Development and validation of a sodar simulator for atmospheric boundary layer characterization

Abstract

A sodar simulator capable of producing time-series data emulating sodar signals has been developed and tested. The atmospheric elds used to populate the sodar simulator are taken from output of a large eddy simulation code. The characteristics of the sodar (number of beams, azimuth and zenith angles of the beams, beamwidth, transmit frequency, range resolution, etc.) are de ned by the user to allow evaluation of and comparison with existing systems. The range of the re ected acoustic signal is calculated based on a temperature-dependent speed of sound. Realistic acoustic background noise is simulated using ltered white noise. The raw acoustic time-series data are processed using a Fourier transform to yield acoustic Doppler spectra, from which the radial velocities are calculated. The design of the simulator allows for the testing of and comparison between various signal-processing techniques and averaging periods. Several di erent methods for validating the results of the time-series sodar simulator are presented, including validation of the derived wind speeds against a simulated instrumented tower and a moment sodar simulator, which evaluates the wind components using the radial velocities measured by the sodar beams, and as such includes the e ects of the DBS technique. The results of the sodar simulator are also used to evaluate vertical pro les of the structure function parameter for temperature, and these pro les are compared against those derived from a simulated unmanned aerial system, and evaluated from the large eddy simulation output directly. Two example cases are presented of populating the sodar simulator with large eddy simulation data representative of one developing and one fully developed convective boundary layer, and a third example case using large-eddy simulation output of a stable boundary layer.