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We present the development of a multi-spectral, integrated-path differential absorption (IPDA) lidar based on a dual-comb spectrometer for greenhouse gas monitoring. The system uses the lidar returns from topographic targets and does not require retroreflectors. The two frequency combs are generated by electro-optic modulation of a single continuous-wave laser diode. One of the combs is pulsed, amplified, and transmitted into the atmosphere, while the other acts as a local oscillator for coherent detection. We discuss the physical principles of the measurement, outline a performance model including speckle effects, and detail the fiber-based lidar architecture and signal processing. A maximum likelihood algorithm is used to estimate simultaneously the gas concentration and the central frequency of the comb, allowing the system to work without frequency locking. H 2 O (at 1544 nm) and CO 2 (at 1572 nm) concentrations are monitored with a precision of 3% and 5%, respectively, using a non-cooperative target at 700 m. In addition, the measured water vapor concentrations are in excellent agreement with in-situ measurements obtained from nearby weather stations. To our knowledge, this is the first complete experimental demonstration and performance assessment of greenhouse gas monitoring with a dual-comb spectrometer using lidar echoes from topographic targets.
Rosas et al. (Wed,) studied this question.