scholarly journals Quantitative imaging of volcanic SO<sub>2</sub> plumes using Fabry–Pérot interferometer correlation spectroscopy

2021 ◽  
Vol 14 (1) ◽  
pp. 295-307
Author(s):  
Christopher Fuchs ◽  
Jonas Kuhn ◽  
Nicole Bobrowski ◽  
Ulrich Platt
Keyword(s):  
Temporal Resolution ◽  
Cross Sections ◽  
Imaging Techniques ◽  
Quantitative Imaging ◽  
Trace Gases ◽  
High Specificity ◽  
Correlation Spectroscopy ◽  
Volcanic Plume ◽  
Model Calculations ◽  
Fabry Perot

Abstract. We present first measurements with a novel imaging technique for atmospheric trace gases in the UV spectral range. Imaging Fabry–Pérot interferometer correlation spectroscopy (IFPICS) employs a Fabry–Pérot interferometer (FPI) as the wavelength-selective element. Matching the FPI's distinct, periodic transmission features to the characteristic differential absorption structures of the investigated trace gas allows us to measure differential atmospheric column density (CD) distributions of numerous trace gases with high spatial and temporal resolution. Here we demonstrate measurements of sulfur dioxide (SO2), while earlier model calculations show that bromine monoxide (BrO) and nitrogen dioxide (NO2) are also possible. The high specificity in the spectral detection of IFPICS minimises cross-interferences to other trace gases and aerosol extinction, allowing precise determination of gas fluxes. Furthermore, the instrument response can be modelled using absorption cross sections and a solar atlas spectrum from the literature, thereby avoiding additional calibration procedures, e.g. using gas cells. In a field campaign, we recorded the temporal CD evolution of SO2 in the volcanic plume of Mt. Etna, with an exposure time of 1 s and 400×400 pixel spatial resolution. The temporal resolution of the time series was limited by the available non-ideal prototype hardware to about 5.5 s. Nevertheless, a detection limit of 2.1×1017 molec cm−2 could be reached, which is comparable to traditional and much less selective volcanic SO2 imaging techniques.

scholarly journals Quantitative imaging of volcanic SO<sub>2</sub> plumes with Fabry Pérot Interferometer Correlation Spectroscopy

2020 ◽  
Author(s):  
Christopher Fuchs ◽  
Jonas Kuhn ◽  
Nicole Bobrowski ◽  
Ulrich Platt
Keyword(s):  
Cross Sections ◽  
Imaging Techniques ◽  
Quantitative Imaging ◽  
Trace Gases ◽  
High Specificity ◽  
Precise Determination ◽  
Correlation Spectroscopy ◽  
Integration Time ◽  
Volcanic Plume ◽  
Fabry Perot

Abstract. We present first measurements with a novel imaging technique for atmospheric trace gases in the UV spectral range. Imaging Fabry Pérot Interferometer Correlation Spectroscopy (IFPICS), employs a Fabry Pérot Interferometer (FPI) as wavelength selective element. Matching the FPIs distinct, periodic transmission features to the characteristic differential absorption structures of the investigated trace gas allows to measure differential atmospheric column density (CD) distributions of numerous trace gases, e.g. sulphur dioxide (SO2), bromine monoxide (BrO), or nitrogen dioxide (NO2), with high spatial and temporal resolution. The high specificity in the spectral detection of IFPICS minimises cross interferences to other trace gases and aerosol extinction allowing precise determination of gas fluxes. Furthermore, the instrument response can be modelled using absorption cross sections and a solar atlas spectrum from the literature, thereby avoiding additional calibration procedures, e.g. using gas cells. In a field campaign, we recorded the temporal CD evolution of SO2 in the volcanic plume of Mt. Etna with an integration time of 1 s and 400 × 400 pixels spatial resolution. The first IFPICS prototype can reach a detection limit of 2.1 × 1017 molec cm−2 s−1/2, which is comparable to traditional and much less selective volcanic SO2 imaging techniques.

