An LES-based airborne Doppler lidar simulator for investigation of wind profiling in inhomogeneous flow conditions

Gasch, Philipp; Wieser, Andreas; Lundquist, Julie K.; Kalthoff, Norbert

doi:10.5194/amt-2019-118

Cited by 3 publications

(4 citation statements)

References 43 publications

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“…Data availability. The simulation results are available through RADAR4KIT via https://doi.org/10.35097/1810 (Gasch, 2023) under "CC BY 4.0". The underlying LES dataset is available upon request.…”

Section: Discussionmentioning

confidence: 99%

Advancing airborne Doppler lidar wind profiling in turbulent boundary layer flow – an LES-based optimization of traditional scanning-beam versus novel fixed-beam measurement systems

Gasch,

Kasic,

Maas

et al. 2023

Atmos. Meas. Tech.

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Abstract. There is a need for improved wind measurements inside the planetary boundary layer (PBL), including the capability to sample turbulent flow. Airborne Doppler lidar (ADL) provides unique capabilities for spatially resolved and targeted wind measurements in the PBL. However, ADL wind profiling in the PBL is challenging, as turbulence violates the flow homogeneity assumption used in wind profile retrieval and thereby introduces error in the retrieved wind profiles. As turbulence is a dominant source of error it is necessary to investigate and optimize ADL wind profiling capabilities in turbulent PBL flow. This study investigates the potential of a novel multiple-fixed-beam ADL system design to provide improved wind information in turbulent PBL flow compared to traditional single-scanning-beam ADL systems. To achieve this, an LES-based (LES: large eddy simulation) airborne Doppler lidar simulator presented in Gasch et al. (2020) is employed and extended in this study. Results show that a multiple-fixed-beam system with settings comparable to those of commonly used single-scanning-beam systems offers distinct advantages. Advantages include overall reduced wind profile retrieval error due to turbulence and improved spatial representation alongside higher wind profile availability. The study also offers insight into the dependence of the retrieval error on system setup parameters and retrieval parameters for both fixed-beam and scanning-beam systems. When using a fixed-beam system, an order of magnitude higher wind profile resolution appears possible compared to traditional scanning systems at comparable retrieval accuracy. Thus, using multiple-fixed-beam systems opens the door to better sampling of turbulent PBL flow. Overall, the simulator provides a cost-effective tool to investigate and optimize wind profile error characteristics due to turbulence and to optimize system setup and retrieval strategies for ADL wind profiling in turbulent flow.

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Section: Discussionmentioning

confidence: 99%

Advancing airborne Doppler lidar wind profiling in turbulent boundary layer flow – an LES-based optimization of traditional scanning-beam versus novel fixed-beam measurement systems

Gasch,

Kasic,

Maas

et al. 2023

Atmos. Meas. Tech.

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“…Lindelöw (2008), for example, adapted the form to account for a focused beam which scales the RWF by the focusing efficiency. The basic, unadapted form presented here and implemented in our model for this study is also used in several other virtual lidar models (Stawiarski et al, 2013;Lundquist et al, 2015;Gasch et al, 2019;Forsting et al, 2017).…”

Section: Sampling Along a Single Lidar Beammentioning

confidence: 99%

“…The wind speed and direction are not averaged directly but re-computed from the time-averaged wind components (equation 10) so that they correspond to a vector average of the wind. Wainwright et al (2014) and Gasch et al (2019) distinguish the 'scalar' average from this kind of 'vector' average while more detailed analysis comparing the averages have Under quasi-stationary conditions, the notions of pointwise and volume-averaged truth start to converge to a general spatiotemporal average, which is reflected in the merging of the two error distribution metrics. The correspondence suggests that field studies comparing against time-averaged 'point' tower measurements can effectively reflect the error with respect to the volume-average as well.…”

