Visible To Near-infrared Research Articles

A Cubesat enabled Spatio-Temporal Enhancement Method (CESTEM) utilizing Planet, Landsat and MODIS data

Satellite sensing in the visible to near-infrared (VNIR) domain has been the backbone of land surface monitoring and characterization for more than four decades. However, a limitation of conventional single-sensor satellite missions is their limited capacity to observe land surface dynamics at the very high spatial and temporal resolutions demanded by a wide range of applications. One solution to this spatio-temporal divide is an observation strategy based on the CubeSat standard, which facilitates constellations of small, inexpensive satellites. Repeatable near-daily image capture in RGB and near-infrared (NIR) bands at 3–4 m resolution has recently become available via a constellation of >130 CubeSats operated commercially by Planet. While the observing capacity afforded by this system is unprecedented, the relatively low radiometric quality and cross-sensor inconsistencies represent key challenges in the realization of their full potential as a game changer in Earth observation. To address this issue, we developed a Cubesat Enabled Spatio-Temporal Enhancement Method (CESTEM) that uses a multi-scale machine-learning technique to correct for radiometric inconsistencies between CubeSat acquisitions. The CESTEM produces Landsat 8 consistent atmospherically corrected surface reflectances in blue, green, red, and NIR bands, but at the spatial scale and temporal frequency of the CubeSat observations. An application of CESTEM over an agricultural dryland system in Saudi Arabia demonstrated CubeSat-based reproduction of Landsat 8 consistent VNIR data with an overall relative mean absolute deviation of 1.6% or better, even when the Landsat 8 and CubeSat acquisitions were temporally displaced by >32 days. The consistently high retrieval accuracies were achieved using a multi-scale target sampling scheme that draws Landsat 8 reference data from a series of scenes by using MODIS-consistent surface reflectance time series to quantify relative changes in Landsat-scale reflectances over given Landsat-CubeSat acquisition timespans. With the observing potential of Planet's CubeSats approaching daily nadir-pointing land surface imaging of the entire Earth, CESTEM offers the capacity to produce daily Landsat 8 consistent VNIR imagery with a factor of 10 increase in spatial resolution and with the radiometric quality of actual Landsat 8 observations. Realization of this unprecedented Earth observing capacity has far reaching implications for the monitoring and characterization of terrestrial systems at the precision scale.

Rapid assessment of algal biomass and pigment contents using diffuse reflectance spectroscopy and chemometrics

Rapid and cost-effective analysis of algal pigments and biomass with minimum processing would be an invaluable tool for industrial applications especially in pharmaceutical and food industries. In this study, diffuse reflectance spectroscopy (DRS) was used for quantifying biomass and pigments from Chlorella vulgaris, Nostoc muscorum and their mixed culture via partial least squares regression (PLSR) algorithm. Results indicated that all PLSR models were able to accurately predict algal biomass using visible to near infrared (VisNIR) spectrum, producing an identical R2 of 0.98. While using pigment spectra for modeling pigments for individual culture, DRS exhibited excellent model generalization capability with calibration R2 ranging from 0.92–0.99. Qualitative spectral analysis has identified culture specific spectral signatures. Moreover, while using the pooled data for predicting algal pigments, culture spectra produced similar model accuracies to those produced by using pigment spectra. For predicting total carotenoids, the PLSR model using culture spectra (R2=0.94) outperformed the model, which used pigment spectra (R2=0.35), indicating the potential for developing a new approach for estimating pigment concentrations in algae samples without consuming the sample.

