scholarly journals Towards improved turbulence estimation with Doppler wind lidar velocity-azimuth display (VAD) scans

2020 ◽  
Vol 13 (8) ◽  
pp. 4141-4158 ◽  
Author(s):  
Norman Wildmann ◽  
Eileen Päschke ◽  
Anke Roiger ◽  
Christian Mallaun
Keyword(s):  
Dissipation Rate ◽  
Elevation Angle ◽  
Volume Averaging ◽  
Bias Reduction ◽  
Sonic Anemometers ◽  
Meteorological Observatory ◽  
Lidar Measurements ◽  
Research Aircraft ◽  
Wind Measurements ◽  
Tke Dissipation Rate

Abstract. The retrieval of turbulence parameters with profiling Doppler wind lidars (DWLs) is of high interest for boundary layer meteorology and its applications. DWLs provide wind measurements above the level of meteorological masts while being easier and less expensive to deploy. Velocity-azimuth display (VAD) scans can be used to retrieve the turbulence kinetic energy (TKE) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. At the elevation angle of 35.3∘ it is also possible to derive TKE. Modifications to existing retrieval methods are introduced in this study to reduce errors due to advection and enable retrievals with a low number of scans. Data from two experiments are utilized for validation: first, measurements at the Meteorological Observatory Lindenberg–Richard-Aßmann Observatory (MOL-RAO) are used for the validation of the DWL retrieval with sonic anemometers on a meteorological mast. Second, distributed measurements of three DWLs during the CoMet campaign with two different elevation angles are analyzed. For the first time, the ground-based DWL VAD retrievals of TKE and its dissipation rate are compared to in situ measurements of a research aircraft (here: DLR Cessna Grand Caravan 208B), which allows for measurements of turbulence above the altitudes that are in range for sonic anemometers. From the validation against the sonic anemometers we confirm that lidar measurements can be significantly improved by the introduction of the volume-averaging effect into the retrieval. We introduce a correction for advection in the retrieval that only shows minor reductions in the TKE error for 35.3∘ VAD scans. A significant bias reduction can be achieved with this advection correction for the TKE dissipation rate retrieval from 75∘ VAD scans at the lowest measurement heights. Successive scans at 35.3 and 75∘ from the CoMet campaign are shown to provide TKE dissipation rates with a good correlation of R>0.8 if all corrections are applied. The validation against the research aircraft encourages more targeted validation experiments to better understand and quantify the underestimation of lidar measurements in low-turbulence regimes and altitudes above tower heights.

scholarly journals Towards improved turbulence estimation with Doppler wind lidar VAD scans

2020 ◽  
Author(s):  
Norman Wildmann ◽  
Eileen Päschke ◽  
Anke Roiger ◽  
Christian Mallaun
Keyword(s):  
Theoretical Model ◽  
Dissipation Rate ◽  
Elevation Angle ◽  
Turbulence Measurement ◽  
Sonic Anemometers ◽  
Tke Dissipation Rate ◽  
Wind Lidar ◽  
Turbulence Parameters ◽  
Doppler Wind Lidar

Abstract. The retrieval of turbulence parameters with profiling Doppler wind lidars (DWL) is of high interest for boundarylayer meteorology and its applications. The DWL measurements extend beyond the observations with meteorological masts and are comparably flexible in their installation. Velocity-azimuth display (VAD) type scans can be used to retrieve turbulence kinetic energy (TKE) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. At the elevation angle of 35.3° it is also possible to derive TKE. We show in this study how modifications to existing methods allow to retrieve TKE and its dissipation rate even with a small number of scans, how a simple correction for advection improves the results at low altitudes and that VAD scans at different elevation angles with the same instrument provide comparable results of TKE dissipation rate after all filters and corrections. For this purpose, data of two experiments are utilized: First, measurements at the Observatory Lindenberg – Richard-Aßmann Observatory (MOL-RAO) are used for validation of the DWL retrieval with sonic anemometers on a meteorological mast. Second, distributed measurements of three DWL during the CoMet campaign are analyzed and compared to in-situ measurements of the DLR Cessna Grand Caravan 208B. The comparison to in-situ instruments shows that the methods to improve turbulence retrievals from VAD scans introduced in this study are effective, especially at low altitudes and for narrow cone angles, but it also shows the limits of turbulence measurement with state-ofthe-art DWL in low turbulence regimes.

