“…Examples include the Differential Optical Absorption Spectrometer (DOAS), Passive Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) [12], Imaging Differential Optical Absorption Spectrometer (I-DOAS), open-path Fourier transform infrared spectrometers (open-path FTIR) [13], DOAS and Raman LIDAR, and thermal infrared cameras (nicAIR IIC) [14]. Among them, LIDAR is an active detecting technology and can accurately and quickly measure the SO 2 column density along the laser beam path through the volcanic plume, but it cannot observe the entire volume of plume emission [15]. DOAS and FTIR are superior because of their good portability, high spectral resolution, high sensitivity, and simple operation, but they are limited by spatial resolution and the availability of sample data.…”