Due to variations of influencing factors and atmospheric effects, the propagation efficiency (transmittance, thermal distortion parameter and 63.2% encircled average power density) of high-energy laser propagating in the atmosphere is uncertain. In this paper, aiming to evaluate the uncertainty of propagation efficiency and identify the main influencing factors, the following research is made. (1) The scaling law is established through numerical simulation, which is suitable for the Gaussian waveform laser and considers the interaction between different effects. (2) The probability distribution characteristics and uncertainty of propagation efficiency are evaluated in the horizontal propagation scenario by the Latin hypercube sampling method. (3) The Elementary Effect Test is applied, with the aim to give the parameters prioritization and identify the crucial parameters affecting encircled average power density. The results show that the uncertainty and parameters prioritization of propagation efficiency vary with the propagation distance. Considering the results of the Elementary Effect Test at different distances, the crucial parameters for 63.2% encircled average power density are transverse wind speed, absorption coefficient, power, and initial beam quality. This research is of great significance for the application of laser systems.
The atmospheric boundary layer is the layer most closely associated with human life, and the occurrence and development of atmospheric optical turbulence in the atmospheric boundary layer are of great significance for atmospheric optical transport, etc. Meanwhile, the study of optical turbulence in the whole ocean environment is also of vital importance, and it is important to statistically analyze the variations of the atmospheric optical turbulence parameters by using the existing optical turbulence models due to the lack of ocean data. In this paper, the atmospheric turbulence parameters are estimated by different external scale models (HMNSP99, Dewan, HV and WSTG models), and the atmospheric refractive index structure constant(C2n) computed by different models are compared by using the coastal sounding measured data, through error analysis and correlation studies, it has been found that the HV model changes with height in the atmospheric boundary layer, but cannot reflect the characteristics of the change of C2n well. The HMNSP99 model is about one order of magnitude smaller than the measured data, while the WSTG model is about one order of magnitude larger than the measured data. However, the trends of the two models are in good agreement. In contrast, the Dewan model and the HMNSP99 model show good consistency with the measured data, and the correlation is above 0.6. The Dewan and HMNSP99 model are closer in magnitude to the measured data, therefore, when studying optical turbulence parameters in the atmospheric boundary layer, the Dewan and HMNSP99 models are more reliable. They can also provide key indicators for optical turbulence prediction and astronomical site selection.
We verify a simple alternative method to estimate the Fried parameter over a horizontal propagation path using the refractive index measured by a pair of micro-thermometers. The results show a relatively reliable estimate, especially when the optical turbulence in the path is relatively strong. Moreover, we also discuss the relationship between the Fried parameter value with the overall intensity of optical turbulence and the length of the propagation path theoretically. The influence of these two factors shows a prominent exponential characteristic, which also can be speculated from the formula.
Using the continuous observation data of wind profiler radar, the temporal and spatial variation characteristics of wind direction and wind speed in the summer Boundary layer atmosphere wind field in the southern foot of Tianshan Mountains in Xinjiang are analyzed. The preliminary exploration of the impact of low-level jet streams on near surface atmospheric turbulence activity is of great significance for studying laser atmospheric transport, triggering convective weather, and atmospheric pollution and diffusion. Experimental area is located in a valley, and the circulation characteristics dominated by Mountain breeze and valley breeze are the basic characteristics of the daily variation of the wind field in the region, and also the main reason for the occurrence of low-level jet. Through statistics and analysis, it was found that the summer turbulent activity near the surface in this area is strong, which is caused by thermal stress on the underlying surface. During the day, the surface temperature is high, and there is a strong exchange of air flow near the surface with the upper layer, resulting in strong turbulent activity. In the evening, it may be the low-level jet that brings the horizontal wind shear near the ground, which intensifies the turbulence vortex activity and leads to the occurrence of turbulence.
