Optical flow gas velocity analysis in plumes using UV cameras – Implications for SO2-emission-rate retrievals investigated at Mt. Etna, Italy, and Guallatiri, Chile

Abstract. Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO2 cameras is commonly used for monitoring of SO2 emissions from volcanoes and anthropogenic sources (e.g. power plants, ships). The camera systems capture the emission plumes at high spatial and temporal resolution. This allows to retrieve the gas velocities in the plume directly from the images. The latter can be measured at a pixel level using optical flow (OF) algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constraint OF motion-vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion-fields. The new method is applied to two example datasets recorded at Mt. Etna (Italy) and Guallatiri (Chile). We show that in many cases, the uncorrected OF yields significantly underestimated SO2-emission-rates. We further show, that our proposed correction can account for this and that it significantly improves the reliability of optical flow based gas velocity retrievals. In the case of Mt. Etna, the SO2 emissions of the north-east crater are investigated. The corrected SO2-emission-rates range between 4.8–10.7 kg/s (average: 7.1 &pm; 1.3 kg/s) and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO2-emission-rates are between 0.5–2.9 kg/s (average: 1.3–0.5 kg/s) and provide the first report of SO2 emissions from this remotely located and inaccessible volcano.

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Improved optical flow velocity analysis in SO2 camera images of volcanic plumes – implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

Atmospheric Measurement Techniques ◽

10.5194/amt-11-781-2018 ◽

2018 ◽

Vol 11 (2) ◽

pp. 781-801 ◽

Cited By ~ 12

Author(s):

Jonas Gliß ◽

Kerstin Stebel ◽

Arve Kylling ◽

Aasmund Sudbø

Keyword(s):

Optical Flow ◽

Power Plants ◽

New Method ◽

Anthropogenic Sources ◽

Emission Rates ◽

Gas Velocity ◽

So2 Emissions ◽

So2 Emission ◽

Sensing Applications ◽

Mt Etna

Abstract. Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO2 cameras is commonly used to monitor SO2 emissions from volcanoes and anthropogenic sources (e.g. power plants, ships). The camera systems capture the emission plumes at high spatial and temporal resolution. This allows the gas velocities in the plume to be retrieved directly from the images. The latter can be measured at a pixel level using optical flow (OF) algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion fields. The new method is applied to two example data sets recorded at Mt Etna (Italy) and Guallatiri (Chile). We show that in many cases, the uncorrected OF yields significantly underestimated SO2 emission rates. We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals. In the case of Mt Etna, the SO2 emissions of the north-eastern crater are investigated. The corrected SO2 emission rates range between 4.8 and 10.7 kg s−1 (average of 7.1 ± 1.3 kg s−1) and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO2 emission rates are between 0.5 and 2.9 kg s−1 (average of 1.3 ± 0.5 kg s−1) and provide the first report of SO2 emissions from this remotely located and inaccessible volcano.

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Pyplis - A Python Software Toolbox for the Analysis of SO2 Camera Data

10.20944/preprints201710.0085.v1 ◽

2017 ◽

Author(s):

Jonas Gliß ◽

Kerstin Stebel ◽

Arve Kylling ◽

Anna Solvejg Dinger ◽

Holger Sihler ◽

...

Keyword(s):

Power Plants ◽

Dilution Effect ◽

Anthropogenic Sources ◽

Emission Rates ◽

So2 Emission ◽

Mt Etna ◽

Cross Platform ◽

Using Data ◽

Terrain Features ◽

Software Toolbox

UV SO2 cameras have become a common tool to measure and monitor SO2-emission-rates, mostly from volcanoes but also from anthropogenic sources (e.g. power plants or ships). In the past years, the analysis of UV SO2 camera data has seen many improvements. As a result, for many of the required analysis steps, several alternatives exist today. This inspired the development of Pyplis, an open-source software toolbox written in Python 2.7, which aims to unify the most prevalent methods from literature within a single, cross-platform analysis framework. Pyplis comprises a vast collection of algorithms relevant for the analysis of UV SO2 camera data. These include several routines to retrieve plume background radiances as well as routines for cell and DOAS based camera calibration. The latter includes two independent methods to identify the DOAS field-of-view within the camera images. Plume velocities can be retrieved using an optical flow algorithm as well as signal cross-correlation. Furthermore, Pyplis includes a routine to perform a first order correction of the signal dilution effect. All required geometrical calculations are performed within a 3D model environment allowing for distance retrievals to plume and local terrain features on a pixel basis. SO2-emission-rates can be retrieved simultaneously for an arbitrary number of plume intersections. Pyplis has been extensively and successfully tested using data from several field campaigns. Here, the main features are introduced using a dataset obtained at Mt. Etna, Italy on 16 September 2015.

