Experimental determination of offshore turbulence spectra and lateral coherences with multiple lidars

We demonstrate that we can measure spectral coherence of offshore atmospheric turbulence at heights and with lateral displacements relevant for dynamic loads on modern, large wind turbines. This is done by five coordinated, pulsed Doppler lidars standing on the coast of the North Sea with beams intersecting almost perpendicularly. The six crossing points are 150 to 250 m above the ocean and have lateral separations of up to 200 m, reflecting the scale of modern offshore wind turbines. We compare the measurements with spectral and cross-spectral models. The model of Syed and Mann (Boundary-Layer Meteorology, 2024, vol 190), in general fits the spectra well and predicts the lateral coherences well. However, there are cases where the measured lateral coherence of the v-component is much larger than predicted. This seems not to be due to malfunction of the instruments, but rather due to non-turbulence processes in the atmosphere, e.g . interval gravity waves. We will also touch upon the potential consequences for loads on wind turbines.