Characterisation of wind field with high resolution in time and space by the use of electromagnetic and acoustic waves

The authors present a bistatic radioacoustic system where a Bragg grid produced by a spherical pressure wave enhances the forward scattering capability by some 40 dB when matched to the EM phase front. The system is used to measure 3-D wind, turbulence and vortex parameters as wind phenomena alter the scattering characteristics of the acoustic Bragg grid. The criterion for Bragg scattering is only valid over a limited height interval in this system. This confines the scattering volume to the limits of the radio beam and the acoustic beam in the horizontal direction and the Bragg-criteria limitations in the vertical direction. This scattering volume can be shifted vertically by tuning the acoustic frequency to give spatial resolution. Illuminating the acoustic Bragg grid with a CW EM signal gives a continuously received signal from a small scattering volume at a given height. It is possible to continuously measure the real-time cross-path wind component and at the same time perform coherent integration over longer time intervals in investigating turbulence phenomena. Experimental verification supports the theoretical models and underlines the system´s capacity to measure wind phenomena, vortex structures and turbulence parameters