Comparing Passive Microwave with Visible-To-Near-Infrared Phenometrics in Croplands of Northern Eurasia

Planting and harvesting times drive cropland phenology. There are few datasets that derive explicit phenological metrics, and these datasets use the visible to near infrared (VNIR) spectrum. Many different methods have been used to derive phenometrics such as Start of Season (SOS) and End of Season (EOS), leading to differing results. This discrepancy is partly due to spatial and temporal compositing of the VNIR satellite data to minimize data gaps resulting from cloud cover, atmospheric aerosols, and solar illumination constraints. Phenometrics derived from the downward Convex Quadratic model (CxQ) include Peak Height (PH) and Thermal Time to Peak (TTP), which are more consistent than SOS and EOS because they are minimally affected by snow and frost and other non-vegetation related issues. Here, we have determined PH using the vegetation optical depth (VOD) in three microwave frequencies (6.925, 10.65 and 18.7 GHz) and accumulated growing degree-days derived from AMSR-E (Advanced Microwave Scanning Radiometer on EOS) data at a spatial resolution of 25 km. We focus on 50 AMSR-E cropland pixels in the major grain production areas of Northern Eurasia (Ukraine, southwestern Russia, and northern Kazakhstan) for 2003–2010. We compared the land surface phenologies of AMSR-E VOD and MODIS NDVI data. VOD time series tracked cropland seasonal dynamics similar to that recorded by the NDVI. The coefficients of determination for the CxQ model fit of the NDVI data were high for all sites (0.78 < R2 < 0.99). The 10.65 GHz VOD (VOD1065GHz) achieved the best linear regression fit (R2 = 0.84) with lowest standard error (SEE = 0.128); it is therefore recommended for microwave VOD studies of cropland land surface phenology. Based on an Analysis of Covariance (ANCOVA) analysis, the slopes from the linear regression fit were not significantly different by microwave frequency, whereas the intercepts were significantly different, given the different magnitudes of the VODs. PHs for NDVI and VOD were highly correlated. Despite their strong correspondence, there was generally a lag of AMSR-E PH VOD10.65GHz by about two weeks compared to MODIS peak greenness. To evaluate the utility of the PH determination based on maximum value, we correlated the CxQ derived and maximum value determined PHs of NDVI and found that they were highly correlated with R2 of 0.87, but with a one-week bias. Considering the one-week bias between the two methods, we find that PH of VOD10.65GHz lags PH of NDVI by three weeks. We conclude, therefore, that maximum-value based PH of VOD can be a complementary phenometric for the CxQ model derived PH NDVI, especially in cloud and aerosol obscured regions of the world.

A 40,000 yr record of clay mineralogy at Lake Towuti, Indonesia: Paleoclimate reconstruction from reflectance spectroscopy and perspectives on paleolakes on Mars

Sediment deposited within lake basins can preserve detailed records of past environmental conditions on planetary surfaces, including both Earth and Mars. Establishing how to best characterize these paleoclimate records is thus critical for understanding the evolution of past planetary climates. Here, we present an ∼40 k.y. lake sediment record from Lake Towuti, Indonesia, developed using visible to near-infrared (VNIR) reflectance spectroscopy. Source sediment from the main river input to Lake Towuti, the Mahalona River, is spectrally dominated by Mg-rich serpentine; however, we also identify a distinct Al-phyllosilicate component, which we interpret as kaolinite, that increases in relative proportion to serpentine with decreasing grain size. Sink sediment from two cores collected at the distal margins of the Mahalona River delta has similar spectral signatures to the input source sediment. The cores capture systematic variations in the proportion of Al-phyllosilicate to serpentine over time, which is also expressed in changes in bulk elemental chemistry of the sediment. We show that the abundance of serpentine relative to Al-phyllosilicate increases dramatically during the globally cooler, regionally drier climate of the Last Glacial Maximum. This change records the grain size−dependent mineralogy of deltaic sediment, which is ultimately driven by forced delta progradation and river incision during lake lowstands. Our analyses show that VNIR reflectance spectroscopy offers a rapid, nondestructive, and effective method for developing paleoenvironmental records from sedimentary phyllosilicate mineralogy. Exposed paleolake deposits on Mars should preserve similar paleoenvironmental information that can be accessed through detailed remote sensing observations of stratigraphy and VNIR reflectance spectroscopy in a source-to-sink framework.

