3D turbulence measurements in inhomogeneous boundary layers with three wind LiDARs

One of the most challenging tasks in atmospheric anemometry is obtaining reliable turbulence measurements of inhomogeneous boundary layers at heights or in locations where is not possible or convenient to install tower-based measurement systems, e.g. mountainous terrain, cities, wind farms, etc. Wind LiDARs are being extensively used for the measurement of vertical wind profiles as well as for the estimation of different turbulence quantities. Nevertheless, most of the techniques used until now rely on a combination of raw measurements with atmospheric turbulence models or assumptions like horizontal homogeneity of the boundary layer. The limitations stated above can be overcome by a new triple LiDAR technique which uses simultaneous measurements from three intersecting Doppler wind LiDARs. It allows for the reconstruction of time series of the three-component velocity vector as well as local velocity gradients at the point of intersection without the need of any turbulence model and with minimal assumptions. The accuracy of the technique has been assessed against sonic anemometers installed on the KNMI's meteorological mast at Cabauw's experimental site for atmospheric research (CESAR) in the Netherlands. Theoretical analyses carried out indicate that relative angles between the laser beams are directly related to the uncertainty on each component of the velocity vector, which, in turn, determine the uncertainties on the calculated turbulence quantities. As a consequence, the success of a measurement campaign will depend on the turbulence quantities addressed and the layout of the instruments on the terrain, which should be assessed in advance. The triple LiDAR technique has been applied to the study of the flow over the campus of EPFL in Lausanne (Switzerland). The results show the potential of the technique, which can provide new insight into the study of atmospheric turbulent processes. The proposed technique can address highly complex boundary layer flows including inhomogeneity, thermal stability, transients or turbulence intermittency. Supplementary URL: http://journals.ametsoc.org/doi/abs/10.1175/JTECH-D-13-00206.1

Presented at:
21st Symposium on Boundary Layers and Turbulence, Leeds, UK, June 09 - 13, 2014

 Record created 2014-09-03, last modified 2018-03-17

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