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The stratigraphic architectures of three fan-shaped deposits at Bradbury crater, Mars were investigated to test the hypothesis that the deposits were formed in standing bodies of water. Quantitative stratigraphic methods were applied to the northernmost deposit, which displays meter-thick layering. Planes fit to exposed strata display a constant dip throughout the section, with no obvious slope breaks and a mean dip of 6.1° to the northwest. We conclude that the stratal geometries of this outcrop are most consistent with formation as an alluvial/fluvial or debris flow fan. As this deposit lacks the diagnostic stratigraphic architecture of a delatic system, it presents no conclusive evidence for a sustained standing body of water at Bradbury crater.

Roughly 16,000, ∼20–50 m wide, morphologically diverse, erosionally resistant ridges have been exhumed and mapped in Noachian-aged terrain across a large region in Nili Fossae and the Nilosyrtis Highlands. However, the formation of these landforms has been widely debated. Their morphology and geologic context suggest surface processes such as aeolian, fluvial, and glacial sedimentary deposition are unlikely candidates for their formation. Possible subsurface ridge formation mechanisms include: 1) volcanic dike intrusions along pre-existing fractures, 2) breccia dikes from impact cratering, 3) clastic dikes or deformation bands, and 4) chemical alteration or precipitation of minerals in or along pre-existing fractures or faults. The ridges are being exhumed from a phyllosilicate-bearing host rock, but whether the ridges themselves have an aqueous origin remains unknown. Although, previous studies used comparative morphology to assess their formation, each hypothesized formation mechanism implies different mineralogical suites possibly detectable in remotely sensed spectral data. Here we combine spectral and morphological analyses to assess the origin of a subset of ridges (n = 797) that have irregular polygonal ridge network morphology. We use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment (HiRISE), supplemented with Context Camera (CTX) imagery, to analyze the spectral signatures and geometry in order to 1) measure ridge morphology (orientation and intersection angles) and 2) isolate the spectral signatures of the ridges from their host unit to evaluate hypothesized ridge formation mechanisms. The irregular polygonal nature, near-orthogonal intersections, and lack of dominant orientation are characteristics consistent with fracture propagation under horizontal near-isotropic extensional stress in a physically heterogeneous host rock (inconsistent with impact- or volcanic-related features). Alternatively, very shallow clastic intrusion could produce similar ridge geometry. Our key findings are: 1) ridge orientation-frequency and distribution suggest mineralization or cementation of subsurface fractures or shallow clastic intrusions as favored formation mechanisms and 2) ridges share all the diagnostic spectral features of Mg-smectite (saponite) and/or mixed-layered talc-saponite clays of the host materials; however, ridges express weaker absorptions. If the CRISM spatial and/or spectral resolution has not limited our ability to detect a spectrally unique cementing agent, then both grain size or texture and visible to near-infrared inactive mineralogy could be responsible for the ridge's weaker spectral absorptions (such as quartz and silica, some oxide group minerals, and amorphous materials). Our results imply that shallow subsurface groundwater and hydrothermal activity was likely extensive prior to and during the opening of the Nili Fossae and played an integral role in the formation of the ridges observed throughout the region.