Technological advances to improve the quantification of volcanic emissions

2021 ◽  
Author(s):  
Christopher Fuchs ◽  
Jonas Kuhn ◽  
Nicole Bobrowski ◽  
Ulrich Platt
Keyword(s):  
Remote Sensing ◽  
Temporal Resolution ◽  
Volcanic Activity ◽  
Imaging Techniques ◽  
Correlation Spectroscopy ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Integration Time ◽  
Volcanic Plume ◽  
Flux Measurements

&lt;p&gt;Variations in volcanic trace gas composition and fluxes are a valuable indicator for changes in magmatic systems and therefore allow monitoring of the volcanic activity. An established method to measure trace gas emissions is to use remote sensing techniques like, for example, Differential Optical Absorption Spectroscopy (DOAS) and more recently SO&lt;sub&gt;2&lt;/sub&gt;-cameras, that can quantify volcanic sulphur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;) emissions during quiescent degassing and eruptive phases, making it possible to correlate fluxes with volcanic activity.&amp;#160;&lt;/p&gt;&lt;p&gt;We present flux measurements of volcanic SO&lt;sub&gt;2&lt;/sub&gt; emissions based on the novel remote sensing technique of Imaging Fabry-P&amp;#233;rot Interferometer Correlation Spectroscopy (IFPICS) in the UV spectral range. The basic principle of IFPICS lies in the application of an Fabry-P&amp;#233;rot Interferometer (FPI) as wavelength selective element. The FPIs periodic transmission profile is matched to the periodic spectral absorption features of SO&lt;sub&gt;2&lt;/sub&gt;, resulting in high spectral information for its detection. This technique yields a higher trace gas selectivity and sensitivity than imaging approaches based on interference filters, e.g. SO&lt;sub&gt;2&lt;/sub&gt;-cameras and an increased spatio-temporal resolution over spectroscopic imaging techniques, e.g. imaging DOAS. Hence, IFPICS shows reduced cross sensitivities to broadband absorption (e.g. to ozone, aerosols), which allows the application to weaker volcanic SO&lt;sub&gt;2&lt;/sub&gt; emitters and increases the range of possible atmospheric conditions. It further raises the possibility to apply IFPICS to other trace gas species like, for example, bromine monoxide, that still can be characterized with a high spatial and temporal resolution (&lt; 1 HZ).&lt;/p&gt;&lt;p&gt;In October 2020, we acquired SO&lt;sub&gt;2&lt;/sub&gt; column density distribution images of Mt Etna volcanic plume with a detection limit of 2x10&lt;sup&gt;17&lt;/sup&gt; molec cm&lt;sup&gt;-2&lt;/sup&gt;, 1 s integration time, 400x400 pixel spatial, and 0.3 Hz temporal resolution.&amp;#160; We compare the SO&lt;sub&gt;2&lt;/sub&gt; fluxes retrieved by IFPICS with simultaneous flux measurements using the mutli-axis DOAS technique.&lt;/p&gt;

scholarly journals Towards imaging of atmospheric trace gases using Fabry Perot Interferometer Correlation Spectroscopy in the UV and visible spectral range

2018 ◽  
Author(s):  
Jonas Kuhn ◽  
Ulrich Platt ◽  
Nicole Bobrowski ◽  
Thomas Wagner
Keyword(s):  
Temporal Resolution ◽  
State Of The Art ◽  
Trace Gases ◽  
Visible Spectral Range ◽  
Correlation Spectroscopy ◽  
Trace Gas ◽  
Atmospheric Trace Gases ◽  
Fabry Perot ◽  
Sensitivity And Selectivity ◽  
Spatio Temporal

