Lidar Observations Of Fe And Na Meteor Trails And Technique Of All-time Observation Of Na Layer

Approximately 100 metric tons of extraterrestrial matter per day enters the Earth's atmosphere and eventually settles on the ground. However, there is little knowledge about the process of meteoroid ablation. The input flux of metal resulting from meteoroid ablation is a key parameter of the model of metallic layer but has not been measured yet. It is considered that metallic atoms, such as sodium, kalium, iron, calcium, and et al., gathered in the mesopause (about 80-110km), are originated from the ablation of meteoroids, but relationship between the ablation of meteoroids and metal atom layers is not clear. Another interesting phenomenon is the sporadic metal layers, characterized by large density enhancements in a narrow altitude range. Although various mechanisms of the formation of the sporadic metal atom layers have been put forward since sporadic layers were discovered, none of them can completely explain all the observed phenomenon associated with the sporadic layers. Lidar is extensively applied in the exploration of the earth's atmosphere, especially in the study of atomic metal layers in mesopause. Nevertheless, due to the solar radiation, most of the lidars can only operate during night. It's necessary to develop lidars which can work continuously in a diurnal circle.This dissertation first introduces the results of the meteor trails observed by the Fe and Na resonance fluorescence lidar of Wuhan University, followed by the technique of the daytime lidar observation of sodium layers based on the Fabey-Perot Etalon (FPE). At last, the behaviors of sporadic Fe and Na layers in small time scale observed by two lidars are presented. The specific researches are as follows:1. The features of meteor trails and meteoroid ablating process are shown based on nearly two years observations of Fe and Na lidars at Wuhan (30°N,114.4°N). A total of 155 Fe trails and 136 Na trails were registered respectively from the 260-h Fe and 320-h Na photon count profiles, which yield a trail rate 0.6 h-1 for Fe and 0.43 h-1 for Na. Their statistical characteristics are presented. The altitude distributions of Fe and Na trails show that most lidar-observed meteor trails, particularly those strong trails, tend to occur around the peak of the regular metal layer, while the weak trails tend to occur on its bottom and top. The mean altitude of Na trails is-2 km higher than that of Fe trails. The mean atom input fluxes from the lidar meteor trail measurements are 1.5×105 cm-2 s-1 for Fe and 1.4×104 cm-2 s-1 for Na. The two values provide a unique quantitative observational basis for setting the meteor input fluxes of Fe and Na in the metal layer models. During 210-h simultaneous and common volume observations,8 two-element trails are observed. The observed two-element meteor trails yield the mean Fe/Na abundance ratio of～9.0. much smaller than the average atomic ratio of Fe to Na in chondritic meteorite. The features of lidar-observed meteor trails strongly show that micro-meteoroids ablate differentially in the earth's up atmosphere.2. Based on the night-operating Na resonance fluoresces lidar, a technique of daytime observation of Na metal layer have been realized. To reduce the solar radiation induced noises, we decrease the Field Of View (FOV) of the telescope to 0.3mrad and meantime compress the divergence angle of laser beam by a 5X beam expander to match the FOV. More important, a FPE is used as a narrowband filter. By doing these, the intense background noise in the daytime is reduced so that a continuous 24-hour measurement of Na layer over Wuhan is achieved. Different from other groups, we use a FPE instead of PFI to reduce the complexity and cost. Because of the advantages of taking FPE as narrowband filters compared to a sodium-vapor dispersive Faraday filter, such as stability, wavelength adaptability and high transmittance, it is a good option for daytime observation of other daytime lidars.3. By analyzing the high resolution data of sporadic Fe and Na layers, it is found that there are similar temporal and spatial variational characteristics between sporadic Fe layers and Na layers in short time scale. Furthermore, each sporadic Fe and Na layer is composed of a series of short time scale density enhancement. The density variances of Fes layer are more intense than Nas layer. According to the observations of meteor trails, the input flux of Fe is also found to be much larger than that of Na. This provides a clue to the potential mechanism of sporadic layer—meteoroid ablation. The relationship between them demands to be further ascertained.