High-resolution Transmission Molecular Absorption Database Research Articles

BASECOL2023 scientific content

Context. The global context of making numerous data produced by researchers available requires collecting and organising the data, assigning meaningful metadata, and presenting the data in a meaningful and homogeneous way. The BASECOL database, which collects inelastic rate coefficients for application to the interstellar medium and to circumstellar and cometary atmospheres, meets those requirements. Aims. We aim to present the scientific content of the BASECOL2023 edition. Methods. While the previous versions relied on finding rate coefficients in the literature, the current version is populated with published results sent by the producers of data. The paper presents the database, the type of data that can be found, the type of metadata that are used, and the Virtual Atomic and Molecular Data Centre (VAMDC) standards that are used for the metadata. Finally, we present the different datasets species by species. Results. As the BASECOL database, interconnected with the VAMDC e-infrastructure, uses the VAMDC standards, the collisional data can be extracted with tools using VAMDC standards and can be associated with spectroscopic data extracted from other VAMDC connected databases such as the Cologne database for molecular spectroscopy (CDMS), the jet propulsion laboratory molecular spectroscopy database (JPL), and the high-resolution transmission molecular absorption database (HITRAN).

Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of N2O Using an Open-Path Sensor System

This paper examines the effects of temperature and humidity on the absorption spectrum and concentration of nitrous oxide (N2O) using a compact, portable open optical-path gas detection sensor system. We obtained the absorption coefficient and widened the linear function of the N2O absorption spectrum related to temperature by theoretical analysis and the high-resolution transmission molecular absorption database (HITRAN). Afterward, we conducted real-time monitoring of N2O in both campus and laboratory environments using lasers for a duration of 32 h and 6 h, respectively, and the results were compared and analyzed with the theoretical derivation. The results show that the concentration of N2O increased with increasing environmental temperature but decreased with increasing humidity. Furthermore, the variations in temperature and humidity significantly affected the peak values of the second-harmonic (2f) and first-harmonic (1f) signals. Finally, the temperature N2O concentration and humidity N2O curves were calibrated separately, and temperature changes were positively correlated with the N2O concentration, while humidity changes were negatively correlated with the N2O concentration. The experimental results indicate that the concentration of N2O and its absorption spectra are influenced by humidity and temperature, which has a significant reference value in the absorption and measurement of N2O in practical applications.

Adaptive learning and expansion of spectral parameters in HITRAN database: A novel SCLB model for predicting high-temperature gas spectra

Recent advancements in aerospace optics have highlighted the significance of high-temperature gas optical radiation properties in the fields of optical research and optical detection. The High-Resolution Transmission Molecular Absorption Database (HITRAN) provides a comprehensive range of high-temperature gas spectral radiation parameters, which are essential for studying the optical radiation of these gases. However, the coverage of common gas spectral line parameters in the HITRAN database is insufficient, particularly in supporting the multi-spectral research in the burgeoning fields of aerospace optics and optical detection, especially in the ultraviolet range. This underscores the necessity of expanding the wavelength range of gas spectral parameters covered in the HITRAN database. In this study, we propose a physics-constrained LSTM-BPTransformer (SCLB) model that utilizes the distribution characteristics of gas spectral parameters in the database to predict spectral parameters for unknown wavelengths. The model combines data distribution quantification and distribution matching modules and incorporates the physical mechanisms of gas spectral radiation, thus enhancing prediction accuracy. Experimental results validate the effectiveness of the SCLB model, demonstrating that it can extend the data volume of gas spectral parameters in the HITRAN database by 4-5 times, while maintaining an error range within 1%. This predictive model enriches the research in high-temperature gas optics and lays a solid foundation for the application of high-temperature gases in the fields of optical research and optical detection.