Hydrated minerals are good indicators of aqueous environments on Mars. Accurate mineral species identification and quantitative estimation of their abundance is very important for understanding past and present geologic and climatic processes of Mars. We present a novel methodology to analyze hydrated minerals using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data. The methodology is driven by a sparse unmixing model, which can select the optimal subset of signatures from a large endmember library to best model mixed spectra. Laboratory measured spectra of minerals and rocks, scene-derived spectra of common components such as dust and synthetic flat and pure slope spectra are used to populate an endmember library. CRISM and the endmember library reflectance spectra are converted to single-scattering albedo with the Hapke radiative transfer model. The single-scattering albedos of the CRISM and endmember library spectra are then L1 normalized to eliminate the effects of the different measurement conditions between laboratory and orbital data. The sparse unmixing algorithm is finally applied to CRISM normalized single-scattering albedo data using the spectral library. Mineral identification and quantitative analysis are accomplished at the same time. The methodology shows good performance in synthetic and laboratory mineral mixture suites. Examples of six CRISM targeted mode images in three locations (Nili Fossae, Northeast Syrtis Major and Kashira crater), which have been previously thoroughly studied, were analyzed in detail in this study. In comparison with previous studies, our methodology identifies the mineral deposits detected through more manually intensive methods by expert analysts while simultaneously determining the mineral abundances. Furthermore, this new method provides an objective pathway to the determination of mineral presence from a large library of potential options. As an example of unexpected results, we detected putative serpentine in the Nili Fossae images for the first time. Even though the typical diagnostic spectral features used to identify minerals directly from CRISM data are obscured due to the mixing among mineral phases, T-test analyses of serpentine abundance provide critical statistical proof of its presence. Overall, the methodology we present works well for hydrated mineral detection with CRISM data and could provide a rigorous, objective method to map mineralogy in planetary hyperspectral remotely sensed data.

Spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), specifically full-resolution targeted (FRT) observations, can provide quantitative information about the martian polar surface at local scales; however, it has been minimally used in such ways. This is partly due to the challenging feat of photometric and atmospheric data corrections needed, especially for icy surfaces at the poles. The scattering behavior of the dirty ice is not well-constrained. The presence of dust and ice aerosols makes it difficult to retrieve the surface's inherent albedos needed for quantitative studies of polar ice. The following work demonstrates how the limited phase angle range of CRISM “central scene” data and the assumptions made about the properties and conditions of the atmosphere (ice and dust aerosol opacity) and surface (surface phase function) going into the processing and correction of the data affect the derived surface properties of the north polar ice cap of Mars (i.e., H2O ice band depth parameter and Hapke-modeled grain size and abundance). Through this work, we discovered the following. 1) Both dirty ice and more pure ice were best modeled as broad, moderate forward scatterers out of the four different behaviors tested. 2) The sensitivity of Hapke-modeled grain size and abundance to ice and dust aerosol opacity and phase function uncertainty is minor (well below Hapke model error). However, all possible measures should be taken to not propagate more error since Hapke modeling already inherently has large error bars (10–30%). 3) H2O index values are affected—up to ~10% deviation—when aerosols are untreated or not treated appropriately. This should only be of concern for temporal studies. 4) Hapke-modeled grain size and abundance estimates were most sensitive to the phase angle range used for the retrieval of SSA.

Mineral mapping of a planetary surface is of prime importance to better understanding its composition and constraining its geologic evolution. Visible-to-Near-Infrared (VNIR) hyperspectral remote sensing is the primary tool to detect the composition of the martian surface at high spatial resolution. However, it is not straightforward to validate the mapping results since mineralogical groundtruth is typically unavailable. Furthermore, determining whether common approaches used to decode terrestrial VNIR data are applicable to Mars requires rigorous evaluation. In this work, we collected a suite of laboratory hyperspectral images with groundtruth, consisting of binary mixtures of Mars Global Simulant (MGS-1) and various hydrous minerals. The spectral effects of mixing MGS-1 with hydrous minerals were analyzed through conventional spectral parameters. It is observed that MGS-1 substantially reduces the spectral contrast of hydrous minerals. We then conducted a systematic comparison of seven benchmark target detection algorithms on the laboratory datasets, including Constrained Energy Minimization, Adaptive Coherence Estimator, Matched filter, Hierarchical Constrained Energy Minimization, Sparse Representation for Target Detection, Joint Sparse Representation and Multi-task Learning method, and Multi-task Joint Sparse and low-rank Representation (MTJSLR) method. Extensive experiments demonstrate that MTJSLR outperforms other competitors in successfully detecting low modal abundance hydrous minerals. The detection limits for nontronite, montmorillonite, kaolinite, gypsum, and calcite are 2.5%, 2.5%, 1%, 5%, and 5%, respectively. Carbonates are more challenging to detect than phyllosilicates even at the same abundance, which could partially contribute to the relative paucity of observed carbonates on Mars relative to phyllosilicates.