Section: Ten-minute Time Averaged Velocitiesmentioning

confidence: 99%

“…The dependence of profiling lidar on horizontal homogeneity complicates its use in complex terrain; Klaas et al (2015) investigated observation deviations due to terrain and choice of instrument location. Gasch et al (2019) implemented an airborne virtual lidar with PALM and studied errors due to flow inhomogeneities. Wind energy applications have been a notable driver of virtual lidar studies.…”

Section: Introductionmentioning

confidence: 99%

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Behavior and Mechanisms of Doppler Wind Lidar Error in Varying Stability Regimes

Robey

Lundquist

2022

Preprint

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Abstract. Wind lidar are widespread and important tools in atmospheric observations. An intrinsic part of lidar measurement error is due to atmospheric variability in the remote sensing scan volume. This study describes and quantifies the distribution of measurement error due to turbulence in varying atmospheric stability. While the lidar error model is general, we demonstrate the approach using large ensembles of virtual WindcubeV2 lidar performing profiling doppler-beam-swinging (DBS) scans in quasi-stationary large-eddy simulations (LES) of convective and stable boundary layers. Error trends vary with the stability regime, time-averaging of results, and observation height. A systematic analysis of the observation error explains dominant mechanisms and supports the findings of the empirical results. Treating the error under a random variable framework allows for informed predictions about the effect of different configurations or conditions on lidar performance. Convective conditions are most prone to large errors, driven by the large vertical velocities in convective plumes and exacerbated by the high elevation angle of the scanning beams. The violations of the assumption of horizontal homogeneity due to filtered turbulent velocity variances dominate the error variance, with the vertical velocity variations of particular importance. Range gate weighting contributes little to the variability of the error, but induces an underestimating bias into the horizontal velocity near the surface shear layer. Error in the horizontal wind speed and direction computed from wind components is sensitive to the background wind speed but has negligible dependence on the relative orientation of the instrument. Especially during low winds and in the presence of large errors in the u and v velocity estimates, the reported wind speed is subject to a systematic positive bias. Vector time-averaged measurements can improve the behavior of the error distribution with a predictable effectiveness related to the number of decorrelated samples in the time window. The approach in decomposing the error mechanisms with the help of the LES flow field extends to more complex measurement scenarios and scans.

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Representation of coherent structures and turbulence spectra from a virtual SpinnerLidar for future LES wake validation

Brown

Hsieh

Herges

et al. 2020

J. Phys.: Conf. Ser.

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Work has begun towards model validation of wake dynamics for the large-eddy simulation (LES) code Nalu-Wind in the context of research-scale wind turbines in a neutral atmospheric boundary layer (ABL). Interest is particularly directed at the structures and spectra which are influential for wake recovery and downstream turbine loading. This initial work is to determine the feasibility of using nacelle-mounted, continuous-wave lidars to measure and validate wake physics via comparisons of full actuator line simulation results with those obtained from a virtual lidar embedded within the computational domain. Analyses are conducted on the dominant large-scale flow structures via proper orthogonal decomposition (POD) and on the various scales of wake-added turbulence through spectral comparisons. The virtual lidar adequately reproduces spatial structures and energies compared to the full simulation results. Correction of the higher-frequency turbulence spectra for volume-averaging attenuation was most successful at locations where mean gradients were not severe. The results of this work will aid the design of experiments for validation of high-fidelity wake models.

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An LES-based airborne Doppler lidar simulator for investigation of wind profiling in inhomogeneous flow conditions

Cited by 3 publications

References 43 publications

Advancing airborne Doppler lidar wind profiling in turbulent boundary layer flow – an LES-based optimization of traditional scanning-beam versus novel fixed-beam measurement systems

Advancing airborne Doppler lidar wind profiling in turbulent boundary layer flow – an LES-based optimization of traditional scanning-beam versus novel fixed-beam measurement systems

Behavior and Mechanisms of Doppler Wind Lidar Error in Varying Stability Regimes

Representation of coherent structures and turbulence spectra from a virtual SpinnerLidar for future LES wake validation

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