Atmospheric Turbulence Measurements Research Articles

A Real-Time Measurement System for Atmospheric Turbulence Intensity and Distribution Based on the GLAO System

Measuring the intensity and distribution of atmospheric optical turbulence at large-aperture astronomical telescope sites is crucial to optimizing turbulence correction for different layers. A real-time measurement of turbulence distribution in large-aperture telescopes would be valuable for the parameter optimization of adaptive optics (AO) systems, especially for large field-of-view AO systems such as multi-conjugate adaptive optics (MCAO) and ground-layer adaptive optics (GLAO). Based on the GLAO system of NVST at FSO, a real-time measurement system was deployed to assess the site’s atmospheric turbulence intensity and distribution. This system is, to our knowledge, the first real-time turbulence parameter measurement system in the world with an AO system. We adopt pseudo-open loop methods to restore the turbulence information from the close-loop data of GLAO and measure the turbulence strength and distribution. Multiple subaperture pairs are used instead of a pair of subapertures for fitting calculation to increase the measurement accuracy. Two conventional measurement algorithms, SLODAR and S-DIMM+, are compared with the data from the open-source simulator SOAPY, to cross-verify the correctness of our calculation based on the data process of pseudo-open loop data and multiple subaperture pairs. The simulation results show that for two layers’ turbulence input, approximately 93% of the turbulence is correctly detected with the SLODAR method and the given parameters of wavefront sensors and correctors, while the S-DIMM+ is 87%. Real-time measurements of atmospheric turbulence at the NVST site were carried out on 28 May 2023. The observation results indicated that approximately 80% of the turbulence was located below an altitude of 2000 m; only a few appear in the upper height.

LiDAR technology and experimental research for comprehensive measurement of atmospheric transmittance, turbulence, and wind

LiDAR technology and experimental research for comprehensive measurement of atmospheric transmittance, turbulence, and wind

Revelation of hidden 2D atmospheric turbulence strength fields from turbulence effects in infrared imaging.

Turbulence exists widely in the natural atmosphere and in industrial fluids. Strong randomness, anisotropy and mixing of multiple-scale eddies complicate the analysis and measurement of atmospheric turbulence. Although the spatially integrated strength of atmospheric turbulence can be roughly measured indirectly by Doppler radar or laser, direct measurement of two-dimensional (2D) strength fields of atmospheric turbulence is challenging. Here we attempt to solve this problem through infrared imaging. Specifically, we propose a physically boosted cooperative learning framework, termed the PBCL, to quantify 2D turbulence strength from infrared images. To demonstrate the capability of the PBCL, we constructed a dataset with 137,336 infrared images and corresponding 2D turbulence strength fields. The experimental results show that cooperative learning brings performance improvements, enabling the PBCL to simultaneously learn turbulence strength fields and inhibit adverse turbulence effects in images. Our work demonstrates the potential of imaging in measuring physical quantity fields.

Flow Structure around a Multicopter Drone: A Computational Fluid Dynamics Analysis for Sensor Placement Considerations

This study presents a computational fluid dynamics (CFD) based approach to determine the optimal positioning for an atmospheric turbulence sensor on a rotary-wing uncrewed aerial vehicle (UAV) with X8 configuration. The vertical (zBF) and horizontal (xBF) distances of the sensor to the UAV center to reduce the effect of the propeller-induced flow are investigated by CFD simulations based on the k−ϵ turbulence model and the actuator disc theory. To ensure a realistic geometric design of the simulations, the tilt angles of a test UAV in flight were measured by flying the drone along a fixed pattern at different constant ground speeds. Based on those measurement results, a corresponding geometry domain was generated for the CFD simulations. Specific emphasis was given to the mesh construction followed by a sensitivity study on the mesh resolution to find a compromise between acceptable simulation accuracy and available computational resources. The final CFD simulations (twelve in total) were performed for four inflow conditions (2.5 m s−1, 5 m s−1, 7.5 m s−1 and 10 m s−1) and three payload configurations (15 kg, 20 kg and 25 kg) of the UAV. The results depend on the inflows and show that the most efficient way to reduce the influence of the propeller-induced flow is mounting the sensor upwind, pointing along the incoming flow direction at xBF varying between 0.46 and 1.66 D, and under the mean plane of the rotors at zBF between 0.01 and 0.7 D. Finally, results are then applied to the possible real-case scenario of a Foxtech D130 carrying a CSAT3B ultrasonic anemometer, that aims to sample wind with mean flows higher than 5 m s−1. The authors propose xBF=1.7 m and zBF=20 cm below the mean rotor plane as a feasible compromise between propeller-induced flow reduction and safety. These results will be used to improve the design of a novel drone-based atmospheric turbulence measurement system, which aims to combine accurate wind and turbulence measurements by a research-grade ultrasonic anemometer with the high mobility and flexibility of UAVs as sensor carriers.

