Exponential Gaussian approach for spectral modelling: The EGO algorithm II. Band asymmetry

Abstract

The present investigation is complementary to a previous paper which introduced the EGO approach to spectral modelling of reflectance measurements acquired in the visible and near-IR range (Pompilio, L., Pedrazzi, G., Sgavetti, M., Cloutis, E.A., Craig, M.A., Roush, T.L. [2009]. Icarus, 201 (2), 781–794). Here, we show the performances of the EGO model in attempting to account for temperature-induced variations in spectra, specifically band asymmetry. Our main goals are: (1) to recognize and model thermal-induced band asymmetry in reflectance spectra; (2) to develop a basic approach for decomposition of remotely acquired spectra from planetary surfaces, where effects due to temperature variations are most prevalent; (3) to reduce the uncertainty related to quantitative estimation of band position and depth when band asymmetry is occurring. In order to accomplish these objectives, we tested the EGO algorithm on a number of measurements acquired on powdered pyroxenes at sample temperature ranging from 80 up to 400 K. The main results arising from this study are: (1) EGO model is able to numerically account for the occurrence of band asymmetry on reflectance spectra; (2) the returned set of EGO parameters can suggest the influence of some additional effect other than the electronic transition responsible for the absorption feature; (3) the returned set of EGO parameters can help in estimating the surface temperature of a planetary body; (4) the occurrence of absorptions which are less affected by temperature variations can be mapped for minerals and thus used for compositional estimates. Further work is still required in order to analyze the behaviour of the EGO algorithm with respect to temperature-induced band asymmetry using powdered pyroxene spanning a range of compositions and grain sizes and more complex band shapes.