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Spectroscopy for the investigation of the characteristics of the atmosphere of Venus (SPICAV) is a suite of three spectrometers in the UV and IR range with a total mass of 13.9 kg flying on the Venus Express (VEX) orbiter, dedicated to the study of the atmosphere of Venus from ground level to the outermost hydrogen corona at more than 40,000 km. It is derived from the SPICAM instrument already flying on board Mars Express (MEX) with great success, with the addition of a new IR high-resolution spectrometer, solar occultation IR (SOIR), working in the solar occultation mode. The instrument consists of three spectrometers and a simple data processing unit providing the interface of these channels with the spacecraft. A UV spectrometer (118–320 nm, resolution 1.5 nm) is identical to the MEX version. It is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation. In nadir orientation, SPICAV UV will analyse the albedo spectrum (solar light scattered back from the clouds) to retrieve SO2, and the distribution of the UV-blue absorber (of still unknown origin) on the dayside with implications for cloud structure and atmospheric dynamics. On the nightside, γ and δ bands of NO will be studied, as well as emissions produced by electron precipitations. In the stellar occultation mode the UV sensor will measure the vertical profiles of CO2, temperature, SO2, SO, clouds and aerosols. The density/temperature profiles obtained with SPICAV will constrain and aid in the development of dynamical atmospheric models, from cloud top (not, vert, similar60 km) to 160 km in the atmosphere. This is essential for future missions that would rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow studies of the ionosphere through the emissions of CO, CO+, and CO2+, and its direct interaction with the solar wind. It will study the H corona, with its two different scale heights, and it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAV VIS-IR sensor (0.7–1.7 μm, resolution 0.5–1.2 nm) employs a pioneering technology: an acousto-optical tunable filter (AOTF). On the nightside, it will study the thermal emission peeping through the clouds, complementing the observations of both VIRTIS and Planetary Fourier Spectrometer (PFS) on VEX. In solar occultation mode this channel will study the vertical structure of H2O, CO2, and aerosols. The SOIR spectrometer is a new solar occultation IR spectrometer in the range λ=2.2–4.3 μm, with a spectral resolution λ/Δλ>15,000, the highest on board VEX. This new concept includes a combination of an echelle grating and an AOTF crystal to sort out one order at a time. The main objective is to measure HDO and H2O in solar occultation, in order to characterize the escape of D atoms from the upper atmosphere and give more insight about the evolution of water on Venus. It will also study isotopes of CO2 and minor species, and provide...

A new compact spaceborne high-resolution spectrometer developed for the European Space Agency's Venus Express spacecraft is described. It operates in the IR wavelength range of 2.2 to 4.3 microm and measures absorption spectra of minor constituents in the Venusian atmosphere. It uses a novel echelle grating with a groove density of 4 lines/mm in a Littrow configuration in combination with an IR acousto-optic tunable filter for order sorting and an actively cooled HgCdTe focal plane array of 256 by 320 pixels. It is designed to obtain an instrument line profile of 0.2 cm(-1). First results on optical and spectral properties are reported.

NOMAD is a spectrometer suite on board ESA's ExoMars trace gas orbiter due for launch in January 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at dayside and nightside, and during solar occultations. In this paper, the design, manufacturing, and testing of the two infrared channels are described. We focus upon the optical working principle in these channels, where an echelle grating, used as a diffractive element, is combined with an acousto-optical tunable filter, used as a diffraction order sorter.

Solar occultation in the infrared, part of the Spectoscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument onboard Venus Express, combines an echelle grating spectrometer with an acousto-optic tunable filter (AOTF). It performs solar occultation measurements in the IR region at high spectral resolution. The wavelength range probed allows a detailed chemical inventory of Venus's atmosphere above the cloud layer, highlighting the vertical distribution of gases. A general description of the instrument and its in-flight performance is given. Different calibrations and data corrections are investigated, in particular the dark current and thermal background, the nonlinearity and pixel-to-pixel variability of the detector, the sensitivity of the instrument, the AOTF properties, and the spectral calibration and resolution.