Midinfrared Sensor System Based on Tunable Laser Absorption Spectroscopy for Dissolved Carbon Dioxide Analysis in the South China Sea: System-Level Integration and Deployment

System-level integration of a midinfrared carbon dioxide (CO 2 ) sensor system based on tunable laser absorption spectroscopy (TLAS) was realized for the analysis of dissolved CO 2 in seawater, employing an interband cascade laser (ICL) centered at 4319 nm and a multipass cell (MPC) with an optical path length of 29.8 m. At a low measurement pressure of 30 Torr, three absorption lines of 12 CO 2 were selected to realize different measurement ranges and a 13 CO 2 absorption line was targeted for simultaneous isotopic abundance analysis of δ 13 CO 2 . The sensor system was compactly integrated into a standalone system with automatic operation for underwater field deployment, and the working process was controlled by a specially designed electrical system. A gas–liquid separator system was developed for CO 2 extraction from water, and a pressure-control mechanism with two operation modes (i.e., static and dynamic modes) was proposed to make the sensor system applicable under a deep-sea environment. A series of experiments were carried out in the laboratory for performance assessment of the developed sensor system employed for the analysis of dissolved CO 2 in water. The sensor was deployed for a field test for natural gas hydrates exploration at an underwater depth of 0–2000 m in the South China Sea, with the sensor operating normally during the deployment.