Improved Terahertz Time-Domain Spectroscopy via the Extended Kalman Filter

To implement terahertz time-domain spectroscopy (THz-TDS) systems that have short integration time and maintain performance, the extended Kalman filter (EKF) has been used. Performance of EKF with THz-TDS on vapor samples and solid samples is untested. Previous EKF methods were not adaptive for use on multiple THz-TDS systems. We provide an adaptive EKF method that can work on any THz setup, to improve maximum measurable absorption coefficient. Our adaptive EKF method responds to THz pulse properties. The adaptive EKF is exhaustively demonstrated for six different time-constant data sets spanning 1 ms to 300 ms for THz-TDS on vapor with electro-optic THz detection. The acquisition time saved is quantified and shown to significantly reduce acquisition time from 2.58 ms to 1 ms. This improvement of 2.58 times will have a significant effect to move spectral imaging from taking hours to taking minutes. Vapor absorption lines are maintained. We show the adaptive EKF maintain correct spectral information when compared to the high-resolution transmission molecular absorption (HITRAN) database. The adaptive EKF is also demonstrated for THz-TDS on vapor with photoconductive THz detection, thus demonstrating adaptability, and is applied for THz-TDS of a solid sample of polyethylene terephthalate glycol.

Pilot study CCQM-P172 – spectroscopic methods for HNO3 value assignment

Pilot study CCQM-P172 – spectroscopic methods for HNO3 value assignment

On the consistency of methane retrievals using the Total Carbon Column Observing Network (TCCON) and multiple spectroscopic databases

Abstract. The next and current generations of methane-retrieving satellite instruments are reliant on the Total Carbon Column Observing Network (TCCON) for validation. Understanding the biases inherent in TCCON and satellite methane retrievals is as important now as when TCCON started in 2004. In this study we highlight possible biases between different methane products by assessing the retrievals of the main methane isotopologue 12CH4. Using the TCCON GGG2014 retrieval environment, retrievals are performed using five separate spectroscopic databases from four separate TCCON sites (namely, Ascension Island, Ny-Ålesund, Darwin and Tsukuba) over the course of a year. The spectroscopic databases include those native to TCCON, GGG2014 and GGG2020; the high-resolution transmission molecular absorption database 2016 (HITRAN2016); the Gestion et Etude des Informations Spectroscopiques Atmosphériques 2020 (GEISA2020) database; and the ESA Scientific Exploitation of Operational Missions – Improved Atmospheric Spectroscopy Databases (SEOM-IAS). We assess the biases in retrieving methane using the standard TCCON windows and the methane window used by the Sentinel-5 Precursor (S5P) TROPOspheric Ozone Monitoring Instrument (TROPOMI) for each of the different spectroscopic databases. By assessing the retrieved 12CH4 values from individual windows against the standard TCCON retrievals, we find bias values of between 0.05 and 2.5 times the retrieval noise limit. These values vary depending on the window and TCCON site, with Ascension Island showing the lowest biases (typically <0.5) and Ny-Ålesund or Tsukuba showing the largest. For the spectroscopic databases, GEISA2020 shows the largest biases, often greater than 1.5 across the TCCON sites and considered windows. The TROPOMI spectral window (4190–4340 cm−1) shows the largest biases of all the spectral windows, typically >1, for all spectroscopic databases, suggesting that further improvements in spectroscopic parameters are necessary. We further assess the sensitivity of these biases to locally changing atmospheric conditions such as the solar zenith angle (SZA), water vapour and temperature. We find evidence of significant non-linear relationships between the variation in local conditions and the retrieval biases based on regression analysis. In general, each site, database and window combination indicates different degrees of sensitivity, with GEISA2020 often showing the most sensitivity for all TCCON sites. Ny-Ålesund and Tsukuba show the most sensitivity to variations in local condition, while Ascension Island indicates limited sensitivity. Finally, we investigate the biases associated with retrieving 13CH4 from each TCCON site and spectroscopic database, through the calculation of δ13C values. We find high levels of inconsistency, in some cases >100 ‰ between databases, suggesting more work is required to refine the spectroscopic parameters of 13CH4.

