scholarly journals Real-time dual frequency comb spectroscopy in the near infrared

2013 ◽  
Vol 102 (12) ◽  
pp. 121116 ◽  
Author(s):  
F. Zhu ◽  
T. Mohamed ◽  
J. Strohaber ◽  
A. A. Kolomenskii ◽  
Th. Udem ◽  
...  
Keyword(s):  
Real Time ◽  
Near Infrared ◽  
Frequency Comb ◽  
Dual Frequency

Real-time liquid-phase organic reaction monitoring with mid-infrared attenuated total reflectance dual frequency comb spectroscopy

2019 ◽  
Vol 356 ◽  
pp. 39-45 ◽  
Author(s):  
Daniel I. Herman ◽  
Eleanor M. Waxman ◽  
Gabriel Ycas ◽  
Fabrizio R. Giorgetta ◽  
Nathan R. Newbury ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Real Time ◽  
Frequency Comb ◽  
Attenuated Total Reflectance ◽  
Reaction Monitoring ◽  
Dual Frequency ◽  
Organic Reaction ◽  
Mid Infrared ◽  
Total Reflectance

scholarly journals Intercomparison of Open-Path Trace Gas Measurements with Two Dual Frequency Comb Spectrometers

2017 ◽  
Author(s):  
Eleanor M. Waxman ◽  
Kevin C. Cossel ◽  
Gar-Wing Truong ◽  
Fabrizio R. Giorgetta ◽  
William C. Swann ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Near Infrared ◽  
Frequency Comb ◽  
Deuterated Water ◽  
Dual Frequency ◽  
Measurement Campaign ◽  
Diurnal Cycles ◽  
Open Path ◽  
Local Sources ◽  
Carbon Dioxide Co2

Abstract. We present the first quantitative intercomparison between two open-path dual comb spectroscopy (DCS) instruments which were operated across adjacent 2-km open-air paths over a two-week period. We used DCS to measure the atmospheric absorption spectrum in the near infrared from 6021 to 6388 cm−1 (1565 to 1661 nm), corresponding to a 367 cm−1 bandwidth, at 0.0067 cm−1 sample spacing. The measured absorption spectra agree with each other to within 5 × 10−4 without any external calibration of either instrument. The absorption spectra are fit to retrieve concentrations for carbon dioxide (CO2), methane (CH4), water (H2O), and deuterated water (HDO). The retrieved dry mole fractions agree to 0.14 % (0.57 ppm) for CO2, 0.35 % (7 ppb) for CH4, and 0.40 % (36 ppm) for H2O over the two-week measurement campaign, which included 23 °C outdoor temperature variations and periods of strong atmospheric turbulence. This agreement is at least an order of magnitude better than conventional active-source open-path instrument intercomparisons and is particularly relevant to future regional flux measurements as it allows accurate comparisons of open-path DCS data across locations and time. We additionally compare the open-path DCS retrievals to a WMO-calibrated cavity ringdown point sensor located along the path with good agreement. Short-term and long-term differences between the two systems are attributed, respectively, to spatial sampling discrepancies and to inaccuracies in the current spectral database used to fit the DCS data. Finally, the two-week measurement campaign yields diurnal cycles of CO2 and CH4 that are consistent with the presence of local sources of CO2 and absence of local sources of CH4.

Artificial Intelligence for Real-Time Dual-Frequency Comb Hyperspectral Imaging

2020 ◽  
Author(s):  
Thibault Voumard ◽  
Thibault Wildi ◽  
Victor Brasch ◽  
Raul Gutierrez Alvarez ◽  
German Vergara Ogando ◽  
...  
Keyword(s):  
Artificial Intelligence ◽  
Real Time ◽  
Hyperspectral Imaging ◽  
Frequency Comb ◽  
Dual Frequency

scholarly journals Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

2017 ◽  
Vol 10 (9) ◽  
pp. 3295-3311 ◽  
Author(s):  
Eleanor M. Waxman ◽  
Kevin C. Cossel ◽  
Gar-Wing Truong ◽  
Fabrizio R. Giorgetta ◽  
William C. Swann ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Near Infrared ◽  
Frequency Comb ◽  
Integration Time ◽  
Deuterated Water ◽  
Dual Frequency ◽  
Measurement Campaign ◽  
Diurnal Cycles ◽  
Open Path ◽  
Local Sources

Abstract. We present the first quantitative intercomparison between two open-path dual-comb spectroscopy (DCS) instruments which were operated across adjacent 2 km open-air paths over a 2-week period. We used DCS to measure the atmospheric absorption spectrum in the near infrared from 6023 to 6376 cm−1 (1568 to 1660 nm), corresponding to a 355 cm−1 bandwidth, at 0.0067 cm−1 sample spacing. The measured absorption spectra agree with each other to within 5 × 10−4 in absorbance without any external calibration of either instrument. The absorption spectra are fit to retrieve path-integrated concentrations for carbon dioxide (CO2), methane (CH4), water (H2O), and deuterated water (HDO). The retrieved dry mole fractions agree to 0.14 % (0.57 ppm) for CO2, 0.35 % (7 ppb) for CH4, and 0.40 % (36 ppm) for H2O at  ∼  30 s integration time over the 2-week measurement campaign, which included 24 °C outdoor temperature variations and periods of strong atmospheric turbulence. This agreement is at least an order of magnitude better than conventional active-source open-path instrument intercomparisons and is particularly relevant to future regional flux measurements as it allows accurate comparisons of open-path DCS data across locations and time. We additionally compare the open-path DCS retrievals to a World Meteorological Organization (WMO)-calibrated cavity ring-down point sensor located along the path with good agreement. Short-term and long-term differences between the open-path DCS and point sensor are attributed, respectively, to spatial sampling discrepancies and to inaccuracies in the current spectral database used to fit the DCS data. Finally, the 2-week measurement campaign yields diurnal cycles of CO2 and CH4 that are consistent with the presence of local sources of CO2 and absence of local sources of CH4.

