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激光雷达系统主要包括激光发射系统、回波接收系统和信息处理系统三部分,如图1所示。激光发射系统的核心是激励光源,通常选择能够发射短脉冲的单色高能量激光器,进入大气的激光脉冲与大气中的分子和悬浮粒子相互作用,产生吸收和散射等效应,作为光学接收天线的望远镜系统接收大气的后向散射信号,然后送入信息处理系统进行处理,通常主要由光谱分光器、光电探测器和计算机组成。
对于大气遥感的散射激光雷达,地面接收器接收的不同距离Z至Z+∆Z处的回波信号功率P(Z),即激光雷达方程,可表示为:
$$P\left( Z \right) = C \cdot {P_0} \cdot \Delta Z \cdot \frac{{{A_T}}}{{{Z^2}}} \cdot O\left( Z \right)\beta \left( {Z,\lambda } \right) \cdot T{r^2}\left( {Z,\lambda } \right)$$ (1) 式中:C为与探测器效率以及系统光路透射率等有关的系统常数;P0为激光脉冲发射功率;AT为望远镜的接收面积;∆Z=c·τ/2为探测路径长度,τ为探测积分时间;O(Z)为几何重叠因子,其表示发射激光束与接收望远镜视场的重合程度,在不完全重合时,其值小于1,当达到完全重合时,其值为1;β(Z, λ)为大气中某种被探测组分的后向散射系数(m−1·sr−1),表示高度Z处大气对激光的后向散射能力,可表示为某大气组分的分子数密度Nm(Z) (m−3)与其微分后向散射截面积(m2·sr–1)的乘积,或大气分子数密度N(Z) (m−3)与其等效微分后向散射截面积(m2·sr–1)的乘积,即
$$\beta \left( {Z,\lambda } \right) = {N_m}\left( Z \right) \cdot {\left( {\frac{{{\rm d}\sigma }}{{{\rm d}\Omega }}} \right)_m}\left( \lambda \right) = N\left( Z \right) \cdot \left( {\frac{{{\rm d}\sigma }}{{{\rm d}\Omega }}} \right)\left( \lambda \right)$$ (2) 从大气组分角度来看,大气后向散射系数β(Z, λ)包括大气分子后向散射系数βm(Z, λ)和气溶胶粒子βa(Z, λ)两部分,即β(Z, λ)= βm(Z, λ) +βa(Z, λ);Tr(Z, λ)分别是大气分子大气总透射率,其表达式分别为:
$${T_r}\left( {Z,\lambda } \right) = \exp \left[ { - \int_0^Z {\alpha \left( {Z,\lambda } \right){\rm d}Z} } \right]$$ (3) 式中:α(Z, λ)为大气总消光系数,通常由大气分子和气溶胶消光系数两部分组成,即α(Z, λ)= αm(Z, λ) +αa(Z, λ);而透射率Tr(Z, λ)的平方表明在激光雷达和探测距离Z之间激光能量来回两次受到大气分子和气溶胶粒子的衰减。
Research status and progress of Lidar for atmosphere in China (Invited)
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摘要: 激光雷达是一种主动遥感探测仪器,具有大探测范围、高时空分辨率与高精度的特点,在大气环境参数(气溶胶、CO2及臭氧等)及气象参数(温度、水汽、压力及风速风向等)探测方面获得了广泛的应用。随着近些年民众对雾霾类大气现象及气候变化的广泛关注,国家环境治理与气象预报部门以及行业企业等对大气观测技术的迫切需求,大气探测激光雷达在国内得到了快速的发展,并且取得了较好的研究成果。文中总结介绍了近些年国内大气探测激光雷达的研究进展与发展现状。根据探测对象的不同,激光雷达有米散射激光雷达、拉曼探测激光雷达、高光谱分辨探测激光雷达和差分吸收探测激光雷达等,文章较全面地介绍了目前比较常见的激光雷达在大气探测应用中的优缺点及其在不同探测对象中的应用,最后对激光雷达面临的技术瓶颈进行了总结与探讨,并对激光雷达的发展趋势进行了展望。Abstract: Lidar is an active remote sensing instrument, which has the characteristics of high precision and high spatial-temporal resolution. It has been widely used in the detection of atmospheric environmental parameters (aerosol, CO2, ozone, etc.) and meteorological parameters (temperature, water vapor, pressure, wind speed and direction, etc.). In recent years, atmospheric phenomena such as haze and climate change have been widely concerned by the public, and the national environmental governance and meteorological forecasting departments have an urgent demand for atmospheric observation technology. Atmospheric Lidar has been developed rapidly in China, and has achieved good research achievements. The research progress and development status of Lidar for atmospheric detection in recent years were introduced and summarized in this paper. According to the different detection objects detected by Lidars, Lidars can be classified as Mie scattering Lidar, Raman Lidar, high-spectral-resolution Lidar, differential absorption Lidar and et al. The advantages and disadvantages of all kinds of atmospheric detection Lidars and their applications in different detection objects were comprehensively introduced in this paper. Finally, the bottlenecks of Lidar technology were summarized, and the development trend of Lidar was also prospected.
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Key words:
- Lidar /
- atmosphere /
- aerosol /
- meteorological parameters
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