468 research outputs found
Recent advances in ground-based ultraviolet remote sensing of volcanic SO2 fluxes
Measurements of volcanic SO2 emission rates have been the mainstay of remote-sensing volcanic gas geochemistry for almost four decades, and they have contributed significantly to our understanding of volcanic systems and their impact upon the atmosphere. The last ten years have brought stepchange improvements in the instrumentation applied to these observations, which began with the application of miniature ultraviolet spectrometers that were deployed in scanning and traverse configurations, with differential optical absorption spectroscopy evaluation routines. This study catalogs the
more recent empirical developments, including: ultraviolet cameras; wideangle
field-of-view differential optical absorption spectroscopy systems;
advances in scanning operations, including tomography; and improved understanding of errors, in particular concerning radiative transfer.
Furthermore, the outcomes of field deployments of sensors during the last
decade are documented, with respect to improving our understanding of volcanic dynamics and degassing into the atmosphere
Vulcamera: a program for measuring volcanic SO2 using UV cameras
We report here on Vulcamera, a stand-alone program for the determination of volcanic SO2 fluxes using ultraviolet cameras. The code enables field image acquisition and all the required post-processing operations
UV camera measurements of fumarole field degassing (La Fossa crater, Vulcano Island)
The UV camera is becoming an important new tool in the armory of volcano geochemists to derive high time resolution SO2 flux measurements. Furthermore, the high camera spatial resolution is particularly useful for exploring multiple-source SO2 gas emissions, for instance the composite fumarolic systems topping most quiescent volcanoes. Here, we report on the first SO2 flux measurements from individual fumaroles of the fumarolic field of La Fossa crater (Vulcano Island, Aeolian Island), which we performed using a UV camera in two field campaigns: in November 12, 2009 and February 4, 2010. We derived ~ 0.5 Hz SO2 flux time-series finding fluxes from individual fumaroles, ranging from 2 to 8.7 t dâ1, with a total emission from the entire system of ~ 20 t dâ1 and ~ 13 t dâ1, in November 2009 and February 2010 respectively. These data were augmented with molar H2S/SO2, CO2/SO2 and H2O/SO2 ratios, measured using a portable MultiGAS analyzer, for the individual fumaroles. Using the SO2 flux data in tandem with the molar ratios, we calculated the flux of volcanic species from individual fumaroles, and the crater as a whole: CO2 (684 t dâ1 and 293 t dâ1), H2S (8 t dâ1 and 7.5 t dâ1) and H2O (580 t dâ1 and 225 t dâ1).Published47-52JCR Journalrestricte
Periodic volcanic degassing behavior: The Mount Etna example
In contrast to the seismic and infrasonic energy released
from quiescent and erupting volcanoes, which have long been
known to manifest episodes of highly periodic behavior,
the spectral properties of volcanic gas flux time series
remain poorly constrained, due to a previous lack of hightemporal
resolution gas-sensing techniques. Here we report
on SO2 flux measurements, performed on Mount Etna
with a novel UV imaging technique of unprecedented
sampling frequency (0.5 Hz), which reveal, for the first
time, a rapid periodic structure in degassing from this
target. These gas flux modulations have considerable
temporal variability in their characteristics and involve two
period bands: 40â250 and 500â1200 s. A notable correlation
between gas flux fluctuations in the latter band and
contemporaneous seismic root-mean-square values suggests
that this degassing behavior may be generated by periodic
bursting of rising gas bubble trains at the magma-air interface.Published4818â48221.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveJCR Journalrestricte
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Ultraviolet camera measurements of passive and explosive (Strombolian) sulphur dioxide emissions at Yasur Volcano, Vanuatu
Here, we present the first ultraviolet (UV) camera measurements of sulphur dioxide (SO2) flux from Yasur volcano, Vanuatu, for the period 6â9 July 2018. These data yield the first direct gas-measurement-derived calculations of explosion gas masses at Yasur. Yasur typically exhibits persistent passive gas release interspersed with frequent Strombolian explosions. We used compact forms of the âPiCamâ Raspberry Pi UV camera system powered through solar panels to collect images. Our daily median SO2 fluxes ranged from 4 to 5.1 kg sâ1, with a measurement uncertainty of â12.2% to +14.7%, including errors from the gas cell calibration drift, uncertainties in plume direction and distance, and errors from the plume velocity. This work highlights the use of particle image velocimetry (PIV) for plume velocity determination, which was preferred over the typically used cross-correlation and optical flow methods because of the ability to function over a variety of plume conditions. We calculated SO2 masses for Strombolian explosions ranging 8â81 kg (mean of 32 kg), which to our knowledge is the first budget of explosive gas masses from this target. Through the use of a simple statistical measure using the moving minimum, we estimated that passive degassing is the dominant mode of gas emission at Yasur, supplying an average of ~69% of the total gas released. Our work further highlights the utility of UV camera measurements in volcanology, and particularly the benefit of the multiple camera approach in error characterisation. This work also adds to our inventory of gas-based data, which can be used to characterise the spectrum of Strombolian activity across the globe.</jats:p