Analysis of inversion error characteristics of stellar occultation simulation data

Atmospheric stellar occultation observation technology is an advanced space-based detection technology that can measure the vertical distribution of trace gas composition, temperature, and aerosol content in a planet’s atmosphere. In this study, an inversion algorithm of the onion-peeling method was constructed to invert the transmittance obtained from the forward mask. The method used a three-dimensional ray-tracing simulation to obtain the transmission path of the light in the Earth’s atmosphere. The relevant parameters were then combined in the high-resolution transmission molecular absorption (HITRAN) database, and line-by-line integration was performed to calculate the atmospheric transmittance. The transmittance value was then used as an input to calculate the vertical distribution of oxygen molecules when using the single-wavelength inversion of the onion-peeling method. Finally, the oxygen molecule content was compared with the value attained by the Mass Spectrometer and Incoherent Scatter Radar Extended (MSISE00) atmospheric model to determine the relative error of our model. The maximum error was found to be 0.3%, which is low enough to verify the reliability of our algorithm. Using Global-scale Observations of the Limb and Disk (GOLD) measured data to invert the oxygen number density, we calculated its relative deviation from the published result to further verify the algorithm. The inversion result was affected by factors such as prior data, the absorption spectral line type, the ellipticity of the Earth, and the accuracy of the orbit. Analysis of these error-influencing factors showed that the seasons and the Earth’s ellipticity affected the accuracy of the model only 0.001% and could therefore be ignored. However, latitude and solar activity had a greater impact on accuracy, on the order of 0.1%. The absorption line type affected the accuracy of the model by as much as 1%. All three of these factors therefore need to be considered during the inversion process.

Ammonia-methane ratios from H-band near-infrared spectra of late-T and Y dwarfs

Aims. Our goals are to investigate the relative absorption strengths of ammonia and methane using low-resolution H-band (1.5−1.7 microns) spectra obtained in the laboratory and compared with observational spectra of late-T and Y dwarfs, and to estimate what can be expected from the wide-angle low-resolution near-infrared spectroscopic survey that will be provided by the upcoming Euclid space mission. Methods. Gas cells containing ammonia and methane at atmospheric pressure were custom-made in our chemical laboratory. Low-resolution near-infrared spectroscopy of these gas cells was collected in our optical laboratory. It is compared with simulated spectra using the high-resolution transmission molecular absorption database (HITRAN) for temperatures of 300 K and 500 K, and with near-infrared spectra of late-T dwarfs, Y dwarfs, Jupiter, and Saturn. We selected for this investigation the spectral region between 1.5 and 1.7 microns (H band) because it is covered by the Euclid red grism, it is particularly sensitive to the relative proportions of ammonia and methane opacity, and it is free from strong contributions of other abundant molecules, such as water vapor. Results. The laboratory spectra showed that the ammonia and methane features present in the simulations that used the HITRAN database are incomplete. Using our laboratory spectra, we propose a modified version of the NH3-H spectral ratio with expanded integration limits that increases the amplitude of variation in the index with respect to spectral type. Combinations of our laboratory spectra were used to find the best fits to the observed spectra with the relative absorption ratio of ammonia to methane as a free parameter. A relationship was found between the Teff and the ratio of ammonia to methane from spectral classes T5 to Y2 (1100 K–350 K), in fairly good qualitative agreement with theoretical predictions for high-gravity objects and temperatures from 1100 K to 500 K. The ammonia-to-methane ratios in late-T and Y dwarfs are similar to that of Jupiter, suggesting a similar chemical composition. Simulations of the spectroscopic performance of Euclid suggest that it will yield Teff values and ratios of ammonia to methane for over 103 late-T dwarfs in the entire wide survey.

Securing the Insecure: A First-Line-of-Defense for Body-Centric Nanoscale Communication Systems Operating in THz Band.

