This paper reports the development of a compact in situ real-time concentration analysis system for methane dissolved in seawater by using a continuous-wave cavity ringdown spectroscopy (CRDS) technique. The miniaturized design of the system, including optical resonance cavity and control and data acquisition-analysis electronics, has a cylindrical dimension of 550 mm in length and 100 mm in diameter. Ringdown signal generation, data acquisition and storage, current driver, and temperature controller of the diode laser are all integrated in the miniaturized system circuits, with an electrical power consumption of less than 12 W. Fitting algorithms of the ringdown signal and spectral line are implemented in a digital signal processor, which is the main control chip of the system circuit. The detection sensitivity for methane concentration can reach 0.4 ppbv with an approximate averaging time of 240 s (or 4 min). Comparing the system's measurement of ambient air against a high-quality commercial CRDS instrument has demonstrated a good agreement in results. In addition, as a "proof of concept" for measuring dissolved methane, the developed instrument was tested in an actual underwater environment. The results showed the potential of this miniaturized portable instrument for in situ gas sensing applications.

中文翻译：

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基于腔衰荡光谱的海水溶解甲烷原位分析系统的研制

本文报告了使用连续波腔衰荡光谱 (CRDS) 技术开发的紧凑型原位实时浓度分析系统，用于分析海水中溶解的甲烷。该系统的小型化设计，包括光学谐振腔和控制和数据采集分析电子设备，圆柱尺寸为长 550 毫米，直径 100 毫米。二极管激光器的振铃信号产生、数据采集和存储、电流驱动器和温度控制器都集成在小型化的系统电路中，电功耗小于12W。实现了振铃信号和谱线的拟合算法在数字信号处理器中，它是系统电路的主要控制芯片。甲烷浓度的检测灵敏度可达 0.4 ppbv，平均时间约为 240 秒（或 4 分钟）。将系统对环境空气的测量与高质量的商用 CRDS 仪器进行比较，结果显示出良好的一致性。此外，作为测量溶解甲烷的“概念证明”，开发的仪器在实际水下环境中进行了测试。结果显示了这种小型便携式仪器在原位气体传感应用中的潜力。开发的仪器在实际的水下环境中进行了测试。结果显示了这种小型便携式仪器在原位气体传感应用中的潜力。开发的仪器在实际的水下环境中进行了测试。结果显示了这种小型便携式仪器在原位气体传感应用中的潜力。