► The analysis of OMEGA data highlights variations of lava flow composition. ► Spectral analysis distinguishes two types of spectra on Daedalia Planum. ► Spectral maps of Daedalia Planum created with ...SAM classifier resolve new subunits. ► SAM map reveals a close relationship between spectral behavior and surface texture. ► Martian geological maps can be improved integrating morphological and spectral data.
The great variety of morphologies observed in the Daedalia Planum lava flows (Mars) encouraged a detailed study of their spectral characteristics, in order to obtain information about lava composition and detect possible differences in the spectra of the flows. The OMEGA spectral data collected from the lava field appear rather similar, with absorptions between 0.8 and 1.4μm and 1.8 and 2.5μm, suggesting the presence of mafic minerals, which are typical primary mineral phases of volcanic rocks. Moreover, after the subtraction of the background absorption (continuum removal), we highlighted the presence of two classes of spectra both compatible with tholeiitic basalts but with different proportions of Ca in the pyroxene. Despite the similar absorption bands, Daedalia spectra show differences in albedo and spectral slope. By employing the average spectra of the different flow units as end-members, a SAM (Spectral Angle Mapper) classification was performed. The resulting spectral map reveals a relationship between spectral behavior and flow surface textures.
•We retrieve the surface component from near-IR reflectance spectra.•We apply the principal component analysis and target transformation to OMEGA spectra.•Atmospheric dust is removed by means of a ...radiative transfer model.•A test spectral population is used to validate the method used in this work.•MGM analysis shows an improved match of our result with laboratory analogues.
The aim of this work is to extract the surface contribution in the martian visible/near-infrared spectra removing the atmospheric components by means of Principal Component Analysis (PCA) and target transformation (TT). The developed technique is suitable for separating spectral components in a data set large enough to enable an effective usage of statistical methods, in support to the more common approaches to remove the gaseous component. In this context, a key role is played by the estimation, from the spectral population, of the covariance matrix that describes the statistical correlation of the signal among different points in the spectrum. As a general rule, the covariance matrix becomes more and more meaningful increasing the size of initial population, justifying therefore the importance of sizable datasets. Data collected by imaging spectrometers, such as the OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité) instrument on board the ESA mission Mars Express (MEx), are particularly suitable for this purpose since it includes in the same session of observation a large number of spectra with different content of aerosols, gases and mineralogy. The methodology presented in this work has been first validated using a simulated dataset of spectra to evaluate its accuracy. Then, it has been applied to the analysis of OMEGA sessions over Nili Fossae and Mawrth Vallis regions, which have been already widely studied because of the presence of hydrated minerals. These minerals are key components of the surface to investigate the presence of liquid water flowing on the martian surface in the Noachian period. Moreover, since a correction for the atmospheric aerosols (dust) component is also applied to these observations, the present work is able to completely remove the atmospheric contribution from the analysed spectra. Once the surface reflectance, free from atmospheric contributions, has been obtained, the Modified Gaussian Model (MGM) has been applied to spectra showing the hydrated phase. Silicates and iron-bearing hydrated minerals have been identified by means of the electronic transitions of Fe2+ between 0.8 and 1.2μm, while at longer wavelengths the hydrated mineralogy is identified by overtones of the OH group. Surface reflectance spectra, as derived through the method discussed in this paper, clearly show a lower level of the atmospheric residuals in the 1.9 hydration band, thus resulting in a better match with the MGM deconvolution parameters found for the laboratory spectra of martian hydrated mineral analogues and allowing a deeper investigation of this spectral range.
During the 2011–2012 hemispheric voyage of the M/V Italica from Italy to the Atlantic Ocean, southern Indian Ocean, New Zealand and Antarctica, atmospheric CO2 concentrations were continuously ...recorded and 52 air samples collected in 4-L Pyrex flasks for the measurement of the δ13C of atmospheric CO2. In the case of CO2 concentrations, new data include the following: 1) in the Adriatic, between Ravenna and Otranto, CO2 was never measured in order to avoid the expected heavy contribution from industrial plants; the 2011 measurements fully confirm this contribution; 2) in the Atlantic, along the Moroccan coast, high values of up to 415 ppmv were recorded, apparently due to considerable industrial development in Morocco; 3) minor CO2 concentrations were also recorded along other sections of the African coast north of the Equator, whereas relatively low constant values were recorded south of the Equator; 4) in the southern Indian Ocean, CO2 concentrations were measured almost along a parallel, yielding homogeneous values not much higher than the mean values recorded at NOAA stations in nearby areas. With only one exception, the δ13C values were systematically less negative than −9‰ (VPDB), the mean values for the three oceanic sections being the following: Atlantic Ocean −8.64 ± 0.20‰; Indian Ocean −8.54 ± 0.06‰; New Zealand to Antarctica −8.49 ± 0.02‰. A small but progressive increase in δ13C values with increasing latitude was in good agreement with the expected trend. The homogeneity of such values between New Zealand and Antarctica was remarkable, as these samples had been collected in particularly rough oceanic conditions with high winds. In spite of these particular environmental conditions these values were very close to those of samples collected in the same area in 2009 and 2010 in conditions of calm sea and low wind. This similarity contrasts sharply with the theory and models of air-sea gas exchange.
