Coherent Wind Research Articles

1.645 µm Er:YAG single-mode dual-wavelength emitter for CH4 differential absorption lidar.

We present a hybrid fiber/bulk laser source at 1.645 µm designed for methane (CH4) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH4 line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented.

Numerical optimization of auxiliary biaxial receiver to detect blind zone of pulsed coherent wind lidar.

The conventional pulsed monostatic coaxial coherent Doppler wind lidar (CDWL) has a blind detection zone of tens of meters, causing the loss of near-field wind field data. While maintaining the long-range detection capabilities of pulsed lidar, we introduce a novel auxiliary biaxial receiver (ABR) aimed at acquiring dependable coherent signals within blind zones. This is achieved by incorporating a receiver in close proximity to the monostatic coaxial transceiver (MCT), thereby mitigating end-face reflections and laser pulse tailing effects. A specific model of multiple aperture coherent wind detection is established for the ABR system without blind zone problem (BZP). The numerical simulations demonstrate that the biaxial receiver with reasonable design can meet the detection needs of the entire range of the blind zone. By using an ABR with a smaller focal length under appropriate transceiver pointing and general pointing accuracy, the BZP can be solved. The study also exhaustively obtained all parameter combinations that can solve the near-field BZP for a specific system. The results provide a new idea and engineering design guidance for the optical system design of pulsed CDWL without BZP.

Real-Time Synchronous Acquisition and Processing of Signal in Coherent Doppler Wind Lidar Using FPGA

Coherent Doppler wind lidar has become a primary remote sensing technique for measuring atmospheric wind fields in recent years. However, the high bandwidth of the time domain echo signal has limited real-time data acquisition and processing. In this work, we propose a real-time data acquisition and preprocessing integrated solution. This approach is implemented using on-chip system field programmable gate array (FPGA) hardware while utilizing a 7-channel base-4 polyphase fast Fourier transform calculation module and a pipelined structure operation. Within a 1 s data collection time, the real-time rapid acquisition and spectral preprocessing of lidar echo signals at a range of 9.9 km can be achieved. We compare the observation data with the measurement data from Windcube100s and radiosondes, and the results indicate that the coherent wind lidar developed in this paper can detect heights above 4.0 km, with effective data acquisition rates of 82% and 61% in the height ranges of 1500–2000 m and 2000–2500 m, respectively. At the height range of 3.5 km, the correlations for horizontal wind speed and direction measured by the lidar were all above 0.99, with the wind speed and direction measurement deviations being better than 0.56 m/s and 8.40∘, respectively.

Field Verification of Vehicle-Mounted All-Fiber Coherent Wind Measurement Lidar Based on Four-Beam Vertical Azimuth Display Scanning

Wind parameters play a vital role in studying atmospheric dynamics and climate change. In this study, a vehicle-mounted coherent wind measurement Lidar (CWML) with a wavelength of 1.55 µm is demonstrated based on a four-beam vertical azimuth display (VAD) scanning mode, and a method to estimate wind vector from power spectrum is proposed. The feasibility of the application of wind profile Lidar in vehicles is verified by calibration tests, comparison experiments, and continuous observation experiments, successively. The effective detection height of Lidar can reach 3 km. In contrasting experiments, the correlation coefficients of the magnitude and direction of horizontal wind speed measured by vehicle-mounted Lidar and fixed Lidar are 0.94 and 0.91, respectively. The experimental results reveal that the accuracies of wind speed and direction measurements with the vehicle-mounted CWML are better than 0.58 m/s and 4.20°, respectively. Furthermore, to understand the role of the wind field in the process of energy and material transport further, a proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) is utilized to measure the concentration of volatile organic compounds (VOCs). Relevant experimental results indicate that the local meteorological conditions, including wind speed and humidity, influence the VOC concentrations.