Distributed wind measurements with multiple quadrotor UAVs in the atmospheric boundary layer

2021 ◽  
Author(s):  
Tamino Wetz ◽  
Norman Wildmann ◽  
Frank Beyrich
Keyword(s):  
Boundary Layer ◽  
Spatial Distribution ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Horizontal Wind ◽  
Vertical Profiles ◽  
Sonic Anemometers ◽  
Meteorological Observatory ◽  
Wind Measurements ◽  
Quadrotor Uavs

<p>A swarm of quadrotor UAVs is presented as a system to measure the spatial distribution of atmospheric boundary layer flow. The big advantage of this approach is, that multiple and flexible measurement points in space can be sampled synchronously. The algorithm to obtain horizontal wind speed and direction is designed for hovering flight phases and is based on the principle of aerodynamic drag and the related quadrotor dynamics using only on-board sensors.</p><p>During the FESST@MOL campaign at the Boundary Layer Field Site (Grenzschichtmessfeld, GM) Falkenberg of the Lindenberg Meteorological Observatory - Richard-Aßmann-Observatory (MOL-RAO), 76 calibration and validation flights were performed. The 99 m tower equipped with cup and sonic anemometers at the site is used as the reference for the calibration of the wind measurements. The validation with an independent dataset against the tower anemometers reveals that an average accuracy of σ<sub>rms </sub>< 0.3 m s<sup>-1</sup> for the wind speed and σ<sub>rms</sub>,<sub>Ψ</sub><sub></sub>< 8° for the wind direction was achieved.</p><p>Furthermore, we compare the spatial distribution of wind measurements with the swarm to the tower vertical profiles and Doppler wind lidar scans. We show that the observed shear in the vertical profiles matches well with the tower and the fluctuations on short time scales agree between the systems. Flow structures that appear in the time series of a line-of-sight measurement and a two-dimensional vertical scan of the lidar can be observed with the swarm and are even sampled with a higher resolution than the deployed lidar can provide.</p><p>In addition to the intercomparison of the mean wind velocity measurements, turbulence data of the UAV-swarm measurements are analyzed and a comparison to sonic anemometer measurements is provided.</p>

scholarly journals Characteristics of Energy Dissipation Rate Observed from the High-Frequency Sonic Anemometer at Boseong, South Korea

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 837
Author(s):  
Jeonghoe Kim ◽  
Jung-Hoon Kim ◽  
Robert D. Sharman
Keyword(s):  
South Korea ◽  
High Frequency ◽  
Dissipation Rate ◽  
Sonic Anemometer ◽  
Atmospheric Stability ◽  
Turbulence Theory ◽  
Estimation Methods ◽  
The Third ◽  
Sonic Anemometers ◽  
Meteorological Observatory

The characteristics of low-level turbulence at Boseong, located on the southern coast of South Korea, were investigated in terms of eddy dissipation rate (EDR) using 1-year (2018) of wind data obtained from the Boseong Meteorological Observatory (BMO), a World Meteorological Organization testbed. At BMO, a 307 m tall tower is installed on which four high-frequency (20 Hz) sonic anemometers are mounted at 60, 140, and 300 m above ground level (AGL). In addition, a sonic anemometer at 2.5 m AGL is located to the south of the tower. EDRs are estimated from the wind measurements based on three different EDR estimation methods. The first two methods use the inertial dissipation method derived from Kolmogorov turbulence theory, and the third uses a maximum likelihood estimation assuming a von Kármán spectral model. Reasonable agreement was obtained between the three methods with various fluctuations, including diurnal variations for all seasons, while the EDR calculated from the third method displayed slightly higher EDR values than the other two methods. The result of the analysis showed that the mean (standard deviations) of logarithms of EDR had larger values as height decreased (increased), and the means were higher in the unstable planetary boundary layer (PBL) than in the stable PBL for this heterogeneous location adjacent to the coastlines. The probability density functions (PDFs) of the EDRs showed that the distribution was well-represented by a lognormal distribution in both the stable and unstable PBL, although the PDFs at the lowest level (2.5 m) deviated from those at other levels due to surface effects. Seasonal variations in the PDFs showed that there was less difference in the shape of the PDFs depending on atmospheric stability in the wintertime. Finally, we calculate the 1-yr statistics of the observed EDR, which will be used for future LLT forecast systems in Korea.

