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.

[1]  L. V. Moroz,et al.  Reflectance spectra of olivine-orthopyroxene-bearing assemblages at decreased temperatures: implications for remote sensing of asteroids , 2000 .

[2]  Michael J. Gaffey,et al.  Pyroxene spectroscopy revisited - Spectral-compositional correlations and relationship to geothermometry , 1991 .

[3]  S. Taylor,et al.  Planetary Crusts: Their Composition, Origin and Evolution , 2009 .

[4]  M. Osborne,et al.  Temperature-dependence of Fe-Ti spectra in the visible region - Implications to mapping Ti concentrations of hot planetary surfaces , 1978 .

[5]  R. Singer,et al.  The Effect of Thermal Variations on Reflectance Spectra of Mafic Minerals , 1983 .

[6]  R. Clark,et al.  Reflectance spectroscopy: Quantitative analysis techniques for remote sensing applications , 1984 .

[7]  E. Cloutis.  Pyroxene reflectance spectra: Minor absorption bands and effects of elemental substitutions , 2002 .

[8]  T. Hiroi,et al.  The mystery of 506.5 nm feature of reflectance spectra of Vesta and Vestoids: Evidence for space weathering? , 2001 .

[9]  R. Singer,et al.  Possible temperature variation effects on the interpretation of spatially resolved reflectance observations of asteroid surfaces , 1987 .

[10]  F. Vilas,et al.  The McDonald Observatory Serendipitous UV/Blue Spectral Survey of Asteroids , 1997 .

[11]  M. Darby Dyar,et al.  Spectroscopy of synthetic Mg‐Fe pyroxenes I: Spin‐allowed and spin‐forbidden crystal field bands in the visible and near‐infrared , 2007 .

[12]  Carle M. Pieters,et al.  Deconvolution of mineral absorption bands: An improved approach , 1990 .

[13]  R. Singer.  Near-infrared spectral reflectance of mineral mixtures - Systematic combinations of pyroxenes, olivine, and iron oxides , 1981 .

[14]  R. G. J. Strens,et al.  Mineralogical Applications of Crystal Field Theory , 1973 .

[15]  R. Burns.  The Polarized Spectra of Iron in Silicates: Olivine. A Discussion of Neglected Contributions from Fe2+ Ions in M(1) Sites , 1974 .

[16]  Loredana Pompilio,et al.  Exponential Gaussian approach for spectral modeling: The EGO algorithm I. Band saturation , 2009 .

[17]  Paul G. Lucey,et al.  Implications of temperature‐dependent near‐IR spectral properties of common minerals and meteorites for remote sensing of asteroids , 1999 .

[18]  K. Keil,et al.  The influence of temperature on the spectra of the A‐asteroids and implications for their silicate chemistry , 1998 .

[19]  U. Schade,et al.  Near‐infrared reflectance spectra from bulk samples of the two Martian meteorites Zagami and Nakhla , 1999 .

[20]  R. Burns,et al.  High temperature crystal field spectra of transition metal-bearing minerals - Relevance to remote-sensed spectra of planetary surfaces , 1980 .

[21]  Roger G. Burns,et al.  Mineralogical applications of crystal field theory , 1970 .

[22]  Robert B. Singer,et al.  Effects of temperature on remotely sensed mineral absorption features , 1985 .

[23]  Paul G. Lucey,et al.  Temperature-Dependent Near-Infrared Spectral Properties of Minerals, Meteorites, and Lunar Soil , 2002 .

[24]  Roger,et al.  Spectroscopy of Rocks and Minerals , and Principles of Spectroscopy , 2002 .