Application of ASTER and Landsat 8 imagery data and mathematical evaluation method in detecting iron minerals contamination in the Chadormalu iron mine area, central Iran

Satellite images are widely used to map geological and environmental features at different map scales. The ability of visible to near-infrared (VNIR) scanner systems to map gossans, rich in iron and associated with weathered sulfide occurrences, as well as to characterize regoliths, is perhaps one of the most important current applications of this technology. Initial results of this study show that advanced space-borne thermal emission and reflection (ASTER), VNIR, and short-wave infrared radiometer scanner systems can be used successfully to map iron ores. By applying internal average relative reflectance, false color composite, minimum noise fraction transform, and mathematical evaluation method (MEM) techniques, iron contaminations were successfully detected in the Chadormalu iron mine area of central Iran. An attempt was also made to discriminate between the geogenic and anthropogenic iron contaminations in the vicinity of the Chadormalu iron deposit. This research compares ASTER and Landsat 8 data images and the MEM with the band ratio method in a full scope view scale and demonstrates ASTER image data capability in detecting iron contaminations in the Chadormalu area. This indicates that ASTER bands 3, 2, and 1 have a higher spatial (15 m) resolution compared with sensors used in previous works. In addition, the capability of the MEM in detecting Fe-contaminants, unlike the color judgments of the band ratio method, can discriminate between iron pollution in an alluvial plain and the Fe-contents of the host and country rocks in the study area. This study proved that Landsat 8 data illustrate exaggeration both in the MEM and band ratio final results (outputs) and cannot display iron contamination in detail.

Incremental laser space weathering of Allende reveals non-lunar like space weathering effects

We report findings from a series of laser-simulated space weathering experiments on Allende, a CV3 carbonaceous chondrite. The purpose of these experiments is to understand how spectra of anhydrous C-complex asteroids might vary as a function of micrometeorite bombardment. Four 0.5-gram aliquots of powdered, unpacked Allende meteorite were incrementally laser weathered with 30mJ pulses while under vacuum. Radiative transfer modeling of the spectra and Scanning Transmission Electron Microscope (STEM) analyses of the samples show lunar-like similarities and differences in response to laser-simulated space weathering. For instance, laser weathered Allende exhibited lunar-like spectral changes. The overall spectra from visible to near infrared (Vis-NIR) redden and darken, and characteristic absorption bands weaken as a function of laser exposure. Unlike lunar weathering, however, the continuum slope between 450–550nm does not vary monotonically with laser irradiation. Initially, spectra in this region redden with laser irradiation; then, the visible continua become less red and eventually spectrally bluer. STEM analyses of less mature samples confirm submicroscopic iron metal (SMFe) and micron sized sulfides. More mature samples reveal increased dispersal of Fe-Ni sulfides by the laser, which we infer to be the cause for the non-lunar-like changes in spectral behavior. Spectra of laser weathered Allende are a reasonable match to T- or possibly K-type asteroids; though the spectral match with a parent body is not exact. The key take away is, laser weathered Allende looks spectrally different (i.e., darker, and redder or bluer depending on the wavelength region) than its unweathered spectrum. Consequently, connecting meteorites to asteroids using unweathered spectra of meteorites would result in a different parent body than one matched on the basis of weathered spectra. Further, spectra for these laser weathering experiments may provide an explanation for inconsistencies observed in both laboratory (e.g., Hiroi et al., 2003, 2001; Lazzarin et al., 2006; Moroz et al., 2004, 1996; Shingareva et al., 2004) and telescopic data (Lazzarin et al., 2006; Marchi et al., 2006; Nesvorný et al., 2005).

Detection of moldy core in apples and its symptom types using transmittance spectroscopy