Abstract. Many processes in the lower atmosphere including transport, turbulent mixing and chemical conversions happen on time scales of the order of seconds (e.g. at point sources). Remote sensing of atmospheric trace gases in the UV and visible spectral range (UV/Vis) commonly uses dispersive spectroscopy (e.g. Differential Optical Absorption Spectroscopy, DOAS). The recorded spectra allow for the direct identification, separation and quantification of narrow band absorption of trace gases. However, these techniques are typically limited to a single viewing direction and limited by the light throughput of the spectrometer setup. While two dimensional imaging is possible by spatial scanning, the temporal resolution remains poor (often several minutes per image). Therefore, processes on time scales of seconds cannot be directly resolved by state of the art dispersive methods. We investigate the application of Fabry-Perot Interferometers (FPIs) for the optical remote sensing of atmospheric trace gases in the UV/Vis. By choosing a FPI transmission spectrum, which is optimised to correlate with narrow band (ideally periodic) absorption structures of the target trace gas, column densities of the trace gas can be determined with a sensitivity and selectivity comparable to dispersive spectroscopy, using only a small number of spectral channels (FPI tuning settings). Different from dispersive optical elements, the FPI can be implemented in full frame imaging setups (cameras), which can reach high spatio-temporal resolution. In principle, FPI Correlation Spectroscopy can be applied for any trace gas with distinct absorption structures in the UV/Vis. We present calculations for the application of FPI Correlation Spectroscopy to SO2, BrO and NO2 for exemplary measurement scenarios. Besides high sensitivity and selectivity we find that the spatio temporal resolution of FPI Correlation Spectroscopy can be more than two orders of magnitude higher than state of the art DOAS measurements. As proof of concept we built a one-pixel prototype implementing the technique for SO2 in the UV. Good agreement with our calculations and conventional measurement techniques are demonstrated and no cross sensitivities to other trace gases are observed.

scholarly journals Towards imaging of atmospheric trace gases using Fabry–Pérot interferometer correlation spectroscopy in the UV and visible spectral range

2019 ◽  
Vol 12 (1) ◽  
pp. 735-747 ◽  
Author(s):  
Jonas Kuhn ◽  
Ulrich Platt ◽  
Nicole Bobrowski ◽  
Thomas Wagner
Keyword(s):  
Temporal Resolution ◽  
Spectral Range ◽  
Trace Gases ◽  
Visible Spectral Range ◽  
Correlation Spectroscopy ◽  
Trace Gas ◽  
Atmospheric Trace Gases ◽  
Fabry Perot ◽  
Sensitivity And Selectivity ◽  
Spatio Temporal

Abstract. Many processes in the lower atmosphere including transport, turbulent mixing and chemical conversions happen on timescales of the order of seconds (e.g. at point sources). Remote sensing of atmospheric trace gases in the UV and visible spectral range (UV–Vis) commonly uses dispersive spectroscopy (e.g. differential optical absorption spectroscopy, DOAS). The recorded spectra allow for the direct identification, separation and quantification of narrow-band absorption of trace gases. However, these techniques are typically limited to a single viewing direction and limited by the light throughput of the spectrometer set-up. While two-dimensional imaging is possible by spatial scanning, the temporal resolution remains poor (often several minutes per image). Therefore, processes on timescales of seconds cannot be directly resolved by state-of-the-art dispersive methods. We investigate the application of Fabry–Pérot interferometers (FPIs) for the optical remote sensing of atmospheric trace gases in the UV–Vis spectral range. By choosing a FPI transmission spectrum, which is optimised to correlate with narrow-band (ideally periodic) absorption structures of the target trace gas, column densities of the trace gas can be determined with a sensitivity and selectivity comparable to dispersive spectroscopy, using only a small number of spectral channels (FPI tuning settings). Different from dispersive optical elements, the FPI can be implemented in full-frame imaging set-ups (cameras), which can reach high spatio-temporal resolution. In principle, FPI correlation spectroscopy can be applied for any trace gas with distinct absorption structures in the UV–Vis range. We present calculations for the application of FPI correlation spectroscopy to SO2, BrO and NO2 for exemplary measurement scenarios. In addition to high sensitivity and selectivity we find that the spatio temporal resolution of FPI correlation spectroscopy can be more than 2 orders of magnitude higher than state-of-the-art DOAS measurements. As proof of concept we built a 1-pixel prototype implementing the technique for SO2 in the UV. Good agreement with our calculations and conventional measurement techniques is demonstrated and no cross sensitivities to other trace gases are observed.

