Figure 18. Plots are shown for the lowest RMSE differences between the endmember spectra for Mount Desert Island and Sands of Forvie and Hapke nonlinear modeling. The wavelength interval centered on 1.00 to 1.08 µm is blanked out because of increased uncertainty of retrieved spectra because of low sensitivity at the wavelength limits for the S and L spectrometers.
Specifically, the MDI sand endmember best fit had an RMSE of 0.00165 and an R2 of 0.997, and the SoF sand endmember best fit had an RMSE of 0.00124 and an R2 of 0.994. Figures 19 and 20 also show these spectra, along with the simulated SSA spectra that the procedure chose as the best fit combination to make the model spectrum. The retrieved mineral abundances and grain sizes are also shown. For both deposits, GMS glass and labradorite are the most abundant phases, similar to the rankings of the amorphous phase(s) and feldspar abundances as determined by CheMin for the MDI sand sample (Rampe et al., 2020). GMS glass and labradorite, in addition to any olivine present in both deposits, contribute to the broad 1 µm feature observed in both MDI and SoF spectra (Figures 16 and 17). Between MDI and SoF, the main spectral difference (other than albedo) is in the relative proportions of the two pyroxenes (pigeonite and augite). The long wavelength spectra rise for MDI is consistent with the model result pigeonite/augite = 4.8, and the SoF ~2.2 µm spectral minimum is consistent with the model result pigeonite/augite = 0.0 (Figures 19 and 20). Grain size results, which in the Hapke (2012) model are much less constrained relative to phase abundances (Lapotre et al., 2017a), show a slight trend of coarser grains for SoF as compared to MDI deposits. This result is consistent with MAHLI-based observations from Curiosity (Weitz et al., 2022).