OH airglow observation is a key component of understanding the dynamics of the Mesosphere - Lower Thermosphere, as its maximum altitude of roughly 87 km and the relatively good transmittance of the atmosphere make it an interesting tracer of middle atmosphere dynamics. Our study focuses on ground-based OH observation using both SWIR and visible cameras, with an instrumental setup capable of retrieving gravity-wave parameters and temperature in the OH layer, thus enabling measurements of the Krassovsky ratio (ranging from 1 to 10). These measurements provide us a good point of comparison with a model of OH perturbation by gravity waves, DOWRI, which we will present and describe in this article, introducing a new polarization relation on airglow intensity, supplemented by observational validation and SABER comparisons.

The infrared emission lines observed between 80 and 100 km known as nightglow allow the investigation of dynamic phenomena such as gravity waves with adapted cameras. In particular, the OH nightglow emission peaking at 87 km can be observed with short wave infrared InGaAs cameras and most of studies use these observations to investigate dynamics at this height. In this study, we briefly describe the methodology to assess the availability of nightglow observations at ground level depending on the spectral bands and the local atmospheric conditions. The impact of clouds on the spectral radiance propagation is estimated by the use of radiative transfer models. Sensitivity tests are completed on clouds characteristics, such as vertical width or the type of clouds. In addition, we integrate directional fluxes on the celestial dome to assess the level of radiance available at the ground level for night vision imaging. Statistical temporal comparisons are performed using available observations campaigns at Observatory of Haute-Provence (OHP) and at Maïdo Observatory.

Lower ionosphere is the theater of interactions between the ionized atmosphere and homogeneous atmosphere. Some phenomena such as gravity and acoustic waves which originate from the homogeneous atmosphere also impact the ionosphere and are suspected to be the source of sporadic disturbances in the E-region. Our goal is to correlate these disturbances to acoustic and gravity waves through modelling and ionosphere sounding. We first present the first steps towards this goal, a bi-dimensionnal, inviscid and compressible acoustic-gravity wave model coupled to a nightglow emission model (NEMO). Then subsequent cross-comparisons with acoustic and gravity waves seen in the OH nightglow emission layer using an infrared sensor and MRA (Multi-Resolution Analysis) are discussed. These comparisons will help to improve the model’s rendering of wave impacts on their transportation medium, before extending the model’s range to ionospheric heights and properties.

Nightglow radiation is a very good marker of high-altitude dynamics. After a first detection of a tsunami signature by a camera in the O+ emission (red airglow at 250km) in 2011, only a few other tsunami detections have been recorded and none have been observed in OH SWIR emission, which is the brightest of all the nightglow emissions and the only compatible for shorter periods signals, such as seismic waves. On the other hand, these acoustic waves associated with earthquakes are systematically detected by other ionospheric instruments (GPS, radar), they have never been directly observed by an airglow camera. Can they be also detected by airglow?We present here our strategy for such proof of concept. If achieved, it will provide unique access to seismic waves propagation where ground instruments are not available: oceans, which cover more than 70% of the Earth's surface, but also to provide the harsh planetary environment of Venus, where airglow also exists and where it is not possible to send spacecraft to the ground.The recent development of SWIR cameras and the first detection of infrasound in OH radiation in 2020 opened the way for these detections. To better understand the continuous dynamics of the OH layer, we have deployed a first camera at La Réunion island in May 2023. Another one will be installed on the Japanese island of Oshima in February-March 2024 to try to detect the signature of a seismic event if one occurs during the course of this scientific study. The presentation details our methodology for observing the airglow OH perturbations, from the instrument specifications to the first results of almost one year-acquisition at la Réunion and the expected events that we will observe from Japan.

The dynamic vertical coupling in the middle and lower thermosphere (MLT) is documented over the Maïdo observatory at La Réunion island (21°S, 55°E). The investigation uses data obtained in the framework of the Atmospheric dynamics Research InfraStructure in Europe (ARISE) project. In particular, Rayleigh lidar and nightglow measurements combined with other observations and modeling provide information on a mesospheric inversion layer (MIL) and the related gravity waves (GWs) on 9 and 10 October 2017. A Rossby wave breaking (RWB) produced instabilities in the sheared background wind and a strong tropospheric activity of GWs on 9–11 October above La Réunion. The MIL was observed on the night of 9 October when a large amount of tropospheric GWs propagated upward into the middle atmosphere and disappeared on 11 October when the stratospheric zonal wind filtering became a significant blocking. Among other results, dominant mesospheric GW modes with vertical wavelengths of about 4–6 km and 10–13 km can be traced down to the troposphere and up to the mesopause. Dominant GWs with a wavelength of ~2–3 km and 6 km also propagated upward and eastward from the tropospheric source into the stratosphere on 9–11 October. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature and OH profiles indicate that GW activity in the middle atmosphere affects the upper atmosphere with waves breaking at heights below the MIL and in the mesopause. Several techniques are illustrated on nightglow images to access GW activity and spectral characteristics at the mesopause for high and low frequency GWs on the nights of 9–10 October. In conclusion, intense tropospheric activity of GWs induced by RWB events can be linked with MILs at the subtropical barrier in the South-West Indian Ocean during austral winter.

