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VenSpec-H: High resolution polarimetry of Venus using filter combinations

Presentation #507.01 in the session Venus II (Oral Presentation)

Published onOct 23, 2023
VenSpec-H: High resolution polarimetry of Venus using filter combinations

VenSpec-H is a high-resolution, infrared spectrometer that will be part of ESA’s EnVision mission to be launched in 2031. The instrument will use spectral filters and an echelle grating, with instrument design heritage from the NOMAD and SOIR instruments. It will make day-side and night-side NADIR measurements in 4 atmospheric windows between 1.1 and 2.5-micron. VenSpec-H will measure gases related to volcanism and surface changes on Venus.

Day-side measurement will primarily be NADIR observation of light scattered by the cloud layers to determine abundance H2O, HDO, SO2, OCS among other species. Light scattered by the clouds will be partially linearly polarized, and the instrument will have polarization sensitivity (mostly due to the grating). Preliminary modeling and estimates suggest that ignoring polarization will lead to unacceptably large measurement bias.

We present a method of combining a spectral filter measurement and a polarizer filter measurement to correct for this bias. In addition, the same combination can be used to determine the component of linear polarization. This method takes advantage of the NADIR geometry, and assumptions on the Stokes vector with respect to the meridional plane. The SNR performance is preserved with an exception when the slit direction and meridional plane are 45° apart. The result is effectively the first high resolution polarimeter in orbit around Venus. This correction assures that VenSpec-H can perform the required science of EnVision. As a bonus, the baseline shape and linear polarization may be used to study the Venus clouds.

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