CEDAR: Vapor Filters: Developing New Measurement Capabilities for Narrowband Na Lidar

该项目是一项为期两年的努力，旨在启动开发用于中层顶区激光雷达测量的蒸汽过滤器。它提出了两种不同类型的蒸汽过滤器，它们的使用将为窄带钠荧光激光雷达增加新的测量能力。首先是一种基于法拉第色散的窄带通滤光片。该滤波器的有效带宽约为2 GHz，峰值透过率为85%，视场较宽。当用于夫琅和费线时，它可以比法布里-珀罗系统更有效地抑制天空背景光，比法布里-珀罗系统高出50倍以上，使Na温度激光雷达的白天操作变得实用。第二种是温度稳定的碘蒸汽池，用作传输滤光片。作为频率函数的I2蒸汽室的透射率在几GHz内变化很大。由于弹性散射和钠荧光信号以不同的频率出现，比较两个工作频率v2和vc的激光雷达回波，在通过和不通过I2蒸汽室的情况下，将为确定温度和量化弹性散射提供足够的信息。因此，在极冠区域使用具有良好特性的碘蒸汽过滤器和钠温度激光雷达，将能够同时监测温度分布和夜光云。

This project is a two-year effort to initiate the development of vapor filters for lidar measurements in the mesopause region. It proposes two different types of vapor filters whose use will add new measurement capabilities to the narrowband Na fluorescence lidar. First is a narrow band-pass filter based on Faraday dispersion in Na vapor near resonance. This filter has an effective bandwidth of approximately 2 GHz, 85% peak transmission, and wide field-of-view. When used at a Fraunhofer line, it can reject sky background light more effectively than a Fabry-Perot system by more than a factor of 50, making the daytime operation of the Na temperature lidar practical. Second is a temperature stabilized iodine vapor cell to be used as a transmission filter. The transmittance of the I2 vapor cell as a function of frequency varies considerably within a few GHz. Since elastically scattered and Na fluorescence signals occur at different frequencies, a comparison of lidar returns at the two operating frequencies, v2 and vc, with and without passing through the I2 vapor cell will provide enough information for the determination of temperature and quantification of elastic scattering. Therefore, the use of a well characterized iodine vapor filter with a Na temperature lidar in the polar cap region will allow simultaneous monitoring of temperature profiles and noctilucent clouds.