This manuscript presents a novel mechanism (at the physical layer) for authentication and transmitter identification in a body-centric nanoscale communication system operating in the terahertz (THz) band. The unique characteristics of the propagation medium in the THz band renders the existing techniques (say for impersonation detection in cellular networks) not applicable. In this work, we considered a body-centric network with multiple on-body nano-senor nodes (of which some nano-sensors have been compromised) who communicate their sensed data to a nearby gateway node. We proposed to protect the transmissions on the link between the legitimate nano-sensor nodes and the gateway by exploiting the path loss of the THz propagation medium as the fingerprint/feature of the sender node to carry out authentication at the gateway. Specifically, we proposed a two-step hypothesis testing mechanism at the gateway to counter the impersonation (false data injection) attacks by malicious nano-sensors. To this end, we computed the path loss of the THz link under consideration using the high-resolution transmission molecular absorption (HITRAN) database. Furthermore, to refine the outcome of the two-step hypothesis testing device, we modeled the impersonation attack detection problem as a hidden Markov model (HMM), which was then solved by the classical Viterbi algorithm. As a bye-product of the authentication problem, we performed transmitter identification (when the two-step hypothesis testing device decides no impersonation) using (i) the maximum likelihood (ML) method and (ii) the Gaussian mixture model (GMM), whose parameters are learned via the expectation–maximization algorithm. Our simulation results showed that the two error probabilities (missed detection and false alarm) were decreasing functions of the signal-to-noise ratio (SNR). Specifically, at an SNR of 10 dB with a pre-specified false alarm rate of , the probability of correct detection was almost one. We further noticed that the HMM method outperformed the two-step hypothesis testing method at low SNRs (e.g., a increase in accuracy was recorded at SNR = −5 dB), as expected. Finally, it was observed that the GMM method was useful when the ground truths (the true path loss values for all the legitimate THz links) were noisy.

Quantitative analysis of accuracy of concentration inversion under different temperature and pressure

The CO<sub>2</sub>, CH<sub>4</sub> and other greenhouse gases are measured by using a home-made Fourier transform infrared spectrometer at the Longfengshan atmospheric background station. Compared with the measurement results of the instrument from the background station which meets the standards of the World Meteorological Organization, the correlation coefficient and the root mean square error of the CO<sub>2</sub> concentration value are 0.9576 and 18.6015, so the measurement results from the home-made instrument are reliable. In the home-made instrument the calibration spectrum of standard temperature and the calibration spectrum of stand pressure are used to invert the concentration. With the temperature changing, the temperature of the measured gas will vary, thus resulting in error. The research of environmental variable factors can improve the accuracy of concentration inversion. For example, compared with CO<sub>2</sub> absorption spectrum under 296 K, the CO<sub>2</sub> absorption spectrum under 297 K will have 1.8% spectrum deviation and its inversion concentration error is 0.41%. This is the main cause of inversion concentration error. Based on the above analysis, the absorption cross section is calculated by using the high-resolution transmission molecular absorption database parameters. Combining with the instrument line shape, the calibration spectra at different temperatures and pressures can be obtained. The calibration spectra at different temperatures and pressures are used to calibrate the concentration inversion. After calibration, compared with the measurement results of the background station instrument, the correlation coefficient and the root mean square error of the CO<sub>2</sub> concentration value are 0.9637 and 6.7803. The correlation coefficient of CO<sub>2</sub> concentration value measured by self-developed instrument is improved and root mean square error is reduced. The result shows that the calibration algorithm enhances the accuracy of the measurement results to a certain extent. The above results illustrate the reliability of the home-made FTIR instrument and this experiment provides important data, which lay the foundation forstudying the home-made Fourier transform infrared spectrometer. Of course, improvement can be made in the following areas. Other minor factors may affect the effect of the inversion algorithm. The concentration inversion will have subtle differences at different bands of calibration spectra. So in order to improve the measurement accuracy, we need to choice more reasonable band inversion and more precise parameters from the high-resolution transmission molecular absorption database.

A Potential Approach to Compensate the Gas Interference for the Analysis of NO by a Non-dispersive Infrared Technique.

Interference is a pivotal issue of a non-dispersive infrared (NDIR) sensor and analyzer. Therefore, the main contribution of this study is to introduce a potential method to compensate for the interference of the NDIR analysis. A potential method to compensate for the interference of a nitric oxide (NO) NDIR analyzer was developed. Double bandpass filters (BPFs) with HITRAN (high-resolution transmission molecular absorption database)-based wavelengths were used to create an ultranarrow bandwidth, where there were least-interfering effects with respect to the coal-fired power plant emission gas compositions. Key emission gases from a coal-fired power plant, comprising carbon monoxide (CO), NO, sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon dioxide (CO2), and water (H2O) (in the form of vapor), were used to investigate the gas interference. The mixtures of those gases were also used to investigate the performance of the double BPFs. We found that CO, CO2, SO2, and H2O significantly affected the detection of NO when a commercial, single narrow BPF was used. In contrast, the double BPFs could remove the interference of CO, NO2, SO2, and CO2 in terms of their concentrations. In the case of H2O, the filter performed well until a level of 50% relative humidity at 25 °C. Moreover, the signal-to-noise ratio of the analyzer was approximately 10 when the double BPFs were applied. In addition, the limit of detection of the analyzer with the double BPFs was approximately 4 ppm, whereas that with the commercial one was 1.3 ppm. Therefore, double BPFs could be used for an NO NDIR analyzer instead of a gas filter correlation to improve the selectivity of the analyzer under the condition of a known gas composition, such as a coal-fired power plant. However, the sensitivity of the analyzer would be decreased.

