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Operational Application of Optical Flow Techniques to Radar-Based Rainfall Nowcasting

Forecast Development Division, Hong Kong Observatory, Hong Kong 999077, China
Author to whom correspondence should be addressed.
Academic Editor: Guifu Zhang
Atmosphere 2017, 8(3), 48;
Received: 11 November 2016 / Revised: 10 February 2017 / Accepted: 22 February 2017 / Published: 25 February 2017
(This article belongs to the Special Issue Radar Meteorology)
Hong Kong Observatory has been operating an in-house developed rainfall nowcasting system called “Short-range Warning of Intense Rainstorms in Localized Systems (SWIRLS)” to support rainstorm warning and rainfall nowcasting services. A crucial step in rainfall nowcasting is the tracking of radar echoes to generate motion fields for extrapolation of rainfall areas in the following few hours. SWIRLS adopted a correlation-based method in its first operational version in 1999, which was subsequently replaced by optical flow algorithm in 2010 and further enhanced in 2013. The latest optical flow algorithm employs a transformation function to enhance a selected range of reflectivity for feature tracking. It also adopts variational optical flow computation that takes advantage of the Horn–Schunck approach and the Lucas–Kanade method. This paper details the three radar echo tracking algorithms, examines their performances in several significant rainstorm cases and summaries verification results of multi-year performances. The limitations of the current approach are discussed. Developments underway along with future research areas are also presented. View Full-Text
Keywords: rainfall; nowcast; motion tracking; optical flow rainfall; nowcast; motion tracking; optical flow
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Woo, W.-C.; Wong, W.-K. Operational Application of Optical Flow Techniques to Radar-Based Rainfall Nowcasting. Atmosphere 2017, 8, 48.

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