Validation of Dual-Doppler Wind Profiles with in situ Anemometry

Abstract

Typical methods used to acquire wind profiles from Doppler radar measurements rely on plan position indicator (PPI) scans being performed at multiple elevation angles to utilize the velocity-azimuth display technique or to construct dual-Doppler synthesis. These techniques, as well as those employed by wind profilers, often produce wind profiles that lack the spatial or temporal resolution to resolve finescale features. If two radars perform range-height indicator (RHI) scans (constant azimuth, multiple elevations) along azimuths separated by approximately 908, then the intersection of the coordinated RHI planes represents a vertical set of points where dual-Doppler wind syntheses are possible and wind speed and direction profiles can be retrieved. This method also allows for the generation of high-resolution wind time histories that can be compared to anemometer time histories. This study focuses on the use of the coordinated RHI scanning strategy by two high-resolution mobile Doppler radars in close proximity to a 200-m instrumented tower. In one of the first high-resolution, long-duration comparisons of dual-Doppler wind synthesis with in situ anemometry, the mean and turbulence states of the wind measured by each platform were compared in varying atmospheric conditions. Examination of mean wind speed and direction profiles in both clear-air (nonprecipitating) and precipitating environments revealed excellent agreement above approximately 50 m. Below this level, dual-Doppler wind speeds were still good but slightly overestimated as compared to the anemometer-measured wind speeds in heavy precipitation. Bulk turbulence parameters were also slightly underestimated by the dual-Doppler syntheses.

Evaluation of single and multiple Doppler lidar techniques to measure complex flow during the XPIA field campaign

“…The coordinated VTS scan pattern involves interrogating a common volume using multiple Doppler lidars at pre-defined heights at a given location to form a "virtual tower" (Calhoun et al, 2006;Mann et al, 2009;Fuertes et al, 2014;Gunter et al, 2015;Newman et al, 2016). A schematic of the triple lidar VTS scan tested during the XPIA field experiment is shown in Fig.…”

“…For example, measurement uncertainties in wind measurements made using the DBS technique in complex terrain were investigated by Bingöl et al (2009) while Lundquist et al (2015) studied the uncertainties in wind measurements using the DBS technique in presence of complex flow by simulating lidar measurements within a wind turbine wake using a wind field created with large-eddy simulation. Wind-field measurements made using the virtual tower technique have been validated (Damian et al, 2014;Gunter et al, 2015) to show high skill in measuring 2-D wind fields and Stawiarski et al (2013) did a detailed error analysis of dual Doppler co-planar PPI technique. Uncertainties in 3-D wind-field retrievals using triple-Doppler lidar techniques have also been investigated.…”

Assessment of virtual towers performed with scanning wind lidars and Ka-band radars during the XPIA experiment

“…Two Texas Tech University Ka-band (8.6 mm wavelength) mobile Doppler radars (Hirth and Schroeder, 2013;Hirth et al, 2015;Gunter et al, 2015) were deployed during XPIA. These Ka-band radars were designed to operate in a variety of weather conditions, including precipitation and clear air.…”

Wind Energy Instrumentation Atlas

“…Comparisons of dual-Doppler retrievals of wind speed and direction from the TTUKa radars with tower-based anemometers suggest that retrievals of mean wind speed and direction profiles in both clear-air (nonprecipitating) and precipitating environments agree well at altitudes above approximately 50 m. At lower altitudes, radar-based estimates were slightly higher than in situ measurements. Further, bulk turbulence parameters were also slightly underestimated by the dual-Doppler Kaband radar retrievals (Gunter et al 2015). Examples of dual-Doppler retrievals in a wind farm are shown in Figure 9.…”