H216O and HDO measurements with IASI/MetOp

International audienceIn this paper we analyze distributions of water vapour isotopologues in the troposphere using infrared spectra recorded by the Infrared Atmospheric Sounding Interferometer (IASI), which operates onboard the Metop satellite in nadir geometry. The simultaneous uncorrelated retrievals of H216O and HDO are performed on radiance measurements using a line-by-line radiative transfer model and an inversion procedure based on the Optimal Estimation Method (OEM). The characterizations of the retrieved products in terms of vertical sensitivity and error budgets show that IASI measurements contain up to 6 independent pieces of information on the vertical distribution of H216O and up to 3.5 for HDO from the surface up to the upper troposphere (0–20 km). Although the purpose of the paper is not validation, a restricted comparison with sonde measurements shows that the retrieved H216O profiles capture the seasonal/latitudinal variations of the water content, with good accuracy in the lowest layer but with larger uncertainties higher in the free and upper troposphere. Our results then demonstrate the ability of the IASI instrument to monitor atmospheric isotopologic water vapour distributions and to provide information on the partitioning of HDO as compared to H216O. The derivation of the δD is challenging and associated with large errors in the uncorrelated retrieval approach chosen here. As a result averaging on the vertical to produce a column-averaged δD is required to produce meaningful results for geophysical interpretation. As a case study, we analyse concentration distributions and spatio-temporal variations of H216O and δD during the October 2007 Krosa super-typhoon over South-East Asia. We show that individual δD have uncertainties of 37‰ for the vertically averaged values. Using the latter, we suggest that the typhoon produces a so-called amount-effect, where the δD is negatively correlated to the water amounts as a result of intense depletion of the deuterated species

Towards IASI-New Generation (IASI-NG): impact of improved spectral resolution and radiometric noise on the retrieval of thermodynamic, chemistry and climate variables

Besides their strong contribution to weather forecast improvement through data assimilation, thermal infrared sounders onboard polar-orbiting platforms are now playing a key role for monitoring atmospheric composition changes. The Infrared Atmospheric Sounding Interferometer (IASI) instrument developed by the French space agency (CNES) and launched by Eumetsat onboard the Metop satellite series is providing essential inputs for weather forecasting and pollution/climate monitoring owing to its smart combination of large horizontal swath, good spectral resolution and high radiometric performance. EUMETSAT is currently preparing the next polar-orbiting program (EPS-SG) with the Metop-SG satellite series that should be launched around 2020. In this framework, CNES is studying the concept of a new instrument, the IASI-New Generation (IASI-NG), characterized by an improvement of both spectral and radiometric characteristics as compared to IASI, with three objectives: (i) continuity of the IASI/Metop series; (ii) improvement of vertical resolution; (iii) improvement of the accuracy and detection threshold for atmospheric and surface components. In this paper, we show that an improvement of spectral resolution and radiometric noise fulfill these objectives by leading to (i) a better vertical coverage in the lower part of the troposphere, thanks to the increase in spectral resolution; (ii) an increase in the accuracy of the retrieval of several thermodynamic, climate and chemistry variables, thanks to the improved signal-to-noise ratio as well as less interferences between the signatures of the absorbing species in the measured radiances. The detection limit of several atmospheric species is also improved. We conclude that IASI-NG has the potential for strongly benefiting the numerical weather prediction, chemistry and climate communities now connected through the European GMES/Copernicus initiative

Towards IASI-New Generation (IASI-NG): impact of improved spectral resolution and radiometric noise on the retrieval of thermodynamic, chemistry and climate variables

Besides their strong contribution to weather forecast improvement through data assimilation, thermal infrared sounders onboard polar-orbiting platforms are now playing a key role for monitoring atmospheric composition changes. The Infrared Atmospheric Sounding Interferometer (IASI) instrument developed by the French space agency (CNES) and launched by Eumetsat onboard the Metop satellite series is providing essential inputs for weather forecasting and pollution/climate monitoring owing to its smart combination of large horizontal swath, good spectral resolution and high radiometric performance. EUMETSAT is currently preparing the next polar-orbiting program (EPS-SG) with the Metop-SG satellite series that should be launched around 2020. In this framework, CNES is studying the concept of a new instrument, the IASI-New Generation (IASI-NG), characterized by an improvement of both spectral and radiometric characteristics as compared to IASI, with three objectives: (i) continuity of the IASI/Metop series; (ii) improvement of vertical resolution; (iii) improvement of the accuracy and detection threshold for atmospheric and surface components. In this paper, we show that an improvement of spectral resolution and radiometric noise fulfill these objectives by leading to (i) a better vertical coverage in the lower part of the troposphere, thanks to the increase in spectral resolution; (ii) an increase in the accuracy of the retrieval of several thermodynamic, climate and chemistry variables, thanks to the improved signal-to-noise ratio as well as less interferences between the signatures of the absorbing species in the measured radiances. The detection limit of several atmospheric species is also improved. We conclude that IASI-NG has the potential for strongly benefiting the numerical weather prediction, chemistry and climate communities now connected through the European GMES/Copernicus initiative

