Fully automated, real-time monitoring of ambient water vapour using a compact 1392 nm tunable diode laser-based system

This paper describes the development and deployment of an ambient water vapour measurement system based on tunable diode laser absorption spectroscopy (TDLAS). The system was designed with a near-infrared 1392 nm distributed feedback (DFB) tunable semiconductor laser that targeted the 1391.672 nm absorption line of water vapour. A compact and field-deployable system used made using a combination of a Raspberry Pi unit and Picoscope 2406B for data acquisition, signal processing and estimation of mole fraction using $R_{1 f} / \Delta I_{1}$ wavelength modulation spectroscopy (WMS) technique implemented in Python. The battery-powered setup was fully automated and remotely accessible over a wifi connection. The system was mounted on a vehicle and in-field measurements were carried out at fixed locations and with the vehicle moving in Gandhinagar.