Backscatter 2-μm Lidar Validation for Atmospheric CO2 Differential Absorption Lidar Applications

A 2-mu m backscatter lidar system has been developed by utilizing tunable pulsed laser and infrared phototransistor for the transmitter and the receiver, respectively. To validate the system, the 2-mu m atmospheric backscatter profiles were compared to profiles obtained at 1 and 0.5 mu m using avalanche photodiode and photomultiplier tube, respectively. Consequently, a methodology is proposed to compare the performance of different lidar systems operating at different wavelengths through various detection technologies. The methodology is based on extracting the system equivalent detectivity and comparing it to that of the detectors, as well as the ideal background detectivity. Besides, the 2-mu m system capability for atmospheric CO2 temporal profiling using the differential absorption lidar (DIAL) technique was demonstrated. This was achieved by tuning the laser at slightly different wavelengths around the CO2 R22 absorption line in the 2.05-mu m band. CO2 temporal profiles were also compared to in situ measurements. Preliminary results indicated average mixing ratios close to 390 ppm in the atmospheric boundary layer with 3.0% precision. The development of this system is an initial step for developing a high-resolution, high-precision direct-detection atmospheric CO2 DIAL system. A successful development of this system would be a valuable tool in obtaining and validating global atmospheric CO2 measurements.