Airborne coherent wind lidar measurements of the momentum flux profile from orographically induced gravity waves

Abstract. In the course of the GW-LCYCLE II campaign, conducted in Jan/Feb 2016 from Kiruna, Sweden, coherent Doppler wind lidar (2 µm DWL) measurements were performed from the DLR Falcon aircraft to investigate gravity waves induced by flow across the Scandinavian Alps. During a mountain wave event on 28 January 2016, a novel momentum flux (MF) scan pattern with fore and aft propagating laser beams was applied to the 2 µm DWL. This allows us to measure the vertical wind and the horizontal wind along the flight track simultaneously with a high horizontal resolution of ≈800 m and hence enables us to derive the horizontal MF profile for a broad wavelength spectrum from a few hundred meters to several hundred kilometers. The functionality of this method and the corresponding retrieval algorithm is validated using a comparison against in situ wind data measured by the High Altitude and Long Range (HALO) aircraft which was also deployed in Kiruna for the POLSTRACC (Polar Stratosphere in a Changing Climate) campaign. Based on that, the systematic and random error of the wind speeds retrieved from the 2 µm DWL observations are determined. Further, the measurements performed on that day are used to reveal significant changes in the horizontal wavelengths of the vertical wind speed and of the leg-averaged momentum fluxes in the tropopause inversion layer (TIL) region, which are likely to be induced by interfacial waves as recently presented by Gisinger et al. (2020).

Cross‐wavelet analysis of coherent wind and saltation events

AbstractThis paper presents high‐resolution field measurements of the wind and saltation fields using miniphones and anemometers located 20–40 mm apart (bed‐parallel) and 10–40 mm above the bed. The average wind speeds at the Shoalhaven Heads, Australia and the Jericoacoara, Brazil field sites are both 4.4 m s−1, and the average saltation rates are 5.0 and 22.2 counts/mm2 s−1, respectively. Normalized cross‐covariance analysis between the wind and saltation time series indicates a dominant saltation response time of 0 s. Cross‐wavelet analysis focusing on short‐duration events characterizes statistically significant wind–sand events and intervals. In the high aeolian saltation rate environment (Brazil), the events and intervals averaged 1.9 and 12.2 s. The low transport environment (Australia) resulted in 2.1 s events and 10.8 s intervals. This study demonstrates that wind–sand events occur about 15% of the time but account for about 23% of the sand transport. These results were possible because of the presentation of a wavelet‐derived event time series. The criticality of tightly controlled field experiments to measure coincident wind and saltation fluctuations with co‐located sensors was demonstrated. This paper emphasizes the importance of the contribution of saltation events to time‐averaged transport rates, which influences sediment flux modelling.

A Study of Dynamic Equivalence Method for Multiple Wind Farms in Urban Power Grids

As the number of wind farms (WFs) in urban power grids gradually increases, their dynamic equivalence is needed for stability analysis. This paper proposes a dynamic equivalence method for distributed multiple wind farms in an urban power grid. The key idea is to characterize wind farms dynamics and then use them for coherence by considering the differences between doubly-fed induction generators (DFIG) and permanent magnet direct-drive synchronous generators (PMSG). The mathematical-physical models and operational control characteristics are firstly analyzed to find the essential attributes representing the dynamic characteristics. Then we introduce the similarity based on the dynamic timing warping (DTW) distances, which help construct the clustering index for coherency wind farms. Meanwhile, comprehensive constraints, which ensure the consistency of the urban power grid topology, are adequately considered. Finally, the parameters of coherent wind farms are aggregated based on the clustering groups. The proposed method is validated in an urban grid by the time-domain simulation.

Mesoscale Spatial Variability of Lower Thermospheric Winds During the Anomalous Transport Rocket Experiment

AbstractWe present observations and analysis of seven horizontal wind profiles obtained by the trimethyl aluminum (TMA) tracer method on 27 March 2012 over the Atlantic ocean near Wallops Island, Virginia (37.9°N, 75.4°W). Payloads were launched in order to produce quasi‐simultaneous trails separated by tens to hundreds of kilometers. Tracer positions evolving in time and space were triangulated from three locations along the Atlantic seaboard and wind profiles between 90 and 140 km calculated. The wind profiles present a coherent wind structure dominated by very strong diurnal and semidiurnal tides up to 110 km and an upward propagating inertia‐gravity wave between 110 and 140 km. Properties such as horizontal and vertical wavelength could be extracted from the simultaneous observations at separate locations. A statistical analysis of the wind differences was performed to estimate power‐law coefficients of the second structure function at mesoscales. They show scale‐independence in the region of the largest wind shears, 100–110 km, and a scaling coefficient characteristic for isotropic wind fluctuations above and below this region.

