Abstract

The physical and chemical structure and the spatial evolution of volcanic plumes are of great interest since they influence the Earth’s atmospheric composition and the climate. Equally important is the monitoring of the abundance and emission patterns of volcanic gases, which gives insight into processes in the Earth’s interior that are difficult to access otherwise. Here, we review spectroscopic approaches (from ultra-violet to thermal infra-red) to determine multi-species emissions and to quantify gas fluxes. Particular attention is given to the emerging field of plume imaging and quantitative image interpretation. Here UV SO2 cameras paved the way but several other promising techniques are under study and development. We also give a brief summary of a series of initial applications of fast imaging techniques for volcanological research.

Highlights

  • The physical and chemical structure and the spatial evolution of volcanic plumes is of great interest for a number of reasons beyond scientific curiosity:(A) Volcanic gas emissions influence the atmosphere and the climate and other Earth system parameters in a number of ways and on different temporal and spatial scales (e.g., [1,2,3]).Investigations of plume chemistry and plume dispersal will help constrain these influences.(B) The composition and emission rate of volcanic gases are linked to processes occurring in theEarth’s interior, measuring volcanic gases provides insights into these otherwise largely inaccessible processes

  • While there is a large number of possible combinations of the above approaches only several of the techniques have been used for remote sensing in volcanological environments and became popular, we describe these in the following: 1

  • The difference spectra isolate the information on the targeted plume composition which is straightforward to retrieve as outlined in Goff et al [54], Stremme et al [55], and Krueger et al (2013) [59], used a thermal emission Fourier-Transform Infra-red (FTIR) to sequentially scan the SO2 and SiF4 plume of Popocatepetl volcano from 12 km distance providing a series of two-dimensional images of the volcanic gas columns

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Summary

Introduction

The physical and chemical structure and the spatial evolution of volcanic plumes is of great interest for a number of reasons beyond scientific curiosity:. Several authors (e.g., [8,9]) used the measured SO2 emission to calculate the amount of magma involved in the simultaneously observed volcanic activity These remote sensing techniques have a number of decisive advantages over in-situ observations: The largest being that under most conditions the total amount of gas in the plume can be determined, Geosciences 2018, 8, 44; doi:10.3390/geosciences8020044 www.mdpi.com/journal/geosciences. In the following we give an overview of the principles of optical remote sensing and of plume imaging techniques These techniques can be applied from the ground, from (manned or unmanned) aircraft (e.g., [23]), or from satellite platforms.

Remote Sensing of Volcanic Gases
Absorption Spectroscopy
Thermal Emission Spectroscopy
Applications to Remote Sensing of Volcanic Plumes
Absorption Spectroscopy in the Infra-Red
Thermal Emission Spectroscopic Techniques
Imaging of Plumes
Categories of Plume Imaging
Non-Dispersive Plume Imaging
Non-dispersive IR Imaging of Plumes
Dispersive Imaging
Combining both Approaches
Volcanic Gas Flux Determination
The Principle of Volcanic Gas Flux Determination
A More Detailed View—Determination of the Wind Direction
Sample Applications
UV Spectroscopy
IR Spectroscopy
Findings
Summary and Outlook
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