Spectroscopie sélective de TiCl et NO (détection infrarouge ultrasensible de N2O et N2)

Cette thèse concerne l'application de nouvelles méthodes de spectroscopie sélective ou ultrasensible à la détermination de paramètres spectroscopiques de molécules stables et instables, difficilement accessibles par ailleurs.Dans un premier temps, la spectroscopie par transformation de Fourier sélective a été utilisée pour caractériser des plasmas TiCl4/He et N2O/He. Le spectre de l'ensemble des émissions d'un plasma et des spectres qui sélectionnent une classe particulière de molécules (faible durée de vie ou ions) sont enregistrés simultanément. En particulier, la transition X - C de 48Ti35Cl a été observée dans la région de 3 m. Son analyse a mis en évidence des perturbations de très faible amplitude. De plus, les spectres sélectifs du plasma N2O/He, supposés ne retenir que les raies des ions, ont révélé d'intenses transitions entre états de Rydberg de NO. Ces raies subissent un déplacement Doppler similaire à celui d'un ion positif. Une interprétation de ce phénomène inattendu, mis en évidence pour la première fois pour une molécule neutre, est proposée. Dans un second temps, des spectres avec des longueurs d'absorption de plusieurs dizaines de kilomètres ont été enregistrés en utilisant le couplage de la spectroscopie d'absorption intracavité laser et de la spectroscopie de Fourier résolue en temps. Deux expériences différentes ont permis de sonder, de façon très sensible, des domaines spectraux infrarouge relativement étendus. Autour de 2.5 m, de nombreuses transitions de faible intensité de la molécule d'intérêt atmosphérique N2O ont été identifiées et analysées. Des espèces instables formées dans un plasma N2/He ont également été détectées autour de 1.05 m.This PhD thesis deals with the application of recent high resolution spectroscopic methods that are either selective or ultrasensitive. Spectroscopic parameters of stable and transient molecular species, difficult to reach otherwise, are determined.First, selective Fourier transform spectroscopy is used to characterize TiCl4/He and N2O/He plasmas. The spectrum of the whole emission of a plasma and spectra, which select a given class of molecules (for instance short-lived or ions) are simultaneously recorded. In particular, the rovibronic transition X - C of the 48Ti35Cl radical is observed around 3 m. Its analysis has shown a very weak perturbation, which affects the C 4D1/2 state. Moreover, selective spectra of a N2O/He plasma, expected to only retain the ion lines, have revealed NO rovibronic transitions between the A, C, D and E Rydberg states. Under specific experimental conditions, a Doppler shift of the NO transitions, similar to the one of a positive ion, is observed. An interpretation of this unexpected phenomenon, highlighted for the first time for a neutral molecule, is proposed. Second, spectra with absorption lengths of several tens kilometers are recorded by coupling intracavity laser absorption spectroscopy (ICLAS) and time-resolved Fourier transform spectroscopy (TRFTS). Two different experiments have make it possible to probe, with high sensitivity, relatively wide infrared spectral ranges. Around 2.5 m, lots of weak intensity rovibrational transitions of the atmospherically relevant molecule N2O are identified and analysed. Unstable species created in a N2/He plasma are also detected for the first time around 1.05 m.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Measuring Volcanic Ash With High-Spectral Resolution Infrared Sounders: Role of Refractive Indices

International audienc

Complex refractive index of crystalline quartz particles from UV to thermal infrared

International audienceCrystalline quartz is an important element of many materials and one of the major compounds of mineral dust. Thus, knowledge of its optical properties is essential for many applications, in particular for remote sensing techniques. However, despite the fact that crystalline quartz has been an object of study for many years using various experimental approaches, its optical properties and in particular its complex refractive indices (CRI) remain uncertain. The focus of this investigation is the determination of a new set of CRI of crystalline quartz particles retrieved from a methodology which has already demonstrated its efficiency on pure amorphous materials and volcanic ashes. The experimental set-up allows recording simultaneously size distribution (from 15 nm to 20 µm) of airborne particles and extinction spectra over a wide continuous spectral range from thermal infrared (650 cm−1) to UV (40,000 cm−1) with high spectral resolution (up to 0.5 cm−1). By associating these measurements and a numerical procedure coupling scattering theories, the single subtractive Kramers-Kronig relation, and an optimal estimation method in an iterative process, we precisely determine the real and imaginary parts of the CRI of crystalline SiO2 with mean values of the uncertainties of 2.5% and 1.7%, respectively. Moreover, the use of these CRIs allows to simulate an extinction spectrum of another quartz sample very well, which shows their suitability as well as the good reproducibility of the whole process

Concentration-modulation FT emission spectroscopy of TiCl_4/He plasma. Analysis of the C ^4\Delta- X ^4 \Phi \Delta v=0 perturbed transitions of TiCl.

