A direct detection 1.6 μm DIAL with three wavelengths for high accuracy measurements of vertical CO_2 concentration and temperature profiles

摘要

The accurate vertical CO_2 profiles in the troposphere are highly desirable in the inverse techniques to improve quantification and understanding of the global budget of CO_2 and also global climate changes. Moreover, wind information is an important parameter for transport simulations and inverse estimation of surface CO_2 flux. A differential absorption lidar (DIAL) is an attractive method for obtaining vertical CO_2 profiles and we have developed an 1.6μm DIAL system to perform simultaneous measurements of CO_2 concentration, atmospheric temperature profile and wind profile. The absorption cross sections of gas and air density depends on atmospheric temperature and pressure. Then precise temperature and pressure profiles are necessary for accurate CO_2 mixing ratio measurement by DIAL. Laser beams of three wavelengths around a CO_2 absorption line are transmitted alternately to the atmosphere for simultaneous measurements of CO_2 concentration and temperature. The receiving optics include the near-infrared photomultiplier tube and a fiber Bragg grating (FBG) filter to detect a Doppler shift.