A comprehensive site testing campaign was carried on in the northwestern area of China from July to November 2022. We conduct the study focusing on the daytime optical turbulence and precipitable water vapor long-term variation in this area, which are essential for time-domain astronomy and site scheduling. A relatively quiet and dry atmosphere situation that benefits observation can be more easily found in September and October. The so-called ’conversion time’, an excellent condition for observation at dawn and dusk, behaved differently in different months. Meanwhile, better observation conditions can be found at dawn in July, August and September but at dusk in October and November in the daytime.
As the "roof of the world", the Tibetan Plateau (TP, in short) exhibits the distinctive "heat island" characteristics compared to the same latitude region, and plays a decisive role in the atmospheric thermal structure of the TP and surroundings. ERA5 reanalysis data from January 2017 to December 2020 are used to analyze the meridional distribution characteristics of the average skin temperature and the potential temperature lapse rate at coldest point tropopause (CPT) in the highaltitude areas of the TP in summer. The Pearson correlation coefficient between the measured data and the reanalyzed data in the Da Qaidam area (95°21’E, 37° 51’N, 3180m above sea level (ASL)) in August 2020 is 0.88, indicating good usability of the reanalyzed data. The average skin temperature of TP in summer shows a feature of "high in the south and low in the north", which is ~20° higher than the atmospheric temperature of surrounding low-altitude area at the same altitude. The distribution of heat sources on the TP not only affects the location and intensity of the South Asian High, but also aggravates the thermal difference between land and sea, which promotes the formation of the Asian summer monsoon. The strong heat source in the southern TP, on the one hand, directly affects the atmospheric thermal structure over the southern TP through enhancing upward transportation; on the other hand, indirectly affects the high-altitude atmospheric thermal structure of the region north to TP through the background transportation of westerly and summer monsoons. The potential temperature lapse rate at CPT over the high-altitude area of TP also has significant characteristics of north-south differences, indicating that the "heat source effect" can regulate the intensity of atmospheric turbulence.
In order to study the optical properties of marine aerosols, the optical thickness, wavelength index, spectral distribution, refractive index, single scattering albedo and elevation of aerosol particles were measured by means of solar radiometer, micro pulse lidar and automatic weather station in Qingdao, South China Sea, East China Sea and South China Sea from July to November 2019. The results show that the aerosol optical thickness measured by the shipborne data is smaller than that measured by Qingdao and islands, and the aerosol elevation range is about 0.4-0.7, The diurnal variation is relatively stable, and the distribution of aerosol colloidal product spectrum in the offshore and the open sea has the same change trend. The radius of the coarse mode is about 2.4 μm-3.6 μ M. compared with other data, the real part of the refractive index is larger, the imaginary part is smaller, and the difference in the long wave band is more obvious. The single scattering albedo basically does not change with the wavelength.
Lidar has been widely used in remote sensing of atmospheric environment because of its high spatial-temporal resolution and detection sensitivity. As the main noise source in lidar detection, solar background radiation is an important factor to determine target from background. The background noise, which is estimated by taking the average value of the lidar echo signal at a certain height, is usually removed directly. However, the background noise also contains some useful information on the whole layer of the atmosphere. In this paper, atmospheric radiation transmission model software MODTRAN 5.0 was used to simulate the lidar background noise under clear sky condition, combined with micro-pulse lidar (MPL) and meteorological element sounding data. The daytime background noise received by lidar were simulated by standard model method and user-defined model method. The standard model method uses standard atmospheric and aerosol model, which is the common way in traditional background radiation simulation. The user-defined model method uses aerosol and meteorological data measured in Maoming, Guangdong Province in October 2018 to build a user-defined atmospheric model. Results shows that the overall trends of the simulated background radiation from two methods are quite similar to the MPL observation. The user-defined model method can produce more consistent results with the observation than the standard model method, mainly due to that standard model cannot be completely consistent with the real experimental environment. The simulation results in this paper can be used to improve the daytime MPL retrieval, and can also be applied to the retrieving of aerosol particle size information and optical characteristics of cloud in further study.