The impact of a mesospheric temperature inversion on the vertical propagation of gravity waves has been investigated using OH airglow images and ground-based Rayleigh lidar measurements carried out in December 2017 at the Haute-Provence Observatory (OHP, France, 44N). These measurements provide complementary information that allows the vertical propagation of gravity waves to be followed. An intense mesospheric inversion layer (MIL) observed near 60 km of altitude with the lidar disappeared in the middle of the night, offering a unique opportunity to evaluate its impact on gravity wave (GW) propagation observed above the inversion with airglow cameras. With these two instruments, a wave with a 150 min period was observed and was also identified in meteorological analyses. The gravity waves' potential energy vertical profile clearly shows the GW energy lost below the inversion altitude and a large increase of gravity wave energy above the inversion in OH airglow images with waves exhibiting higher frequency. MILs are known to cause instabilities at its top part, and this is probably the reason for the enhanced gravity waves observed above.

The infrared emission lines observed between 80 and 100 km known as nightglow allow the investigation of dynamic phenomena such as gravity waves. These perturbations act on local temperature and density. However, the observation of the local perturbations in the nightglow layer is mainly performed by spectrally broad cameras. Swenson and Gardner (1998) introduced the cancellation factor linking relative variations of intensity with relative variations of temperature. The cancellation factor is a function of the perturbation vertical wavelength estimated from simulation that do not include spectral variations. In this study, we intend to estimate the spectral variability of the cancellation factor, in particular within the range 0.9-1.7 µm corresponding to infrared InGaAs camera, used during measurement campaigns. We describe briefly the model that resolves the vibrational states of the nightglow main source (OH). Then vertically propagating gravity waves are applied on a 1D scheme and the cancellation factor is computed based on the impact on both temperature and intensity. Spectral variations of the cancellation factor are observed and compared along the variation of the vertical wavelength.

Mesospheric temperature inversions are subject to investigations due to the links with multiscale dynamics such as planetary wave and gravity waves. Knowing the impact on climatological inversions also requires understanding the phenomena occurring before, through, and after a mesospheric inversion. We use data obtained during a measurement campaign over Maïdo observatory in La Réunion Island and focus on a specific event occurring in the night between the 9th and the 10th of October 2017. Among the several observations available, LIDAR measurements provided vertical profiles of temperature and gravity waves potential energy completed by high vertical resolution radiosoundings. The airglow layer observed by an InGaAs camera shows the evolution of gravity wave structures at about 87 km between 0.9 and 1.7 µm. Gravity wave parameters such as horizontal wavelengths or intensity emission variations are extracted, along with potential energy compared with LIDAR data. We use atmospheric models (ERA5, WACCM, WRF) and specific tools (NEMO, GROGRAT) to add supplementary information about the night selected. We present here the first results related to the gravity waves and energy exchanges in the frame of the temperature inversion.

While meteorological numerical models extend upward to the mesopause, mesospheric observations are required for leading simulations and numerical weather forecasts and climate projections. This work reviews some of the challenges about temperature observation requirements and the limiting factors of the actual measurements associated with atmospheric tides. A new strategy is described here using a limb-scattering technique that is based on previous experiments in space. Such observations can be used with cube satellites. Technical issues are the large dynamic range (4 orders of magnitude) required for the measurements, the accuracy of the limb pointing, and the level of stray light. The technique described here will expect accuracy of 1–2 K with a vertical resolution of 1–2 km. A constellation of 100 platforms could provide temperature observations with space (100 km) and time (3 h) resolutions recommended by the World Meteorological Organization, and tidal issues could be resolved with a minimum of 3–5 platforms with specific orbit maintained to avoid drifts.

A mesospheric model of the airglow emission is developed to recover the night variations observed at ground level. The model is based on a 1D vertical photochemical model, including the photodissociation and heating processes. The spectral radiation is calculated at high altitude and propagated through the atmosphere to the ground. We also include short scale vertical dynamic such as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared with space observations. In addition, we estimate the impact of changes associated with parameterized atmospheric tides. The comparison with observations is performed over high altitude and ground level. We confront the model outputs at high altitude with satellite observations (SABER and GOMOS) and the simulations propagated at ground level are compared to local measurements campaigns performed in France and India. Biases between observed and simulated radiances and volume emission rates are suspected to be due to the impact of gravity waves or the large scale dynamic.

In the frame of the European H2020 project ARISE, a short wave infrared (SWIR) InGaAs camera has been operated at the Haute-Provence Observatory, during a night that corresponds to the peak of Geminid meteor shower to investigate infrasound associated with meteor arrivals. This camera allows continuous observations during clear-sky nighttime of the OH airglow layer centered at 87 km. These observations were collocated with Rayleigh lidar measurements providing vertical temperature profiles from the lower stratosphere to the altitude of the OH layer around the mesopause. Spectral analysis of OH images did not allow to detect infrasound associated with meteor trails, however it reveals a peak corresponding to infrasound signals in the frequency band of those produced by ocean swell. Infrasound wave activity observed from ground-based microbarometers as well as the OH camera, appear to be modified with the presence of a temperature inversion described by Rayleigh lidar. Indeed, there is a difference in energy related to infrasonic activity between the first part of the night during the temperature inversion and after the inversion. (C) 2019 COSPAR. Published by Elsevier Ltd.

