Using Wavelet Coherence to Aid the Retrieval of Volcanic SO2 from UV Spectra

Changes in the emission rate of volcanic sulphur dioxide (SO2) are crucial parameters for identifying unrest and forecasting eruptive activity. Ground-based ultraviolet (UV) remote sensing provides a near continuous record SO2 rate, with Differential Optical Absorption Spectroscopy (DOAS) being preferred method quantifying absorption from recorded spectra. However, retrieving accurate column amounts using DOAS requires complex fitting procedure that relies on user expertise selecting suitable fit visually inspecting results. We explore an alternative approach exploits well-defined spatial frequencies present sky-scattered UV use wavelet coherence to compare spectra calibration cells known concentration wavelength–spatial frequency plane. Our findings reveal Magnitude-Squared Wavelet Coherence (MSWC) is inversely proportional concentration, suggesting this relationship could be used quantify natural To validate approach, we analyze by scanning-DOAS instruments Network Volcanic Atmospheric Change (NOVAC) at Masaya volcano, Nicaragua, Soufrière Hills Montserrat. observe favourable comparison between MSWC values calculate slant densities (SCDs) obtained iFit algorithms, respectively. demonstrate robust indicator which may potentially serve as proxy differential SCDs SO2. The straightforward computation offers efficient means identify contain signature plume objective results traditional routines.