SPICAV on Venus Express: Three spectrometers to study the global structure and composition of the Venus atmosphere

Abstract

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...

Venus Atmospheric Thermal Structure and Radiative Balance

“…The SPICAV instrument operated on board the European Venus Express spacecraft for eight years, beginning in 2006 (Bertaux et al 2007a). The remote sensing spectrometer covered spectral regions in the ultraviolet (110 to 320 nm) and in the near-infrared (1000 to 1700 nm).…”

“…Kasprzak et al (1997) have previously discussed the neutral composition, thermal structure, dynamics and effects of the solar activity and Marcq et al (2018) present an update on the composition and chemistry of the neutral atmosphere. Since then, the SOIR infrared Nevejans et al 2006) and SPICAV-UV (Bertaux et al 2007a(Bertaux et al , 2007b spectrometers, the aerobraking experiment VEXADE (Müller-Wodarg et al 2006) and the torque experiment (Persson 2015;Rosenblatt et al 2012) of the Venus Express mission focused on studying the composition, mass density and temperature structure of the thermosphere. Ground based campaigns also collected observations during the spacecraft observation periods such as the ones from the THIS heterodyne spectrometer (Sonnabend et al 2012).…”

Optical system of a prospective imaging spectrometer for mapping ozone and other gases in Earth’s atmosphere

“…В спектрометрах, работа ющих в видимом и особенно в УФ-диапазоне, часто применяются вогнутые решётки, облада-ющие как диспергирующими, так и фокусирующими свойствами и не требующие к тому же предварительной коллимации светового пучка (Bertaux et al, 2006(Bertaux et al, , 2007Pommereau, Goutail, 1988). В результате можно существенно уменьшить число оптических элементов, что в УФ-диапазоне является очень выгодным с точки зрения энергетики.…”

The OH Venus nightglow spectrum: Intensity and vibrational composition from VIRTIS—Venus Express observations

“…Density profiles of several constituents must be adopted to model the OH nightglow instrument on board Venus Express in a stellar occultation observation mode (Bertaux et al, 2007). During an occultation, the spectrum of a selected hot star is first recorded above the atmosphere where it is unaltered by atmospheric absorption and can be used as a reference spectrum.…”

“…As the spacecraft moves towards its pericenter, the star spectrum is progressively occulted by the atmosphere and may be compared to the reference. This technique leads to an absolute concentration of O 3 derived from a relative measurement (independent of the absolute instrument calibration) with a less than 1 km spatial resolution (Bertaux et al, 2007).…”