•Heavily polluted atmospheric conditions were detected off the Moroccan coast.•Our data on yearly decrease of δ13C (Indian Ocean, 2005–2012) match well NOAA data.•In 2009, 2010 and 2012, δ13C of atmospheric CO2 (N.Z. – Antarctica) are very similar.•This similarity is in contrast with drastic differences in environmental conditions.•Frequent very negative δ13C values (1998–2006) sharply disagree with these values.
•We retrieved optical constants from reflectance spectra of minerals by IMSA model.•Imaginary index are retrieved accounting for powder particle size distribution.•Plagioclase–mafic mixtures are ...modeled using the retrieved imaginary indexes.•The particle size distribution affects retrieved minerals abundances.•Plagioclase–mafic abundances can be estimated within a few%.
Remote sensing data reveal the presence of several igneous-rock forming silicates on the surfaces of various Solar System bodies. Mafic (Mg–Fe silicates) materials were clearly recognized in the past on Mars, Moon, Vesta, and recently the weak absorption of plagioclase has been detected on the lunar highland. The advance in the detection of these important mineral phases encourages the improvement in our capability to quantify the contribution of single end-members in mixed materials.
Recently, Serventi et al. (Serventi, G., Carli, C., Sgavetti, M., Ciarniello, M., Capaccioni, F., Pedrazzi, G., 2013. Icarus 226 (1), 282–298.) discussed the plagioclase absorption effects on more evident mafic absorptions in mixtures made of these components. In this work, we apply a radiative transfer model to retrieve the imaginary part of the refractive index of three different particulate plagioclase samples, with variable amount of iron, and three mafic particulate assemblages (pyroxene-bearing and olivine-free, olivine-poor and olivine-rich) used in Serventi et al. (Serventi, G., Carli, C., Sgavetti, M., Ciarniello, M., Capaccioni, F., Pedrazzi, G., 2013. Icarus 226 (1), 282–298.). We considered powders with narrow particle size distributions to obtain a reference value of the refractive index for each end-member, while samples with two different wide particle size ranges were considered to investigate the influence of the size distribution on the model. The wide size distributions were described as monodisperse, using an average value, and as multidisperse, weighing the relative amount of material in particle size sub-ranges. In both these cases we computed the optical constants, concluding that an improved description of the material’s size distribution results in derived optical constants closer to the reference values.
The retrieved optical constants have been used to model reflectance spectra of plagioclase–mafic assemblage mixtures and modeled spectra were compared to measured ones. We find that the particle size distribution of the material plays an important role also in modeling mixtures spectra. Plagioclase abundance is modeled within an error of ±4% for the most of the mixtures if a multidisperse distribution is assumed, with a higher uncertainty only for mixtures with low amount of plagioclase.
We present the Messinian evaporite suite (Mediterranean region) and the Solfatara hydrothermal system (Phlegraean Fields volcanic province, Italy), discuss their implications for understanding the ...origin of sulfates on Mars and show preliminary sets of VNIR laboratory and in situ reflectance spectra of rocks from these geologic systems. The choice was based on a number of evidence relative to Mars: (1) the chemistry of the Martian sulfates, suggesting fluid interactions with possibly alkali-basaltic rocks and/or regolith; (2) close range evidence of sulfates within sedimentary formations on Mars; (3) sulfate spectral signatures associated to large-scale layered patterns interpreted as thick depositional systems on Mars. The Messinian evaporites comprise three units: primary shallow-water sulfates (primary lower gypsum: PLG), shallow- to deep-water mixed sulfates and clastic terrigenous deposits (resedimented lower gypsum: RLG), and shallow-water associations of primary sulfates and clastic fluvio-deltaic deposits (upper evaporites: UE). The onset of the Messinian evaporites records the transition to negative hydrologic budget conditions associated with the Messinian Salinity Crisis, which affected the entire Mediterranean basin and lasted about 640
kyr. The Solfatara is a still evolving hydrothermal system that provides epithermal deposits precipitated from the interaction of fluids and trachybasaltic to phonolitic rocks. Thermal waters include alkali-chloride, alkali-carbonate and alkali-sulfate endmembers.
