EnVision/VenSpec-H

Purpose of VenSpec-H

VenSpec-H is a high-resolution infrared spectrometer working in nadir viewing mode. It is an echelle grating spectrometer coupled to a high-performance, actively-cooled SOFRADIR HgCdTe detector, with an Acousto-Optic Tunable Filter (AOTF) at its entrance for order selection (. These components are optimised for Venus atmospheric observations in the spectral range 1.0–2.5 μm.

VenSpec-H instrument will detect and quantify SO2, H2O and HDO in the lower atmosphere, to enable characterisation of volcanic plumes and other sources of gas exchange with the surface of Venus, complementing VenSAR and VenSpec-M surface and SRS subsurface observations. A nadir pointed high-resolution infrared spectrometer is the ideal instrument for these observations at the1·0 μm, 1·7 μm, and 2·0 – 2·3 μm atmospheric windows that permit measurements of the lower atmosphere during the night, and above the clouds during the day. Baseline observations will be performed on the night side but observations at all times of day are possible.

Block diagram of the VenSpec-H instrument (P.I. Ann Carine Vandaele, IASB-BIRA, Belgium).

VenSpec-H optics

The optical path of NOMAD-LNO is reused for VenSpec-H. The occultation capability (periscope and flip mirror) is skipped in the baseline version of VenSpec-H since it is a pure nadir oriented instrument. However, calibration of the instrument might require pointing to the Sun.

The optics of the VenSpec-H channel are divided in three main units :

  • Entrance optics that collects the light, defines the FOV and restricts the observed wavelength domain using an AOTF;
  • Spectrometer with an echelle grating that defines the free spectral range and the instrument line profile (ILP);
  • Detector system that records the spectra.