Abstract: A detection method based on transmittance spectroscopy and support vector machine (SVM) was proposed to achieve rapid nondestructive detection of moldy core in apples. A visible to near-infrared (Vis/NIR) spectroradiometer was used for scanning transmittance spectra of 215 apple samples in the wavelength range of 200-1025 nm. Wavelet transform was used to reduce the dimensionality of the spectra and extract wavelet coefficients. Two classification algorithms including artificial neural network (ANN) and SVM were used to develop models whose parameters were optimized by genetic algorithms (GA) for determination of the presence and types of moldy core in apples. Comparisons results of the models showed that the GA-SVM model obtained the optimal result with an accuracy of 96.92% for detecting the presence of moldy core and 81.48% for distinguishing symptom types of the disease. These results indicate that it is feasible to detect moldy core in apples nondestructively and rapidly based on transmittance spectroscopy and that wavelet transform is an effective method for extraction of characteristics from spectra. Moreover, the GA-SVM algorithm in conjunction with Vis/NIR transmittance spectroscopy can accurately achieve fast and nondestructive detection of the presence and types of moldy core in apples. Keywords: moldy core of apples, transmittance spectrum, wavelet transform, support vector machine, genetic algorithm, symptom types DOI: 10.3965/j.ijabe.20160906.2235 Citation: Zhou Z Y, Lei Y, Su D, Zhang H H, He D J, Yang C H. Detection of moldy core in apples and its symptom types using transmittance spectroscopy. Int J Agric & Biol Eng, 2016; 9(6): 148－155.

Rapid and Noninvasive Assessment of Atterberg Limits Using Diffuse Reflectance Spectroscopy

Core Ideas Diffuse reflectance spectroscopy has potential for the estimation of Atterberg limits. Visible, near‐, and mid‐infrared regions of electromagnetic spectra were utilized. Atterberg limits were estimated by correlation with other spectrally active soil properties. In this study, Atterberg limits were estimated using pedotransfer functions (PTFs), spectral‐transfer functions (STFs), and spectral PTFs (SPTFs). In the PTF approach, basic soil properties were used to calibrate PTFs using stepwise multiple linear regression and support‐vector regression (SVR) approaches. In the STF approach, spectral reflectance values across the visible to near‐infrared (VNIR) and mid‐infrared (MIR) regions were used to estimate Atterberg limits using the SVR and partial least squares regression (PLSR) approaches along with bootstrapping. Also, two locally weighted PLSR models were developed using covariance and correlation as weighting schemes. Finally, feature selection was combined with the PLSR (PLSRFS) to identify the optimum set of spectral features to use in the estimations. In the SPTF approach, both basic properties and geometrical shape factors of spectral absorption were used for the prediction of Atterberg limits. Comparison of the coefficient of determination (R2) and root mean squared residual values for the validation data sets across different modeling approaches suggested that the PLSRFS model along with pooled VNIR + MIR data yielded the highest R2 of 0.77 for the liquid limit. The PLSRFS model along with VNIR data alone yielded the highest R2 of 0.70 for the plastic limit. A maximum R2 value of 0.65 was obtained for the plasticity index using both the PLSR and SVR models on MIR data and the PLSRFS model on pooled VNIR + MIR data. This study shows that the STF approach may be adopted as an alternate to PTFs to estimate the Atterberg limits because it can account for up to 77% of the variance in the data.

Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio-Imaging.

The assembly sequence of the coordination cluster [Zn5 (H2 L(n) )6 ](NO3 )4 ]⋅8 H2 O⋅2 CH3 OH (Zn5 , H3 L(n) =(1,2-bis(benzo[d]imidazol-2-yl)-ethenol) involves in situ dehydration of 1,2-bis(benzo[d]imidazol-2-yl)-1,2-ethanediol (H4 L) through the formation of the [Zn(H3 L)2 ](+) monomer, dimerization to [Zn2 (H3 L)2 ](+) , dehydration of the ligand to [Zn2 (H2 L(n) )2 ](+) , and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH3 , 2) low cytotoxicity, and 3) pH-sensitive fluorescence in the visible-to-near-infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H-bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm(3) ).

Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio‐Imaging

AbstractThe assembly sequence of the coordination cluster [Zn5(H2Ln)6](NO3)4]⋅8 H2O⋅2 CH3OH (Zn5, H3Ln=(1,2‐bis(benzo[d]imidazol‐2‐yl)‐ethenol) involves in situ dehydration of 1,2‐bis(benzo[d]imidazol‐2‐yl)‐1,2‐ethanediol (H4L) through the formation of the [Zn(H3L)2]+ monomer, dimerization to [Zn2(H3L)2]+, dehydration of the ligand to [Zn2(H2Ln)2]+, and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH3, 2) low cytotoxicity, and 3) pH‐sensitive fluorescence in the visible‐to‐near‐infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H‐bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm3).

