ACCURATE LABORATORY DETERMINATION OF THE MID AND SHORT WAVE INFRARED WATER VAPOR SELF-CONTINUUM. NEW MEASUREMENTS AND TEST OF THE MT_CKD MODEL

The semi empirical MT\_CKD model of the absorption continuum of water vapor is widely used in atmospheric radiative transfer codes of the atmosphere of Earth and, recently, of exoplanets, but lacks of experimental validation in the atmospheric windows. We report on accurate water vapor absorption continuum measurements by Cavity Ring Down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Laser Spectroscopy (OF-CEAS) at selected spectral points of the transparency windows centered around 4.0, 2.1, 1.6 and 1.25 $\mu$m. Temperature dependence of the absorption continuum is also measured in the 23-50 $^{\circ}$C range for a few spectral points. The self-continuum water vapor absorption is derived either from the baseline variation of water vapor spectra recorded for a series of pressure values over a small spectral interval or from baseline monitoring at fixed laser frequency during pressure ramps. After subtraction of the local water monomer lines contribution, self-continuum cross-sections, C$_{S}$, are accurately determined from the pressure squared dependence of the continuum absorption measured up to about 15 Torr. The derived water vapor self-continuum provides a unique set of water vapor self-continuum cross-sections for a test of the MT\_CKD model in four transparency windows

HIGH SENSITIVITY CRDS OF CO2 IN THE 1.74 μM TRANSPARENCY WINDOW. A VALIDATION TEST FOR THE SPECTROSCOPIC DATABASES

The very weak absorption spectrum of natural CO$_{2}$ near 1.74 $\mu$m (5702 - 5879 \wn) is studied at high sensitivity. The investigated region corresponds to a transparency window of very weak opacity which is of particular interest for Venus. Very weak lines with intensity value as low as 10$^{-30}$ cm/molecule at 296 K are detected by Cavity Ring Down Spectroscopy. On the basis of the predictions of effective Hamiltonian models, 1135 lines of six carbon dioxide isotopologues - $^{12}$C$^{16}$O$_{2}$, $^{13}$C$^{16}$O$_{2}$, $^{16}$O$^{12}$C$^{18}$O, $^{16}$O$^{12}$C$^{17}$O, $^{16}$O$^{13}$C$^{18}$O and $^{16}$O$^{13}$C$^{17}$O - were rovibrationnally assigned to 26 bands. The accurate spectroscopic parameters of 16 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are $8 \times 10$$^{-4}$ \wn). These newly observed bands include perturbed bands, weak hot bands and bands of minor isotopologues (in particular $^{16}$O$^{12}$C$^{18}$O in natural abundance) and provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD), HITRAN2016 database and recent ab initio line lists will be presented. Deficiencies are evidenced for some weak perpendicular bands of the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to \textit{ab initio} intensities. New results based on $^{18}$O enriched CO$_{2}$ spectra will also be detailed

COLLISION INDUCED ABSORPTION OF THE a1∆g-X3Σ−g BAND OF OXYGEN NEAR 1.27 μM BY CAVITY RING DOWN SPECTROSCOPY

Collision induced absorption (CIA) coefficients of the a$^{1}$$\Delta$$_{g}$-X$^{3}$$\Sigma$$^{-}$$_{g}$(v=0-0) band of oxygen have been measured using cavity ring down spectroscopy (CRDS) technique at room temperature. More precisely, the B$_{O2-O2}$, B$_{O2-N2}$ and B$_{O2-Air}$ coefficients have been determined with a reduced uncertainty from series of low density spectra (from 0.36 to 0.85 amagat) of pure oxygen and N$_{2}$+O$_{2}$ mixture with O$_{2}$=20.95\%. For that 12 distributed feed-back laser diodes were used below 7920 \wn together with an external cavity diode laser above this wavenumber. We particularly paid attention to the base line stability ($2 \times 10$$^{-10}$ \wn) during the entire measurements. CIA was obtained from the difference between the absorbing samples spectra and argon spectra recorded for the same densities after removal of the local contribution of the absorption lines. The low densities at which the spectra were recorded were very useful to reliably remove this local contribution. The retrieved coefficients were compared to the CIA reported in HITRAN2016. A good overall agreement is found but differences between 5 and 8\% for B$_{O2-Air}$ coefficients are observed below 7850 \wn

