Simulating acoustic scattering from atmospheric temperature fluctuations using a k-space method

Abstract

This paper describes a numerical method for simulating far-field scattering from small regions of inhomogeneous temperature fluctuations. Such scattering is of interest since it is the mechanism by which acoustic wind velocity profiling devices (Doppler SODAR) receive backscatter. The method may therefore be used to better understand the scattering mechanisms in operation and may eventually provide a numerical test-bed for developing improved SODAR signals and post-processing algorithms. The method combines an analytical incident sound model with a k-space model of the scattered sound close to the inhomogeneous region and a near-to-far-field transform to obtain far-field scattering patterns. Results from two test case atmospheres are presented: one with periodic temperature fluctuations with height and one with stochastic temperature fluctuations given by the Kolmogorov spectrum. Good agreement is seen with theoretically predicted far-field scattering and the implications for multi-frequency SODAR design are discussed.

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

“…If pulse compression were possible, there would be a clear advantage in the maximum range. This is consistent with Hargreaves et al (2014); the matched filter is functioning only as a noncoherent detector.…”

“…Bradley (1999) suggested a number of waveforms that may be appropriate for pulse compression in sodar. Unfortunately, pulse compression for wind profiling is not possible in sodar as shown by Hargreaves et al (2014). This is because Bragg scattering, the dominant scattering mechanism, does not provide coherent return signals.…”

Potenciales ventajas del método pseudoespectral en auralizaciones

“…El método pseudoespectral del espacio k ha sido utilizado profusamente en los últimos años en aplicaciones biomédicas relacionadas con la propagación de ondas ultrasónicas en tejidos [17] [18]. También ha sido utilizado para el estudio de la alteración producida por variaciones de la temperatura atmosférica en la propagación de ondas mecánicas [19]. Hemos hallado muy pocos trabajos que utilicen métodos espectrales en acústica de recintos [20].…”

Spectral broadening of acoustic waves by convected vortices

“…Stochastic methods based on a sum of spatial Fourier modes have also been used, for example by Karweit et al (1991) with a ray tracing technique to study the phase variance of acoustic waves propagating through turbulence, or by Cheinet et al (2012) and Ehrhardt et al (2013) combined with a finite-difference time-domain method for the propagation of sound. The scattering by a region of turbulent temperature fluctuations has been investigated by Hargreaves et al (2014) using a k-space numerical model. Campos (1978a,b) developed an analytical model and derived low-and highfrequency approximations for the scattering by a shear layer.…”