scholarly journals Near-infrared broadband dual-frequency-comb spectroscopy with a resolution beyond the Fourier limit determined by the observation time window

2015 ◽  
Vol 23 (26) ◽  
pp. 33184 ◽  
Author(s):  
Sho Okubo ◽  
Yi-Da Hsieh ◽  
Hajime Inaba ◽  
Atsushi Onae ◽  
Mamoru Hashimoto ◽  
...  
Keyword(s):  
Near Infrared ◽  
Time Window ◽  
Frequency Comb ◽  
Observation Time ◽  
Dual Frequency ◽  
Fourier Limit

A PORTABLE DUAL FREQUENCY COMB SPECTROMETER FOR ATMOSPHERIC APPLICATIONS

2016 ◽  
Author(s):  
Kevin Cossel ◽  
Nathan Newbury ◽  
Ian Coddington ◽  
Greg Rieker ◽  
Robert Wright ◽  
...  
Keyword(s):  
Frequency Comb ◽  
Dual Frequency

scholarly journals Real-time observation of tetrapyrrole binding to an engineered bacterial phytochrome

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yusaku Hontani ◽  
Mikhail Baloban ◽  
Francisco Velazquez Escobar ◽  
Swetta A. Jansen ◽  
Daria M. Shcherbakova ◽  
...  
Keyword(s):  
Real Time ◽  
Rational Design ◽  
Near Infrared ◽  
Fluorescent Proteins ◽  
Covalent Bond ◽  
Binding Pocket ◽  
Tissue Imaging ◽  
Covalent Attachment ◽  
Time Resolved

AbstractNear-infrared fluorescent proteins (NIR FPs) engineered from bacterial phytochromes are widely used for structural and functional deep-tissue imaging in vivo. To fluoresce, NIR FPs covalently bind a chromophore, such as biliverdin IXa tetrapyrrole. The efficiency of biliverdin binding directly affects the fluorescence properties, rendering understanding of its molecular mechanism of major importance. miRFP proteins constitute a family of bright monomeric NIR FPs that comprise a Per-ARNT-Sim (PAS) and cGMP-specific phosphodiesterases - Adenylyl cyclases - FhlA (GAF) domain. Here, we structurally analyze biliverdin binding to miRFPs in real time using time-resolved stimulated Raman spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations. Biliverdin undergoes isomerization, localization to its binding pocket, and pyrrolenine nitrogen protonation in <1 min, followed by hydrogen bond rearrangement in ~2 min. The covalent attachment to a cysteine in the GAF domain was detected in 4.3 min and 19 min in miRFP670 and its C20A mutant, respectively. In miRFP670, a second C–S covalent bond formation to a cysteine in the PAS domain occurred in 14 min, providing a rigid tetrapyrrole structure with high brightness. Our findings provide insights for the rational design of NIR FPs and a novel method to assess cofactor binding to light-sensitive proteins.

scholarly journals Improving the Stochastic Model of Ionospheric Delays for BDS Long-Range Real-Time Kinematic Positioning

2021 ◽  
Vol 13 (14) ◽  
pp. 2739
Author(s):  
Huizhong Zhu ◽  
Jun Li ◽  
Longjiang Tang ◽  
Maorong Ge ◽  
Aigong Xu
Keyword(s):  
Real Time ◽  
Long Range ◽  
Ionospheric Delay ◽  
Time Interval ◽  
Short Time Interval ◽  
Dual Frequency ◽  
Triple Frequency ◽  
Ambiguity Fixing ◽  
Power Spectral ◽  
Observation Noise

Although ionosphere-free (IF) combination is usually employed in long-range precise positioning, in order to employ the knowledge of the spatiotemporal ionospheric delays variations and avoid the difficulty in choosing the IF combinations in case of triple-frequency data processing, using uncombined observations with proper ionospheric constraints is more beneficial. Yet, determining the appropriate power spectral density (PSD) of ionospheric delays is one of the most important issues in the uncombined processing, as the empirical methods cannot consider the actual ionosphere activities. The ionospheric delays derived from actual dual-frequency phase observations contain not only the real-time ionospheric delays variations, but also the observation noise which could be much larger than ionospheric delays changes over a very short time interval, so that the statistics of the ionospheric delays cannot be retrieved properly. Fortunately, the ionospheric delays variations and the observation noise behave in different ways, i.e., can be represented by random-walk and white noise process, respectively, so that they can be separated statistically. In this paper, we proposed an approach to determine the PSD of ionospheric delays for each satellite in real-time by denoising the ionospheric delay observations. Based on the relationship between the PSD, observation noise and the ionospheric observations, several aspects impacting the PSD calculation are investigated numerically and the optimal values are suggested. The proposed approach with the suggested optimal parameters is applied to the processing of three long-range baselines of 103 km, 175 km and 200 km with triple-frequency BDS data in both static and kinematic mode. The improvement in the first ambiguity fixing time (FAFT), the positioning accuracy and the estimated ionospheric delays are analysed and compared with that using empirical PSD. The results show that the FAFT can be shortened by at least 8% compared with using a unique empirical PSD for all satellites although it is even fine-tuned according to the actual observations and improved by 34% compared with that using PSD derived from ionospheric delay observations without denoising. Finally, the positioning performance of BDS three-frequency observations shows that the averaged FAFT is 226 s and 270 s, and the positioning accuracies after ambiguity fixing are 1 cm, 1 cm and 3 cm in the East, North and Up directions for static and 3 cm, 3 cm and 6 cm for kinematic mode, respectively.

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