Spatiotemporal Detection of the Carbon Dioxide Using a Compact Differential Absorption LiDAR

Abstract

Carbon dioxide (CO₂) is a major greenhouse gas contributing to climate change. Especially, the real-time monitoring of its spatial and temporal variations have drawn significant attention in the past few decades. In the present work, we proposed a Differential Absorption LiDAR (DIAL) system for the CO₂ concentration profiling. By employing a dual-wavelength 1.5 μm fiber laser and an InGaAs/InP negative feedback avalanche diode (NFAD) based free-running single-photon detector (SPD), it allowed the system to be compact, with low power consumptions. Comparisons between different laser pulse durations, laser pulse energies and peak powers were performed in terms of the signal-to-noise ratio (SNR) of the backscattering signals of the LiDAR. It is shown that the three parameters have a combined effect on the signal response behavior. After the optimization of the laser pulse energy, the signal integration time, and the workflow of CO₂ profile retrieval, the analytical performance of the LiDAR system has been evaluated. The temporal evolution of the measured CO₂ concentration nicely coincides with the values from a standard CO₂ detector, with a correlation coefficient higher than 0.7 and a relative standard deviation within 6.8%. Subsequently, vertical observations were carried out to obtain the height-time plot of the CO₂ concentrations, with a high spatial-temporal resolution of 25 m and 15 min, respectively. The results indicated a diurnal variation of CO₂ concentration at the nearshore region. This compact DIAL system shows promising analytical potential streamlining online monitoring of atmospheric CO₂ over the ocean based on buoy platforms.