# Can LiDARs Replace Meteorological Masts in Wind Energy?
## 1 Introduction  
LiDAR-based wind speed measurements have received significant attention in recent years in a wide range of wind energy applications including initial wind resource assessment, optimization of wind turbine sitting in prospective farms and operation and control of wind farms [1; 2; 3; 4]. Although cup or sonic anemometers mounted on meteorological masts are still commonly used techniques for collecting wind data, the increasing size of utility-scale wind turbines (hub heights of more than 100 mand rotor diameters between 100 and 200 m) necessitates the construction of taller masts which becomes extremely expensive. Furthermore, several countries around the world have stricter regulations for very tall towers. For example, due to strict earthquake-related regulations in Japan, meteorological towers taller than 60 m require more paperwork, take a longer time to receive permission, and on top of all that become way more expensive. LiDARs, on the other hand, can be installed on the ground or on offshore platforms, and have the ability to measure wind speeds over large regions and up to higher altitudes. An additional advantage of LiDARs is that they can be transported and installed at less accessible onshore or offshore sites without too much difficulty. Ground-based LiDARs (and those mounted on offshore platforms) are of two types: profiling LiDARs and scanning LiDARs. Profiling LiDARs are used to measure vertical profiles of wind speed above the LiDARs. The vertical range of most profiling LiDARs is 200 to 300 m. Scanning LiDARs can perform three dimensional volumetric scans to measure radial wind speeds which need further processing in order to retrieve velocity vectors [5; 6; 7]. In this paper, we focus on profiling LiDARs to investigate whether they can be used as a reliable alternative to meteorological masts for the measurement of wind data and resource characterization. A large number of studies verified mean wind speeds measured by profiling LiDARs against those measured with tower-mounted cup or sonic anemometers [8; 9; 10; 1]. These studies employed velocity azimuth display (VAD) and/or Doppler Beam Swinging (DBS) to compute the velocity vectors from the LiDAR-measured radial wind speeds. [PERSON] et al. [8] reported an evaluation of a continuous wave (CW) LiDAR against calibrated anemometers mounted on a meteorological mast at the Rise wind test site. The comparison showed a fairly good correlation between LiDAR and cup anemometers with coefficient of determination (\(R^{2}\)) between 0.96 and 0.988 up to a height of 100 m. [PERSON] et al. [9] employed CW and pulsed LiDARs in their study. While both LiDARs showed good agreement on the 10-min mean horizontal wind speed, when compared against a sonic anemometer, the CW LiDAR showed a larger dispersion. [PERSON] et al. [1] performed intercomparisons of sonic anemometers, SODAR and LIDAR, and reported that the differences in the measurements were a function of the wind speed. They attributed the differences to the flow distortion around the tower and to the limitation in the smoothing technique employed on the LiDAR data. In their verification study, [PERSON] et al. [10] compared three WindCube LiDARs and showed that the three LiDAR units did not show severe abnormality during the test period and that the measured wind speeds showed satisfactory agreement. The studies discussed above have several limitations, such as that the duration of the measurement campaigns were shorter (a few weeks to a few months), or that they filtered out data with inhomogeneities resulting from rough terrain or from the sea-land transition. [PERSON] et al. [1] removed all data outside the wind speed speed range of 4-16 m/s and data for which the variation in wind direction was larger than 5\({}^{\circ}\), resulting in a very specific comparison. However, actual wind resource assessments require that all measured data--regardless of wind direction or homogeneity--are analysed.