Two-micrometer heterodyne differential absorption lidar measurements of the atmospheric CO2 mixing ratio in the boundary layer

A 2 (mu)m heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre Simon Laplace, Laboratoire de Meteorologie Dynamique (Paris) to monitor the CO2 mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO2 is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.