Tunable diode laser measurement of pressure-induced shift coefficients of CO2 around 2.05 μm for Lidar application

Atmospheric carbon dioxide (CO2) is one of the main contributors to the greenhouse effect. A global monitoring of CO2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (2001)III←(0000)I band of CO2 at 2.05 μm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.

Research highlights► We report on air-shift coefficients for 8 absorption lines of CO2 at 2.05 μm. ► A high-resolution TDLAS coupled to a cryogenically-cooled cell was used. ► Temperature-dependencies of the air shift coefficients are also determined. ► These accurate parameters will help to reduce uncertainties on DiAL measurements.