We designed a laboratory visible-to-near-infrared (VNIR) hyperspectral experiment to test the effectiveness of factor analysis/target transformation for detecting minerals mixed with Mars Global Simulant-1 (MGS-1). The purpose of this experiment is to test for true positive, true negative, false positive, and false negative results from application of factor analysis/target transformation methods and determine the parameters that dictate good versus bad algorithm performance. Gypsum, calcite, montmorillonite, nontronite, and kaolinite were each mixed with MGS-1 at abundances of 1%, 2.5%, 5%, 10%, 20%, and 50%. The mixtures were placed in 2.5 × 2.5 × 1 cm sample trays and imaged using a Headwall Imaging Spectrometer with a spectral range of 0.9–2.6 μm, 8.98 nm spectral sampling, and 0.34 mm/pixel spatial resolution. These images include thousands to tens of thousands of hyperspectral pixels covering each individual mixture tray. Full-image factor analysis/target transformation (FA/TT) and Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) were applied to these data to detect the minerals mixed with MGS-1. The results demonstrate that factor analysis/target transformation is prone to both false positive and false negative detections, but in certain applications—including DAFA/TT—it can be useful for highlighting spectrally interesting areas in hyperspectral images for follow-up investigation. The results presented here demonstrate that applications of factor analysis/target transformation to VNIR hyperspectral datasets should be used to highlight small outcrops and/or weak spectral signals in pixels for follow-up investigation. This emphasizes the need for supporting evidence to be obtained—in addition to factor analysis/target transformation—before interpretations of planetary surface processes should be made.

As inferred from orbital spectroscopic data, Northeast Syrtis Major bears considerable mineral diversity that spans the Noachian-Hesperian boundary despite its small geographic area. In this study we use observations from the High Resolution Imaging Science Experiment, supplemented with Context Camera imagery, to characterize and map the lateral extent of geomorphic units in Northeast Syrtis Major, and constrain the geomorphic context of the orbital-identified mineral signatures. Using recent observations, we confirm previous mineralogy identified with the Compact Reconnaissance Imaging Spectrometer for Mars, and greatly extend the lateral extent of visible to near-infrared investigation utilizing the greater coverage. Analysis of Thermal Emission Imaging System observations reveals further physical properties and distribution of the geomorphic units. The stratigraphy, which spans the Noachian-Hesperian boundary, displays significant morphological heterogeneity at the decameter scale, but it is unifiable under five distinct geomorphic units. Our paired morphological and mineralogical analysis allows us to construct a detailed geological history of Northeast Syrtis Major. Several geological events that occurred in Northeast Syrtis Major—including the formation of the post-Isidis crust, the emplacement of an olivine-rich unit, the formation of sulfate minerals, and the emplacement of the Syrtis Major Volcanics—can be related to regional and global processes constraining the local chronology. Other mineralogical indicators, particularly the formation of Al-phyllosilicates, are difficult to place in the temporal sequence. They are observed in isolated patches on the post-Isidis crust, not as a distinct stratigraphic unit as observed elsewhere in Nili Fossae, suggesting their formation via isolated leaching or through alteration of initial compositional heterogeneities within the crust. Exposures of an olivine-rich unit are intermittently observed to form quasi-circular landforms, suggestive of emplacement in circular depressions, which may indicate a period of cratering between the formation of the Isidis basin and the deposition of the olivine-rich unit. We identify and discuss intriguing large linear features of the olivine-rich unit, reminiscent of dyke-fed volcanism, that have raised bounding ridges suggestive of contact metamorphism with the crust. We compile, review, and discuss many of the outstanding questions and running hypotheses relevant to our mapping area. A synthesis of our geomorphic mapping with recent literature reveals a well-defined geological history with extensive aqueous activity at Northeast Syrtis Major that is amassed in a stratigraphic sequence spanning a time likely greater than 250 million years of geological history. Our geomorphic and spectral analyses confirm that Northeast Syrtis Major exhibits considerable geomorphic and mineralogic diversity within a relatively small geographic area that is representative of the geologic processes occurring throughout the broader Nili Fossae region during the Noachian and Hesperian. Northeast Syrtis Major adds to this sequence by exposing the diverse environmental history of this region as observed through the presence of alteration minerals not present in this fidelity or proximity elsewhere in Nili Fossae.

