An Inter-Comparison Study of Multi- and DBS Lidar Measurements in Complex Terrain

Abstract

Wind measurements using classical profiling lidars suffer from systematic measurement errors in complex terrain. Moreover, their ability to measure turbulence quantities is unsatisfactory for wind-energy applications. This paper presents results from a measurement campaign during which multiple WindScanners were focused on one point next to a reference mast in complex terrain. This multi-lidar (ML) technique is also compared to a profiling lidar using the Doppler beam swinging (DBS) method. First-and second-order statistics of the radial wind velocities from the individual instruments and the horizontal wind components of several ML combinations are analysed in comparison to sonic anemometry and DBS measurements. The results for the wind speed show significantly reduced scatter and directional error for the ML method in comparison to the DBS lidar. The analysis of the second-order statistics also reveals a significantly better correlation for the ML technique than for the DBS lidar, when compared to the sonic. However, the probe volume averaging of the lidars leads to an attenuation of the turbulence at high wave numbers. Also the configuration (i.e., angles) of the WindScanners in the ML method seems to be more important for turbulence measurements. In summary, the results clearly show the advantages of the ML technique in complex terrain and indicate that it has the potential to achieve significantly higher accuracy in measuring turbulence quantities for wind-energy applications than classical profiling lidars.

Measurements of Surface-Layer Turbulence in a Wide Norwegian Fjord Using Synchronized Long-Range Doppler Wind Lidars

“…On the other hand, Mann [45] found strong effects of stability on spectra over the Great Belt, Denmark, up to over 16 m·s −1 , albeit at a height of 70 m. When the high-frequency range of the N400 wind spectrum is attenuated using the ABSA model presented in Equation (26), the slope of the high-frequency part of the modified spectrum is sharper than measured, as seen in Figure 9. Similar observations have been reported by e.g., Pauscher et al [7] with the long-range WindScanner system or e.g., Angelou et al [46] with the short-range WindScanner system. The discrepancies between the modelled ABSA and the measured one may be due to fluctuations of the wind direction and the use of multiple scanning beams to retrieve the horizontal wind components.…”

“…For the standard deviation, the squared correlation coefficient is also significantly large and equal to 0.95, but a systematic discrepancy is observed between the lidar data and the sonic anemometer data, which is expected and attributed to the spatial averaging effect. The results presented in Figures 5 and 6 are not surprising, as a similar comparison with sonic data has already been done in the past by Pauscher et al [7]. Nevertheless, the comparison given herein shows that the wind data recorded by the multi-lidar system in the Bjørnafjord and presented in the following are reliable.…”

“…Newsom et al [1] 2008 2 up to 4 L Käsler et al [2] 2009 1 3.0 m 1 , m 2 Cheynet et al [3] 2014 1 1.75 m 1 ,m 2 , L, S Vasiljevic et al [4] 2014 2 up to 1.6 m 1 Berg et al [5] 2015 2 up to 1.4 m 1 Cheynet et al [6] 2015 1 up to 1.5 L, γ Pauscher et al [7] There is hardly any study to be found on the turbulence characteristics in the middle of a wide fjord within a coastal area. For example, it is uncertain whether a spectral wind model developed for an offshore or an onshore environment should be used.…”

Perdigão 2015: methodology for atmospheric multi-Doppler lidar experiments

“…Among the project deliverables, the methodology for WindScanner-based field experiments (which we report in the present paper) was developed based on the previous extensive work done under the WindScanner.dk project (see Vasiljević et al, 2016a;Sjöholm et al, 2014). The methodology was brought in to be tested and was further improved in a campaign held in Kassel (Germany) during the summer of 2014 (Pauscher et al, 2016;Vasiljević et al, 2016a). Perdigão 2015 was a last demonstration campaign within the WindScanner.eu project that served as the preparation for the larger experiment conducted within the NEWA project (New European Wind Atlas, The NEWA project aims to improve wind resource modeling for different site conditions.…”

Dynamic Data Filtering of Long-Range Doppler LiDAR Wind Speed Measurements

“…To minimise the different volume averaging effects and to comply with other comparisons of LiDAR measurements and met mast anemometers [29][30][31][32][33], we applied filtering in clustered temporal segments of ∆T = 10 min. We have deliberately refrained a data availability pre-filtering for the calculation of the 10 min average velocity and velocity standard deviation.…”