scholarly journals Flywheel calibration of a continuous-wave coherent Doppler wind lidar

2020 ◽  
Author(s):  
Anders Tegtmeier Pedersen ◽  
Pedersen Courtney
Keyword(s):  
Laser Beam ◽  
Continuous Wave ◽  
Rotation Axis ◽  
Angular Speed ◽  
Geometrical Model ◽  
Standard Uncertainty ◽  
Beam Radius ◽  
Wind Lidar ◽  
Measured Line ◽  
Doppler Wind Lidar

Abstract. A rig for calibrating a continuous-wave coherent Doppler wind lidar has been constructed. The rig consists of a rotating flywheel on a frame together with an adjustable lidar telescope. The laser beam points toward the rim of the wheel in a plane perpendicular to the wheel's rotation axis, and it can be tilted up and down along the wheel periphery and thereby measure different projections of the tangential speed. The angular speed of the wheel is measured using a high-precision measuring ring fitted to the periphery of the wheel and synchronously logged together with the lidar speed. A simple, geometrical model shows that there is a linear relationship between the measured line-of-sight speed and the beam tilt angle and this is utilised to extrapolate to the tangential speed as measured by the lidar. An analysis of the uncertainties based on the model shows that a standard uncertainty on the measurement of about 0.1 % can be achieved, but also that the main source of uncertainty is the width of the laser beam and it's associated uncertainty. Measurements performed with different beam widths confirms this. Other measurements with a minimised beam radius shows that the method in this case performs about equally well for all the tested reference speeds ranging from about 3 m/s to 18 m/s.

scholarly journals Flywheel calibration of a continuous-wave coherent Doppler wind lidar

2021 ◽  
Vol 14 (2) ◽  
pp. 889-903
Author(s):  
Anders Tegtmeier Pedersen ◽  
Michael Courtney
Keyword(s):  
Laser Beam ◽  
Continuous Wave ◽  
Rotation Axis ◽  
Angular Speed ◽  
Geometrical Model ◽  
Standard Uncertainty ◽  
Beam Radius ◽  
Wind Lidar ◽  
Measured Line ◽  
Doppler Wind Lidar

Abstract. A rig for calibrating a continuous-wave coherent Doppler wind lidar has been constructed. The rig consists of a rotating flywheel on a frame together with an adjustable lidar telescope. The laser beam points toward the rim of the wheel in a plane perpendicular to the wheel's rotation axis, and it can be tilted up and down along the wheel's periphery and thereby measure different projections of the tangential speed. The angular speed of the wheel is measured using a high-precision measuring ring fitted to the periphery of the wheel and synchronously logged together with the lidar speed. A simple geometrical model shows that there is a linear relationship between the measured line-of-sight speed and the beam tilt angle, and this is utilised to extrapolate to the tangential speed as measured by the lidar. An analysis of the uncertainties based on the model shows that a standard uncertainty on the measurement of about 0.1 % can be achieved, but also that the main source of uncertainty is the width of the laser beam and its associated uncertainty. Measurements performed with different beam widths confirm this. Other measurements with a minimised beam radius show that the method in this case performs about equally well for all the tested reference speeds ranging from about 3 to 18 m s−1.

scholarly journals Performance evaluation of an all-fiber image-reject homodyne coherent Doppler wind lidar

2015 ◽  
Vol 8 (10) ◽  
pp. 4145-4153 ◽  
Author(s):  
C. F. Abari ◽  
A. T. Pedersen ◽  
E. Dellwik ◽  
J. Mann
Keyword(s):  
Continuous Wave ◽  
Sonic Anemometer ◽  
Vertical Component ◽  
Intermediate Frequency ◽  
Heterodyne Receiver ◽  
Front End ◽  
Wind Velocities ◽  
Wind Lidar ◽  
Field Campaigns ◽  
Doppler Wind Lidar

Abstract. The main purpose of this study is to evaluate the near-zero wind velocity measurement performance of two separate 1.5 μm all-fiber coherent Doppler lidars (CDLs). The performance characterization is carried out through the presentation of the results from two separate atmospheric field campaigns. In one campaign, a recently developed continuous wave (CW) CDL benefiting from an image-reject front-end was deployed. The other campaign utilized a different CW CDL, benefiting from a heterodyne receiver with intermediate-frequency (IF) sampling. In both field campaigns the results are compared against a sonic anemometer, as the reference instrument. The measurements clearly show that the image-reject architecture results in more accurate measurements of radial wind velocities close to zero. Close-to-zero velocities are usually associated with the vertical component of the wind and are important to characterize.

