Spectral Mixture Modeling with Laboratory Near-Infrared Data I: Insights into Compositional Analysis of Europa

Europa's surface composition and physical characteristics are commonly constrained using spectral deconvolution through linear mixture (LM) modeling and radiative transfer-based (RT) intimate mixture modeling. Here, I compared the results of these two spectral modeling- LM versus RT- against laboratory spectra of water (H₂O) ice and sulfuric acid octahydrate (SAO; H₂SO₄·$8H$₂$O) mixtures measured at near-infrared wavelengths ($~$1.2-2.5 $μ$m) with grain sizes of 90-106 $μ$m (Hayes and Li, 2025). The modeled abundances indicate that the RT more closely reproduces the laboratory abundances, with deviations within $±$5% for both H$₂$O ice and H$₂$SO$₄·8H₂O with ~100 $μ$m grains. In contrast, the LM shows slightly larger discrepancies, typically ranging from ±5-15% from the true abundances. Interestingly, both LM and RT tend to consistently overestimate the abundance of H₂SO₄·$8H$₂$O and underestimate H$₂$O ice across all mixtures. Nonetheless, when H$₂$SO$₄·8H₂O either dominates (>80% as observed on Europa's trailing hemisphere; Carlson et al. 2005) or is present only in trace amounts (~10% on areas in Europa's leading hemisphere; Dalton III et al. 2013; Ligier et al. 2016), both the LM and RT render acceptable results within ±10% uncertainty. Thus, spectral modeling using the RT is preferred for constraining the surface composition across Europa, although the LM remains viable in specific compositional regimes.