phase Matching for Tropospheric Retrieval in GNSS Radio Occultation

Jonghyeon Park, Jaehee Chang and Jiyun Lee

Peer Reviewed

Abstract:	The phase matching (PM) method is widely employed in Global Navigation Satellite System (GNSS) radio occultation (RO) retrievals to derive bending angles under atmospheric multipath conditions. In the lower troposphere, however, horizontal refractivity gradients can cause impact multipath where multiple bending angle solutions correspond to a single impact parameter and lead to large retrieval uncertainty. Existing quality control (QC) approaches typically use short-time Fourier transform (STFT) spectral analysis to identify impact multipath regions by measuring the local spectral width (LSW), an indicator of spectral distribution spread. However, the fixed time-frequency window inherent to STFT imposes a fundamental resolution trade-off that limits simultaneous high vertical and spectral resolution. To address this limitation, we propose a wavelet-transform-based phase matching (WTPM) technique that enables multi-resolution analysis in both the time and frequency domains. Applied to COSMIC-2 RO measurements, WTPM achieves 1 m impact parameter resolution with scale-dependent bending angle resolution ranging from 0.4 to 572 ?rad across the 0-40 mrad domain, compared to the uniform resolution of about 743 ?rad of STFT. The improved resolution enables direct identification and separation of multi-valued bending angles as well as detection of regions with large uncertainty due to impact multipath. Statistical validation against collocated European Centre for Medium-Range Weather Forecasts (ECMWF) analysis profiles demonstrates that WTPM reduces the mean relative bending angle bias at 2-10 km by approximately 10.4% relative to conventional PM. The results suggest that WTPM provides effective impact multipath mitigation through inherent QC based solely on wavelet spectral analysis, improving bending angle retrieval accuracy for numerical weather prediction applications.
Published in:	Proceedings of the ION 2026 Pacific PNT Meeting April 13 - 16, 2026 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	99 - 111
Cite this article:	Park, Jonghyeon, Chang, Jaehee, Lee, Jiyun, "Wavelet-Transform-based Phase Matching for Tropospheric Retrieval in GNSS Radio Occultation," Proceedings of the ION 2026 Pacific PNT Meeting, Honolulu, Hawaii, April 2026, pp. 99-111. https://doi.org/10.33012/2026.20617
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