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Updated SO2 emission estimates over China using OMI/Aura observations

10.5194/amt-2017-256 ◽

2017 ◽

Cited By ~ 1

Author(s):

Maria-Elissavet Koukouli ◽

Nicolas Theys ◽

Jieying Ding ◽

Irene Zyrichidou ◽

Bas Mijling ◽

...

Keyword(s):

Emission Inventory ◽

Satellite Observations ◽

So2 Emissions ◽

Transport Modelling ◽

So2 Emission ◽

Bottom Up ◽

Beijing Area ◽

Entire Domain ◽

North East ◽

The North

Abstract. The main aim of this paper is to update existing sulphur dioxide (SO2), emission inventories over China using novel inversion techniques, state-of-the-art chemistry transport modelling (CTM), and satellite observations of SO2. Within the framework of the EU FP7 Monitoring and Assessment of Regional air quality in China using space Observations, MarcoPolo project, a new SO2 emission inventory over China was calculated using the CHIMERE v2013b CTM simulations, ten years of OMI/Aura total SO2 columns and the pre-existing Multi-resolution Emission Inventory for China (MEIC v1.2). It is shown that including satellite observations in the calculations increases the current bottom-up MEIC inventory emissions for the entire domain studied [102° to 132° E and 15° to 55° N] from 26.30 Tg/annum to 32.60 Tg/annum, with positive updates which are stronger in winter [~ 36 % increase]. New source areas where identified in the South West [25–35° N and 100–110° E] as well as in the North East [40–50° N and 120–130° E] of the domain studied as high SO2 levels were observed by OMI, resulting in increased emissions in the aposteriori inventory that do not appear in the original MEIC v1.2 dataset. Comparisons with the independent Emissions Database for Global Atmospheric Research, EDGAR v4.3.1, show a satisfying agreement since the EDGAR 2010 bottom-up database provides 33.30 Tg/annum of SO2 emissions. When studying the entire OMI/Aura time period [2005 to 2015 inclusive], it was shown that the SO2 emissions remain nearly constant before year 2010 with a drift of −0.51 ± 0.38 Tg/annum and show a statistically significant decline after year 2010 of −1.64 ± 0.37 Tg/Annum for the entire domain. Similar findings were obtained when focusing on the Greater Beijing Area [110° to 120° E and 30° to 40° N] with pre-2010 drifts of −0.17 ± 0.14 and post-2010 drifts of −0.47 ± 0.12 Tg/annum. The new SO2 emission inventory is publicly available and forms part of the official EU MarcoPolo emission inventory over China which also includes updated NOx, VOCs and PM emissions.

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Supplementary material to "Optical flow gas velocity analysis in plumes using UV cameras – Implications for SO2-emission-rate retrievals investigated at Mt. Etna, Italy, and Guallatiri, Chile"

10.5194/amt-2017-185-supplement ◽

2017 ◽

Author(s):

Jonas Gliß ◽

Kerstin Stebel ◽

Arve Kylling ◽

Aasmund Sudbø

Keyword(s):

Optical Flow ◽

Emission Rate ◽

Velocity Analysis ◽

Gas Velocity ◽

Mt Etna ◽

Supplementary Material

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Retrieval of absolute SO2 column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

Atmospheric Measurement Techniques ◽

10.5194/amt-9-5677-2016 ◽

2016 ◽

Vol 9 (12) ◽

pp. 5677-5698 ◽

Cited By ~ 5

Author(s):

Peter Lübcke ◽

Johannes Lampel ◽

Santiago Arellano ◽

Nicole Bobrowski ◽

Florian Dinger ◽

...

Keyword(s):

Scattered Light ◽

Principal Component ◽

Optical Absorption Spectroscopy ◽

Retrieval Algorithm ◽

Light Sources ◽

Reference Spectrum ◽

Emission Rates ◽

Instrumental Effects ◽

So2 Emissions ◽

So2 Emission

Abstract. Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1 − 2 × 1016 [molecules cm−2]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to ≈ 15 % when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements.We compared our method to an evaluation that is similar to the NOVAC approach, where a spectrum that is recorded directly before the scan is used as an FRS and an SO2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO2 contamination of the FRS. The investigation showed that 21.4 % of the scans (containing significant amounts of SO2) at Nevado del Ruiz and 7 % of the scans at Tungurahua showed much larger SO2 CDs when evaluated using modelled FRS (more than a factor of 2). For standard evaluations the overall distribution of the SO2 CDs in a scan can in some cases indicate whether the plume affects all viewing directions and thus these scans need to be discarded for NOVAC emission rate evaluation. However, there are other cases where this is not possible and thus the reported SO2 emission rates would be underestimated. The new method can be used to identify these cases and thus it can considerably improve SO2 emission budgets.

