scholarly journals The NO<sub>2</sub> camera based on Gas Correlation Spectroscopy

2021 ◽  
Author(s):  
Leon Kuhn ◽  
Jonas Kuhn ◽  
Thomas Wagner ◽  
Ulrich Platt
Keyword(s):  
Temporal Resolution ◽  
Sensor Arrays ◽  
Visible Spectral Range ◽  
Correlation Spectroscopy ◽  
High Concentration ◽  
Gas Cell ◽  
Signal Ratio ◽  
Large Power ◽  
Spectral Window ◽  
Spatio Temporal

Abstract. Monitoring of NO2 is in the interest of public health, because NO2 contributes to the decline of air quality in many urban regions. Its abundance can be a direct cause of asthmatic and cardiovascular diseases and plays a significant part in forming other pollutants such as ozone or particulate matter. Spectroscopic methods have proven to be reliable and of high selectivity by utilizing the characteristic spectral absorption signature of trace gasses such as NO2. However, they typically lack the spatio-temporal resolution required for real-time imaging measurements of NO2 emissions. We propose imaging measurements of NO2 in the visible spectral range using a novel instrument, an NO2 camera based on the principle of Gas Correlation Spectroscopy (GCS). For this purpose two gas cells (cuvettes) are placed in front of two camera modules. One gas cell is empty, while the other is filled with a high concentration of the target gas. The filled gas cell operates as a non-dispersive spectral filter to the incoming light, maintaining the two-dimensional imaging capability of the sensor arrays. NO2 images are generated on the basis of the signal ratio between the two images in the spectral window between 430 and 445 nm, where the NO2 absorption cross section is strongly structured. The capabilities and limits of the instrument are investigated in a numerical forward model. The predictions of this model are verified in a proof-of-concept measurement, in which the column densities in specially prepared reference cells were measured with the NO2 camera and a conventional DOAS instrument. Finally, results from measurements at a large power plant, the Großkraftwerk Mannheim (GKM), are presented. NO2 column densities of the plume emitted from a GKM chimney are quantified at a spatio-temporal resolution of 1/6 frames per second (FPS) and 0.92 m × 0.92 m. A detection limit of 1.89 · 1016 molec cm−2 was reached. An NO2 mass flux of Fm = (7.41 ± 4.23) kg h−1 was estimated on the basis of momentary wind speeds obtained from consecutive images. The camera results are verified by comparison to NO2 slant column densities obtained from elevation scans with a MAX-DOAS instrument. The instrument prototype is highly portable and cost-efficient at building costs of below 2,000 Euro.

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 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;

scholarly journals A data reduction and compression description for high throughput time-resolved electron microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Abhik Datta ◽  
Kian Fong Ng ◽  
Deepan Balakrishnan ◽  
Melissa Ding ◽  
See Wee Chee ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Temporal Resolution ◽  
Data Reduction ◽  
Accurate Estimation ◽  
Data Streaming ◽  
Compression Scheme ◽  
Raw Data ◽  
Time Resolved ◽  
Detection And Counting ◽  
Spatio Temporal

AbstractFast, direct electron detectors have significantly improved the spatio-temporal resolution of electron microscopy movies. Preserving both spatial and temporal resolution in extended observations, however, requires storing prohibitively large amounts of data. Here, we describe an efficient and flexible data reduction and compression scheme (ReCoDe) that retains both spatial and temporal resolution by preserving individual electron events. Running ReCoDe on a workstation we demonstrate on-the-fly reduction and compression of raw data streaming off a detector at 3 GB/s, for hours of uninterrupted data collection. The output was 100-fold smaller than the raw data and saved directly onto network-attached storage drives over a 10 GbE connection. We discuss calibration techniques that support electron detection and counting (e.g., estimate electron backscattering rates, false positive rates, and data compressibility), and novel data analysis methods enabled by ReCoDe (e.g., recalibration of data post acquisition, and accurate estimation of coincidence loss).

scholarly journals The Development and Applications of Ultrafast Electron Nanocrystallography

2009 ◽  
Vol 15 (4) ◽  
pp. 323-337 ◽  
Author(s):  
Chong-Yu Ruan ◽  
Yoshie Murooka ◽  
Ramani K. Raman ◽  
Ryan A. Murdick ◽  
Richard J. Worhatch ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Structural Dynamics ◽  
Atomic Scale ◽  
Energy Redistribution ◽  
Gold Nanocrystals ◽  
Charge Dynamics ◽  
Atomic Structures ◽  
Molecular Scale ◽  
Spatio Temporal ◽  
3D Retrieval

AbstractWe review the development of ultrafast electron nanocrystallography as a method for investigating structural dynamics for nanoscale materials and interfaces. Its sensitivity and resolution are demonstrated in the studies of surface melting of gold nanocrystals, nonequilibrium transformation of graphite into reversible diamond-like intermediates, and molecular scale charge dynamics, showing a versatility for not only determining the structures, but also the charge and energy redistribution at interfaces. A quantitative scheme for 3D retrieval of atomic structures is demonstrated with few-particle (<1,000) sensitivity, establishing this nanocrystallographic method as a tool for directly visualizing dynamics within isolated nanomaterials with atomic scale spatio-temporal resolution.

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