Constraints on the composition and particle size of chloride salt‐bearing deposits on Mars

AbstractChloride salt‐bearing deposits on Mars were discovered using the Mars Odyssey Thermal Emission Imaging System (THEMIS) and have been characterized by both mid‐infrared (MIR) and visible‐to‐near‐infrared (VNIR) remote sensing instruments. The chloride salt‐bearing deposits exhibit a blue slope at MIR wavelengths and a featureless red slope at VNIR wavelengths. These deposits also lack strong 3 µm bands in VNIR spectra, indicating that they are desiccated compared to the surrounding regolith. The lack of VNIR spectral features suggests that an anhydrous chloride salt, the most likely of which is halite, is responsible for the observed spectral slope. In this work, we use laboratory spectra and a hybrid T‐matrix/Hapke light scattering model to constrain the particle sizes and salt abundances of the Martian chloride salt‐bearing deposits. Our work shows that the two broad spectral classes of these deposits observed by THEMIS can be explained by a difference in the particle size of the admixed silicate regolith. In all cases, chloride salt abundances of 10–25% are required to match the THEMIS data. The chloride salt abundances determined in this work suggest deposition in a lacustrine/playa setting or in association with late‐stage groundwater upwelling.

Reflectance spectroscopy of chromium-bearing spinel with application to recent orbital data from the Moon

Visible to near-infrared (V-NIR) remote sensing observations have identified spinel in various locations and lithologies on the Moon. Experimental studies have quantified the FeO content of these spinels (Jackson et al. 2014), however the chromite component is not well constrained. Here we present compositional and spectral analyses of spinel synthesized with varying chromium contents at lunar-like oxygen fugacity ( f O2). Reflectance spectra of the chromium-bearing synthetic spinels (Cr# 1–29) have a narrow (~130 nm wide) absorption feature centered at ~550 nm. The 550 nm feature, attributed to octahedral Cr3+, is present over a wide range in iron content (Fe# 8–30) and its strength positively correlates with spinel chromium content [ln(reflectancemin) = −0.0295 Cr# – 0.3708]. Our results provide laboratory characterization for the V-NIR and mid-infrared (mid-IR) spectral properties of spinel synthesized at lunar-like f O2. The experimentally determined calibration constrains the Cr# of spinels in the lunar pink spinel anorthosites to low values, potentially Cr# < 1. Furthermore, the results suggest the absence of a 550 nm feature in remote spectra of the Dark Mantle Deposits at Sinus Aestuum precludes the presence of a significant chromite component. Combined, the observation of low chromium spinels across the lunar surface argues for large contributions of anorthositic materials in both plutonic and volcanic rocks on the Moon.

Delineation of Debris-Covered Glaciers Based on a Combination of Geomorphometric Parameters and a TIR/NIR/SWIR Band Ratio

Accurate mapping of glaciers is important for the management of water resources, studying glacier mass-balance, and monitoring glacier health. However, many glaciers are partially covered by debris of varying thicknesses, and these debris-covered glacier areas are difficult to distinguish clearly from the adjacent valley rock using optical remote sensing data due to their similar reflectance in the visible-to-near-infrared (VNIR) wavelength region. For better detection of the debris-covered glacier margin, a new method was proposed here which considers glacier terrain features (concave and convex landscapes) as well as VNIR reflectance, shortwave-infrared reflectance (SWIR), and thermal infrared (TIR) information. The proposed method uses several geomorphometric parameters (slope, plan, and profile curvature) and a Landsat Thematic Mapper (TM) band ratio image TM TIR/(TM NIR/TM SWIR) for mapping the Yengisogat glacier in the Shaksgam valley of China. The final debris-covered glacier boundary is generated by thresholding the band ratio image and overlaying it onto the result derived from cluster analysis performed using plan, profile curvature, and combined with mean of slope information. Evaluation of the final debris-covered glacier outline was carried out through comparison with GIS data from several reference data sets, and the final Yengisogat glacier outline had a difference of less than 1% in area compared to the reference data sets.

