# Can LiDARs Replace Meteorological Masts in Wind Energy?
## 3 Comparison of LiDAR Measurement with Sonic and Cup Anemometer
### Mean Wind Speed and Turbulence Intensity
The LiDAR-measured turbulence intensities overlap with the sonic anemometer-measured data when the wind speed is low. However, the bin-averaged turbulence intensity of the LiDAR gradually decreases for higher mean wind speeds. This tendency contradicts with a similar comparison by [PERSON] (2018), who showed that LiDAR-measured turbulence intensities were usually larger than or similar to the sonic anemometer-measured data. It should be mentioned however, that the maximum number of 10-min data sets per bin in their investigation was between 1000 to 2500, whereas in the current study, the maximum number of data per bin is close to 10,000 and there are more than 1000 data sets in each bin up to 10 m/s (cf. Figure 7e). Nevertheless, neither earlier studies nor the current study can describe the general trend regarding the magnitude of turbulence intensities measured by these three devices. For example, as discussed below, the bin-averaged turbulence intensities at a higher altitude of 57 m are larger for the LiDAR than for the sonic anemometer for most of the mean wind speed range (cf. Figure 10). The turbulence intensities measured by these three devices depend on the altitude, terrain as well as atmospheric conditions. One thing that can be stated with certainty is that LiDAR-measured turbulence intensity shows better agreement with sonic anemometer data than does cup anemometer data. As a result, the fatigue load that a wind turbine may experience, computed using LiDAR-measured turbulence intensity, will be more reliable than that estimated using cup anemometer measurements. The lower turbulence levels measured by a cup anemometer are attributed to the longer response time related to its inertia arising from the moving components such as cups and horizontal arms ([PERSON], 2018). One major concern with the use of LiDARs in wind energy applications is their low sampling frequency. The V2 profiling LiDAR deployed in the current study collects wind data at 1 Hz sampling frequency compared to the 10 Hz sampling frequency of sonic anemometers (cf. Table 1). Considering that the lower sampling rate (of both the LiDAR and the cup anemometer) may filter out small-scale turbulence structures, Figure 8 compares the original 10 Hz sonic anemometer data against the sonic anemometer data re-sampled at 1 Hz. As is clear from both the mean wind speed and standard deviation, the difference between the 10 Hz and 1 Hz data is negligible. As a reference, the distribution of the turbulence intensity using this re-sampled sonic anemometer data is also plotted in Figure 7d. The 1 Hz data overlaps with the original sonic anemometer data. This suggests that turbulence structures with time scales smaller than one second have negligible contribution to the total turbulence kinetic energy and therefore can be ignored for atmospheric boundary layer (ABL) turbulence. A sampling frequency of 1 Hz is sufficient for wind resource assessment and characterization of the site turbulence. Figure 9 compares the LiDAR-measured mean wind speed and standard deviation against the measured data from the sonic anemometer installed at 57 m height. This is the highest point on the tower where a sensor is installed and disturbance of the wind due to the tower is negligible at this height. The mean wind speeds from the LiDAR show good agreement with those measured by the sonic anemometer, with the slope and offset of the regression line being 1.0 and 0.178 while \(R^{2}=0.995\). Furthermore, underestimation of higher mean wind speeds by the LiDAR, which was observed at 40 m height, disappears at this height. The uncertainty in \(\sigma\) measured by the LiDAR decreases at 57 m height; the slope, offset and \(R^{2}\) are 1.04, 0.039 and 0.977 respectively. The DBS  
Figure 8: Comparison of the original sonic anemometer data collected at a sampling frequency of 10 Hz and the sonic anemometer data re-sampled at 1 Hz sampling frequency. The measurement height is 40 m. (**a**) 10-min average horizontal wind speeds and (**b**) standard deviation.