Library reflectance spectra of igneous rocks resampled to DAVINCI bands

The surface of Venus is difficult to observe remotely due to the CO2-rich atmosphere, but there is an atmospheric window ~1µm in the near-infrared (NIR) that is sensitive to surface properties including ferrous iron content. The DAVINCI mission will collect surface images at ~1µm using the Venus Imaging System for Observational Reconnaissance (VISOR) instrument, which collects nighttime emissivity at three NIR bands, and the Venus Descent Imager (VenDI), which measures daytime reflectance in two NIR channels (broad and narrow band) [see Garvin et al 2022 Planet. Sci. J. 3 117]. Ferrous iron content is important because felsic minerals may suggest past plate recycling processes that require water-rich conditions.

To better understand the DAVINCI data, we have developed an R code that can ingest laboratory spectra and resample them to VISOR and VenDI bands. In this study, we run spectra from United States Geological Survey (USGS), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Reflectance Experiment Laboratory (RELAB) mineral databases, and our own laboratory-collected spectra. The resampled spectra of known samples can help us explore the instruments' sensitivity to grain size and mineralogy. The following results are relative and room temp reflectance data only, but the code can ingest any spectrum.

We resampled spectra from a suite of ultramafic to felsic igneous rocks (as defined on a La Bas (1986) total alkali vs. silica diagram) with known silica content and total iron content. Resampled spectra display and inverse relationship to iron content as predicted by theory. We find that for laboratory data subset at VenDI channels, mafic and ultamafic rocks plot ≤ 35% reflectance in both the wide band (average reflectance = 18%) and narrow band (average reflectance =16%). Felsic rocks have higher reflectance in both bands (average of ~ 39.3% and ~ 40.5% respectively). The ratio of the VenDI narrow/wide bands classify rocks more clearly with low overlap between the two groups. Mafic rocks have ratio values ranging from ~0.5-1; the felsic range is ~0.9-1.2. For laboratory data subset at VISOR channels, most felsic rocks plot ≥ 35% reflectance (average = 40%) and mafic below ≤ 35% (average ~ 16.0%) across all three channels. The ratio of the VenDI narrow/wide bands classify rocks more clearly with low overlap between the two groups. Mafic rocks have ratio values ranging from ~0.5-1; the felsic range is ~0.9-1.2. The igneous rocks in this study can be discriminated using DAVINCI bands.