一个新的海边光学湍流外尺度和C_n~2的廓线模式

2016年12月13日至2017年1月2日期间,在茂名博贺海洋气象科学实验基地,采用自行研制的湍流气象探空仪,获取了30份海边温、湿、压、风速、风向和C_n~2等探空数据.基于HMNSP99外尺度模式,利用海边的探空数据拟合得到一个茂名大气光学湍流外尺度经验公式.同时对实验测得的高空湍流廓线数据进行统计平均,然后基于Hufnagel-Valley模式拟合得到符合海边湍流廓线规律的统计平均模式(C_n~2sea model).根据Tatarski高空湍流参数化方案,将用茂名外尺度公式估算的C_n~2分别与探空测量的C_n~2以及用其他外尺度模式估算的C_n~2进行了比较.对其进行统计性分析发现,利用新拟合的茂名外尺度公式、HMNSP99,Dewan以及(Coulman等外尺度模式计算的log10C_n~2)与实测值的整体相关系数分别为0.924,0.848,0.763和0.651,在变化趋势和量级上都表现出较好的一致性;以上四种外尺度模式估算结果的误差都很小,其整体平均绝对误差和平均相对误差分别为0.514和2.963%,0.627和3.612%,0.943和5.439%,0.766和4.417%,新拟合的外尺度模式的误差最小.进一步验证了新的海边外尺度和C_n~2廓线模式的可靠性和有效性,此外还发现高空大气光学湍流的发生与风切变和温度梯度具有十分密切的关系,为光电工程在海边场景应用所需的大气光学湍流廓线模式提供支持.

A new model for the profiles of optical turbulence outer scale and Cn2 on the coast

Atmospheric optical turbulence severely restricts the performances of electro-optical systems. The turbulent atmosphere causes the intensity of a light beam to fluctuate or scintillate, leads the light beam to wander and makes the images randomly displace, which directly relates to the refractive index structure parameter C_n². Therefore the knowledge of C_n² is essential to evaluate and to predict the effects of optical turbulence on electro-optical imagery systems. During the period from December 13, 2016 to January 2, 2017, 30 sets of sounding data, which include temperatures, humidities, pressures, wind speeds, wind directions and atmospheric refractive index structure parameters, are obtained by using a self-developed meteorological radiosonde for turbulence at Marine Meteorological Science Experiment Base at Bohe of Maoming. On the basis of the HMNSP99 outer scale model, an atmospheric optical turbulence outer scale formula of Maoming is obtained by fitting the sounding data. At the same time, the experimental data of the turbulence profiles are statistically averaged, and then based on the Hufnagel-Valley model, a statistical model is obtained, which is appropriate to the variation of the turbulence profile on the coast. According to Tatarski turbulence parameterization and the Maoming outer scale formula, the new estimated C_n² values are compared with their experimental observations and the results from other already defined models, respectively. Statistical analysis shows that the overall correlation coefficients of log₁₀(C_n²) between observed values and estimated values by using the new fitting Maoming outer scale formula, the HMNSP99 model, the Dewan model and the Coulman model are 0.924, 0.848, 0.763 and 0.651, respectively. Also, both the trends and magnitudes for these four outer scale models are consistent with each other. The errors of the above four outer scale models are very small:their overall average absolute errors and average relative errors are 0.514 and 2.963%, 0.627 and 3.612%, 0.943 and 5.439%, 0.766 and 4.417%, respectively, and the error of the Maoming outer scale model is smallest. The reliabilities and validities of the new outer scale and C_n² models are further verified. In addition, it is found that the occurrence of upper air optical turbulence is closely related to wind shear and temperature gradient. The results support the prediction of the atmospheric optical turbulence profile required for electro-optical engineering on the coast.