Abstract: A high resolution laser heterodyne spectroradiometer, with a distributed feedback semiconductor laser operating near 1571 nm as the local oscillator and the sunlight as the signal light source, was built in this work to develop an efficient measurement method of atmospheric CO2 vertical profiles. Taking a narrow linewidth semiconductor laser (2 MHz) instead of sunlight as a simulated signal light source to measure the linear function of the developed system, the spectral resolution with 0.008 cm-1 was obtained. The solar tracker is used in the spectroradiometer to track and collect sunlight, and sunlight is modulated by a optical chopper and mixed with the local oscillator in a fiber to achieve heterodyne detection, and then the CO2 heterodyne absorption spectrum is obtained through demodulation using a lock-in amplifier. Finally, the experimentally measured CO2 heterodyne spectrum is normalized and fitted to retrieve the atmospheric CO2 vertical profiles by using the self-programmed optimal estimation algorithm. The results show that the total error of inversion with 9.5% has been achieved, and the variation trend of CO2 vertical profile agrees well with that reported in existing literatures, which proves the feasibility of the system for atmospheric CO2 vertical profiles measurement. In the future, we will further upgrade the system and realize long-term observation of atmospheric CO2 profiles in the region.

Key words: laser heterodyne, vertical profile measurement, optimal estimation algorithm, CO2, high spectral resolution