Extracting High Temperature Event radiance from satellite images and correcting for saturation using Independent Component Analysis

We present a novel method for extracting the radiance from High Temperature Events (HTEs) recorded by geostationary imagers using Independent Component Analysis (ICA). We use ICA to decompose the image cube collected by the instrument into a sum of the outer products of independent, maximally non-Gaussian time series and images of their spatial distribution, and then reassemble the image cube using only sources that appear to be HTEs. Integrating spatially gives the time series of total HTE radiance emission. In this study we test the technique on a number of simulated HTE events, and then apply it to a number of volcanic HTEs observed by the SEVIRI instrument. We find that the technique performs well on small localised eruptions and can be used to correct for saturation. The technique offers the advantage of obviating the need for a priori knowledge of the area being imaged, beyond some basic assumptions about the nature of the processes affecting radiance in the scene, namely that (i) HTE sources are statistically independent from other processes, (ii) the radiance registered at the sensor is a linear mixture of the HTE signal and those from other processes, and (iii) HTE sources can be reliably identified for the reconstruction process. This results in only five free parameters — the dimensions of the image cube, an estimate of the data dimensionality and a threshold for distinguishing between HTE and nonHTE sources. While we have focused here on volcanic HTEs, the methodology can, in principle, be extended to studies of other kinds of HTEs such as those associated with biomass burning.This research was undertaken as part of the NERC consortium project “How does the Earth's crust grow at divergent plate boundaries? A unique opportunity in Afar, Ethiopia” (grant number NE/E005535/1). CO is additionally supported by the UK National Centre for Earth Observation “Dynamic Earth and Geohazards” theme (http://comet.nerc.ac.uk/).This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0034425714004337?np=y#

Exploring the origin of ice-filled craters in the north polar region of Mars

We investigate the origins of enigmatic ice-filled craters in the north polar region of Mars. We test several explanations for their origin, namely: (1) as polar cap remnants (2) accumulation independently of the polar cap, and (3) upwelling of subsurface water, analogous to either aufice or pingo formation on Earth. Each of these hypotheses has a significant impact on our understanding of Mars’ recent geological and climatic history and the behaviour of water and water ice at high latitudes. We used several lines of evidence to assess the most likely formation mechanism. We first performed a crater survey based on THEMIS visual data and MOLA elevation data to identify any craters that had domal central lumps which were different from normal central peaks. From this survey we identified 17 craters for further study. These include Louth, Korolev, Dokka and other unnamed craters. Using data from orbiting spectrometers; OMEGA on ESA’s Mars Express and CRISM on NASA’s Mars Reconnaissance Orbiter; we verified that the composition of the exposed central domes was predominantly water ice. We found the domes fell into three groups: (1) those completely covered by dunes, (2) those partially covered by dunes and (3) those with no dunes. We investigated the morphology and the relative position of the domes using MOLA elevation data. We found that the domes are always asymmetrically placed within the craters. However, this asymmetry could not easily be linked to wind directions as revealed by dune slip-faces [2]. The domes often have a moat-like structure and in some cases do not cover the entire crater floor, e.g. Louth Crater. From image data, we identified six craters which possessed internal stratigraphy, in the form of regularly spaced layers, and of these we have inspected three in detail. We found that the layers possess both strong sinuosity and high angle unconformities. We interpret the internal stratigraphy as representing a sequence of regular cyclic accumulations, which produced the layers, followed by asymmetric ablation and subsequent resumption of accumulation, to produce the unconformities. Hence, the present-day shape of the domes indicates that they are in a phase of ablation.We attribute the colour contrasts between layers to different levels of dust, or particulate content. This could form a source for the dunes, which are often located on the summits of these domes. We find that this sequence is best explained by a model of atmospheric condensation. Our measurements of internal layer spacing and observations of layer stratigraphy argues that these deposits are not linked directly to a former, more extensive polar cap

Use of motion estimation algorithms for improved flux measurements using SO<inf>2</inf> cameras

