High-range-resolution and long-distance CO₂ profiling using a single-photon differential absorption lidar

Lidar has become an increasingly attractive approach for CO₂ monitoring. However, simultaneously achieving long-range detection and high-range resolution remains a fundamental tradeoff. To address this issue, first, a superconducting nanowire single-photon detector is integrated into lidar to significantly enhance long-range sensitivity, enabling detection of backscattered signals up to 10 km. In addition, a new retrieval algorithm is proposed to retrieve range-resolved CO₂ concentrations from high-SNR column measurements, effectively improving profile resolution and stability. Three consecutive nights of field tests show that the system achieves 30 m range resolution, 5 min temporal resolution, and a near-8-km range. Compared with the traditional CO₂ retrieval algorithm, the proposed method improves the range resolution by more than one order of magnitude while still achieving a 3.8-fold enhancement in retrieval accuracy. Cross-validation with in-situ observations shows that the standard deviation between the two datasets is approximately 10 ppm, further confirming the accuracy and robustness of the method. This work underpins future high-resolution CO₂ monitoring networks and supports carbon-cycle studies.