Reflectance spectroscopy (0.3–2.5 µm) at various scales for bulk-rock identification

We discussed the possibilities and open questions concerning laboratory refl ectance spectroscopy, spectroscopic measurements in the fi eld, hyperspectral image data from spacecraft, and integration of multiscale data. Open questions included: (1) bulk-rock spectral complexity, which provides the geologic basis for every spectroscopic analysis; (2) criteria for laboratory and fi eld spectra classifi cation, as a tool for (3) end-member selection for image data classifi cation; (4) peculiar spectral characteristics of Mount Etna basalts; and (5) effects of remote-sensing data quality. The last three items emerged during a multiscale survey on the Mount Etna volcano. Our laboratory spectroscopic analyses, supported by specifi c petrographic analyses, showed the relationship between absorption-band frequency and spectrally active functional groups and the unexpected effects of bulk-rock composition on this relationship. We studied the muscovite Al-OH band in quartzite and micaschist and Fe 2+ band in pyroxene-bearing cumulates. Laboratory refl ectance spectra of rocks were classifi ed using the concept of spectrofacies. In the case of metamorphic rocks, the result was a tree-structure of rock spectral classes mainly based on the predominant vibrational processes. In the case of basalts, characterized by an overall similarity in their composition, the classes were determined on the basis of overall shape of the spectral curve and on electronic process intensities. Here, we report fi rst results of multiscale data integration for the Mount Etna volcano. Etna rocks consist of basalts, with very low albedo and variable degrees of alteration, and recent lava fl ows are characterized by overall low refl ectance in both ASTER (advanced spaceborne thermal emission and refl ection radiometer) and Hyperion color-composite images. We carried out Spectral Angle Mapper (SAM) classifi cation of Hyperion images, where individual fi eld spectra represented suitable end members for classifi cation of recent lava and pyroclastic deposits. We used fi eld spectra linear combinations to classify mixed pixels and to approximate the classifi cation of altered and oxidized effusive products. Only two laboratory spectral classes coincided with fi eld spectra classes; laboratory spectra were mainly used for spectral features attribution. The overall spectral shape of some of these spectra is still under study. Noise level in Hyperion data precluded the identifi cation of subtle diagnostic iron absorption bands

Atmospheric CO 2 concentrations and δ 13 C values between New Zealand and Antarctica, 1998 to 2010: some puzzling results

From 1998 to 2010, during eight cruises of the M/V Italica between New Zealand and Antarctica, sets of flask air samples were collected and atmospheric CO 2 concentrations were recorded. The δ 13 C of CO 2 from the 1998 to 2003 air samples have already been published and show large interannual variability and an increasing frequency of 13 C-depleted samples. These results were related to a mosaic of areas with positive air–sea fluxes. We report here δ 13 C results from air samples collected from four further cruises. δ 13 C values obtained during the 2004/2005 cruise show an inexplicable saw-toothed distribution. Air samples from the 2005/2006 cruise have δ 13 C values which match previous sets of samples (1998 to 2004) and show more frequent and more negative isotopic events. From 2006 until 2009, further samples could not be collected. However, during December 2009 and January 2010, two more sets of air samples were collected, the δ 13 C values of which greatly differ from previous results, being absolutely homogeneous and paralleled by flat CO 2 concentrations. The results of these last two sets of air samples may be due either to fortuitous environmental conditions or to an improbable and substantial change in oceanic and atmospheric conditions in this section of the circumpolar area. Keywords: New Zealand to Antarctica, flask air samples, atmospheric CO 2 concentrations, carbon isotopic composition of CO 2 , puzzling results (Published: 5 December 2012) Citation: Tellus B 2012, 64 , 17472, http://dx.doi.org/10.3402/tellusb.v64i0.1747

Accuracy in mineral identification: image spectral and spatial resolutions and mineral spectral properties

Problems related to airborne hyperspectral image data are reviewed and the requirements for data analysis applied to mineralogical (rocks and soils) interpretation are discussed. The variability of mineral spectral features, including absorption position, shape and depth is considered and interpreted as due to chemical composition, grain size effects and mineral association. It is also shown how this variability can be related to well defined geologic processes. The influence of sensor noise and diffuse atmospheric radiance in classification accuracy is also analyzed

Visible and near-infrared reflectance spectroscopy of pyroxene-bearing rocks: New constraints for understanding planetary surface compositions

Laboratory visible and near-infrared reflectance spectra of solid rock slabs, mineral separates and systematic mixtures were simultaneously investigated. We apply an empirical approach to evaluate spectra, in order to achieve qualitative and quantitative information. We use cumulates (mostly norites, leuconorites, melanorites and anorthosites) belonging to the Bjerkreim-Sokndal Layered Intrusion, a sequence of genetically related rocks with simple textures. Laboratory spectra are measured on slightly polished rock slabs in the 350- to 2500-nm interval and directional-hemispherical reflectance geometry. Composition is determined using traditional techniques other than reflectance spectroscopy. We find that: (1) band minima measured on rock spectra are strongly influenced by the concurrent effects due to modal abundance of the spectroscopically active mineral and mineral chemistry; (2) band depths can be used for semiquantitative analyses, limited to the set of rocks investigated; (3) the spectral parameters derived from powdered pyroxene are in agreement with previously published calibrations; (4) the mineral mixture systematics can be reasonably considered as linear, when pyroxene is mixed with neutral components; and (5) the empirical evaluation of solid rock surface spectra needs further insights to give a great improvement to planetary researches. In addition, genetic sequences of rocks should be investigated in detail to help the geological interpretation of planetary evolution. Therefore more laboratory and analytical studies are required in order to understand the influence of composition and petrographic textures on the spectral analysis