Wind fields from atmospheric turbulence measurements

We present recent advances in the modeling of wind fields and their reconstruction from real-world atmospheric turbulence measurements. The proposed wind field model provides a statistically coherent framework for modeling the empirically observed occurrence of extreme atmospheric events. Furthermore, we demonstrate that the model is general enough to enmesh real-world measurement points, e.g., from meteorological masts or LIDAR, and thus provides a rather convenient method for the reconstruction of highly resolved, three-dimensional wind fields. Our methodology is based on the so-called superstatistics of Gaussian-distributed (or Mann-type) velocity fields with fluctuating covariances and exactly reproduces higher-order statistics due to extreme small-scale wind fluctuations. Therefore, it could lead to more realistic inflow conditions and might potentially enhance the current design standard of wind turbines. We further discuss potential applications of the wind field model in the context of LIDAR measurements as well as for wake situations.

Adjustments to the law of the wall above an Amazon forest explained by a spectral link

Modification to the law of the wall represented by a dimensionless correction function ϕRSL(z/h) is derived using atmospheric turbulence measurements collected at two sites in the Amazon in near-neutral stratification, where z is the distance from the forest floor and h is the mean canopy height. The sites are the Amazon Tall Tower Observatory for z/h∈[1,2.3] and the Green Ocean Amazon (GoAmazon) site for z/h∈[1,1.4]. A link between the vertical velocity spectrum Eww(k) (k is the longitudinal wavenumber) and ϕRSL is then established using a co-spectral budget (CSB) model interpreted by the moving-equilibrium hypothesis. The key finding is that ϕRSL is determined by the ratio of two turbulent viscosities and is given as νt,BL/νt,RSL, where νt,RSL=(1/A)∫0∞τ(k)Eww(k)dk, νt,BL=kv(z−d)u*, τ(k) is a scale-dependent decorrelation time scale between velocity components, A=CR/(1−CI)=4.5 is predicted from the Rotta constant CR=1.8, and the isotropization of production constant CI=3/5 given by rapid distortion theory, kv is the von Kármán constant, u* is the friction velocity at the canopy top, and d is the zero-plane displacement. Because the transfer of energy across scales is conserved in Eww(k) and is determined by the turbulent kinetic energy dissipation rate (ε), the CSB model also predicts that ϕRSL scales with LBL/Ld, where LBL is the length scale of attached eddies to z=d, and Ld=u*3/ε is a macro-scale dissipation length.

A new approach to atmospheric turbulence measurements using HOSE on radar backscattered echoes

A Novel approach has been proposed for the measurement of turbulent energy dissipation rate (ε) from Nonlinear index (NLI) based measurements using the Higher Order Spectral Estimation (HOSE) technique. The higher order spectral analysis, also known as Bispectrum, is useful for identifying nonlinearities present in the signals. Earlier studies used Bispectrum measurements to experimentally study the spectral energy transfer due to wavenumber interactions in a turbulent flow, which is briefly discussed in the manuscript. This is one of the main motivations for considering HOSE on Atmospheric signals. The Bicoherence obtained by this method has been applied to the backscattered signals received from the Mesosphere, Stratosphere, and Troposphere (MST) radar, Gadanki. Here we considered both convective and clear air atmospheric observations for the analysis and calculated the Nonlinear Index (which represents the amount of nonlinearity in signals) obtained from the Bicoherence for each range bin. We observed that the nonlinearity index indirectly provides information about turbulent intensity. An empirical relationship between the nonlinear index and turbulent energy dissipation rate has been established through regression models. The results of the turbulence energy dissipation rate (ε) obtained from the nonlinear index based method have been compared with the turbulence energy dissipation rate (ε) obtained from the spectrum width based method.