Study of ozone smog episodes by Lidar 3D measurements in Lyon and Paris during summer 1999

Every summer, ozone smog episodes systematically take place in large agglomerations. In order to prevent them, a better understanding of formation dynamics is needed using numerical models. These models must, however, be validated. Lidar is a unique tool for this task since it provides 3D measurements, for example combining 2D spatial measurements with time in an "animation movie". We present here two recent examples of such ozone Lidar measurement campaigns: the first over Lyon, was mainly used to evaluate a UAM-V type photochemical model and obtain ozone inter comparison data between ground level monitors and Lidar results. The other was performed in Paris and dedicated to validating the Lidar measurements themselves

The water vapour continuum in near-infrared windows – current understanding and prospects for its inclusion in spectroscopic databases

Spectroscopic catalogues, such as GEISA and HITRAN, do not yet include information on the water vapour continuum that pervades visible, infrared and microwave spectral regions. This is partly because, in some spectral regions, there are rather few laboratory measurements in conditions close to those in the Earth’s atmosphere; hence understanding of the characteristics of the continuum absorption is still emerging. This is particularly so in the near-infrared and visible, where there has been renewed interest and activity in recent years. In this paper we present a critical review focusing on recent laboratory measurements in two near-infrared window regions (centred on 4700 and 6300 cm−1) and include reference to the window centred on 2600 cm−1 where more measurements have been reported. The rather few available measurements, have used Fourier transform spectroscopy (FTS), cavity ring down spectroscopy, optical-feedback – cavity enhanced laser spectroscopy and, in very narrow regions, calorimetric interferometry. These systems have different advantages and disadvantages. Fourier Transform Spectroscopy can measure the continuum across both these and neighbouring windows; by contrast, the cavity laser techniques are limited to fewer wavenumbers, but have a much higher inherent sensitivity. The available results present a diverse view of the characteristics of continuum absorption, with differences in continuum strength exceeding a factor of 10 in the cores of these windows. In individual windows, the temperature dependence of the water vapour self-continuum differs significantly in the few sets of measurements that allow an analysis. The available data also indicate that the temperature dependence differs significantly between different near-infrared windows. These pioneering measurements provide an impetus for further measurements. Improvements and/or extensions in existing techniques would aid progress to a full characterisation of the continuum – as an example, we report pilot measurements of the water vapour self-continuum using a supercontinuum laser source coupled to an FTS. Such improvements, as well as additional measurements and analyses in other laboratories, would enable the inclusion of the water vapour continuum in future spectroscopic databases, and therefore allow for a more reliable forward modelling of the radiative properties of the atmosphere. It would also allow a more confident assessment of different theoretical descriptions of the underlying cause or causes of continuum absorption

Methane and water spectroscopic database for TROPOMI/Sentinel-5 Precursor in the 2.3 μm region

The ESA project „SEOM-Improved Atmospheric Spectroscopy Databases (IAS)“ will improve the spectroscopic database for retrieval of the data products CO, CH4, O3 and SO2 column amounts measured by the TROPOMI instrument (TROPOspheric Monitoring Instrument) aboard the Sentinel-5 Precursor. The project was launched in February 2014 with 3 years duration extended to 4 years recently. The spectroscopy of CO, CH4 and O3 in the 2.3 ?m region is covered first while UV measurements of SO2 and UV/FIR/IR measurements of ozone will be carried out later. Measurements were mainly taken with a high resolution Fourier Transform spectrometer combined with a coolable multi reflection cell. Cavity ring down measurements served for validation. The analysis has been completed. A clear improvement can be seen when using the new data for CH4, H2O and CO retrieval from ground-based high resolution solar occultation measurements obtained with instrumentation in the TCCON and NDACC network