A novel technique for studying volcanic gas chemistry and dispersion on short time scales

2020 ◽  
Author(s):  
Christopher Fuchs ◽  
Jonas Kuhn ◽  
Nicole Bobrowski ◽  
Ulrich Platt
Keyword(s):  
Time Scales ◽  
Correlation Spectroscopy ◽  
Limiting Factors ◽  
Trace Gas ◽  
Volcanic Plume ◽  
Ambient Atmosphere ◽  
Volcanic Gas ◽  
Gas Emissions ◽  
Novel Technique ◽  
Fabry Perot

&lt;p&gt;Volcanic gas emissions, in particular, of sulphur and halogen species, play an important role in atmospheric chemistry. Due to the complex reaction kinetics of halogen radicals inside the volcanic plume, many properties like e.g. chemistry limiting factors and timescales of reactions, are still not well understood. &lt;br&gt;Imaging techniques based on optical remote sensing can get valuable insights into the study of both volcanic degassing fluxes and chemical conversions within the plume that continuously mixes with the atmosphere. However, state-of-the-art techniques are either too slow to resolve plume chemistry processes on its intrinsic time scales (e.g. DOAS) or show many cross sensitivities and hence are limited to rather high trace gas concentrations (e.g. SO&lt;sub&gt;2&lt;/sub&gt; cameras).&amp;#160;&lt;/p&gt;&lt;p&gt;We introduce a novel technique for volcanic trace gas imaging, which, by employing a Fabry-Perot interferometer (FPI), uses detailed spectral information for the detection of the target trace gas. Cross sensitivities are thereby drastically reduced, allowing for the detection of much lower SO&lt;sub&gt;2 &lt;/sub&gt;concentrations and imaging of other trace gas species like, e.g., BrO, OClO. Furthermore, the inherent calibration of the new techniques avoids the requirement of additional DOAS measurements or gas cells for calibration.&lt;/p&gt;&lt;p&gt;We present the first measurements of volcanic SO&lt;sub&gt;2&lt;/sub&gt; with an imaging Fabry-Perot interferometer correlation spectroscopy (IFPICS) prototype. The sensitivity of &amp;#8776; 10&lt;sup&gt;19 &lt;/sup&gt;cm&lt;sup&gt;2&lt;/sup&gt; molec&lt;sup&gt;-1&lt;/sup&gt; is comparable to filter based SO&lt;sub&gt;2&lt;/sub&gt; cameras, whereas the selectivity is much higher (e.g. no ozone interference). This will largely increase the accuracy of SO&lt;sub&gt;2&lt;/sub&gt; emission rates, which are routinely used to approximate fluxes of other volcanic gas emissions into the atmosphere.&lt;/p&gt;&lt;p&gt;Additionally, sensitivity studies for further trace gases combining laboratory measurements and radiation transfer modelling show promising prospected BrO detection limits of &lt; 10&lt;sup&gt;14&lt;/sup&gt; molec cm&lt;sup&gt;-&lt;/sup&gt;&amp;#178;, corresponding to mixing ratios of 10 to 100 ppt in volcanic plumes. The direct visualisation of BrO within the volcanic plume mixing with the ambient atmosphere will give important insights into the plume&amp;#8217;s halogen chemistry and, thereby, its impact on the atmosphere.&lt;/p&gt;

A two-camera instrument for highly resolved Gas Correlation Spectroscopy measurements of NO2

2020 ◽  
Author(s):  
Leon Kuhn ◽  
Jonas Kuhn ◽  
Thomas Wagner ◽  
Ulrich Platt
Keyword(s):  
Remote Sensing ◽  
Wavelength Range ◽  
Temporal Resolution ◽  
Trace Gases ◽  
Correlation Spectroscopy ◽  
Gas Cell ◽  
Band Pass ◽  
Spatio Temporal ◽  
Spectral Channels

