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Unmixing of high-T emissivity VNIR laboratory spectra for the interpretation and calibration of VEM/Venspec-M data

Presentation #406.01 in the session Venus (Poster)

Published onOct 23, 2023
Unmixing of high-T emissivity VNIR laboratory spectra for the interpretation and calibration of VEM/Venspec-M data

The Venus Emissivity Mapper (VEM/Venspec-M) is designed specifically for mapping the surface of Venus using visible to near-infrared (VNIR) atmospheric windows. It will provide the first global map of rock types on the surface of Venus and constantly monitor for volcanic activity. The VEM instrument will fly on the NASA VERITAS mission and on the ESA EnVision mission as VenSpec-M.

Observing the surface of Venus in the VNIR requires a dedicated laboratory effort that is essential for instrument calibration and data validation. Interpretation of emissivity spectra from the ca. 460 ºC surface requires high-temperature laboratory measurements on Venus-analog rocks. The Planetary Spectroscopy Laboratory (PSL) of DLR in Berlin now routinely measures emissivity spectra of geologic materials at relevant Venus surface temperatures (400ºC, 440ºC, and 480ºC) using a very powerful induction system to heat custom-made sample cups in a vacuum environment (0.7 mbar). With the main goal of extending the PSL spectral library for interpretation and calibration of VEM/Venspec-M data, this project focuses on the investigation of the spectral behavior of laboratory mixtures in the VNIR spectral range. As a starting point, pairs of pure endmember samples with similar grain sizes but with contrasting spectral features (bright vs dark material) were selected for measurements in the high-temperature chamber at PSL. In parallel, unmixing models are applied to the measured spectral endmembers to model and test the reproducibility of the spectral behavior of these mixtures in the VNIR. Unmixing models have been extensively applied in the thermal infrared region and proved to provide a good reproduction of the laboratory spectra of mixtures. However, these models have not been extensively applied to VNIR emissivity spectra due to the likely that photons will encounter multiple phases. Using VNIR emissivity spectra of mixtures at Venus condition, we are investigating application of such models in this spectral region.

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