SO2 cameras are rapidly gaining popularity as a tool for monitoring SO2 emissions from volcanoes. Several different SO2 camera systems have been developed with varying patterns of image acquisition in space, time and wavelength. Despite this diversity, there are two steps common to the workflows of most of these systems; aligning images of different wavelengths to calculate apparent absorbance and estimating plume transport speeds, both of which can be achieved using motion estimation algorithms. Here we present two such algorithms, a Dual Tree Complex Wavelet Transform-based algorithm and the Farneback Optical Flow algorithm. We assess their accuracy using a a synthetic dataset created using the numeric cloud-resolving model ATHAM, and then apply them to real world data from Villarrica volcano. Both algorithms are found to perform well and the ATHAM simulations offer useful datasets for benchmarking and validating future algorithms.RCUK, OtherThis is the final published version of the article "Use of Motion Estimation Algorithms for Improved Flux Measurements Using SO 2 Cameras" which is also available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0377027314002807

Does the lava lake of Erta ‘Ale volcano respond to regional magmatic and tectonic events? An investigation using Earth Observation data

Erta ‘Ale volcano lies at the centre of the Erta ‘Ale rift segment in northern Afar, Ethiopia and hosts one of the few persistent lava lakes found on Earth in its summit caldera. Previous studies have reported anecdotal evidence of a correlation between lake activity and magmatic and tectonic events in the broader region. We investigated this hypothesis for the period 2000–15 by comparing a catalogue of regional events with changes in lake activity reconstructed from Earth Observation data. The lava lake underwent dramatic changes during the study period, exhibiting an overall rise in height with concomitant changes in geometry consistent with a change in heat energy balance. Numerous paroxysms occurred in the lake and in the north pit; a significant dyke intrusion with subsequent re-intrusions indicated a role for dykes in maintaining the lake. However, despite some coincidences between the paroxysms and regional events, we did not find any statistically significant relationship between the two on a timescale of days to weeks. Nevertheless, changes in lake activity have preceded the broad increase in regional activity since 2005 and we cannot rule out a relationship on a decadal scale

A multidisciplinary study of the final episode of the Manda Hararo dyke sequence, Ethiopia, and implications for trends in volcanism during the rifting cycle

The sequence of dyke intrusions between 2005 and 2010 in the Manda Hararo rift segment, Ethiopia, provided an opportunity to test conceptual models of continental rifting. Based on trends up to dyke 13 in the sequence, it was anticipated that, should magma supply continue, dykes would shorten in length and eruptions would increase in size and decrease in distance from the segment centre as extensional stress was progressively released. In this paper we revisit these predictions by presenting a comprehensive overview of the May 2010 dyke and fissure eruption, the 14th and last in the sequence, from InSAR, seismicity, satellite thermal data, ultra violet SO2 retrievals, and multiple LiDAR surveys. We find the dyke is longer than other eruptive dykes in the sequence, propagating in two directions from the segment centre, but otherwise fairly typical in terms of opening, propagation speed and geodetic and seismic moment. However, though the eruption is located closer to the segment centre, it is much smaller than previous events. We interpret this as indicating that either the Manda Hararo rifting event was magma limited, or that extensional stress varies north and south of the segment centre

Volcanic gas emissions and degassing dynamics at Ubinas and Sabancaya volcanoes; implications for the volatile budget of the central volcanic zone

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO2 flux of 15.3 ± 2.3 kg s− 1 (1325-ton day− 1) at Sabancaya and of 11.4 ± 3.9 kg s− 1 (988-ton day− 1) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H2O, CO2, SO2, H2S and H2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H2O, CO2, SO2 and H2S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27, 1.2 and 0.01 kg s− 1 of H2O, CO2, SO2, H2S and H2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes

Insights into volcanic hazards and plume chemistry from multi-parameter observations: the eruptions of Fimmvörðuháls and Eyjafjallajökull (2010) and Holuhraun (2014–2015)

