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Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atm... more Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere. For instance, the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft is very useful to analyze the O 2 (a 1 ∆) nightglow at 1.27 µm in the Venus mesosphere. Nadir observations can be used to create a statistical map of the emission on Venus nightside. It appears that the maximum of the emission is located near the antisolar point. Limb observations also provide information on the altitude and on the shape of the emission layer. Combining nadir observations and vertically integrated limb observations improves the statistics of the emission map on Venus nightside. An associated limb profile can also be deduced for any point of the nightside. Given all these O 2 (a 1 ∆) intensity profiles, O 2 * density profiles can be calculated. O density profiles can also be calculated as long as CO 2 density profiles are available. These can be retrieved either from the VTS3 model or from SPICAV stellar occultation measurements. Finally, three-dimensional maps of excited molecular and atomic oxygen densities can be generated. The oxygen density map shows significant differences from the VTS3 model predictions.

The O2 (a1Δ) emission at 1.27 μm results from threebody recombination of O atoms produced on the ... more The O2 (a1Δ) emission at 1.27 μm results from threebody recombination of O atoms produced on the day side and transported to the night side by the global solar to antisolar circulation. It is variable in brightness and shows a peak generally located between 95 and 100 km. In this study, we present individual nadir images of the O2 (a1Δ) nightside airglow emission [1,2] obtained with VIRTIS IR on board Venus Express [3]. A total of 460 VIRTIS images lasting several hours are used to determine the spatial and temporal variations of regions of enhanced excited O2 (a1Δ) density. The intensity may either increase or decrease during the observation period. Intensity drop is expected as a result of three competing processes: (1) the radiative lifetime of the O2 (a1Δ) metastable state of 75 min, (2) the effective lifetime of oxygen atoms versus chemical recombination and (3) changes in the local downward flux of O atoms carried by dynamical processes (diffusion, advection).

Astronomy & Astrophysics, 2000

We present thermal infrared images of Saturn recorded with the Canada-France-Hawaii 3.6 meter Tel... more We present thermal infrared images of Saturn recorded with the Canada-France-Hawaii 3.6 meter Telescope (CFHT) in 1992, during Saturn's northern summer (145.5° of solar longitude). These observations were made using C10mu , a 64x64 pixel camera, at 6 different wavelengths (10.91, 11.69, 12.47, 13.09, 13.29 and 13.48 symb{char22 m), sensitive to phosphine (PH_3), ethane (C_2H_6), and acetylene (C_2H_2). Many features

The Three Galileos: The Man, the Spacecraft, the Telescope, 1997

The chemical processes responsible for the formation of minor trace species and the structure of ... more The chemical processes responsible for the formation of minor trace species and the structure of clouds in Jupiter’s atmosphere are discussed. Comparisons with relevant Galileo Probe and Orbiter measurements give important new insight into chemistry, thermodynamics, and meteorology in the atmosphere. A brief overview of the bulk atmospheric composition is included since it forms the basis for the chemical and cloud formation processes.

A new retrieval approach is applied to Venus nightside measurements from VIRTIS-M-IR on Venus Exp... more A new retrieval approach is applied to Venus nightside measurements from VIRTIS-M-IR on Venus Express. This is used to improve former analyses in order to refine estimates on the surface emissivity and deep atmosphere of Venus.

Venus Express gives the opportunity to study in great detail the O 2 nightglow in the IR spectral... more Venus Express gives the opportunity to study in great detail the O 2 nightglow in the IR spectral range, thanks to the extensive dataset acquired by VIRTIS, the Visible and Infrared Thermal Imaging Spectrometer on board the orbiter. The variability of the nightglow intensity has been debated in various papers [1, 2, 3, 4], and recently in [5]. One puzzle to solve is the unsatisfactory fit between data and synthetic spectrum at about 1.28 μm and thus we have further investigated the spectral properties of the emission. The spectral region around 1.27 μm is characterized by the presence of the bright (a−X)(0,0) O 2 band, the most intense nightglow emission observed on the night side of Venus. Another band, the (a−X)(1,1) O 2 band, is expected to occur at 1.28 μm, although it cannot be independently resolved from the (0-0) with VIRTIS, because of the relatively low spectral resolution. We find that the inclusion of this emission significantly improves the spectral fit around 1.27-1.28 μm. We also report the discovery of the presence of the (1-1) band and describe its vertical distribution.

