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Doppler sodar (SOund Detection and Ranging) is a technology used for acoustic based remote sensing of the lower planetary boundary layer. Sodars are often used to measure wind profiles however, they suffer from problems due to noise (both acoustic and electrical) and echoes from fixed objects, which can bias radial velocity estimates. An experimental bi-static sodar was developed with 64 independent channels. The device enables flexible beam forming; beams can be tilted at the same angle irrelevant of frequency, a limitation in most commercial devices. This paper presents an alternative sodar signal processing algorithm for wind profiling using a multi-frequency stepped-chirp pulse. A non-coherent matched filter was used to analyse returned signals. The non-coherent matched filter combines radial velocity estimates from multiple frequencies into a single optimisation. To identify and separate sources of backscatter, noise and fixed echoes, a stochastic pattern recognition technique, Gaussian Mixture Modelling, was used to post-process the non-coherent matched filter data. This allowed the identification and separation of different stochastic processes. After identification, noise and fixed echo components were removed a clean wind profile produced. This technique was compared with traditional spectrum-based radial velocity estimation methods and demonstrated an improvement in the rejection of fixed echo components; this is one of the major limitations of sodar performance when located in complex terrain and urban environments.

Fixed Echo Rejection in Sodar Using Noncoherent Matched Filter Detection and Gaussian Mixture Model–Based Postprocessing