Characterizing clay mineralogy in Lake Towuti, Indonesia, with reflectance spectroscopy

We tested the use of visible to near-infrared (VNIR) reflectance spectroscopy to characterize the relative abundances of clay minerals in sediments from Lake Towuti, a large tectonic lake in Sulawesi, Indonesia. We measured VNIR spectra of lake and river sediments from Lake Towuti and its catchment to identify clay minerals, fit major VNIR absorption features with a modified Gaussian model to estimate relative abundances of these minerals, and compared these absorptions to the samples’ chemistry to test the utility of VNIR spectroscopy to characterize sediment compositional variations. We found that major absorptions are caused by vibrations of Al–OH in kaolinite (2.21 μm), Fe–OH in nontronite (2.29 μm), Mg–OH in saponite and serpentine (2.31 μm), and Mg–OH in serpentine (2.34 μm). This was confirmed with X-ray diffraction data. The correlations between absorption band areas for Fe–OH, Al–OH, and Mg–OH vibrations and Fe, Al and Mg concentrations, respectively, are statistically significant, varying between r = 0.51 and r = 0.90, and spatial variations in inferred clay mineralogy within the lake are consistent with variations in the geology of the catchment. We conclude that VNIR spectroscopy is an effective way to characterize the clay mineralogy of lake sediments, and can be used to investigate changes in mineral inputs to lake deposits.

Continuous and long-term measurements of reflectance and sun-induced chlorophyll fluorescence by using novel automated field spectroscopy systems

In this paper we present novel automated field spectroscopy systems for collecting unattended, continuous and long-term measurements of plant canopies and, more in general, of Earth's ecosystems. These systems simultaneously collect high and ultra-high resolution spectra in the visible to near-infrared (VNIR) domain employing two spectrometers: i) the first covers the spectral range 400–1000nm with a 1.0nm spectral resolution; ii) the second provides a sub-nanometer spectral resolution within the 700–800nm spectral range. The data collected by the first spectrometer allow retrieval of VNIR reflectance, while the higher spectral resolution data from the second device permit estimation of vegetation Sun-Induced Fluorescence (SIF) in the O2–A band. The instruments are constructed by assembling commercial and on-the-shelf optoelectronic devices to facilitate reproduction of the instrument for promoting measurements over different ecosystems. The instrument's optical design, data collection and processing, laboratory and in-field calibration methods are reported and discussed. The high spectral resolution and the rigorous calibration methods enable accurate estimation of SIF in physical units by exploiting almost the same retrieval concept as that of the European Space Agency FLuorescence EXplorer mission. The instruments have been operated in several field campaigns with the aim to show: i) the possibility of continuous and seasonal monitoring of plant growth and activity of an agricultural crop; and ii) the diverse and specific daily course patterns of different types of canopy. The datasets of canopy reflectance, vegetation indices and SIF collected are shown and discussed.

Lunar cryptomaria: Mineralogy and composition of ancient volcanic deposits

Ancient lunar volcanic deposits, known as cryptomaria, have been detected by remote telescopic and orbital measurements since the 1970s. Cryptomaria are most easily identified by the presence of dark-halo impact craters and are associated with a mare basalt mineralogy, which is indicated by two pyroxene spectral absorption features near 1μm and 2μm in the visible to near-infrared (VNIR) wavelengths. However, there are many early igneous lithologies that have been identified in the Apollo sample collection that have a similar VNIR spectral signal, implying a pyroxene-dominant mineralogy. In this study we use high resolution Moon Mineralogy Mapper (M3) VNIR spectral data and the Modified Gaussian Model (MGM) to determine cryptomare mineralogy as well as Lunar Prospector gamma-ray spectrometer (LP GRS) FeO and Th compositional measurements to evaluate which ancient igneous rocks (e.g., low-Ti mare basalt, high-Ti mare basalt, Mg-suite rocks, dunite, high-Al mare basalt, KREEP basalt) are consistent with our mineralogical observations. In addition, spectra from different M3 optical periods were compared to determine how the MGM-derived absorption band centers vary between datasets. Band center differences between optical periods are on the order of ~6±4nm and ~25±10nm for the 1μm and 2μm features, respectively. Cryptomare mineralogies are dominated by clinopyroxene and are consistent with measurements from locally exposed mare basalts. LP GRS measurements support a mare basalt rock type when regolith mixing is taken into account.