The wide spectrum of sedimentary gypsum facies within the Messinian formation includes some of the depositional environments hitherto identified on Mars and others not found on Mars. The PLG unit includes facies associations correlated over long distances, that could be a possible analog of the stratified rock units exposed from Arabia Terra at least as far as Valles Marineris. The facies cycles within the UE unit can be compared to the sequences of strata observed in craters such as Holden and Eberswalden. The UE unit records paleoenvironmental changes which are ultimately controlled by terrestrial climatic variations. They can be considered as a reliable climatic proxy and may be useful for the reconstruction of climatic events on Mars. The intermediate Messinian RLG unit has not, at present, a well-defined depositional counterpart on Mars, although there are some similarities with the northern lowlands and Vastitas Borealis Formation. The dramatic variation of hydrologic budget conditions at the onset of the Messinian evaporites may provide criteria for the interpretation of similar variations on Mars.
The volcanic rocks at the Solfatara bear some similarities with the “alkaline magmatic province” observed at the Gusev crater on Mars, and the assemblages of hydrothermal phases resulting from the Solfatara's parent rocks could be analogues for processes involving Gusev-type rocks.
The Messinian sulfates have a prevalent Ca-sulfatic composition and wide textural variability. Preliminary laboratory reflectance spectra of rock samples in the VNIR region reveal the signature of sulfates and mixtures of several Fe-bearing phases. At the Solfatara, in situ reflectance measurements of epithermal minerals close to active fumaroles showed the presence of Fe-bearing sulfates, hematite, Al- and K-sulfates and abundant amorphous fraction. XRD analysis supported this interpretation.
The range of depositional facies observed in the Messinian units and the variety of minerals detected in the Solfatara will be useful for the interpretation of close range data of Mars. The spectral characterization at various scales of the Messinian sedimentary facies and the Solfatara hydrothermal minerals will both help in the exploration of Mars from orbit and with close range inspection.
Laboratory reflectance (0.4-2.5 w m ) spectra of 41 samples of metamorphic rocks from the Precambrian basement of Madagascar were analysed on the basis of absorption band position and shape, and ...classified on the basis of recurrent associations of absorption bands. Petrographic analyses allowed us to interpret the absorption features in compositional terms. Spectral and petrographic classes coincided when the principal mineralogy was also spectrally dominant (e.g. in carbonate rocks). When the principal mineralogy did not produce diagnostic spectral features (e.g. in siliceous rocks in the visible-short wave infrared region), the classification was based on spectrally dominant secondary phases. The reflectance spectra were measured on both freshly cut and exposed surfaces of the samples. Apart from a few cases of spectral features obliteration due to kaolinization, or overall albedo change related to texture variation, the two sets of spectra did not significantly differ. The responses of airborne MIVIS and AVIRIS hyperspectral sensors were simulated from spectra representative of the spectral classes, showing that significant identification and classification of well exposed metamorphic rocks are potentially possible using remote instruments providing high quality spectra. Although at present there are no plans for a spaceborne instrument of this quality, TM simulations and band composite images showed that a preliminary gross discrimination of the rocks belonging to the different classes was however possible.
From 16 to 26 July 2003 an extensive field campaign was carried out around Mt Etna, Sicily, Italy. During the campaign a new airborne system, Fire Airborne Spectral Analyzer (FASA), was tested. The ...main instrument of the payload is a high resolution Michelson Interferometer with Rotating Retroreflector (MIROR), which operates in the nominal infrared 600-3000 cm
−1
spectral range with a high resolution of 0.12 cm
−1
. This work investigates the feasibility of using MIROR data to retrieve the surface temperature, the hyper-spectral emissivity and the SO
2
volcanic plume abundance. The results for the surface parameters show a good agreement with those obtained by satellite data and on ground measurements. In particular, the spectral emissivity shows a meaningful minimum, around 1040 cm
−1
, consistent with the basaltic properties of Mt Etna's surface. A sensitivity study has also been carried out to show the difficulties of SO
2
columnar abundance retrieval due to the too low SO
2
volcanic emission and the too high instrumental noise.