Data Processing and Analysis of Eight-Beam Wind Profile Coherent Wind Measurement Lidar

Real-time measurement of atmospheric wind field parameters plays an important role in weather analysis and forecasting, including improving the efficiency of wind energy, particle tracking, boundary layer measurements, and airport security. In this study, a wind profile coherent wind Light Detection and Ranging (Lidar) measurement with a wavelength of 1.55 µm was developed and demonstrated based on the principle of eight-beam velocimetry. The wind speed information was retrieved, and vertical and horizontal profiles were calculated via power spectrum estimation of sampled echo signals through the measurement of the atmospheric wind field in Hefei for several consecutive days. The experimental results show that the wind profiles produced using different techniques are quite consistent and the standard error is less than 0.42 m/s compared with three-beam and five-beam wind measurements.

4.08 mJ, 0.976 μs Er: YAG ring laser oscillator

Er:YAG ring laser with high-energy and wide pulse duration, which is resonantly pumped by a fiber laser at 1532 nm, is reported in this paper. Maximum power 2.62 W was implemented from ring resonator at 1645 nm. By transforming pulse repetition frequency (PRF), pulsed output energy was 4.08 mJ under 100 Hz PRF with a pulse width of 0.976 μs under the Q-switching regime. Since the wind measurement accuracy of coherent wind lidar is determined by the pulse width of the emission laser, this 1.6 µm single-frequency laser with high energy and wide pulse width is an ideal laser source for coherent wind lidar.

Performance simulation of space-based coherent wind LIDAR system under various meteorological conditions

Performance simulation of space-based coherent wind LIDAR system under various meteorological conditions

Research on technology of 1550nm all-fiber continuous wave coherent Doppler wind lidar

In order to obtain the telemetry data of wind field 80 m ahead of the wind turbine, an all-fiber continuous wave coherent Doppler lidar (CW-CDL) system is demonstrated in this paper. The CW-CDL of all-fiber structure has advantages of the compact structure, good stability and low cost. However, there is inherent crosstalk in the optical circulator of the optical fiber module, the crosstalk light and the reference light enter the photon detector together to produce phase induced intensity noise (PIIN). Aiming to effectively solve the noise, we proposed a polarization control method by combining a polarization beam splitter and a quarter wave plate to reduce the PIIN in the system. The wind speed Doppler signal at 80 meters is obtained on a sunny day, and the typical signal-to-noise ratio can reach 21.7 dB.

Research on high resolution range-gate adaptive technology of coherent wind lidar

Research on high resolution range-gate adaptive technology of coherent wind lidar

相干测风激光雷达的数值建模和仿真分析

相干测风激光雷达的数值建模和仿真分析

Performance Optimization and Experimental Research of Continuous Wave Coherent Wind Lidar

Performance Optimization and Experimental Research of Continuous Wave Coherent Wind Lidar

Fog and Low Stratus Obstruction of Wind Lidar Observations in Germany—A Remote Sensing-Based Data Set for Wind Energy Planning

Coherent wind doppler lidar (CWDL) is a cost-effective way to estimate wind power potential at hub height without the need to build a meteorological tower. However, fog and low stratus (FLS) can have a negative impact on the availability of lidar measurements. Information about such reductions in wind data availability for a prospective lidar deployment site in advance is beneficial in the planning process for a measurement strategy. In this paper, we show that availability reductions by FLS can be estimated by comparing time series of lidar measurements, conducted with WindCubes v1 and v2, with time series of cloud base altitude (CBA) derived from satellite data. This enables us to compute average maps (2006–2017) of estimated availability, including FLS-induced data losses for Germany which can be used for planning purposes. These maps show that the lower mountain ranges and the Alpine regions in Germany often reach the critical data availability threshold of 80% or below. Especially during the winter time special care must be taken when using lidar in southern and central regions of Germany. If only shorter lidar campaigns are planned (3–6 months) the representativeness of weather types should be considered as well, because in individual years and under persistent weather types, lowland areas might also be temporally affected by higher rates of data losses. This is shown by different examples, e.g., during radiation fog under anticyclonic weather types.

A high signal-to-noise ratio balanced detector system for 2 μm coherent wind lidar

A balanced detector system with a high signal-to-noise ratio (SNR) is the key technology for 2 μm coherent wind lidar, which can enhance the ability for the digital receiver to detect extremely weak signals. The photodiode is the main detection component of a balanced detector system. The variance of junction capacitance of different photodiodes will cause the degradation of SNR. Based on the linear relationship between the junction capacitance of a photodiode and the reverse voltage in the double logarithmic coordinates, a balanced detector system is designed to have the ability to adjust the reverse voltage by using the external digital-to-analog converter. An optimization of the circuit performance can be achieved by adjusting the junction capacitance, which significantly affects the circuit noise and signal bandwidth in the design of the high bandwidth transimpedance amplifier, which is sensitive to parasitic capacitance and component error. A simplified optical system is built to test the performance of the designed balanced detector system. The results show that the SNR of the detector system is ∼10% higher than that of the commercial product, which can further increase the detection distance of the wind lidar by ∼1.5 km for the detection limit of 10 km.

