Development of a portable water vapor profiler in the lower troposphere using a small Raman lidar

我们开发了一种可移动的拉曼激光雷达，用于在200米左右的高度进行水汽剖面分析，这是l波段风廓线雷达的下边界。采用SHG为532 nm的小型Nd:YAG激光器进行传输，通过35.5 cm的望远镜，用光子计数系统接收相同波长（532 nm）的N2拉曼（607 nm）和H20拉曼（660 nm）散射。该系统在日本滋贺市滋垣MU观测站长期安装，可观测200 m左右的水汽混合比。系统校准系数在4 - 5%的偏差范围内没有变化超过6个月。除了低空云或雾的罕见情况外，大部分时间都可以很好地描绘水蒸气。当我们将系统调整为使用更大的虹膜时，可以在3 - 4 km高度观测到水蒸气混合比曲线。这种激光雷达经过改进，可以通过网络远程控制。另一方面，在水平方向进行了观测，并在车辆上进行了实地观测。我们发现，在柴垣天文台周围的国家森林上空，波浪蒸汽的波动幅度高达10%，并且与气溶胶强度相关。成功测量了麻生山中田火山气体中的水蒸气含量，这是首次对火山气体中的水蒸气进行遥感测量。如上所述，作为小型拉曼激光雷达的应用，这项研究取得了比我们一开始预期的要多得多的成果。

We have developed a transportable Raman lidar for water vapor profiling at around 200 m altitude, which is the lower boundary of a L-band wind profiler radar. A small Nd:YAG laser with a SHG of 532 nm is used for transmission and the same wavelength (532 nm), N2 Raman (607 nm) and H20 Raman (660 nm) scatters are received with a photon counting system, by means of a 35.5 cm telescope. The water vapor mixing ratio around 200 m could be observed both day and night, and the system was equipped at the Shigaraki MU observatory, Shiga, Japan for a long time. The system calibration factor did not change for more than 6 months within a deviation of 4 - 5 %. Water vapor could be profiled well for most of the times except for a rare case of the low altitude clouds or fogs. When we adjust the system to use a larger iris, water vapor mixing ratio profiles could be observed up to 3 - 4 km altitude. This lidar has been improved to be controlled remotely through a network. On the other hand, observations in a horizontal direction as well as a field observation on board a vehicle have been carried out. We found that fluctuations of waver vapor as large as 10 % over the national forest around Shigaraki observatory, as well as correlation with aerosol intensity. The measurement of water vapor content in the volcanic gas emitted from Nakadake, Mt. Aso has been successfully carried out, which is the first time of the remote-sensing measurement of H20 in the volcanic gas. As mentioned above, this study has achieved much more than we had expected at the beginning, as an application of a small Raman lidar.