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Trace element contamination in the mine-affected stream sediments of Oued Rarai in north-western Tunisia: a river basin scale assessment

Environmental Geochemistry and Health ◽

10.1007/s10653-021-00887-1 ◽

2021 ◽

Author(s):

Jamel Ayari ◽

Maurizio Barbieri ◽

Yannick Agnan ◽

Ahmed Sellami ◽

Ahmed Braham ◽

...

Keyword(s):

Trace Elements ◽

Ecological Risk ◽

Risk Index ◽

Potential Ecological Risk ◽

Stream Sediments ◽

Anthropogenic Sources ◽

Contamination Level ◽

North East ◽

Basin Scale ◽

North Western

AbstractHigh-quality and accurate environmental investigations are essential for the evaluation of contamination and subsequent decision-making processes. A combination of environmental geochemical indices, multivariate analyses and geographic information system approach was successfully used to assess contamination status and source apportionment of trace elements (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, V and Zn) in surface stream sediments from the Oued Rarai basin in north-western Tunisia, containing various metal and metalloid ores. The contamination level reported in this study indicates a non-negligible potential ecological risk, mainly related to sediment transport along the river. Antimony (concentrations ranged from 0.02 to 297 mg kg−1 and Igeo > 5), arsenic (from 0.5 to 1490 mg kg−1 and Igeo > 5), lead (from 2.9 to 5150 mg kg−1 and Igeo > 5) mercury (from 0.05 to 54.4 mg kg−1 and Igeo > 5) and silver (from 0.05 to 9.4 mg kg−1 and Igeo > 5) showed the most crucial contamination. Besides, potential ecological risk index values were maximum for arsenic with a median of 302, indicating a very high to serious ecological risk (> 160). Results from correlation analysis and principal component analysis revealed three main geochemical associations related to lithologic, tectonic and anthropogenic sources. V, Cr and Cu mainly originated from natural bedrock and soil. Ag and Cd were more controlled by both natural and mining enrichments. Mercury and Pb were mostly influenced by the ancient ore-related activities at the Oued Rarai site and north-east–south-west trending faults. Finally, Sb, As, Ni and Zn were largely controlled by the siliciclastic continental Neogene sequences. Finally, the physical and chemical dynamics of the watershed system, lithological properties, mineralisation, tectonic settings and mobilisation of subsurface sediments largely controlled both concentrations and spatial patterns of trace elements in the study basin. These results need to be considered in the strategies of suitable environmental management at former and current mining sites in north-western Tunisia.

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Chemical-physical constraints of the 2015 eruptive activity of Mt. Etna: new insights from thermo-barometry and geochemistry of olivine-hosted melt inclusions

10.5194/egusphere-egu21-15199 ◽

2021 ◽

Author(s):

Pier Paolo Giacomoni ◽

Federico Casetta ◽

Virginia Valenti ◽

Carmelo Ferlito ◽

Gabriele Lanzafame ◽

...

Keyword(s):

Melt Inclusions ◽

New South ◽

Basalt Magma ◽

Feeding System ◽

Physical Constraints ◽

Eruptive Event ◽

North East ◽

Central Crater ◽

Mt Etna ◽

Crystallization Conditions

The concomitant activation off all four summit craters of Mt. Etna during the December 2015 eruptive event allow us to investigate the chemical-physical crystallization conditions and magma dynamics in the shallower portion of the open-conduit feeding system. In this study, we discuss new petrological, geochemical and thermo-barometric data as well as the composition of major element and volatile content (H2O, CO2, F, Cl and S) of olivine-hosted melt inclusions from the explosive and effusive products emitted during the December 2015 eruptive event.Results and rhyolite-MELTS thermodynamic modelling of mineral phase stability highlight the relatively shallow crystal equilibrium depth prior to the eruption ranging from 400-500 MPa for Central Crater and North East Crater, up to 200 MPa below the New South East Crater. The study of high-pressure and high-temperature homogenized olivine-hosted melt inclusions allowed us to identify the composition of the almost primary alkali-basalt magma (11.8 wt% MgO) containing up to 4.9 wt% and 8151 ppm of H2O and CO2 respectively. The results, together with those already reported for the previous paroxystic events of the 2011-2012 (Giacomoni et al., 2018), reinforce the model of a vertically extended feeding system and highlight that the activity at the New South East Crater was fed by a magma residing at significant shallower depth with respect to Central Craters and North East Crater, although all conduits are fed by a common deep (P = 530-440 MPa) basic magmatic refilling. Plagioclase stability model and dissolution and resorption textures confirm its dependence on H2O content, thus suggesting that further studies on the effect that flushing from fluids with different H2O/CO2 ratio are needed in order to understand the eruption triggering mechanisms of paroxystic fountaining.&#160;ReferencesGiacomoni P., Coltorti M., Mollo S., Ferlito C., Braiato M., Scarlato P. 2018. The 2011-2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system. JVGR 349, 370-391.

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