Horizontal Wind Speed motion-induced error assessment on a floating Doppler Wind lidar

2021 ◽  
Author(s):  
Andreu Salcedo-Bosch ◽  
Joan Farré-Guarné ◽  
Josep Sala-Álvarez ◽  
Javier Villares-Piera ◽  
Robin Tanamachi ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Profile ◽  
Continuous Wave ◽  
Superposition Principle ◽  
Translational Motion ◽  
Horizontal Wind ◽  
Error Assessment ◽  
Horizontal Wind Speed ◽  
Wind Lidar ◽  
Doppler Wind Lidar

<p>A wind retrieval simulator of a floating Doppler Wind Lidar (DWL) with six Degrees of Freedom (DoF) in its motion is presented. The simulator considers a continuous-wave, conically scanning, floating DWL which retrieves the local wind profile from 50 line of sight (LoS) radial velocity measurements per scan. Rotational and translational motion effects over horizontal wind speed (HWS) measurements are studied parametrically. The 6 DoF motion framework as well as the most important buoy motion equations are based on the model presented in [1].</p><p>Each rotational and translational motion is simulated as 1 second sinusoidal signal defined by an amplitude, frequency and motion phase. In order to study the problem of motion-induced error on the retrieved HWS, a dimension reduction is needed (22 variables). A consideration followed in the literature [2] to alleviate the problem is to set the same motional frequency (f=0.3 Hz) for all DoF, a wind vector with constant HWS and null vertical wind speed (VWS). Moreover, the parametric study is carried out under certain constraints in order to finally reduce the problem dimensionality to three, which enables the generation of tri-dimensional colorplots of the error on the retrieved HWS.</p><p>Simulation results show that in the presence of motion, HWS error has a strong dependency on FDWL initial scan phase. Moreover, the directions of the rotation axis and translational velocity vector (with respect to wind direction, WD) show great impact on HWS error. For translational motion, a 3 DoF superposition principle is corroborated.</p><p>The simulator is as a useful tool for understanding particular lidar motion scenarios and their contributions to HWS measurements error. However, further analysis of the effect of lidar initial scan phase is needed. Additionally, these simulations are conducted under idealized assumptions of horizontally homogeneous wind profiles in the vicinity of the FDWL. Simulations using non-homogeneous wind fields (e.g., turbulence, air mass boundaries) would give insights on how well floating lidars can be expected to retrieve the wind profile in these common scenarios.</p><p><strong>Acknowledgements</strong></p><p>This work was supported via Spanish Government–European Regional Development Funds project PGC2018-094132-B-I00 and H2020 ACTRIS-IMP (GA-871115). The European Institute of Innovation and Technology (EIT), KIC InnoEnergy project NEPTUNE (Offshore Metocean Data Mea-suring Equipment and Wind, Wave and Current Analysis and ForecastingSoftware, call FP7) supported measurements campaigns. CommSensLab isa María-de-Maeztu Unit of Excellence funded by the Agencia Estatal de Investigación (Spanish National Science Foundation). The work of Andreu Salcedo-Bosch was supported by the “Agència de Gestió d’Ajuts Universitaris i de la Recerca (AGAUR)”, Generalitat de Catalunya, under Grant no. 2020 FISDU 00455.</p><p><strong>References</strong></p><p>[1] F. Kelberlau, V. Neshaug, L. Lønseth, T. Bracchi, and J. Mann, “Taking the Motion out of Floating Lidar: Turbulence Intensity Estimates with a Continuous-Wave Wind Lidar,” Remote Sens., vol. 12, no. 898, 2020.</p><p>[2] J. Tiana-Alsina, F. Rocadenbosch, and M. A. Gutierrez-Antunano, “Vertical Azimuth Display simulator for wind-Doppler lidar error assessment,” in 2017 IEEE Int. Geosci. Remote. Se. (IGARSS). IEEE, Jul. 2017.</p>

scholarly journals Performance evaluation of an all-fiber image-reject homodyne coherent Doppler wind lidar