The eruptions of Eyjafjallajökull volcano in 2010 (including its initial effusive phase at Fimmvörðuháls and its later explosive phase from the central volcano) and Bárðarbunga volcano in 2014–2015 (at Holuhraun) were widely reported. Here, we report on complementary, interdisciplinary observations made of the eruptive gases and lavas that shed light on the processes and atmospheric impacts of the eruptions, and afford an intercomparison of contrasting eruptive styles and hazards. We find that (i) consistent with other authors, there are substantial differences in the gas composition between the eruptions; namely that the deeper stored Eyjafjallajökull magmas led to greater enrichment in Cl relative to S; (ii) lava field SO2 degassing was measured to be 5–20% of the total emissions during Holuhraun, and the lava emissions were enriched in Cl at both fissure eruptions—particularly Fimmvörðuháls; and (iii) BrO is produced in Icelandic plumes in spite of the low UV levels

Structural Analysis of the Western Afar Margin, East Africa: Evidence for Multiphase Rotational Rifting

The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N-S striking WAM is still actively deforming and is characterized by NNW-SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first-ever borehole-calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large-scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.</p

Volcanic gas emissions and degassing dynamics at Ubinas and Sabancaya volcanoes; implications for the volatile budget of the central volcanic zone

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO2 flux of 15.3 +/- 23 kg s(-1) (1325-ton day(-1)) at Sabancaya and of 11.4 +/- 3.9 kg s(-1) (988-ton day(-1)) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H2O, CO2, SO2, H2S and H-2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H2O, CO2, SO2 and H2S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27,1.2 and 0.01 kg s(-1) of H2O, CO2, SO2, H2S and H-2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes

Magmatic gas percolation through the old lava dome of El Misti volcano

The proximity of the major city of Arequipa to El Misti has focused attention on the hazards posed by the active volcano. Since its last major eruption in the fifteenth century, El Misti has experienced a series of modest phreatic eruptions and fluctuating fumarolic activity. Here, we present the first measurements of the compositions of gas emitted from the lava dome in the summit crater. The gas composition is found to be fairly dry with a H2O/SO2 molar ratio of 32 ± 3, a CO2/SO2 molar ratio of 2.7 ± 0.2, a H2S/SO2 molar ratio of 0.23 ± 0.02 and a H2/SO2 molar ratio of 0.012 ± 0.002. This magmatic gas signature with minimal evidence of hydrothermal or wall rock interaction points to a shallow magma source that is efficiently outgassing through a permeable conduit and lava dome. Field and satellite observations show no evolution of the lava dome over the last decade, indicating sustained outgassing through an established fracture network. This stability could be disrupted if dome permeability were to be reduced by annealing or occlusion of outgassing pathways. Continued monitoring of gas composition and flux at El Misti will be essential to determine the evolution of hazard potential at this dangerous volcano.This research was conducted as part of the ‘Trail By Fire’ expedition (PI: Y. Moussallam). The project was supported by the Royal Geographical Society (with the Institute of British Geographers) with the Land Rover Bursary; the Deep Carbon Observatory DECADE Initiative; Santander, Ocean Optics; Crowcon; Air Liquide; Thermo Fisher Scientific; Cactus Outdoor; Turbo Ace and Team Black Sheep. We thank Jean-loup Guyot, Sebastien Carretier, Rose-Marie Ojeda, Pablo Samaniego and Jean-Luc Lepennec together with IRD South-America personnel for all their logistical help. We are extremely grateful to Marco Rivera and all OVI personnel for their help and support. YM acknowledges support from the Scripps Institution of Oceanography Postdoctoral Fellowship program. A.A and G.T acknowledge the ERC grant no. 305377 (BRIDGE). CIS acknowledges a research start-up grant from Victoria University of Wellington. C.O. is supported by the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics. The Earth Observing-1 (EO-1) spacecraft is managed by NASA’s Goddard Space Flight Center, Greenbelt, Maryland, USA