scholarly journals Distributed wind measurements with multiple quadrotor UAVs in the atmospheric boundary layer

2021 ◽  
Author(s):  
Tamino Wetz ◽  
Norman Wildmann ◽  
Frank Beyrich
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Aerodynamic Drag ◽  
Horizontal Wind ◽  
Horizontal Wind Speed ◽  
Sonic Anemometers ◽  
Meteorological Observatory ◽  
Wind Measurements ◽  
Quadrotor Uavs ◽  
Layer Flow

Abstract. In this study, a swarm of quadrotor UAVs is presented as a system to measure the spatial distribution of atmospheric boundary layer flow. The big advantage of this approach is, that multiple and flexible measurement points in space can be sampled synchronously. The algorithm to obtain horizontal wind speed and direction is designed for hovering flight phases and is based on the principle of aerodynamic drag and the related quadrotor dynamics. During the FESST@MOL campaign at the Boundary Layer Field Site (Grenzschichtmessfeld, GM) Falkenberg of the Lindenberg Meteorological Observatory - Richard-Aßmann-Observatory (MOL-RAO), 76 calibration and validation flights were performed. The 99 m tower equipped with cup and sonic anemometers at the site is used as the reference for the calibration of the wind measurements. The validation with an independent dataset against the tower anemometers reveals that an average accuracy, regarding the root mean square deviation, of σrms

scholarly journals Retrieving clear-air turbulence information from regular commercial aircraft using Mode-S and ADS-B broadcast

2015 ◽  
Vol 8 (11) ◽  
pp. 11817-11852 ◽  
Author(s):  
J. M. Kopeć ◽  
K. Kwiatkowski ◽  
S. de Haan ◽  
S. P. Malinowski
Keyword(s):  
Dissipation Rate ◽  
Vertical Acceleration ◽  
Background Wind ◽  
Commercial Aircraft ◽  
Processing Methods ◽  
Turbulence Measurements ◽  
Significant Potential ◽  
Air Turbulence ◽  
Research Aircraft ◽  
Comparison Of The Results

Abstract. Navigational information broadcast by commercial aircraft in the form of Mode-S and ADS-B messages can be considered a new and valid source of upper air turbulence measurements. A set of three processing methods is proposed and analysed using a quality record of turbulence encounters made by a research aircraft. The proposed methods are based on processing the vertical acceleration or the background wind into the eddy dissipation rate. All the necessary parameters are conveyed in the Mode-S/ADS-B messages. The comparison of the results of application of the processing against a reference eddy dissipation rate obtained using on-board accelerometer indicate a significant potential of those methods. The advantages and limitation of the presented approaches are discussed.

scholarly journals Calibration of 3-D wind measurements on a single engine research aircraft

2015 ◽  
Vol 8 (2) ◽  
pp. 1731-1785
Author(s):  
C. Mallaun ◽  
A. Giez ◽  
R. Baumann
Keyword(s):  
Measurement Techniques ◽  
Calibration Method ◽  
Medium Size ◽  
Sideslip Angle ◽  
Airborne Measurement ◽  
Research Aircraft ◽  
Wind Measurements ◽  
Measurement Uncertainties ◽  
Coordinated Flight ◽  
Wind Speed Measurement