Observation of Jet Stream Winds during NAWDEX and Characterization of Systematic Meteorological Analysis Errors

Abstract Observations across the North Atlantic jet stream with high vertical resolution are used to explore the structure of the jet stream, including the sharpness of vertical wind shear changes across the tropopause and the wind speed. Data were obtained during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) by an airborne Doppler wind lidar, dropsondes, and a ground-based stratosphere–troposphere radar. During the campaign, small wind speed biases throughout the troposphere and lower stratosphere of only −0.41 and −0.15 m s−1 are found, respectively, in the ECMWF and Met Office analyses and short-term forecasts. However, this study finds large and spatially coherent wind errors up to ±10 m s−1 for individual cases, with the strongest errors occurring above the tropopause in upper-level ridges. ECMWF and Met Office analyses indicate similar spatial structures in wind errors, even though their forecast models and data assimilation schemes differ greatly. The assimilation of operational observational data brings the analyses closer to the independent verifying observations, but it cannot fully compensate for the forecast error. Models tend to underestimate the peak jet stream wind, the vertical wind shear (by a factor of 2–5), and the abruptness of the change in wind shear across the tropopause, which is a major contribution to the meridional potential vorticity gradient. The differences are large enough to influence forecasts of Rossby wave disturbances to the jet stream with an anticipated effect on weather forecast skill even on large scales.

Intercomparison of wind observations from the European Space Agency's Aeolus satellite mission and the ALADIN Airborne Demonstrator

Abstract. Shortly after the successful launch of the European Space Agency's wind mission Aeolus, co-located airborne wind lidar observations were performed in central Europe; these observations employed a prototype of the satellite instrument – the ALADIN (Atmospheric LAser Doppler INstrument) Airborne Demonstrator (A2D). Like the direct-detection Doppler wind lidar on-board Aeolus, the A2D is composed of a frequency-stabilized ultra-violet (UV) laser, a Cassegrain telescope and a dual-channel receiver to measure line-of-sight (LOS) wind speeds by analysing both Mie and Rayleigh backscatter signals. In the framework of the first airborne validation campaign after the launch and still during the commissioning phase of the mission, four coordinated flights along the satellite swath were conducted in late autumn of 2018, yielding wind data in the troposphere with high coverage of the Rayleigh channel. Owing to the different measurement grids and LOS viewing directions of the satellite and the airborne instrument, intercomparison with the Aeolus wind product requires adequate averaging as well as conversion of the measured A2D LOS wind speeds to the satellite LOS (LOS*). The statistical comparison of the two instruments shows a positive bias (of 2.6 m s−1) of the Aeolus Rayleigh winds (measured along its LOS*) with respect to the A2D Rayleigh winds as well as a standard deviation of 3.6 m s−1. Considering the accuracy and precision of the A2D wind data, which were determined from comparison with a highly accurate coherent wind lidar as well as with the European Centre for Medium-Range Weather Forecasts (ECMWF) model winds, the systematic and random errors of the Aeolus LOS* Rayleigh winds are 1.7 and 2.5 m s−1 respectively. The paper also discusses the influence of different threshold parameters implemented in the comparison algorithm as well as an optimization of the A2D vertical sampling to be used in forthcoming validation campaigns.

Development of Synergetic-Active Sensor-System for Evaluation of Observations by Earthcare

We develop the synergetic ground-based active-sensor-system for the evaluation of observations by space-borne lidars. The system consists of second version of multi-field-view multiple-scattering polarization lidar (MFMSPL-2), multiple-field-of-view high spectral resolution polarization lidar, direct-detection Doppler wind lidar, coherent Doppler wind lidar and 94GHz cloud profiling radar. The system can simulate observed signals from sensors onboard the joint Japanese/European mission Earth Clouds, Aerosols and Radiation Explorer (EarthCARE). The observation system can provide unique opportunity to study interaction of cloud microphysics, aerosol microphysics, vertical air motion and vertical distribution of horizontal wind and it will lead to evaluate cloud-convective parameterization and to reduce uncertainties in climate change predictions.