Selecting the solar radiometer and ground-based laser-radar data of several typical regions, we could invert the laser-radar ratio of each region by using the entire aerosol optical thickness measured by the solar radiometer as a constraint, and we conducted vertical aerosol distribution observation research based on this. The average laser-radar ratio in the four regions of Delingha Qingha(i spring), Hefei Anhu(i summer), Zhangye Gansu (summer), and Maoming Guangdong(winter)are 38, 62, 47, and 17 respectively. Comparing with selecting fixed LR,the extinction tends to change with the height approximately similarly,but the values of the extinction at different heights are different evenly.The vertical distribution of aerosols in different spatial and temporal distribution characteristics.
The characteristics of wind profile radar signal-to-noise ratio, spectral width and vertical velocity under different rainfall in summer are summarized respectively. The range of signal-to-noise ratio, spectral width and vertical velocity varies with the level of rainfall amount. The difference between sunny days, light rain and others is obvious, and the difference between moderate rain, heavy rain and rainstorm decreases. On the basis of this, a method to identify the classification of rainfall using spectral width is proposed and validated, of which the accuracy rate can reach over 50%. In addition, the reasons that influence the identifying accuracy of the classification of rainfall by spectral width are also analyzed, and some improvement measures are put forward.
The long-term measurement of atmospheric aerosol is constructed via such equipment as visibility meter, optical particle counter, solar radiometer, automatic weather station, aerosol laser radar and aerosol scattering absorption coefficient measurer and so on during the year of 2010 and 2017 in the coastal areas of Guangzhou, China to study the optical parameter characteristics of atmospheric aerosol and establish the aerosol optical parameter mode in such areas. The effects of temperature and humidity on aerosol concentration, extinction and absorption coefficient are analyzed and the statistical characteristics of atmospheric temperature and humidity, visibility, extinction profiles and other parameters in different months are tallied, preliminarily establishing the atmospheric aerosol optical parameter pattern in Guangzhou coastal areas.
In this study, we investigate the fractal properties of optical turbulence profiles. Through rescaled range analysis, optical turbulence profiles roughly exhibit three different regimes. The effects of stratifications are the underlying mechanism contributing to this phenomenon. The results of detrended fluctuation analysis and multifractal detrended fluctuation analysis indicate that optical turbulence profiles have multifractal structure.
A portable imaging lidar using continuous wave(CW) laser is built for the remote sensing of aerosol in lower boundary layer. The output beam from a simple, stable powered CW laser no modulated is transmitted into the atmosphere, and backscattered light from along the visible beam path is imaged onto a charge-coupled-device (CCD) camera. It can be used to scan atmosphere from different angles. The horizontal measurements are obtained and compared with those obtained by the America Belfort model 6230A visibility meter. The horizontal results show that the average relative error is below 20%. The temporal-spatial variations of aerosol profiles in low boundary layer are presented and discuss.
When light-wave propagates in the turbulent atmosphere, it will be affected by atmospheric turbulence and brought various effect , such as flicker, phase fluctuation. So the investigation of atmosphere optics parameters always must be important. Because of the differences in geographical conditions and climate, atmospheric optical parameters in different regions have different spatial and time distribution. In this paper, various atmosphere optics parameters are measured by atmosphere optics parameters measure system in the Delingha area of Qinghai province and Xinjiang Korla area, through statistical analysis of atmospheric optical parameters corresponding area, we know clearly different geographical climate character of the northwest area of atmospheric optical parameters of structure characteristics, the results provide a valuable reference for further practical engineering application of optical remote sensing location and atmospheric optical transmission and atmospheric properties.