OAM-based optical wavelet using a single pixel detection system for probing dynamic environments with application to real-time measurements of strong atmospheric turbulence.

This paper presents a novel method for optical probing by generating optical fields with characteristics of wavelets. The optical wavelets form a basis of rotated asymmetric beams with scaled orbital angular momentum (OAM) and beam sizes. The probing method was used experimentally to measure the continuous wavelet transform of a turbulent propagation path, giving insight into the angular properties about a fixed radius. The wavelet transform of a three-dimensional turbulence distribution was measured; the measurements are much faster than the turbulence changes, allowing characterization of an instantaneous realization of turbulence over time. Results show highly localized regions of OAM in space through the turbulence and characteristics of the turbulence can be extracted from the wavelet transforms.

Measurements of atmospheric turbulence with airborne beacons by using a differential scintillation method.

By using the differential scintillation method suggested and described in this work, vibrations of unmanned aircraft vehicle platforms can be eliminated. Therefore, airborne beacons have great potential applications in turbulence measurements along an arbitrary atmospheric path. The experiment with a constant beacon shows that the retrieved results of the differential scintillation method have good consistency with the scintillation index inversion method. Additionally, a similar verification was carried out between a simulative airborne beacon and a constant beacon; the differential scintillation method indicated more consistent results than the scintillation index inversion method, and its retrieved results of different beacons were in good agreement with a correlation coefficient close to 1, reaching 0.994. In verification experiments over a slant path, the retrieved results of the differential scintillation method showed good statistical properties when an airborne beacon was measured under various weather conditions. The results indicated that the new, to the best of our knowledge, proposed differential scintillation method is a reliable and feasible technique for eliminating stability issues in the measurements of airborne beacons.

Surrogate modelling of wind fields from point-wise atmospheric turbulence measurements

We present an advanced model for the generation of synthetic wind fields that can be understood as an extension of the well-known Mann model. In contrast to such Gaussian random field models which control second-order statistics (i.e., velocity correlation tensors or spectra), we demonstrate that our extended model incorporates the effects of higherorder statistics as well. In particular, the empirically observed phenomenon of small-scale intermittency, a key feature of atmospheric turbulent flows, can be reproduced with high accuracy and at considerably low computational cost. Our method is based on a recently developed multipoint statistical description of a turbulent velocity field [J. Friedrich et al., J. Phys. Complex. 2 045006 (2021)] and consists of a superposition of multivariate Gaussian statistics with fluctuating covariances. Furthermore, we explicitly show how such superstatistical Mann fields can be constraint on a certain number of point-wise measurement data. We give an outlook on the relevance of such surrogate wind fields in the context of fatigue loads on wind turbines.

Numerical simulation of a large area scintillometer and laser differential image motion monitor.

Measurements of atmospheric turbulence along a path can be quantified by scintillometers and differential image motion monitors (DIMMs). The two instruments often measure different levels of turbulence, sometimes varying by nearly an order of magnitude. A high-fidelity numerical simulation was leveraged to assess the measurement performance of both a scintillometer and a DIMM system. When a non-ideal detector is combined with range-dependent turbulence, significant differences between the scintillometer and DIMM are observed. The difference in measurements obtained with the numerically simulated scintillometer and DIMM was consistent with those observed in side-by-side measurements with the instruments.

Correction to: Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog

Correction to: Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog

Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog

Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog

Universal Return to Isotropy of Inhomogeneous Atmospheric Boundary Layer Turbulence.

