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ISSN 2070-7401 (Print), ISSN 2411-0280 (Online)
Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa
CURRENT PROBLEMS IN REMOTE SENSING OF THE EARTH FROM SPACE

  

Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2026. Т. 23. № 3. С. 74-87

Canonical transform method for detection of superrefraction

M.E. Gorbunov 1, 2 
1 A.M. Obukhov Institute of Atmospheric Physics RAS, Moscow, Russia
2 Hydrometeorological Research Center of the Russian Federation, Moscow, Russia
Accepted: 10.03.2026
DOI: 10.21046/2070-7401-2026-23-3-74-87
The phenomenon of superrefraction, or ducting, strongly affects radio occultation observations in the lower troposphere, making the solution of the inverse problem non-unique. Application of the standard inversion algorithms, in presence of ducts, results in negative bias. Superrefraction is mostly observed in the marine boundary layer and other zones with typical persistent stratocumulus clouds. In this paper, we describe a modification of the canonical transform method for the detection of superrefraction from radio occultation observations and the determination of duct parameters. The method is based on application of the Fourier Integral Operator to the observed wave field filtered in the time domain. The filter is based on bending angle estimates exceeding a pre-specified threshold. An advantage of this method over the existing ones is that it allows for direct determination of the impact height of the duct. The impact height is transformed into the geometric altitude by using the retrieved refractivity profile. Two other parameters of the ducts are their strength and width. The method is validated by the analysis of MetOp-B data for January, 2025. We plot the three parameters of detected superrefraction events and demonstrate that the strongest events form clusters in the tropical zones of the Atlantic, Pacific, and Indian Oceans, as well as in the Sahara desert and some other regions. Another observation is that the ducts over oceans in tropics are generally thinner as compared to those in middle latitudes and over land.
Keywords: radio occultation, superrefraction, wave optics, canonical transform
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