Abstract. An innovative calibration method for the wind speed measurement using a boom mounted Rosemount model 858 AJ air velocity probe is introduced. The method is demonstrated for a sensor system installed on a medium size research aircraft which is used for measurements in the atmospheric boundary layer. The method encounters a series of coordinated flight manoeuvres to directly estimate the aerodynamic influences on the probe and to calculate the measurement uncertainties. The introduction of a differential Global Positioning System (DGPS) combined with a high accuracy Inertial Reference System (IRS) has brought major advances to airborne measurement techniques. The exact determination of geometrical height allows the use of the pressure signal as an independent parameter. Furthermore, the exact height information and the stepwise calibration process lead to maximum accuracy. The results show a measurement uncertainty for the aerodynamic influence of the dynamic and static pressures of 0.1 hPa. The applied parametrisation does not require any height dependencies or time shifts. After extensive flight tests a correction for the flow angles (attack and sideslip angles) was found, which is necessary for a successful wind calculation. A new method is demonstrated to correct for the aerodynamic influence on the sideslip angle. For the 3-D wind vector (with 100 Hz resolution) a novel error propagation scheme is tested, which determines the measurement uncertainties to be 0.3 m s−1 for the horizontal and 0.2 m s−1 for the vertical wind components.

scholarly journals Observations of Breaking Waves and Energy Dissipation in Modulated Wave Groups

2018 ◽  
Vol 48 (12) ◽  
pp. 2937-2948 ◽  
Author(s):  
David W. Wang ◽  
Hemantha W. Wijesekera
Keyword(s):  
Energy Dissipation ◽  
Wave Height ◽  
Wave Breaking ◽  
Dissipation Rate ◽  
Breaking Waves ◽  
Wave Groups ◽  
Dissipation Rates ◽  
Local Wave ◽  
Tke Dissipation Rate ◽  
The Impact

AbstractIt has been recognized that modulated wave groups trigger wave breaking and generate energy dissipation events on the ocean surface. Quantitative examination of wave-breaking events and associated turbulent kinetic energy (TKE) dissipation rates within a modulated wave group in the open ocean is not a trivial task. To address this challenging topic, a set of laboratory experiments was carried out in an outdoor facility, the Oil and Hazardous Material Simulated Environment Test Tank (203 m long, 20 m wide, 3.5 m deep). TKE dissipation rates at multiple depths were estimated directly while moving the sensor platform at a speed of about 0.53 m s−1 toward incoming wave groups generated by the wave maker. The largest TKE dissipation rates and significant whitecaps were found at or near the center of wave groups where steepening waves approached the geometric limit of waves. The TKE dissipation rate was O(10−2) W kg−1 during wave breaking, which is two to three orders of magnitude larger than before and after wave breaking. The enhanced TKE dissipation rate was limited to a layer of half the wave height in depth. Observations indicate that the impact of wave breaking was not significant at depths deeper than one wave height from the surface. The TKE dissipation rate of breaking waves within wave groups can be parameterized by local wave phase speed with a proportionality breaking strength coefficient dependent on local steepness. The characterization of energy dissipation in wave groups from local wave properties will enable a better determination of near-surface TKE dissipation of breaking waves.

scholarly journals Very short-term forecast of near-coastal flow using scanning lidars

2017 ◽  
Author(s):  
Laura Valldecabres ◽  
Alfredo Peña ◽  
Michael Courtney ◽  
Lueder von Bremen ◽  
Martin Kühn
Keyword(s):  
Arima Model ◽  
Atmospheric Stability ◽  
Lead Times ◽  
Atmospheric Conditions ◽  
Short Term ◽  
Wind Speeds ◽  
Lidar Measurements ◽  
Wind Measurements ◽  
Scanning Lidar ◽  
Coastal Flow

Abstract. Wind measurements can reduce the uncertainty in the prediction of wind energy production. Nowadays, commercially available scanning lidars can scan the atmosphere up to several kilometres. Here, we use lidar measurements to forecast near-coastal winds with lead times of five minutes. Using Taylor's frozen turbulence hypothesis together with local topographic corrections, we demonstrate that wind speeds at a downstream position can be forecast by using measurements from a scanning lidar performed upstream in a very short-term horizon. The study covers ten periods characterized by neutral and stable atmospheric conditions. Our methodology shows smaller forecasting errors than those of the persistence method and the ARIMA model. We discuss the applicability of this forecasting technique with regards to the characteristics of the lidar trajectories, the site-specific conditions and the atmospheric stability.

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