A recalcitrant problem in the physics of turbulence is the representation of the tendency of large-scale anisotropic eddies to redistribute their energy content with decreasing scales, a phenomenon referred to as return to isotropy. An unprecedented dataset of atmospheric turbulence measurements covering flat to mountainous terrain, stratification spanning convective to very stable conditions, surface roughness ranging over several orders of magnitude, and Reynolds numbers that far exceed the limits of direct numerical simulations and laboratory experiments was assembled for the first time and used to explore the scalewise return to isotropy. The multiple routes to energy equipartitioning among velocity components are shown to be universal once the initial anisotropy at large scales, linked to turbulence generation, is accounted for.

Evaluation of numerical predictions of sonic boom level variability due to atmospheric turbulence.

A numerical model of full-scale N-wave sonic boom propagation through turbulence is described based on the nonlinear Khokhlov-Zabolotskaya-Kuznetzov (KZK) propagation equation and the most advanced turbulence model used in atmospheric acoustics. This paper presents the first quantitative evaluation of a KZK-based model using data from the recent Sonic Booms in Atmospheric Turbulence measurement campaigns, which produced one of the most extensive databases of full-scale distorted N-waves and concurrent atmospheric parameters. Simulated and measured distributions of the perceived level (PL) metric, which has been used to predict public annoyance due to sonic booms, are compared. For most of the conditions considered, the present model's predictions of the PL variances agree with the measurement to within normal uncertainty, while about half of the mean value predictions agree. The approximate PL distribution measured for high turbulence conditions falls within about 2 dB of the simulated distribution for nearly all probabilities. These favorable results suggest that the KZK-based model is sufficiently accurate for approximating the N-wave PL distribution, and the model may therefore be useful for predicting public reaction to sonic booms in turbulent conditions.

Development of an unmanned aerial vehicle to study atmospheric boundary-layer turbulent structure

One of the main challenges in the boundary-layer turbulence research consists in advancing turbulence theory towards describing turbulent regimes over inhomogeneous and irregular surface which is often the case in nature. Novel observational techniques are required to sample turbulence statistics in such conditions. To that aim, a light-weight payload for atmospheric turbulence measurements is designed and used on a vertical take-off and landing (VTOL) fixed-wing unmanned aerial vehicle (UAV). Such an observational platform complements traditional mast observations and makes it possible to sample turbulence statistics over remote and inhomogeneous landscapes. The advantages of the VTOL scheme consist in: i) minimizing the risk of the payload damage during landing; ii) less strict requirements to the surface conditions in the landing area. The turbulence payload consists of a miniature seven-hole probe, inertial navigation system and a fine-wire resistance thermometer. The seven-hole probe and the fine-wire temperature sensor were designed and calibrated as part of this study. In addition, the payload also includes a slow-response temperature-humidity sensor, relatively fast humidity sensor as well as an infrared surface temperature sensor. For the onboard data-logging, a computer based on Raspberry Pi 4 is used. The whole system has been successfully tested at the Tsimlyansk research station, Russia.

Estimating and measurement of atmospheric optical turbulence according to balloon-borne radiosonde for three sites in China.

The distribution of optical turbulence (Cn2 profiles) is the fundamental parameter closely related to the design and application of optoelectronic systems. Since systematic direct measurements of optical turbulence for many climates and seasons are not available, it is useful to estimate Cn2 effectively from the routine meteorological parameters. The Cn2 profiles are estimated by routine meteorological parameters based on the Tatarskii model, and the estimated results are compared with the corresponding radiosonde measurements from the field campaigns at Rongcheng (122.37∘E, 37.15∘N), Taizhou (121.42∘E, 28.62∘N), and Dachaidan (95.35∘E, 37.74∘N) in China. The agreement between the estimation model and the measurement is very close, except for a portion of the atmosphere where it showed considerable difference. Additionally, statistical operators are used to quantify the performance of the estimated model, and the statistical results also show that the estimated and measured Cn2 profiles are consistent well. Furthermore, the integrated parameters (such as the Fried parameter, r0) from radiosonde measurement are 7.92 cm, 5.39 cm, and 3.68 cm at Rongcheng, Taizhou, and Dachaidan, respectively. Therefore, the Cn2 profiles and their characteristics in these typical climate sites provide useful information to assess the effect of laser transmission in the atmosphere, which are usually used in the design of optoelectronic systems and astronomical site testing.