A review of results about the Venus atmosphere achieved by the VIRTIS instrument on board the ESA... more A review of results about the Venus atmosphere achieved by the VIRTIS instrument on board the ESA Venus Express mission. The VIRTIS imaging spectrometer in the range of 0.25 to 5 µm provide a powerful means to study Venus in depth from the surface up to the upper atmosphere.

Thermal structure of the Venus nightside is investigated using VIRTIS-Venus Express data, coverin... more Thermal structure of the Venus nightside is investigated using VIRTIS-Venus Express data, covering the latitude range from 80°S to 80°N. Comparison with the LCD Venus GCM model show a qualitatively remarkable agreement.

Planetary and Space Science, 1993

The 3-5 pm thermal emission of the nightside of Venus, recorded by the NIMS instrument at the tim... more The 3-5 pm thermal emission of the nightside of Venus, recorded by the NIMS instrument at the time of the Galileo flyby of Venus. is analysed to infer the properties of the upper cloud boundary. From the global maps of Venus at fixed wavelengths, the limb darkening of the flux is measured at several latitudes, within each infrared channel. By using the nominal Pioneer Venus thermal profile. these data give access to two parameters : the cloud deck temperature and the cloud scale height. It is verified independently, from the NIMS spectra. that this thermal profile is consistent with all the NIMS observations. and that the thermal structure does not vary significantly in the latitude range (25 S, 30 N). Within this range, the cloud scale height is found to be constant with latitude. and is H = 5.2 km, with an accuracy of about 15%. taking into account the various sources of theoretical and observational uncertainties. At higher latitudes, the temperature profile becomes more isothermal and the presented method to retrieve His no longer valid.

Planetary and Space Science, 1993

Journal of Geophysical Research: Planets, 2009

The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 ... more The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)–X(v″) progression more than 3 decades ago. We search for its emission at 400 nm–700 nm in spectra obtained with the VIRTIS instrument on Venus Express. Despite the weakness of the signal, integration over a few hours of limb observations of the planet's upper atmosphere reveals the unambiguous pattern of the progression. The selected data sample mainly the northern latitudes within a few hours of local midnight. The emission is ubiquitous on the nightside of Venus and can be discerned at tangent altitudes from 80 km to 110 km. The average emission vertical profiles of the c(0)–X(v″) progression and the O2a(0)–X(0) band, the latter from simultaneous near‐infrared spectra, are quite similar, with their respective peaks occurring within ±1 km of each other. We conclude that the net yield for production of the c(0) state is low, ∼1%–2% of the oxygen reco...

Journal of Geophysical Research: Planets, 2007

Observing and analyzing the variations of pressure on the surface of a planet is essential to und... more Observing and analyzing the variations of pressure on the surface of a planet is essential to understand the dynamics of its atmosphere. On Mars the absorption by atmospheric CO2 of the solar light reflected on the surface allows us to measure the surface pressure by remote sensing. We use the imaging spectrometer OMEGA aboard Mars Express, which provides an excellent signal to noise ratio and the ability to produce maps of surface pressure with a resolution ranging from 400 m to a few kilometers. Surface pressure is measured by fitting spectra of the CO2 absorption band centered at 2 μm. To process the hundreds of thousands of pixels present in each OMEGA image, we have developed a fast and accurate algorithm based on a line‐by‐line radiative transfer model which includes scattering and absorption by dust aerosols. In each pixel the temperature profile, the dust opacity, and the surface spectrum are carefully determined from the OMEGA data set or from other sources to maximize the ...

Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atm... more Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere. For instance, the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft is very useful to analyze the O 2 (a 1 ∆) nightglow at 1.27 µm in the Venus mesosphere. Nadir observations can be used to create a statistical map of the emission on Venus nightside. It appears that the maximum of the emission is located near the antisolar point. Limb observations also provide information on the altitude and on the shape of the emission layer. Combining nadir observations and vertically integrated limb observations improves the statistics of the emission map on Venus nightside. An associated limb profile can also be deduced for any point of the nightside. Given all these O 2 (a 1 ∆) intensity profiles, O 2 * density profiles can be calculated. O density profiles can also be calculated as long as CO 2 density profiles are available. These can be retrieved either from the VTS3 model or from SPICAV stellar occultation measurements. Finally, three-dimensional maps of excited molecular and atomic oxygen densities can be generated. The oxygen density map shows significant differences from the VTS3 model predictions.

The O2 (a1Δ) emission at 1.27 μm results from threebody recombination of O atoms produced on the ... more The O2 (a1Δ) emission at 1.27 μm results from threebody recombination of O atoms produced on the day side and transported to the night side by the global solar to antisolar circulation. It is variable in brightness and shows a peak generally located between 95 and 100 km. In this study, we present individual nadir images of the O2 (a1Δ) nightside airglow emission [1,2] obtained with VIRTIS IR on board Venus Express [3]. A total of 460 VIRTIS images lasting several hours are used to determine the spatial and temporal variations of regions of enhanced excited O2 (a1Δ) density. The intensity may either increase or decrease during the observation period. Intensity drop is expected as a result of three competing processes: (1) the radiative lifetime of the O2 (a1Δ) metastable state of 75 min, (2) the effective lifetime of oxygen atoms versus chemical recombination and (3) changes in the local downward flux of O atoms carried by dynamical processes (diffusion, advection).

Astronomy & Astrophysics, 2000

We present thermal infrared images of Saturn recorded with the Canada-France-Hawaii 3.6 meter Tel... more We present thermal infrared images of Saturn recorded with the Canada-France-Hawaii 3.6 meter Telescope (CFHT) in 1992, during Saturn's northern summer (145.5° of solar longitude). These observations were made using C10mu , a 64x64 pixel camera, at 6 different wavelengths (10.91, 11.69, 12.47, 13.09, 13.29 and 13.48 symb{char22 m), sensitive to phosphine (PH_3), ethane (C_2H_6), and acetylene (C_2H_2). Many features

The Three Galileos: The Man, the Spacecraft, the Telescope, 1997

The chemical processes responsible for the formation of minor trace species and the structure of ... more The chemical processes responsible for the formation of minor trace species and the structure of clouds in Jupiter’s atmosphere are discussed. Comparisons with relevant Galileo Probe and Orbiter measurements give important new insight into chemistry, thermodynamics, and meteorology in the atmosphere. A brief overview of the bulk atmospheric composition is included since it forms the basis for the chemical and cloud formation processes.

A new retrieval approach is applied to Venus nightside measurements from VIRTIS-M-IR on Venus Exp... more A new retrieval approach is applied to Venus nightside measurements from VIRTIS-M-IR on Venus Express. This is used to improve former analyses in order to refine estimates on the surface emissivity and deep atmosphere of Venus.

Venus Express gives the opportunity to study in great detail the O 2 nightglow in the IR spectral... more Venus Express gives the opportunity to study in great detail the O 2 nightglow in the IR spectral range, thanks to the extensive dataset acquired by VIRTIS, the Visible and Infrared Thermal Imaging Spectrometer on board the orbiter. The variability of the nightglow intensity has been debated in various papers [1, 2, 3, 4], and recently in [5]. One puzzle to solve is the unsatisfactory fit between data and synthetic spectrum at about 1.28 μm and thus we have further investigated the spectral properties of the emission. The spectral region around 1.27 μm is characterized by the presence of the bright (a−X)(0,0) O 2 band, the most intense nightglow emission observed on the night side of Venus. Another band, the (a−X)(1,1) O 2 band, is expected to occur at 1.28 μm, although it cannot be independently resolved from the (0-0) with VIRTIS, because of the relatively low spectral resolution. We find that the inclusion of this emission significantly improves the spectral fit around 1.27-1.28 μm. We also report the discovery of the presence of the (1-1) band and describe its vertical distribution.