&lt;p&gt;Imaging of atmospheric trace gases is becoming an increasingly important field of remote sensing. Conventional methods (like imaging-DOAS) typically use dispersive elements and wavelength mapping (at moderate to high spectral resolution) and need intricate optical setup. Therefore, they are limited in spatio-temporal resolution.&lt;/p&gt;&lt;p&gt;Some atmospheric trace gases can, however, be detected only by using a few carefully selected spectral channels, specific to the selected trace gas. These can be filtered using non-dispersive spectral filters without spatial mapping of continuous spectra, vastly increasing the spatio-temporal resolution. This has become a routine in volcanic SO&lt;sub&gt;2&lt;/sub&gt; flux analysis, where band-pass filters provide the spectral filtering.&lt;/p&gt;&lt;p&gt;We propose fast imaging of spatial Nitrogen Dioxide (NO&lt;sub&gt;2&lt;/sub&gt;) distributions employing Gas Correlation Spectroscopy (GCS) in the visible wavelength range. Two spectral channels are used, one with a gas cell that is filled with a high amount of NO&lt;sub&gt;2&lt;/sub&gt; in the light path and one without. An additional band-pass filter preselects a wavelength range containing structured and strong NO&lt;sub&gt;2&lt;/sub&gt; absorption (e.g. 430 - 450 nm). The NO&lt;sub&gt;2&lt;/sub&gt; containing gas cell serves as a NO&lt;sub&gt;2&lt;/sub&gt; specific spectral filter, almost blocking the light at wavelengths of the strong NO&lt;sub&gt;2&lt;/sub&gt; absorption bands within the preselected wavelength range. Absorption by atmospheric NO&lt;sub&gt;2&lt;/sub&gt; has therefore a lower impact on the channel with gas cell compared to the channel without gas cell. This difference is used to generate NO&lt;sub&gt;2&lt;/sub&gt; images.&lt;/p&gt;&lt;p&gt;NO&lt;sub&gt;2&lt;/sub&gt;&amp;#160;plays a major role in urban air pollution, where it is primarily emitted by point sources (power plants, vehicle internal combustion engines), before undergoing chemical conversions. The corresponding spatial gradients can neither be resolved with the established in-situ techniques nor with the widely used DOAS remote sensing method.&lt;/p&gt;&lt;p&gt;Recent advances in the physical implementation of a GCS-based NO&lt;sub&gt;2&lt;/sub&gt; camera suggest, that the quality of the measurement may be vastly enhanced in a two-detector (two-camera) set-up. Here, individual cameras are used for the two spectral channels. Not only does this double the photon budget available, but it also allows for synchronized exposure in both channels. This is critical for the quality of the measurement, since dynamic gas or intensity features on time scales smaller than the exposure delay of a one-camera system can induce strong false signals.&lt;/p&gt;&lt;p&gt;A proof of concept measurement was carried out, where test cells with NO&lt;sub&gt;2&lt;/sub&gt; column densities ranging from 1E16 to 4E18 molecules cm&lt;sup&gt;-2&lt;/sup&gt; were measured both with DOAS and our camera. The results coincided within their uncertainties and allow for camera calibration based on an instrument forward model.&lt;/p&gt;

Cardiovascular Imaging for Guiding Interventional Therapy in Structural Heart Diseases

2020 ◽  
Vol 16 (2) ◽  
pp. 111-122
Author(s):  
Nora Rat ◽  
Iolanda Muntean ◽  
Diana Opincariu ◽  
Liliana Gozar ◽  
Rodica Togănel ◽  
...  
Keyword(s):  
Heart Diseases ◽  
Interventional Procedure ◽  
Imaging Techniques ◽  
Ductus Arteriosus ◽  
Three Dimensional ◽  
High Specificity ◽  
Interventional Therapy ◽  
Structural Defects ◽  
Imaging Method ◽  
Three Dimensional Echocardiography

Development of interventional methods has revolutionized the treatment of structural cardiac diseases. Given the complexity of structural interventions and the anatomical variability of various structural defects, novel imaging techniques have been implemented in the current clinical practice for guiding the interventional procedure and for selection of the device to be used. Three– dimensional echocardiography is the most used imaging method that has improved the threedimensional assessment of cardiac structures, and it has considerably reduced the cost of complications derived from malalignment of interventional devices. Assessment of cardiac structures with the use of angiography holds the advantage of providing images in real time, but it does not allow an anatomical description. Transesophageal Echocardiography (TEE) and intracardiac ultrasonography play major roles in guiding Atrial Septal Defect (ASD) or Patent Foramen Ovale (PFO) closure and device follow-up, while TEE is the procedure of choice to assess the flow in the Left Atrial Appendage (LAA) and the embolic risk associated with a decreased flow. On the other hand, contrast CT and MRI have high specificity for providing a detailed description of structure, but cannot assess the flow through the shunt or the valvular mobility. This review aims to present the role of modern imaging techniques in pre-procedural assessment and intraprocedural guiding of structural percutaneous interventions performed to close an ASD, a PFO, an LAA or a patent ductus arteriosus.

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