The IAG Solar Flux Atlas: Telluric Correction with a Semiempirical Model

Abstract Observations of the Sun as a star have been key to guiding models of stellar atmospheres and additionally provide useful insights on the effects of granulation and stellar activity on radial velocity measurements. Most high-resolution solar atlases contain telluric lines that span the optical and limit the spectral regions useful for analysis. We present here a telluric-corrected solar atlas covering 0.5–1.0 μm derived from solar spectra taken with a Fourier transform spectrograph at the Institut für Astrophysik, Göttingen. This atlas is the highest-resolution spectrum with a wavelength calibration precise to ±10 m s−1 across this 500 nm spectral window. We find that the atlas matches to within 3% of the telluric-corrected Kitt Peak atlas in regions containing telluric absorption weaker than 50% in transmission. The telluric component of the spectral data is fit with a semiempirical model composed of Lorentz profiles initialized to the High-resolution Transmission Molecular Absorption Database (HITRAN) parameters for each absorption feature. Comparisons between the best-fit telluric parameters describing the Lorentz profile for each absorption feature and the original HITRAN values in general show excellent agreement considering the effects atmospheric pressure and temperature have on our final parameters. However, we identify a small subset of absorption features with larger offsets relative to the cataloged line parameters. We make our final solar atlas available online. We additionally make available the telluric spectra extracted from the data that, given the high resolution of the spectrum, would be useful for studying the time evolution of telluric line shapes and their impact on Doppler measurements.

Temperature measurement based on adaptive dual-comb absorption spectral detection

We demonstrate absorption spectroscopy of water vapor for the determination of gas temperature. An adaptive dual-comb detection system is utilized to obtain precise spectroscopic data in a broadband range from 7143 to 7240 cm−1 with a spectral resolution of 0.049 cm−1. The measured spectra are in accordance with the simulated results from the HITRAN (high-resolution transmission molecular absorption) database. Several measurements are investigated in the temperature range of 500–1000 K, revealing relative deviations of less than 5% compared to the thermocouple. This broadband and accurate adaptive dual-comb spectral detection method could be a powerful tool for non-invasive combustion diagnosis.

The v2 = 1, 2 and v4 = 1 bending states of 15NH3 and their analysis at experimental accuracy.

15NH3 is the object of extensive investigation due to the central role of ammonia in astronomical sciences and to the complexity of modeling its interacting vibrationally excited states. Of major interest in astrochemistry is the determination of the 14N/15N ratio in space, characterized by unexpected variability among different solar system objects and reservoirs. Recently, the spectroscopic analysis of ground and v2 = 1 a, s states of 15NH3 has been completed at experimental accuracy. Here, the characterization of the a, s inversion symmetry levels of v2 = 1, 2 and v4 = 1 states is presented. New spectra of 15NH3 have been recorded from 325 to 2000 cm-1 at a resolution ranging from 0.00096 cm-1 to 0.003 cm-1, using the Canadian Light Source synchrotron at CLS. 7518 transitions covering nine bands, ν2, 2ν2, ν4, 2ν2 ← ν2, ν4 ← ν2, 2ν2 ↔ ν4 and the inversion-rotation transitions in the excited states, have been fitted simultaneously. The effective Hamiltonian adopted includes all symmetry allowed interactions between and within the studied excited states, according to the most recent results on ammonia. The transitions have been reproduced at experimental accuracy using 185 spectroscopic parameters, determined with high precision. The leading diagonal parameters, Gv, B, C, D's, compare well with those of 14NH3. The wavenumbers of the assigned transitions are compared with their theoretically predicted values. An improved set of ground state parameters is also derived. These results noticeably improve the wavenumber line list in the high-resolution transmission molecular absorption (HITRAN) database.

