The Acoustics Research Centre has a strong history in the development and characterisation of SODAR (SOund Detection And Ranging) devices. These devices measure the backscattering of sound pulses transmitted into the lower atmosphere, allowing remote sensing of a variety of data including inversion layers and vertical profiling, wind speed, wind direction, turbulence quantities and stability classes. Unlike direct measurement techniques (such as mast anemometers) they are quick to deploy and provide continuous data with height; hence they find application in atmospheric research, pollution monitoring and wind-energy surveying.
In measuring these quantities however SODAR devices face challenges with range and velocity resolution as well as signal to noise ratio problems. To improve the accuracy of these parameters, new signals and analysis methods need to be evaluated. This is difficult to achieve by experimentation however, since the ‘true’ atmospheric data required for comparison is not available and must be acquired either from similar instruments or other devices with their own limitations. Existing analytical models of atmospheric scattering are necessarily stochastic in nature, and cannot provide specific data on the response from a given snapshot of atmospheric properties, only information on bulk averages. Thus, there is a requirement for deterministic a SODAR simulator to inform on SODAR performance characteristics over a range of atmospheric conditions.
Model solution process
This new paper by Jonathan Hargreaves, Paul Kendrick and Sabine von Hunerbein, presents a model which 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 (depicted above) 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 was seen with theoretically predicted far-field scattering and the implications for multi-frequency SODAR design are discussed.
Link to read the paper on USIR: http://usir.salford.ac.uk/30760/
The work was supported by the UK Engineering and Physical Sciences Research Council [grant number EP/G003734/1 “Advanced Signal Processing Methods Applied to Acoustic Wind Profiling for Use in Wind Farm Assessment”]