Integrating CRISM and TES hyperspectral data to characterize a halloysite-bearing deposit in Kashira crater, Mars

We present morphologic observations and spectral modeling results of a large, kaolin-group mineral-bearing deposit within Kashira crater in the southern highlands of Mars. We employ both non-linear unmixing of Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible to near-infrared (VNIR) reflectance data and linear unmixing of Thermal Emission Spectrometer (TES) thermal infrared (TIR) emissivity data to quantitatively analyze the kaolin-group mineral within this deposit. We use a novel approach for quantitative analysis of CRISM data through non-linear unmixing with in-scene, orbitally-derived endmembers combined with laboratory measured endmembers. Results from this approach indicate that the deposit within Kashira crater is best modeled as a combination of surrounding spectral units (i.e., in-scene derived endmembers) with the addition of the kaolin-group mineral halloysite. Linear unmixing of TES data suggest that the deposit contains ∼30% halloysite, a result that is supported by a sensitivity analysis. Potential formation mechanisms for this deposit include hydrothermal alteration, arid-environment pedogenic weathering of a basaltic mound deposit, or pedogenic weathering of a volcanic ash deposit. Our modeling results offer a quantitative reconciliation of the CRISM and TES datasets, and provide a consistent mineralogy from spectral unmixing for an aqueous alteration mineral-bearing deposit on Mars using a combined analysis of both VNIR and TIR hyperspectral data.

Spinel-rich lithologies in the lunar highland crust: Linking lunar samples with crystallization experiments and remote sensing

Mg-Al spinel is rare in lunar rocks (Apollo and meteorite collections), and occurs mostly in troctolites and troctolitic cataclastites. Recently, a new lunar lithology, rich in spinel and plagioclase, and lacking abundant olivine and pyroxene, was recognized in visible to near-infrared (VNIR) reflectance spectra by the Moon Mineralogy Mapper (M3) instrument on the Chandrayaan-1 spacecraft at the Moscoviense basin. These outcrop-scale areas are inferred to contain 20–30% Mg-Al spinel. Possible explanations for the petrogenesis of spinel-bearing and spinel-rich lithology(s) range from low-pressure near-surface crystallization to a deep-seated origin in the lower lunar crust or upper mantle. Here, we describe 1-bar crystallization experiments conducted on rock compositions rich in olivine and plagioclase that crystallize spinel. This would be equivalent to impact-melting, which is moderately common among lunar plutonic rocks and granulites. To explore possible precursor materials and the maximum amount of spinel that could be crystallized, a lunar troctolitic composition similar to Apollo pink spinel troctolite 65785, and a composition similar to ALHA81005 as analog to the source region of this meteorite have been chosen. The crystallization experiments on the composition of AHLA 81005 did not yield any spinel; experiments on the composition similar to Apollo 65785 crystallized a maximum of ~8 wt% spinel, much less than the suggested 20–30% spinel of the new lithology detected by M3. However, our VNIR spectral reflectance analyses of the experimental run products indicate that the spinel composition of the experimental run products not only appears to be similar to the composition of the spinel lithology detected by M3 (characteristics of the spinel absorption), but also that the modal abundances of coexisting phases (e.g., mafic glass) influence the spectral reflectance properties. Thus, the spinel-rich deposits detected by M3 might not be as spinel-rich as previously thought and could contain as little as 4–5 wt% spinel. However, the effect of space weathering on spinel is unknown and could significantly weaken its 2 μm absorptions. If this occurs, weathered lunar rocks could contain more spinel than a comparison with our unweathered experimental charges would suggest.