Effect of Measurement of Dew Point Temperature in Moist Air on the Absorption Line at 1392.53 nm of Water Vapor

The HITRAN database (High-Resolution Transmission molecular absorption database) is an extremely helpful reference for selecting lines of molecular species. In the case of water vapor, a particular strong absorption line around λ ≈ 1392.5 nm is suitable for the detection of molecules, not only because of its high strength but also because it is well separated from the neighboring transitions, thus avoiding any overlap. First, we present the optical system that uses a distributed feedback (DFB) laser diode, emitting around λ ≈ 1392.5 nm with a power ≈ 3 mW and linewidth ≤ 10 MHz. For metrological needs, we are looking for a means to control the water vapor concentration in ambient air in near real time and especially when an optical chilled mirror hygrometer is used. The latter instrument is widely used due to its performance with regard to both accuracy and repeatability of measurements. Here, using the molecular absorption device the use of such an instrument is examined from the point of view of its impact on the measurement of relative humidity. This paper reports the measured frequency positions of the observed line at λ = 1392.5337 nm for different air pressures and compares them with the values given in the HITRAN database. In addition, we discuss the possibility of using water vapor detection by spectroscopy to observe the change of the shape and the position of the absorption line produced during measurements of the dew point temperature by the optical chilled mirror hygrometer.

Quantitative validation of Ames IR intensity and new line lists for 32/33/34S16O2, 32S18O2 and 16O32S18O

The quality of Ames-296K SO2 Infrared (IR) line list intensities is first validated by quantitative exploration of several dipole moment surfaces (DMSs) and partition sum convergence. The DMSs are computed with several of Dunning's correlation-consistent basis sets and their vibrational dependence are compared to the empirical model derived from Stark effect experiments reported by D. Patel, D. Margolese, and T.R. Dyke [J. Chem. Phys.70, 2740 (1979)]. The effective dipole deviations from the DMS adopted in the Ames IR lists is 0.2–0.4% for vibrational states up to 3ν3. The vibrational dependence of the dipole moment is also in good agreement, except for nν1. Partition sum convergence at 296 K is confirmed by new calculations with rotational quantum number J up to 150 and upper state E’ up to 8000 cm−1. The isotopologue consistency of the Ames IR line lists is superior relative to the regular Effective Hamiltonian (EH) models and Effective Dipole Moment (EDM) models. The ν1 + ν2 and ν2 + ν3 intensity consistency check reveals the recently reported experimental intensities need significant improvement or re-analysis. After the accuracy, convergence, and isotopologue consistency have been confirmed, the theoretical Ames-296K intensities are combined with the experimental line positions or EH models that experimental spectroscopists published after 2009. Three high-resolution IR line sets are reported for the 32/33/34S16O2, 32S18O2 and 16O32S18O isotopologues: (1) the “New Lines Sets” include experimentally measured line positions; (2) the “Expanded Line Sets” include possible transitions among new rovibrational levels assigned in experiments and ground state (GS) levels predicted by reliable EH models; (3) the “Ames + MARVEL Sets” include possible transitions among all those levels reported in a recent MARVEL analysis. [Tóbiás et al, JQSRT 208, 152 (2018)]. Compared to the limited data in High-resolution TRANsmission molecular absorption database (HITRAN), these line sets have significantly improved the data coverage up to 4000 cm−1. Some missing bands can be traced to the unpublished experimental data. The isotopologue consistency of these line sets will help identify the uncertainties and defects in the experimental EH and EDM models. These line sets are good candidates for the next HITRAN update, if line shape parameters are available. The line sets can be downloaded from supplementary files or from the Ames Molecular Spectroscopic Database at http://huang.seti.org.