2015 ◽  
Vol 8 (4) ◽  
pp. 3729-3752 ◽  
Author(s):  
C. F. Abari ◽  
A. T. Pedersen ◽  
E. Dellwik ◽  
J. Mann
Keyword(s):  
Continuous Wave ◽  
Sonic Anemometer ◽  
Vertical Component ◽  
Intermediate Frequency ◽  
Heterodyne Receiver ◽  
Front End ◽  
Wind Velocities ◽  
Wind Lidar ◽  
Field Campaigns ◽  
Doppler Wind Lidar

Abstract. The main purpose of this study is to evaluate the near-zero wind velocity measurement performance of two separate 1.5 μm all-fiber coherent Doppler lidars (CDL). The performance characterization is performed through the presentation of the results from two separate atmospheric field campaigns. In one campaign, a recently developed continuous wave (CW) CDL benefiting from an image-reject front-end was deployed. The other campaign utilized a different CW CDL, benefiting from a heterodyne receiver with intermediate frequency (IF) sampling. In both field campaigns the results are compared against a sonic anemometer, as the reference instrument. The measurements clearly show that the image-reject architecture results in more accurate measurements of radial wind velocities close to zero. Close-to-zero velocities are usually associated with the vertical component of the wind and are important to characterize.

Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar

2011 ◽  
Vol 9 (9) ◽  
pp. 090604-90607 ◽  
Author(s):  
刘源 Yuan Liu ◽  
刘继桥 Jiqiao Liu ◽  
陈卫标 Weibiao Chen
Keyword(s):  
Fiber Laser ◽  
Single Frequency ◽  
Wind Lidar ◽  
Doppler Wind Lidar

scholarly journals Dust Transport Across the Atlantic Studied by Airborne Doppler Wind Lidar During the Saltrace Experiment in 2013

2016 ◽  
Vol 119 ◽  
pp. 18008
Author(s):  
Fernando Chouza ◽  
Oliver Reitebuch ◽  
Stephan Rahm ◽  
Bernadett Weinzierl
Keyword(s):  
Dust Transport ◽  
Wind Lidar ◽  
Doppler Wind Lidar

Thermal-induced nonlinearities in rose, linseed, and chamomile oils using continuous wave visible laser beam

2018 ◽  
Vol 96 (2) ◽  
pp. 157-164 ◽  
Author(s):  
H.A. Sultan ◽  
Qusay M.A. Hassan ◽  
H. Bakr ◽  
Ahmed S. Al-Asadi ◽  
D.H. Hashim ◽  
...  
Keyword(s):  
Laser Beam ◽  
Continuous Wave ◽  
Input Power ◽  
Diffraction Ring ◽  
Linear Absorption ◽  
Gaussian Profile ◽  
Diffraction Integral ◽  
Visible Laser ◽  
A Cell ◽  
Kirchhoff Diffraction Integral

Self-diffraction rings or spatial self-phase modulation were observed in rose, linseed, and chamomile oils under 473 nm continuous wave laser irradiation. The measurements were performed by propagating the laser beam through a cell containing each sample. The number of rings as well as diameter of the outer-most ring in each pattern obtained increases monotonically with increasing input power. The diffraction ring patterns are theoretically simulated using Fresnel–Kirchhoff diffraction integral in the case of an optically thin medium. The experimental and simulation results show that when a laser beam with Gaussian profile is transmitted through an oil medium, a series of circular diffraction rings forms in the intensity distribution pattern in the far-field. The nonlinear refractive index, n2, was determined from the number of observed rings and by the Z-scan technique. The results obtained from self-diffraction rings experiment and Z-scan are compared and analyzed for the three different oils. A large value was obtained of the order of n2 = 1.32 × l0−6 cm2/W for chamomile oil using the diffraction ring pattern technique. This large nonlinearity is attributed to a thermal effect resulting from linear absorption. Moreover, the optical limiting characteristics of rose, linseed, and chamomile oils were investigated.

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