Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43c1694c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43C-1694
Other
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing
Scientific paper
In this paper we applied Hapke's radiative transfer model (Hapke, 1993, 1998, 2002, 2008) to laboratory reflectance spectra of four pyroxenes powders of known composition and grain size. We measured spectra in the 350 - 2500 nm range under different viewing conditions: this enabled us to study both spectral and photometric properties of these minerals. In particular we have studied band depth variations with grain sizes for all the investigated pyroxenes, while for one of them we also studied band depth correlation with phase angle (g), the single particle phase function and, as a further step, we tried to estimate the imaginary part of the refractive index . The dataset is composed of reflectance measurements of four pyroxenes: an orthopyroxene En88 (E), and three Ca-rich clinopyroxenes, En48Wo41 (A), En45Wo50 (D) and En33Wo49 (AD). The chemistry of these minerals was determined by Electron Microprobe Analysis (CAMECA SX50, CNR-IGG laboratory, Padova). The bidirectional reflectance spectra were measured, with 1 nm spectral sampling, with a Fieldspec-Pro spectrophotometer mounted on a goniometer in use at the SLAB (Spectroscopy LABoratory) at IASF-INAF, Rome. For the E sample (100-125 μm grain size) we acquired spectra in the 30° - 100° phase angle range. For all the minerals, measurements at fixed viewing geometry (i = 30° e = 0°) have been performed for various grain sizes (<63 μm , 100-125 μm , 125-250 μm , 250-500 μm , 500-800 μm). Analysis of the spectra obtained for the E sample show that band depths vary with the observation geometry. This behavior can be addressed to a relative variation of the contributes of single scattering (which is relevant in the band minimum) and multiple scattering (which dominates on the wings of the band) with phase angle. A fit of the phase function of this mineral for all the wavelengths of the spectral range is performed in order to give a description of the single particle phase function, which drives the single scattering process, and an estimation of w, whose value determines the effectiveness of multiple scattering. Apart from the geometric effects, it must be noted that similar and stronger modifications of the band depth can be produced also by grain size variations and mixing with other compounds: this must be taken into account in the analysis of remote sensing spectra. A further step of this study will be the acquisition of spectra at various phase angles for the pyroxenes A, D and AD. This will permit to show similarities or differences in the scattering mechanisms among the minerals. Another application of the Hapke model will concern the derivation of the optical constants of the four pyroxenes. They can be used to compute simulated spectra of mixtures which then can be compared to lab spectra in order to test the capabilities of the Hapke's model applied to remote sensing of planetary surfaces with unknown composition. This work is financially supported by an Italian Space Agency (ASI) grant.
Capaccioni Fabrizio
Carli Cristian
Ciarniello Mauro
Sgavetti Maria
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