The Havemann-Taylor Fast Radiative Transfer Code (HT-FRTC): A multipurpose code based on principal components

The HT-FRTC can be used across the electromagnetic spectrum from the microwave through to the ultraviolet to calculate transmittance, radiance and flux spectra, which are represented by their principal components. The code uses monochromatic calculations at a small number of frequencies, which are selected by k-means clustering, to predict the principal component scores. It has been found that kernel regression yields more robust predictions than a linear regression. The principal components cover the spectrum at a very high spectral resolution, similar to that of conventional line-by-line models such that the individual spectral lines are resolved. This approach allows very fast line-by-line-like, hyperspectral and broadband simulations for satellite-based, airborne and ground-based sensors. The principal components are derived during a code training phase from monochromatic simulations for a diverse set of atmospheres and surfaces. They are sensor independent and no extra training is required for additional sensors. The HT-FRTC has been trained with all of the trace gases in the HIgh-resolution TRANsmission molecular absorption database (HITRAN) and on a large variety of surface emissivity/reflectance spectra. It can be run for any Lambertian or specular surface. The HT-FRTC is a plane-parallel one-dimensional model but some effects of the Earth’s sphericity are accounted for. Solar, lunar and cosmic microwave background sources have been included. Scattering by frozen and liquid cloud, precipitation particles and twenty different aerosol species has been included, as well as Rayleigh scattering which is significant in the short-wave. The scattering phase function can be fully accounted for by an integrated monochromatic version of the Edwards-Slingo spherical harmonics radiation code or approximately by a modification to the extinction (Chou scaling).

Widely tunable 23 μm III-V-on-silicon Vernier lasers for broadband spectroscopic sensing

Heterogeneously integrating III-V materials on silicon photonic integrated circuits has emerged as a promising approach to make advanced laser sources for optical communication and sensing applications. Tunable semiconductor lasers operating in the 2–2.5 μm range are of great interest for industrial and medical applications since many gases (e.g., CO2, CO, CH4) and biomolecules (such as blood glucose) have strong absorption features in this wavelength region. The development of integrated tunable laser sources in this wavelength range enables low-cost and miniature spectroscopic sensors. Here we report heterogeneously integrated widely tunable III-V-on-silicon Vernier lasers using two silicon microring resonators as the wavelength tuning components. The laser has a wavelength tuning range of more than 40 nm near 2.35 μm. By combining two lasers with different distributed Bragg reflectors, a tuning range of more than 70 nm is achieved. Over the whole tuning range, the side-mode suppression ratio is higher than 35 dB. As a proof-of-principle, this III-V-on-silicon Vernier laser is used to measure the absorption lines of CO. The measurement results match very well with the high-resolution transmission molecular absorption (HITRAN) database and indicate that this laser is suitable for broadband spectroscopy.

Chemometric Approach to the Calibration of Light Emitting Diode Based Optical Gas Sensors Using High-Resolution Transmission Molecular Absorption Data.

Modeling the propagation of light from LED sources is problematic since the emission covers a broad range of wavelengths and thus cannot be considered as monochromatic. Furthermore, the lack of directivity of such sources is also problematic. Both attributes are characteristic of LEDs. Here we propose a HITRAN ( high-resolution transmission molecular absorption database) based chemometric approach that incorporates not-perfect-monochromaticity and spatial directivity of near-infrared (NIR) LED for absorbance calculations in 1-6% methane (CH4) in air, considering CH4 as a model absorbing gas. We employed the absorbance thus calculated using HITRAN to validate the experimentally measured absorbance of CH4. The maximum error between the measured and calculated absorbance values were within 1%. The approach can be generalized as a chemometric calibration technique for measuring gases and gas mixtures that absorb emissions from polychromatic or not-perfect-monochromatic sources, provided the gas concentration, optical path length, as well as blank and attenuated emission spectra of the light source are incorporated into the proposed chemometric approach.

Effect of water vapour absorption on hydroxyl temperatures measured from Svalbard

Abstract. We model absorption by atmospheric water vapour of hydroxyl airglow emission using the HIgh-resolution TRANsmission molecular absorption database (HITRAN2012). Transmission coefficients are provided as a function of water vapour column density for the strongest OH Meinel emission lines in the (8–3), (5–1), (9–4), (8–4), and (6–2) vibrational bands. These coefficients are used to determine precise OH(8–3) rotational temperatures from spectra measured by the High Throughput Imaging Echelle Spectrograph (HiTIES), installed at the Kjell Henriksen Observatory (KHO), Svalbard. The method described in this paper also allows us to estimate atmospheric water vapour content using the HiTIES instrument.