Turbulence Detection in the Atmospheric Boundary Layer Using Coherent Doppler Wind Lidar and Microwave Radiometer

Abstract

The refractive index structure constant (Cn2) is a key parameter used in describing the influence of turbulence on laser transmissions in the atmosphere. Three different methods for estimating Cn2 were analyzed in detail. A new method that uses a combination of these methods for continuous Cn2 profiling with both high temporal and spatial resolution is proposed and demonstrated. Under the assumption of the Kolmogorov “2/3 law”, the Cn2 profile can be calculated by using the wind field and turbulent kinetic energy dissipation rate (TKEDR) measured by coherent Doppler wind lidar (CDWL) and other meteorological parameters derived from a microwave radiometer (MWR). In a horizontal experiment, a comparison between the results from our new method and measurements made by a large aperture scintillometer (LAS) is conducted. The correlation coefficient, mean error, and standard deviation between them in a six-day observation are 0.8073, 8.18 × 10−16 m−2/3, and 1.27 × 10−15 m−2/3, respectively. In the vertical direction, the continuous profiling results of Cn2 and other turbulence parameters with high resolution in the atmospheric boundary layer (ABL) are retrieved. In addition, the limitation and uncertainty of this method under different circumstances were analyzed, which shows that the relative error of Cn2 estimation normally does not exceed 30% under the convective boundary layer (CBL).

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

“…3,8,9 Atmospheric turbulence also has important practical needs in aerospace, environmental monitoring, and optoelectronic systems. [8][9][10] Wind has a significant impact on the distribution of dispersion systems, turbulence distribution, and thermal blooming effects in the field of nonlinear optics. 3,11,12 Therefore, it is crucial to simultaneously detect information on atmospheric transmittance, turbulence, and wind in the laser transmission path.…”

“…With the development and progress of computer technology, laser technology, sensors, and other related technologies, there has been significant progress in the methods of obtaining atmospheric transmittance, turbulence, and wind. 3,10,[12][13][14][15][16] Atmospheric transmittance can be obtained by simulation with atmospheric transport modeling software, but for a real-time changing atmospheric system, there is always a discrepancy between model calculations and actual conditions, so accurate real-time measurements are needed to obtain atmospheric transmittance. 14,[17][18][19] The commonly used direct measurement method is usually to find a star with constant radiation (such as the Sun) and observe this radiation source by optical means (spectrometer, filter, grating, etc.)…”

“…11 For remote sensing measurement means (such as wind profile radar, acoustic radar, and microwave radar), the measurement accuracy is often insufficient due to the influence of surface clutter, resulting in insufficient measurement accuracy, or large size and not conducive to mobile observation. 10,24,25 LiDAR wind measurement can be divided into coherent Doppler LiDAR and direct LiDAR based on different detection principles. 24,26 The direct wind LiDAR system can detect convective and stratospheric wind fields, but its volume is relatively large and its subsequent optical path is complex, making it difficult for system integration and mobile observation.…”

“…15,23,27,28 And LiDAR can detect atmospheric transmittance, turbulence, and wind data along any designated path on the target path. 3,10,15,22,27 For laser atmospheric transmission, it is possible to accurately obtain the attenuation characteristics and intensity distribution characteristics of the specified direction laser, as well as the information of wind which affects atmospheric transmittance and thermal blooming. 27,29 Due to the transition zone and blind zone of LiDAR, the detection of turbulence in the near field is limited, and real-time detection of turbulence in any direction also faces enormous challenges.…”

“…Wind can obtain high-precision wind field data of measured height through in-situ measurement (wind cup, anemometer, and sounding balloon); however, in-situ measurement will be limited by time and space 11 . For remote sensing measurement means (such as wind profile radar, acoustic radar, and microwave radar), the measurement accuracy is often insufficient due to the influence of surface clutter, resulting in insufficient measurement accuracy, or large size and not conducive to mobile observation 10 , 24 , 25 . LiDAR wind measurement can be divided into coherent Doppler LiDAR and direct LiDAR based on different detection principles 24 , 26 .…”