The ACS-NIR spectrometer on board the Trace Gas Orbiter is currently being used to probe the atmosphere of Mars. When ACS-NIR is pointed at the Sun, it detects the spectral signature of atmospheric components present on its line of sight (LOS) as it passes through the atmosphere. The solar spectrum is directly measured when the LOS is above the atmosphere. Special observations were therefore made to construct the solar spectrum in the 0.7-1.7 μm domain. This is mainly useful for ACS-NIR calibrations and for other experiments. The observations consist in recording all the diffraction orders of ACS-NIR by continuously varying the frequency of its AOTF. Here we will present how to process this data to obtain the solar spectrum. We will first show how we get the flat field for image correction. Next, we will present how to overcome order contamination using a geometric method. We will then show how to correct the order intensity variations to obtain the solar spectrum. We will end by showing some results.
In this paper, we describe the concept of the Venus InfraRed Atmospheric Linker (VIRAL) spectrometer for investigation of the composition and structure of the planetary atmosphere at the top and above the cloud layer of Venus onboard the Venus Orbiter Mission announced by the Indian Space Research Organization (ISRO). VIRAL includes two channels, an infrared echelle spectrometer channel and an ultra-high resolution heterodyne interferometer channel. Here, we present the concept of the echelle channel only. The instrument is designed to perform solar occultation, providing an optimal photon yield combined with a superior spectral resolving power that exceeds 20,000. VIRAL echelle spectrometer will cover the wavelength range from 2.3 to 4.3 μm, and achieve high vertical resolution (with a footprint of about 1 km at the limb) to allow the detailed altitude profiling of the Venusian upper atmosphere with its composition and structure. We present the instrument concept, its preliminary optical design and science objectives of the experiment.
Alexander Trokhimovskiy, Oleg Korablev, Yurii Kalinnikov, Anna Fedorova, Alexander Stepanov, Andrei Titov, Ilia Dziuban, Andrei Patrakeev, Franck Montmessin
The near-Infrared echelle-AOTF spectrometer is one channel of the Atmospheric Chemistry Suite (ACS) package dedicated for the studies of the Martian atmosphere on board ExoMars Trace Gas Orbiter planned for launch in 2016. The near-infrared (NIR) channel of ACS is a versatile spectrometer for the spectral range of 0.7–1.6 μm with a resolving power of <20,000. The NIR channel is intended to measure the atmospheric water vapor, aerosols, airglows, in nadir, in solar occultation, and on the limb. The science goals of NIR are basically the same as for SPICAM IR channel presently in flight on board Mars Express ESA orbiter, but it offers significantly better spectral resolution. The instrument employs the principle of an echelle spectrometer with an acoustooptical tunable filter (AOTF) as a preselector. The same principle was employed in SOIR, operated on Venus Express ESA mission in 2006-2014, and in RUSALKA, operated onboard ISS in 2009-2012. The NIR channel of ACS consists of entry optics, the AOTF, a Littrow echelle spectrometer, and an electrically cooled InGaAs detector array. It is a complete block with power and data interfaces, and the overall mass of 3.2 kg. The protoflight model of NIR is completed, calibrated, integrated within the ACS suite, and is undergoing tests at the spacecraft.
Alexander Trokhimovskiy, Oleg Korablev, Yuriy Ivanov, I. Siniyavsky, Anna Fedorova, Alexander Stepanov, Andrei Titov, Andrei Patrakeev, Pavel Moiseev, Tatiana Kozlova, Franck Montmessin
The middle-infrared (MIR) echelle spectrometer is one channel of the Atmospheric Chemistry Suite (ACS) package dedicated for the studies of the Martian atmosphere on board ExoMars Trace Gas Orbiter (TGO) planned for launch in 2016. The MIR channel of ACS is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the range of 2.3–4.2 μm with the resolving power of ~50,000. MIR is dedicated to sensitive measurements of trace gases. The MIR channel consists of entry optics, an echelle spectrometer with a 140x250 mm grating and two-mirror collimator, two secondary steerable gratings, and a cryogenically cooled MCT detector array with proximity optics. The spectrometer operates in high orders of diffraction, allowing to acquire up to 17 orders at one detector frame, and to cover simultaneously ~300-nm spectral interval within the spectral range. The mechanism allows moving the secondary grating with a characteristic time of ~0.1 s. This concept is novel for space application. The instrument is a complete block with power and data interfaces, and the overall mass of 12 kg. The protoflight model of MIR is completed, integrated within the ACS suite, and is undergoing tests at the spacecraft.
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