Spectral masking of goethite in abandoned mine drainage systems: Implications for Mars

Remote sensing studies of the surface of Mars use visible- to near-infrared (VNIR) spectroscopy to identify hydrated and hydroxylated minerals, which can be used to constrain past environmental conditions on the surface of Mars. However, due to differences in optical properties, some hydrated phases can mask others in VNIR spectra, complicating environmental interpretations. Here, we examine the role of masking in VNIR spectra of natural precipitates of ferrihydrite, schwertmannite, and goethite from abandoned mine drainage (AMD) systems in southeastern Pennsylvania. Mixtures of ferrihydrite, schwertmannite, and goethite were identified in four AMD sites by using X-ray diffractometry (XRD), and their XRD patterns compared to their VNIR spectra. We find that both ferrihydrite and schwertmannite can mask goethite in VNIR spectra of natural AMD precipitates. These findings suggest that care should be taken in interpreting environments on Mars where ferrihydrite, schwertmannite, or goethite are found, as the former two may be masking the latter. Additionally, our findings suggest that outcrops on Mars with both goethite and ferrihydrite/schwertmannite VNIR signatures may have high relative abundances of goethite, or the goethite may exist in a coarsely crystalline phase.

Determination of soil properties with visible to near- and mid-infrared spectroscopy: Effects of spectral variable selection

Spectral variable selection is an important step in spectroscopic data analysis, as it tends to parsimonious data representation and can result in multivariate models with greater predictive ability. In this study, we used VIS-NIR (visible to near-infrared) diffuse reflectance and DRIFT (diffuse reflectance infrared Fourier transform in the mid-infrared range, MIR) spectroscopy to determine a series of chemical and biological soil properties. Multivariate calibrations were performed with partial least squares regression (PLSR) using the full absorbance spectra (VIS-NIR: 400–2500nm with 5-nm intervals; MIR: 4000–800cm−1 with 4-cm−1 intervals) and with a combination of PLSR and CARS (competitive adaptive reweighted sampling) to integrate only the most informative key variables. The CARS procedure has as yet not been applied in the field of soil spectroscopy. As set heterogeneity is crucial for an optimal calibration, we tested these approaches to a sample set of 60 agricultural samples covering a broad range of different parent materials, soil textures, organic matter contents and soil pH values. Soil samples were taken from the Ap horizon (0–10cm depth), air-dried and pulverised before the lab spectroscopic measurements were performed. In a cross-validation approach, the CARS–PLSR method was markedly more accurate than full spectrum-PLSR for all investigated soil variables and both spectral regions. With MIR data and CARS–PLSR, excellent results (indicated by a residual prediction deviation (RPD) greater than 3.0) were obtained for organic carbon (OC), nitrogen (N), microbial biomass-C (Cmic) and pH values; for hot water extractable C (Chwe), RPD was 2.60. The accuracies obtained with VIS-NIR data were considerably lower than those with the MIR spectra; best results were retrieved for pH and Cmic (approximately quantitative as indicated by RPD values between 2.0 and 2.5). The information content of the MIR data was substantially different from the VIS-NIR information, as indicated by 2D correlation analysis. We found an overall blurred 2D correlation pattern between both spectral regions with moderate to low correlation coefficients, which suggested that the heterogeneity of the studied soil sample population had led to a very complex blurring of overtones and combination bands in the NIR region.Statistical CARS selections were physically reasonable. MIR key wavenumbers for the studied C fractions were inter alia identified at the bands at 2920cm−1 and 2850cm−1 (both aliphatic CH-groups) and the region between 1740 and 1600cm−1 (CO-groups) and represent hydrophobic and hydrophilic compounds of soil organic matter. Important VIS-NIR wavelengths for assessing C fractions and N were located nearby the prominent water absorption band at 1915nm and the hydroxyl band at 2200nm.The simplicity of the approach, parsimony of the multivariate models, accuracy levels in the cross-validation and physically reasonable selections indicated a successful operation of the CARS procedure. It should be further examined with a larger number of samples using separate calibration and validation sets.