International audienceA TiCl_4/He plasma is observed by high resolution double-modulation FTS using concentration-modulation as a selective detection method. Analysis of the C ^4\Delta- X ^4 \Phi \Delta v=0 transitions of ^48Ti^35Cl reveals perturbations affecting the C ^4\Delta_{1/2} sub-state

UNEXPECTED DOPPLER SHIFTS FROM A NEUTRAL MOLECULE IN AN ELECTRICAL DISCHARGE DETECTED BY VELOCITY MODULATION FTS.

$^{a}$N. Picqu\'{e}, G. Guelachvili, High resolution multi-modulation Fourier transform spectroscopy, Applied Optics 38, 1224-1230, 1999. $^{b}$C.S. Gudeman, M.H. Begeman, J. Pfaff, and R.J. Saykally, Velocity modulated infrared laser spectroscopy of molecular ions: the $\nu_{1}$ band of $HCO^{+}$, Physical Review Letters 50, 727-731, 1983. $^{c}$X. Hong and T. A. Miller, Observation of characteristic, polarity-dependent, Doppler shifts from neutral species in the positive column of a discharge plasma, The Journal of Chemical Physics 103, 8821-8827 (1995). $^{d}$M.H. Suh, X. Hong and T.A. Miller, He metastable concentration measurements in a glow discharge, Chemical Physics 228, 145-156 (1998).Author Institution: Laboratoire de Photophysique Mol\'{e}culaire, Unit\'{e} Propre du CNRS, Universit\'{e} de Paris-SudVelocity-modulation Fourier $transform^{a}$ emission spectra from an $N_{2}O/He$ discharge plasma recorded between 1 800 and $10 000 cm^{-1}$ are described. Surprisingly, they show Doppler shifted lines of the $E ^{2}\Sigma^{+}-D{^{2}}\Sigma^{+}, C{^{2}}\Pi-A {^{2}}\Sigma^{+}$ and $D {^{2}}\Sigma^{+}-A{^{2}}\Sigma^{+}$ Rydberg-Rydberg rovibronic transitions of the nitric oxide neutral molecule. $N_{2}$ transitions, with comparable intensities are also present in the spectra and remain unshifted. Mostly in laser spectroscopy, velocity $modulation^{b}$ has been since 1983 a successful technique developed for the search and characterization of molecular ions. Doppler shifts in transition frequencies of ions, which result from the drift velocities in the electric field of plasma, provide selective detection. Doppler shifted neutral species have been scarcely reported. To our knowledge the only interpretations of such observations were given for $H_{2}^{c}$ and for $He^{d}$. Both behaved like anions and the origin of their shifts was identified as deriving from momentum transfer in electron-molecule collisions. This is not the case in the present experiments where NO acts like a positively charged particle. Experimental investigations and tentative explanations of these observations are discussed

Instrumental characteristics and potential greenhouse gas measurement capabilities of the Compact High-Spectral-Resolution Infrared Spectrometer: CHRIS

International audienceGround-based high-spectral-resolution infrared measurements are an efficient way to obtain accurate tropospheric abundances of different gaseous species, in particular greenhouse gases (GHGs) such as CO2 and CH4. Many ground-based spectrometers are used in the NDACC and TCCON networks to validate the Level 2 satellite data, but their large dimensions and heavy mass make them inadequate for field campaigns. To overcome these problems, the use of portable spectrometers was recently investigated. In this context, this paper deals with the CHRIS (Compact High-Spectral-Resolution Infrared Spectrometer) prototype with unique characteristics such as its high spectral resolution (0.135 cm-1 nonapodized) and its wide spectral range (680 to 5200 cm-1). Its main objective is the characterization of gases and aerosols in the thermal and shortwave infrared regions. That is why it requires high radiometric precision and accuracy, which are achieved by performing spectral and radiometric calibrations that are described in this paper. Furthermore, CHRIS's capabilities to retrieve vertical CO2 and CH4 profiles are presented through a complete information content analysis, a channel selection and an error budget estimation in the attempt to join ongoing campaigns such as MAGIC (Monitoring of Atmospheric composition and Greenhouse gases through multi-Instruments Campaigns) to monitor GHGs and validate the actual and future space missions such as IASI-NG and Microcarb

Measuring Volcanic Ash with High-Spectral Resolution Infrared Sounders: Role of Refractive Indices

info:eu-repo/semantics/publishe