A review of results about the Venus atmosphere achieved by the VIRTIS instrument on board the ESA... more A review of results about the Venus atmosphere achieved by the VIRTIS instrument on board the ESA Venus Express mission. The VIRTIS imaging spectrometer in the range of 0.25 to 5 µm provide a powerful means to study Venus in depth from the surface up to the upper atmosphere.

Thermal structure of the Venus nightside is investigated using VIRTIS-Venus Express data, coverin... more Thermal structure of the Venus nightside is investigated using VIRTIS-Venus Express data, covering the latitude range from 80°S to 80°N. Comparison with the LCD Venus GCM model show a qualitatively remarkable agreement.

Planetary and Space Science, 1993

The 3-5 pm thermal emission of the nightside of Venus, recorded by the NIMS instrument at the tim... more The 3-5 pm thermal emission of the nightside of Venus, recorded by the NIMS instrument at the time of the Galileo flyby of Venus. is analysed to infer the properties of the upper cloud boundary. From the global maps of Venus at fixed wavelengths, the limb darkening of the flux is measured at several latitudes, within each infrared channel. By using the nominal Pioneer Venus thermal profile. these data give access to two parameters : the cloud deck temperature and the cloud scale height. It is verified independently, from the NIMS spectra. that this thermal profile is consistent with all the NIMS observations. and that the thermal structure does not vary significantly in the latitude range (25 S, 30 N). Within this range, the cloud scale height is found to be constant with latitude. and is H = 5.2 km, with an accuracy of about 15%. taking into account the various sources of theoretical and observational uncertainties. At higher latitudes, the temperature profile becomes more isothermal and the presented method to retrieve His no longer valid.

Planetary and Space Science, 1993

Journal of Geophysical Research: Planets, 2009

The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 ... more The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)–X(v″) progression more than 3 decades ago. We search for its emission at 400 nm–700 nm in spectra obtained with the VIRTIS instrument on Venus Express. Despite the weakness of the signal, integration over a few hours of limb observations of the planet's upper atmosphere reveals the unambiguous pattern of the progression. The selected data sample mainly the northern latitudes within a few hours of local midnight. The emission is ubiquitous on the nightside of Venus and can be discerned at tangent altitudes from 80 km to 110 km. The average emission vertical profiles of the c(0)–X(v″) progression and the O2a(0)–X(0) band, the latter from simultaneous near‐infrared spectra, are quite similar, with their respective peaks occurring within ±1 km of each other. We conclude that the net yield for production of the c(0) state is low, ∼1%–2% of the oxygen reco...

Journal of Geophysical Research: Planets, 2007

Observing and analyzing the variations of pressure on the surface of a planet is essential to und... more Observing and analyzing the variations of pressure on the surface of a planet is essential to understand the dynamics of its atmosphere. On Mars the absorption by atmospheric CO2 of the solar light reflected on the surface allows us to measure the surface pressure by remote sensing. We use the imaging spectrometer OMEGA aboard Mars Express, which provides an excellent signal to noise ratio and the ability to produce maps of surface pressure with a resolution ranging from 400 m to a few kilometers. Surface pressure is measured by fitting spectra of the CO2 absorption band centered at 2 μm. To process the hundreds of thousands of pixels present in each OMEGA image, we have developed a fast and accurate algorithm based on a line‐by‐line radiative transfer model which includes scattering and absorption by dust aerosols. In each pixel the temperature profile, the dust opacity, and the surface spectrum are carefully determined from the OMEGA data set or from other sources to maximize the ...