Abstract
Quantification of gaseous emission fluxes from volcanoes can yield valuable insights on processes occurring in the Earth’s interior as part of hazard monitoring. It is also an important task in the framework of climate change, in order to refine estimates of natural emissions. Passive open-path UltraViolet (UV) scattered observation by UV camera allows the imaging of volcanic plumes and evaluation of sulfur dioxide (SO2) fluxes at high temporal resolution during daytime. Another technique of imaging is now available in the InfraRed (IR) spectral domain. Infrared hyperspectral imagers have the potential to overcome the boundary of daytime sampling of the UV, providing measurements also during the night and giving access simultaneously to additional relevant gas species. In this context the IMAGETNA campaign of measurements took place at Mt Etna (Italy) in June 2015. Three different IR imagers (commercial and under developments) were deployed, together with a Fourier Transform InfraRed spectrometer (FTIR) instrument, a UV camera, a Long Wavelength InfraRed (LWIR) camera and a radiometer. We present preliminary results obtained by the two IR cameras under development, and then the IR hyperspectral imager results, coming from full physics retrieval, are compared to those of the UV camera. The comparison points out an underestimation of the SO2 Slant Column Densities (SCD) of the UV camera by a factor of 3.6. The detailed study of the retrieved SO2 SCD highlights the promising application of IR imaging in volcanology for remotely volcanic plume gas measurements. It also provides a way to investigate uncertainties in the SO2 SCD imaging in the UV and the IR.
Highlights
Volcanoes are a substantial source of gases and aerosols to the atmosphere
After checking the quality of the radiance spectrum obtained by Hyper-Cam Long Wavelength InfraRed (LWIR) hyperspectral imager by comparing with the widely used single-pixel Fourier Transform InfraRed spectrometer (FTIR) instrument, we present the radiative transfer retrieval code and method applied to retrieve SO2 slant column densities
We find a Noise Equivalent Spectral Radiance (NESR) of 11 nW/sr/cm2/cm−1, which means a Noise Equivalent Temperature Difference (NETD) of 880 mK at 2100 cm−1 for a blackbody at 20 ◦C
Summary
Volcanoes are a substantial source of gases and aerosols to the atmosphere. A major scientific challenge is the quantification of volcanic gas emissions for the understanding of eruptive processes and to assess the overall impact and climate change response [1,2,3,4]. Changes in the flux rate or the chemical composition of gases emitted from volcanoes can accompany or precede changes in volcanic activity i.e., represent a signal of coming eruption [15,16] This motivates the monitoring of volcanic volatile emissions at numerous volcanoes around the world [17,18,19]. Emission fluxes have been documented by COSPEC [24,25] and networks of ultraviolet scanner spectrometers [19,26] based on differential optical absorption spectroscopy (DOAS) Another technique is UV camera technology [27,28,29] that uses band-pass filters to visualize the SO2 plume as a 2D image. UV cameras can monitor SO2 emission flux variability at much higher frequency (~2 Hz) than COSPEC/DOAS spectrometers, but are subject to uncertainties due to time-varying wind field and possible ground effects for measurements near the point of gas emission
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