The distribution of parameters such as sunshine hours, precipitation, and visibility were obtained by analyzing the meteorological data in 906 stations of China during 1981~2012. And the month and annual variations of the parameters in some typical stations were discussed. The results show that: (1) the distribution of clear days is similar to that of sunshine hours, the values of which decrease from north to south and from west to east. The distributions of cloud, precipitation and vapor pressure are opposite. (2) The northwest areas in China have the characteristic such as low precipitation and vapor pressure, small cloud clever, and good visibility, which are the general conditions of astronomical site selection. (3) The parameters have obvious month variation. There are large precipitation, long sunshine hours and strong radiation in the mid months of one year, which are opposite in beginning and ending of one year. (4) In the selected stations, the value of vapor pressure decreases year by year, and the optical depth is similar or invariable. All the above results provided for astronomical site selection.
The atmospheric coherent length is an important parameter when study the influence of atmosphere to the light propagation. Two kinds of methods are often used to measure the coherent length. One method uses the optical technique, measure the arrive angle of star objects, another method uses the balloon born thermal-meters, which can get profile of structure constants of refractive index, and then the coherent length can be calculated from the integral of structure constants of refractive index.
Because the time scale and space scale are different in these two methods, the results of them are different although the magnitude of results is near. In this paper, a new way to compare the results of two methods above is advised. It is based on the characters of the structure constants of refractive index, and the profile data of balloon born instrument. Not only the average coherent length can be gained, and also the distribution of coherent length can be estimated. So the results of two methods can be compared quite well. The characters of coherent length are also discussed in this paper.
The optical turbulence in atmosphere, especially in the atmospheric boundary layer, plays an important role in the propagation of laser beam. It can make the fluctuation of density and distortion of wave front. The balloon borne radiosonde with temperature fluctuation sensors is often used to study the turbulence profiles in the atmospheric boundary layer. But it can not get the continuous temporal and spatial variance of turbulence structure. In this paper, Doppler sodar and microwave wind profiler are used to study the optical turbulence structure in the atmospheric boundary layer. The fluctuation in the index of refraction can be defined as optical turbulence, so the structure constants of refractive index Cn2 is often used in such problems. Not only the wind profiler but also the high solution temporal and spatial turbulence structure can be gained with Doppler radar. From these experimental results, we study the relative structure of turbulence on different height, study the spectra of Cn2 on different. These results are compared to previous results get with temperature fluctuation sensors. In addition, the seasonal variance of turbulence structure is also discussed in the paper.
In this paper the recent decades, radar remote has played a more and more important role in atmospheric research. In this paper we discuss the 915MHz microwave Doppler radar, which obtain the mean wind profiles in the Atmospheric Boundary Layer. The radar receives backscatter from clear- air's refractive-index fluctuations. It can provide vertical profiles of horizontal wind speed and direction and vertical wind velocity. It can also provide virtual temperature profiles with a Radio Acoustic Sounding System. In this paper, we discussed the radar parameters and some atmospheric factors that can affect the result of the radar. We also discussed the result of radar under different meteorology condition. The refractive index structure function parameter, Cn2, can also be taken from Doppler velocity spectra measured by the radar.
The Atmosphere Boundary Layer is the most accessible layer of earth's atmosphere. It is also the most important layer to the atmospheric research. We measure the wind and turbulence profile in the ABL with a Doppler Sodar which can cover from 30m up to 300 500m, and a boundary microwave wind profiler, which can cover from 100m up to 3000m. With all these experimental sets, we can get the continuous profiles of wind, refractive index structure function parameter, Cn2 and the wind structure Cv2 from the ground up to 3000m. From the result of these sets, we can obtain the characteristics of profiles and diurnal variations.
The Atmospheric Boundary Layer (ABL) is the most accessible layer of Earth's atmosphere. It is also the most important layer to the atmospheric research. We measure the wind arid turbulence profile in the ABL with a Doppler Sodar which can cover from 30m up to 300 500m, and a Boundary Microwave Wind Profiler, which can cover from 1OOm up to 3000m. With all these experimental sets, we can get the
continuous profiles of wind, refractive index structure function parameter, C2 and the wind structure function C2 from the ground up
to 3000m. From the results of these sets, we can obtain the characteristics of profiles and diurnal variations.
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