Measurement and analysis of atmospheric optical turbulence in a near-maritime environment

The index of refraction structure constant, characterizing the intensity of optical turbulence, describes the disruption of a propagating electromagnetic beam passing through an inhomogeneously heated turbulent environment. In order to improve predictive models, it is critical to develop a deeper understanding of the relationships between environmental parameters and optical turbulence. To that end, an overwater, 890 m scintillometer link was established along the Chesapeake Bay adjacent to the Severn River in Annapolis, Maryland. Specifically, data from the scintillometer, as well, as numerous meteorological parameters were collected over the period of approximately 15 months to characterize a scintillometer link in the near-maritime environment. The characteristics of this near-maritime link were distinct from those observed in prior over-land and open ocean links. Further, existing macro-meteorological models for predicting from environmental parameters developed for open-ocean links were shown to perform poorly in the near-maritime environment. While the offshore adapted macro-meteorological model demonstrated lower prediction error, this study suggests that new models could be developed to reduce prediction error in the near-maritime environment. The complete data set, including measurements, and to our knowledge, one of the first to extend beyond one year, is available.

A New Weighting Method by Considering the Physical Characteristics of Atmospheric Turbulence and Decorrelation Noise in SBAS-InSAR

Time series of ground subsidence can not only be used to describe motion produced by various anthropocentric and natural process but also to better understand the processes and mechanisms of geohazards and to formulate effective protective measures. For high-accuracy measurement of small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), atmospheric turbulence and decorrelation noise are regarded as random variables and cannot be accurately estimated by a deterministic model when large spatio-temporal variability presents itself. Various weighting methods have been proposed and improved continuously to reduce the effects of these two parts and provide uncertainty information of the estimated parameters, simultaneously. Network-based variance-covariance estimation (NVCE) and graph theory (GT) are the two main weighting methods which were developed on the basis of previous algorithms. However, the NVCE weighting method only focuses on the influence of atmospheric turbulence and neglects the decorrelation noise. The GT method weights each interferogram in a time series by using the Laplace transformation. Although simple to implement, it is not reasonable to have an equal weight for each pixel in the same interferogram. To avoid these limitations, this study presents a new weighting method by considering the physical characteristics of atmospheric turbulence and decorrelation noise in SBAS-InSAR images. The effectiveness of the proposed method was tested and validated by using a set of simulated experiments and a case study on a Hawaiian island. According to the GPS-derived displacements, the average RMSE of the results from the new weighting method was 1.66 cm, indicating about an 8% improvement compared with 1.79, 1.80 and 1.80 cm from the unweighted method, the NVCE method and the GT method, respectively.

Measurement and analysis of atmospheric optical turbulence in Lhasa based on thermosonde

In this paper, we have analyzed the wind, temperature and optical turbulence index structure constant (Cn2) that are directly measured for the first time at Lhasa, Tibet. Unlike other mid-or-low latitude regions, the wind speed in Lhasa increases with the altitude according to the wind profiles, besides a strong wind speed near the tropopause. The temperature profiles indicate a large temperature change near the tropopause. The optical turbulence profiles show daily variation. When the altitude is below 12 km, except for individual points, the Cn2 values during morning and evening are basically in the same range of 10−17-10−15 m-2/3. When altitude is above 12 km, the intensity of turbulence during the morning in Lhasa is 1–2 orders of magnitude larger than that of the evening. In addition, we propose a turbulence profile model on the basis of Hufnagel-valley model to calculate the integrated values of the refractive index structure constants of the entire atmosphere, such as the Fried parameter, the seeing, the coherence time and the isoplanatic angle. The mean atmospheric coherence length r0 is 5.77 cm. Differences in these parameters between morning and evening also illustrate the stronger turbulence in the morning than evening.