The characteristics and laws of atmospheric turbulence in the atmospheric boundary layer over the ocean region are studied, which can be employed to guide the parameter setting of the adaptive optical system. Therefore, the influence of turbulence is greatly reduced, and the imaging quality and the performance of the photoelectric system are improved to meet the engineering application. In this method, the effects of temperature, humidity, and wind velocity on the calculation results are fully considered, and the physical phenomena that produce optical turbulence effects are fully captured. Additionally, the ultrasonic anemometer array has the advantages of high spatial and temporal resolution and high automation degree, which greatly improves data continuity and reliability. Finally, continuous all-weather measurement can be carried out for a long time, and the limitation of high labor costs and sensitivity to weather conditions is effectively compensated.
Based on the multi-layer ultrasonic measurement experiment in the tropical South China Sea, the ultrasonic wind velocity in three directions in the air is measured, and the velocity structure constant is obtained. In addition, the refractive index structure constant is calculated by combining the refractive index gradient affected by temperature and humidity. Firstly, according to the fluctuation relations of atmospheric refractive index with temperature, humidity, and pressure, the relationships of refractive index structure constant with potential temperature structure constant, humidity structure constant, and temperature-humidity correlation structure constant are obtained. At the same time, the velocity structure constant obtained from Tatarskii theory and the relationship between the energy dissipation rate and the velocity structure constant are discussed. Secondly, based on the relationship between atmospheric refractive index and density, the major large-scale refractive index gradients are removed to ensure consistency and maintain the basic properties of the gradient origin, i.e., turbulent mixing. The expression of the turbulent refractive index gradient is obtained through the high frequency (small scale) fluctuation in the refractive index gradient which determines the refractive index structure constant.
1) This paper verifies the feasibility and reliability of the method by analyzing and comparing the 144-day raw data (Fig. 3). The correlation analysis between the ultrasonic anemometer array calculation method and the ultrasonic single point virtual temperature estimation method is shown in Fig. 6. The Spearman correlation coefficient (R) reaches 0.96113; a fitting slope of 0.95096 is obtained through the least squares linear fitting, and the intercept is 0.48645. The results of the ultrasonic single point virtual temperature estimation method and the ultrasonic anemometer array calculation method are shown in the horizontal and vertical coordinates respectively. The results indicate that both methods can reflect the daily variation of turbulence in the real atmosphere. The result of the ultrasonic anemometer array estimation method at some time is larger than that of the ultrasonic single point virtual temperature estimation method, and the consistency of the two methods also fluctuates slightly. However, the trend is the same with high correlation, which proves the feasibility of the method to estimate the refractive index structure constant of the ultrasonic anemometer array estimation method. 2) The effects of temperature, humidity, and wind velocity on the calculation results are fully considered, and the physical phenomena that produce the optical turbulence effect are fully captured (Table 3). The correlation coefficients between the estimated temperature and the temperature structure constant are 0.98, 0.8, 0.7, and 0.6, respectively. However, the correlation between the estimated results of the ultrasonic anemometer array and the velocity structure is very low, and the correlation coefficient is close to 0. The correlation coefficients with relative humidity, virtual temperature, temperature gradient, and wind shear are 0.8, 0.8, 0.5, and 0.4, respectively. In conclusion, the all-day virtual temperature exerts a major influence on the calculation results, in which the humidity affects the results by affecting the ultrasonic virtual temperature. In addition, the influence of the dynamic factors on the calculation results cannot be ignored, and it further shows the comprehensiveness and superiority of the estimation method of the ultrasonic anemometer. Notably, the dependence of the refractive index structure constant on temperature-related parameters such as ultrasonic virtual temperature, temperature gradient, and relative humidity is lower at night than during the day and is negatively correlated at night. The correlation with the average wind velocity and wind shear of the dynamic factor parameters increases significantly.
1) The correlation analysis shows that the average correlation coefficient is 0.85 with the highest value of 0.99 and the lowest value of 0.71, which is compared with the 174-day results of the ultrasonic anemometer array. By error analysis, the average
