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

Abstract

Abstract. Accurate three-dimensional information of wind flow fields can be an important tool in not only visualizing complex flow but also understanding the underlying physical processes and improving flow modeling. However, a thorough analysis of the measurement uncertainties is required to properly interpret results. The XPIA (eXperimental Planetary boundary layer Instrumentation Assessment) field campaign conducted at the Boulder Atmospheric Observatory (BAO) in Erie, CO, from 2 March to 31 May 2015 brought together a large suite of in situ and remote sensing measurement platforms to evaluate complex flow measurement strategies.In this paper, measurement uncertainties for different single and multi-Doppler strategies using simple scan geometries (conical, vertical plane and staring) are investigated. The tradeoffs (such as time-space resolution vs. spatial coverage) among the different measurement techniques are evaluated using co-located measurements made near the BAO tower. Sensitivity of the single-/multi-Doppler measurement uncertainties to averaging period are investigated using the sonic anemometers installed on the BAO tower as the standard reference. Finally, the radiometer measurements are used to partition the measurement periods as a function of atmospheric stability to determine their effect on measurement uncertainty.It was found that with an increase in spatial coverage and measurement complexity, the uncertainty in the wind measurement also increased. For multi-Doppler techniques, the increase in uncertainty for temporally uncoordinated measurements is possibly due to requiring additional assumptions of stationarity along with horizontal homogeneity and less representative line-of-sight velocity statistics. It was also found that wind speed measurement uncertainty was lower during stable conditions compared to unstable conditions.

The VERTEX field campaign: observations of near-ground effects of wind turbine wakes

“…Doppler lidar data can be used directly or indirectly to estimate relevant atmospheric parameters, such as wind velocity variance, vertical momentum flux, and TKE dissipation rates [35,[57][58][59][60][61][62][63][64]. Whereas a single lidar can obtain the component of wind velocity along the beam, deployment of two Doppler lidars allows for the measurement of two components of the horizontal mean wind vector at the same point in space from different directions [47,[65][66][67].…”

“…Whereas a single lidar can obtain the component of wind velocity along the beam, deployment of two Doppler lidars allows for the measurement of two components of the horizontal mean wind vector at the same point in space from different directions [47,[65][66][67]. Triple Doppler wind lidar [64,68,69], while ideal to measure the three orthogonal wind components at a single point simultaneously to avoid assumptions concerning flow continuity [68], was not possible during this campaign.…”

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

“…The collected lidar data were further post-processed only when the carrier-to-noise ratio of the lidar signal was larger than −25 dB (Carbajo-Fuertes et al, 2014). The post-processing from the three radial velocities (U r ) to Cartesian wind velocity components (U , V , W ) was carried out following the standard triple-Doppler retrieval (Mikkelsen et al, 2008;Mann et al, 2009;CarbajoFuertes et al, 2014;Debnath et al, 2017;Choukulkar et al, 2017;Simley et al, 2016) by means of the following equations:…”

“…The XPIA experiment was carried out at the National Oceanic and Atmospheric Administration (NOAA), Boulder Atmospheric Observatory (BAO), near Erie, Colorado, for the period 2 March-31 May 2015. An overview of the field campaign is provided in Lundquist et al (2016), while a detailed analysis of several multiple-Doppler scanning strategies performed with scanning lidars was provided in Choukulkar et al (2017), and vertical profiles of the three wind velocity components performed with triple RHI scans were presented in Debnath et al (2017).…”

“…To overcome limitations connected with multiplecomponent velocity measurements performed with a single instrument, multiple-Doppler scanning strategies have been explored, which require the simultaneous availability of multiple instruments (Newsom et al, 2005;Mikkelsen et al, 2008;Mann et al, 2009;Carbajo-Fuertes et al, 2014;Debnath et al, 2017;Choukulkar et al, 2017). Multiple-Doppler scans consist of probing the wind velocity field at a specific location with various non-parallel line-of-sight velocities in order to characterize the 3-D nature of the atmospheric boundary layer wind field, such as in the presence of wind shear, veer or wakes produced by upwind obstacles (e.g., wind turbines, buildings, topography), or stratified wind turbulence (Segalini and Arnqvist, 2015).…”