Scientific objectives and instrumental requirements of the IR spectrometer VenSpec-H onboard EnVision

Hooray! The ESA EnVision mission is adopted. <br/> Onboard the spacecraft, there will be a suite of three spectrometers, VenSpec. One of these is called VenSpec-H where the H stands for high spectral resolution. Its scientific objectives consist in measuring variations of minor species’ abundances in the atmosphere of Venus. H₂O, SO₂, CO and OCS will be measured to characterize the potentially ongoing volcanic activity. These observations will allow us to understand both the importance of volatiles in volcanic activity on Venus and their effect on cloud maintenance and dynamics. VenSpec-H will measure these molecules in nadir viewing geometry, in infrared transparency windows of Venus’ nightside to probe the troposphere and in infrared spectral ranges on the dayside to measure the mesosphere. In this paper, the scientific requirements enabling our scientific objectives will be demonstrated. An intercomparison exercise was first led to reproduce modelled and observational reference spectra. The molecular vertical profiles, the aerosols’ model and the CO₂ continuum contribution were validated for the different spectral windows. This enabled us to determine the spectral bands, their bandwidth and the resolving power necessary for our purposes. Along the way, we identified possible improvements and science avenues. Some of them impact the instrument design, such as the need for polarimetric measurements. Others are related to remaining uncertainties in the model and laboratory measurements that will complement the investigation.