A thick Pleistocene shelf and nearshore cyclical succession was deposited in the S. Mauro sub-basin of the Crotone basin (southern Italy). The regressive units of the cycles are mostly represented by ...coastal siliciclastic and bioclastic prograding wedges showing a clinoform geometry. These are separated by blanket-like deposits of high lateral persistence recording major transgressive episodes. The aim of this paper is (1) to describe facies patterns and depositional setting of two prograding wedges, particularly focussing on their polycyclic internal architecture, (2) to analyze these units within a sequence-stratigraphic framework, and (3) to speculate on the possible origin of the small-scale cyclicity. The two wedges analyzed in this paper consist of a number of shingles. Individual shingles consist of two physically connected units: (1) a relatively thin package of sigmoid clinoforms, grading into (2) a volumetrically dominant package of oblique-tangential clinoforms with toplap terminations. The shingles are bounded by seaward-dipping surfaces with sigmoid clinoform geometry, which are ravinement surfaces updip, passing into conformable flooding surfaces downdip. The wedges are thus organized into high-frequency, small-scale sequences, each comprising transgressive, highstand and falling-stage systems tracts. As a whole, individual prograding wedges are interpreted as forced-regressive units, as the shoreline was subject to an overall shift basinwards and downwards along a low-angle trajectory, in spite of the repeated minor relative sea-level rises. Tectonic subsidence, and particularly the syndepositional growth of gentle synclines, are thought to have been the key factors allowing the preservation of these forced-regressive units. Progradation of the wedges took place in a high-energy wave climate characterized by high frequency of storms and very efficient alongshore redistribution of sediments. Recurrent, storm-driven, offshore currents led to intense reworking of sediments on the topset platform and gravity spreading on the foreset slope of the prograding wedges. Well-oxygenated conditions over the shelf due to intensified storm activity during glacial periods may have enhanced the rate of production of skeletal, foramol-type carbonates. It can reasonably be assumed that progradation took place from a line source and that the sand bodies are to be regarded as coastal prograding bodies. In spite of active syndepositional tectonics, the cycles can be correlated to Pleistocene high-amplitude sea-level oscillations. The older of the two wedges can be correlated, through bio-magnetostratigraphy, to the major climatic transition which occurred from the marine oxygen-isotope stage 25 to 24–22 (
Rio et al., 1996). The younger probably developed during the sea-level fall that ended with substage 18.2, as suggested by sequence- and bio-stratigraphic data. The prograding wedges are thus interpreted to record long-lived sea-level falls of fourth-order cycles. Due to the particular depositional setting, we are inclined to exclude authigenic mechanisms in the origin of small-scale cyclicity. Although the concomitance and interaction of different controlling factors may be taken into account, it is tempting to ascribe this cyclicity to minor eustatic changes punctuating long-lived, erratic falling stages, possibly accompanied by climate-driven fluctuations of sediment supply. Shelf-perched and shelf-edge prograding units consisting of foramol-type carbonates are apparently a common falling-stage to lowstand depositional feature in the Mediterranean area during the Late Pliocene and Pleistocene.
Lunar highlands are plagioclase-rich terrains produced by crystal floating in a Magma Ocean system. Lunar samples revealed the presence of anorthositic (plagioclase > 90%) samples from the Highlands, ...associated to more mafic rocks. Recently, remote sensing data permit mapping those terrains with high spatial and spectral resolution allowing detection of plagioclase and mafic crystal field (C.F.) absorptions. In this paper we have studied bidirectional spectral characteristics in the visible near-infrared (VNIR) of rocks from the Stillwater Complex, a cumulitic igneous stratified complex, with composition varying from mafic to sialic (e.g., pyroxenite, anorthosite). We investigated both slabs and powders of these rocks to give indication of the spectral variability of rock analogs of lunar crust, from a mineralogical point of view. Samples have been spectrally separated in four main groups considering the different C.F. absorption association, reflectance and spectral shape for both slab and powder spectra. More spectral details can be obtained from the analysis of powder spectra than from the slab spectra. The composition of rocks can be addressed by studying spectral parameters, such as the position and the intensity of the absorption (e.g., band center and band depth). The analysis of our plagioclase-pyroxene-bearing samples indicates that mafic composition can be clearly obtained for samples characterized by one pyroxene phase, even for few amounts of pyroxene, from powder spectra. On the other hand, slab spectra show clear pyroxene absorptions only for rocks with mafic abundance at least >20%. The intensity of the mafic absorptions of these samples shows a linear trend with respect to the abundance of pyroxenes (orthopyroxene + clinopyroxene, for samples with ferrosilite amount less than ca. 25%). Considering all pyroxene-bearing samples, the band depth of slab spectra are linearly related to the volumetric distribution of ferrous iron in pyroxenes.
Mineral interpretation of a planet surface using spectral libraries can be improved if the spectral variability, often characterizing the spectral data, can be explained as the result of well-defined ...geological processes. Reflectance spectra of metamorphic rocks are analyzed. Selected examples point out systematic and non-systematic relationships between spectral parameters (band wavelength, shape, and reflectance peaks) and geologically controlled variables (composition of minerals and mineral assemblages), thus establishing a conceptual framework that can facilitate the analysis of unknown spectra.
