Monitoring volcanic thermal anomalies from space: Size matters

International audienceMeasuring temperatures on volcanoes from space provides important constraints on the transfer of mass and heat to the Earth's surface. Time series of multispectral infrared images, acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) between 2000 and 2009, were inspected to investigate fluctuations in thermal anomalies at both Mount Erebus (Antarctica) and Láscar volcano (Chile). Several thermal metrics were explored: i) maximum pixel temperatures above background, ii) the spatial extent of low, moderate and high temperature anomalies, and iii) the spatial extent of short-wave infrared anomalies. The maximum pixel temperature metric correlated to eruptive events at Láscar volcano yet displayed significant scatter at Erebus. The spatial extent of both temperature and short-wave infrared anomalies correlates well with eruptive activity at both volcanoes. Limited variation in the size of thermal anomalies was observed at Erebus throughout the time series due to the stability of a long-lived lava lake, with the exception of a seasonal expansion in low temperature anomalies associated with localized snow-melt at the peak. This finding has implications for the interpretation of low temperature anomalies at other volcanoes. At least two different types of precursory signals are identified at Láscar: i) a gradual increase and ii) a dip, in the size and intensity of thermal anomalies. These thermal precursors appear to be associated with different eruptive styles. The former precedes a relatively shallow, short lived eruption; the later a prolonged eruptive period. Such thermal precursors could therefore help to constrain not only the timing but also the style and duration of an imminent eruptive episode

An Overview of Infrared Remote Sensing of Volcanic Activity

Volcanic activity consists of the transfer of heat from the interior of the Earth to the surface. The characteristics of the heat emitted relate directly to the geological processes underway and can be observed from space, using the thermal sensors present on many Earth-orbiting satellites. For over 50 years, scientists have utilised such sensors and are now able to determine the sort of volcanic activity being displayed without hazardous and costly field expeditions. This review will describe the theoretical basis of the discipline and then discuss the sensors available and the history of their use. Challenges and opportunities for future developments are then discussed

Radiant and mass fluxes in multi-platform, multi-payload satellite-based volcano monitoring

The enormous amount of remote sensing (RS) data available today at a range of temporal and spatial resolutions aid emergency management in volcanic crises. RS provides a technological solution for bridging critical gaps in volcanic hazard assessment and risk mitigation. Detection and measurement of high-temperature thermal anomalies enable eruption monitoring and new lava flow propagation forecasts, for example. The accuracy of such thermal estimates relies on the knowledge of input parameters, such as emissivity - the efficiency with which surfaces radiate thermal energy at various wavelengths and temperatures. Emissivity is directly linked to the measurement of radiant flux and therefore affects the mass flux estimate as well as any model-based prediction of lava flow behaviour. Emissivity is not commonly measured across the range of volcanic lava compositions and temperatures, and it is generally assumed to have a constant value between 1.0 and 0.80 for basaltic lava. There is a lack of field and laboratory-based emissivity data for robust, more realistic modelling. To address this deficit, experiments on ‘aa’ lava samples were performed using data from Mount Etna (Italy), representing the range of its eruptive behaviour. In three sequential stages, emissivity was measured over the widest range of temperatures (294 – 1373 K) and wavelengths (2.17 - 15.0 μm) executable in the laboratory environment.The results show that emissivity is temperature, composition and wavelength dependent. Measured emissivity increases non-linearly with temperature decrease (cooling), exhibiting significant variations above 900 K with values considerably lower than the typically assumed 0.80. The measured and modelled emissivity values were applied to various remote sensing applications as input parameters for physical modelling of lava flows. This new evidence has significant impact on the computation of radiant heat flux from spaceborne data, as well as on modelling of lava flow ‘distance-to-run’ simulations. Furnished with improved input parameters (multicomponent emissivity), the novel approach developed here can be used to test an improved version of an unsupervised multi-platform, multi-payload volcano monitoring system