Atmospheric Optical Turbulence Profile Measurement and Model

From August 4th to 30th, 2020 and from November 27th to December 25th, 2020, 11 a self-developed radiosonde balloon system was used to observe high-altitude atmospheric 12 optical turbulence at three sites in northwestern China, and an improved model based on the 13 observational data was established. Through comparative analysis of the observational data 14 and the improved model, the distribution characteristics of atmospheric optical turbulence 15 under the combined action of different meteorological parameters and different landform 16 features in different seasons were obtained. The improved model can show the variation of the 17 detailed characteristics of turbulence with the height distribution, and the degree of 18 correlation with the measured values is above 0.82. The improved model can provide a 19 theoretical basis and supporting data for turbulence estimation and forecasting in 20 northwestern China. 21


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The atmospheric refractive index structure constant ( ) is commonly used to 38.9, E: 100.4), using the radiosonde developed by the Anhui Institute of Optics and Fine

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Mechanics, Chinese Academy of Sciences. The records of the radiosonde balloon (hereinafter 87 referred to simply as 'the balloon') released during the experiment are shown in Table 1 wind speed, wind direction, air temperature, relative humidity and pressure, respectively. The 108 data measurement and conversion module performs unified coding of data format and baud 109 rate, and transmits the signal through the antenna after secondary modulation of 32.8 kHz and 110 400 MHz. Received through the antenna, the signal enters the receiving system; then, after 111 filtering and amplifying, the signal is converted in the receiver to obtain a 32.8 kHz signal, 112 before then being amplified and demodulated by the serial port and finally sent to the 113 computer for processing and storage. The response range of the micro temperature sensor is 114 0.1-30 Hz, so the minimum temperature fluctuation standard deviation of the corresponding 115 measurement is ≤ 0.002℃.

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For fully developed turbulence, it is assumed that Kolmogorov's locally uniform isotropic 118 turbulence theory is satisfied (Kolmogorov, 1968). The relationship between the temperature 119 structure constant T 2 and the temperature difference between two points in space (distance r) 120 is as follows: where 0 ≪ ≪ 0 , in which l0 and L0 are the inner and outer scales of the turbulence, 122 respectively; T is the atmospheric temperature (℃), and then T(x) and T(x + r) are the 123 temperature of two points in space (distance r), respectively; and ⟨⟩ represents the ensemble 124 average. The value of r is 1 m, which is the spatial distance between the two micro 125 temperature sensors in this study. The core of the micro temperature sensor is a platinum wire 126 with a diameter of about 20 μm and a resistance of about 10 Ω. The change of air temperature 127 at two points in space sensed by the micro temperature sensor is ΔT, which is converted to 128 electrical resistance change ΔV. ΔV is related to ΔT as follows: where A is the calibration coefficient. T 2 can be obtained by substituting equation 2 into 130 equation 1. In the visible and near-infrared wavelengths, the fluctuation of refractive index is 131 mainly caused by temperature fluctuation, and the influence of relative humidity can be 132 ignored. Therefore, the refractive index structure constant n 2 can be calculated as 133 = 7.9 × 10 .
According to the locally uniform isotropic theory, Tatarski obtained the relationship 134 between measured meteorological parameters and the estimated as (Tatarski model) 135 (Tatarski, 1961) 136 where α is a constant and the value is 2.8, L0 is the outer scale of turbulence, θ is potential 137 temperature (K), and his height above ground (m). The conversion relationship between 138 potential temperature θ and air temperature T is = .
. It can be found from where W is the root-mean-square wind speed at a height 5-20 km (m/s), V(h) is the wind 149 speed at a certain height (m/s), and A is a parameter describing the intensity of atmospheric where S is wind shear; u and v are radial wind speed and lateral wind speed, respectively; and 160 dT/dh is the vertical temperature gradient.

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Comparison of profiles estimated by different outer models shows that high-altitude 162 wind shear and temperature gradients may be the main factors that induce optical turbulence 163 (Cai et al., 2018). Therefore, it is more realistic to associate outer-scale L0 with high-altitude     Table 2. 276