Combined ground and aerial measurements resolve vent-specific gas fluxes from a multi-vent volcano
Volcanoes with multiple summit vents present a methodological challenge for determining vent-specific gas emissions. Here, using a novel approach combining multiple ultraviolet cameras with synchronous aerial measurements, we calculate vent-specific gas compositions and fluxes for Stromboli volcano. Emissions from vent areas are spatially heterogeneous in composition and emission rate, with the central vent area dominating passive emissions, despite exhibiting the least explosive behaviour. Vents exhibiting Strombolian explosions emit low to negligible passive fluxes and are CO2-dominated, even during passive degassing. We propose a model for the conduit system based on contrasting rheological properties between vent areas. Our methodology has advantages for resolving contrasting outgassing dynamics given that measured bulk plume compositions are often intermediate between those of the distinct vent areas. We therefore emphasise the need for a vent-specific approach at multi-vent volcanoes and suggest that our approach could provide a transformative advance in volcano monitoring applications
GABA levels in left and right sensorimotor cortex correlate across individuals
Differences in -aminobutyric acid (GABA) levels measured with Magnetic Resonance Spectroscopy have been shown to correlate with behavioral performance over a number of tasks and cortical regions. These correlations appear to be regionally and functionally specific. In this study, we test the hypothesis that GABA levels will be correlated within individuals for functionally related regionsâthe left and right sensorimotor cortex. In addition, we investigate whether this is driven by bulk tissue composition. GABA measurements using edited MRS data were acquired from the left and right sensorimotor cortex in 24 participants. T1-weighted MR images were also acquired and segmented to determine the tissue composition of the voxel. GABA level is shown to correlate significantly between the left and right regions (r = 0.64, p < 0.03). Tissue composition is highly correlated between sides, but does not explain significant variance in the bilateral correlation. In conclusion, individual differences in GABA level, which have previously been described as functionally and regionally specific, are correlated between homologous sensorimotor regions. This correlation is not driven by bulk differences in voxel tissue composition
Regionally specific human GABA concentration correlates with tactile discrimination thresholds
The neural mechanisms underlying variability in human sensory perception remain incompletely understood. In particular, few studies have attempted to investigate the relationship between in vivo measurements of neurochemistry and individuals' behavioral performance. Our previous work found a relationship between GABA concentration in the visual cortex and orientation discrimination thresholds (Edden et al., 2009). In the present study, we used magnetic resonance spectroscopy of GABA and psychophysical testing of vibrotactile frequency thresholds to investigate whether individual differences in tactile frequency discrimination performance are correlated with GABA concentration in sensorimotor cortex. Behaviorally, individuals showed a wide range of discrimination thresholds ranging from 3 to 7.6 Hz around the 25 Hz standard. These frequency discrimination thresholds were significantly correlated with GABA concentration (r = â0.58; p < 0.05) in individuals' sensorimotor cortex, but not with GABA concentration in an occipital control region (r = â0.04). These results demonstrate a link between GABA concentration and frequency discrimination in vivo, and support the hypothesis that GABAergic mechanisms have an important role to play in sensory discrimination
Dynamics of Outgassing and Plume Transport Revealed by Proximal Unmanned Aerial System (UAS) Measurements at VolcĂĄn Villarrica, Chile
Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing, and, on geological timescales, constitute an important source of volatiles to the Earthâs atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near-vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here, we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at VolcĂĄn Villarrica, Chile. We compare UAS-derived gas timeseries to simultaneous crater rim multi-GAS data and UV camera imagery to investigate early plume evolution. SO2 concentrations measured in the young proximal plume exhibit periodic variations that are well-correlated with the concentrations of other species. By combining molar gas ratios (CO2/SO2 = 1.48â1.68, H2O/SO2 = 67â75 and H2O/CO2 = 45â51) with the SO2 flux (142 ± 17 t/day) from UV camera images, we derive CO2 and H2O fluxes of ~150 t/day and ~2850 t/day, respectively. We observe good agreement between time-averaged molar gas ratios obtained from simultaneous UAS- and ground-based Multi-GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short-term periodic structure that reflects active degassing through discrete, audible gas exhalations.Alfred P. Sloan Foundation; Leverhulme Trus
Study protocol for VIdeo assisted thoracoscopic lobectomy versus conventional Open LobEcTomy for lung cancer, a UK multicentre randomised controlled trial with an internal pilot (the VIOLET study)
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