The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described

Martian dust storm impact on atmospheric H₂O and D/H observed by ExoMars Trace Gas Orbiter

Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere

Adaptive fine-tuning for large-scale complex nonlinear systems

Practical large-scale nonlinear control systems (PLSNCS) require an intensive and time-consuming fine-tuning process in order to achieve a satisfactory - or, even, acceptable - performance. In the majority of PLSNCS the fine-tuning process is performed by experienced personnel based on field observations and by experimenting with different combinations of controller parameters, without the use of a systematic approach. Adaptive Optimization (AO) methods such as the SPSA or AFT1 provide probably the most promising approach for the development of a systematic methodology for automatic and efficient fine-tuning of PLSNCS. However, despite the success of AO methodologies in particular fine-tuning control applications, these methods suffer from the serious problem of not guaranteeing efficient transient behaviour due to the use of random perturbations. A new algorithm (AFT2) has been developed and analyzed for alleviating this problem. This paper presents a comparative evaluation of AFT2 (versus SPSA and AFT1) when applied to three different traffic control applications: urban traffic control, network-wide motorway ramp metering and motorway variable speed control. It is demonstrated by means of simulation investigations that AFT2 not only overcomes the aforementioned problem of poor transient performance but also achieves significantly faster convergence than SPSA and AFT1

Atmospheric Aerosols Properties via Solar Infrared Occultation Observations by Spicam IR

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Long-Term Observations of Water Vapor in the Middle Atmosphere of Mars by Spicam/mex

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Long-Term Observations of Water Vapor in the Middle Atmosphere of Mars by Spicam/mex

International audienc

Atmospheric Aerosols Properties via Solar Infrared Occultation Observations by Spicam IR

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Performance of the ACS NIR channel and O 2 profiles

International audienceThe Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (-NIR,-MIR, and-TIRVIM) intended to observe Mars atmosphere onboard the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter(TGO) mission