Since 2010 Onera works on the characterization of the nightglow radiation for night-vision applications in moonless conditions. This radiation is mainly due to the deexcitation of hydroxyl molecules in the upper atmosphere (similar to 87km). It is present in the visible range and reaches its maximum value in the short wavelength infrared bands between 1.4 and 1.8 mu m (Meinel bands). Although few energy reaches the ground, this radiation is emitted over the whole sky and therefore may be an interesting additional light source for night vision systems in moonless or cloudy sky conditions. Moreover, observation of the nocturnal sky in the short wave infrared band gives access to dynamic processes studies, these processes perturbing emission of radiation. In this paper, we present works carried out at Onera about observation and modelling of nightglow radiation.

The OH near-infrared nigthglow emission in the upper mesosphere is a marker of the chemistry and dynamics occurring at this level. The stellar occultation spectrometer GOMOS on board ENVISAT allowed to observe the OH(8-4) Meinel band in the spectral range 930-955 nm with a spectrometer dedicated to the observation of the water vapour. Climatology of OH emission has been established for the period 2002-2012. It allowed to confirm already published results as the maximum of intensity and semi-annual variation at the equator. The causes of variability and trends in the brightness and maximum altitude of the OH layer will be discussed. A new result concerns the apparent correlation of the emission rate with the solar activity.

The mesospheric nightglow in the infrared region corresponds to the emission lines photochemically produced by OH radicals, O 2 and atomic oxygen. We develop a model with the intention to reproduce the climatology of the OH nightglow and perform comparisons with observational data. 25 species and more than 80 reactions are used describing most of the atmospheric chemical processes but also the photolysis of a few molecules. The different excited vibrational levels of OH are taken into consideration, as well as the excited state of O 2 . A broad wavelength range with various widths allows an accurate expression of the photolysis coefficients. The first step is to validate a 0D photochemical model with most of the kinetic reactions updated. Sensitivity tests are performed to appreciate the importance of specific reactions. We also observe the nightglow response to density variations. A spectrum of the OH nightglow is developed using the concentrations calculated and is exploited to estimate the mesospheric temperature. The spectrum will also be propagated to the ground for comparisons with observations. The 0D nightglow model will be the basis of a global 3D model which will include the main dynamical processes and latitudinal variations.

Global Ozone Monitoring by Occultation of Stars (GOMOS) was an instrument dedicated to the study of atmospheric chemistry based on the principle of stellar occultation. The signals delivered by the IR spectrometer coupled with two CCD detectors, initially used for absorption measurements, were analyzed in order to observe the night airglow resulting from O-2 and OH emissions at 761.9 and 930 nm, respectively. The method to retrieve those emissions is described as well as the error analysis. The results of this first attempt are presented and discussed with respect to instrument characteristics, earth coverage, altitude resolution, and the ability of GOMOS data to contribute to night airglow investigations. Mean limb intensities are equal to 28.9 and 7.7 MR for O-2 at 760 nm and OH at 930 nm, respectively. Individual O-2 emissions are retrieved with an accuracy better than 15%, while the OH emission, which provides smaller intensities, is retrieved with an accuracy of 10% for the monthly average.

In this paper, we report the development of low flux short wavelength infrared radio-imaging systems to study the radiance due to nightglow emission. This radiation is mainly due to the desexcitation of hydroxyl molecules in the upper atmosphere. It is present in the visible range and reaches its maximum value (at ground level) in the short wavelength infrared band between 1.4 and 1.8μm. The nightglow may be an interesting additional light source for night vision systems in moonless or cloudy sky conditions. In this paper, we describe the experimental setup and present first results of the measurement campaigns that we performed at the Observatoire de Haute-Provence in France and at the European Southern Observatory site of La Silla in Chile.

MATISSE (Advanced Modeling of the Earth for Environment and Scenes Simulation) is an infrared background scene generator developed for computing natural background spectral radiance images. The code also provides atmospheric radiatives quantities along lines of sight. Spectral bandwidth ranges from 0.4 to 14 μm. Natural backgrounds include atmosphere, sea, land and high and low altitude clouds. The new version MATISSE-v2.0, released this year, has been designed to treat spatial multi resolution in the generated images in order to be able to reach metric spatial variability in pixels footprints. Moreover, MATISSE-v2.0 includes a new sea surface radiance model (water waves and surface optical properties) which depends on wind speed, wind direction and fetch value. Preliminary validations using radiometric measurements have been conducted concerning sea radiances and give promising results. In order to go further in the validation process of MATISSE-v2.0, comparisons with MODIS satellite images have been led. The results of comparing the simulated MATISSE images radiances with the MODIS observations show that the code is performing well. This paper gives a description of MATISSE-v2.0 new functionalities and focus on first results on comparison between MATISSE/MODIS images radiances.