We examine the stratigraphic architecture and mineralogy of the western fan deposit in the Jezero crater paleolake on Mars to reassess whether this fan formed as a delta in a standing body of water, as opposed to by alluvial or debris flow processes. Analysis of topography and images reveals that the stratigraphically lowest layers within the fan have shallow dips (

Serpentine and carbonate are products of serpentinization and carbonation processes on Earth, Mars, and other celestial bodies. Their presence implies that localized habitable environments may have existed on ancient Mars. Factor Analysis and Target Transformation (FATT) techniques have been applied to hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to identify possible serpentine and Mg-carbonate-bearing outcrops. FATT techniques are capable of suggesting the presence of individual spectral signals in complex spectral mixtures. Applications of FATT techniques to CRISM data thus far only evaluate whether an entire analyzed image (≈ 3 × 105 pixels) may contain spectral information consistent with a specific mineral of interest. The spatial distribution of spectral signal from the possible mineral is not determined, making it difficult to validate a reported detection and also to understand the geologic context of any purported detections. We developed a method called Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) to highlight the locations in a CRISM observation (or any similar laboratory or remotely acquired data set) most likely to contain spectra of specific minerals of interest. DAFA/TT determines the locations of possible target mineral spectral signals within hyperspectral images by performing FATT in small moving windows with different geometries, and only accepting pixels with positive detections in all cluster geometries as possible detections. DAFA/TT was applied to a hyperspectral image of a serpentinite from Oman for validation testing in a simplified laboratory setting. The mineral distribution determined by DAFA/TT application to the laboratory hyperspectral image was consistent with Raman analysis of the serpentinite sample. DAFA/TT also successfully mapped the spatial distribution of Mg-serpentine and Mg-carbonate previously detected in CRISM data using band parameter mapping and extraction of ratioed spectra. We applied DAFA/TT to CRISM images in some olivine-rich regions of Mars to characterize the spatial distribution of Mg-serpentine and Mg-carbonate-bearing outcrops.

Understanding the temporal patterns of leaf traits is critical in determining the seasonality and magnitude of terrestrial carbon, water, and energy fluxes. However, we lack robust and efficient ways to monitor the temporal dynamics of leaf traits. Here we assessed the potential of leaf spectroscopy to predict and monitor leaf traits across their entire life cycle at different forest sites and light environments (sunlit vs. shaded) using a weekly sampled dataset across the entire growing season at two temperate deciduous forests. The dataset includes field measured leaf-level directional-hemispherical reflectance/transmittance together with seven important leaf traits [total chlorophyll (chlorophyll a and b ), carotenoids, mass-based nitrogen concentration (N mass ), mass-based carbon concentration (C mass ), and leaf mass per area (LMA)]. All leaf traits varied significantly throughout the growing season, and displayed trait-specific temporal patterns. We used a Partial Least Square Regression (PLSR) modeling approach to estimate leaf traits from spectra, and found that PLSR was able to capture the variability across time, sites, and light environments of all leaf traits investigated (R 2 = 0.6–0.8 for temporal variability; R 2 = 0.3–0.7 for cross-site variability; R 2 = 0.4–0.8 for variability from light environments). We also tested alternative field sampling designs and found that for most leaf traits, biweekly leaf sampling throughout the growing season enabled accurate characterization of the seasonal patterns. Compared with the estimation of foliar pigments, the performance of N mass , C mass and LMA PLSR models improved more significantly with sampling frequency. Our results demonstrate that leaf spectra-trait relationships vary with time, and thus tracking the seasonality of leaf traits requires statistical models calibrated with data sampled throughout the growing season. Our results have broad implications for future research that use vegetation spectra to infer leaf traits at different growing stages.

The empirical volcano-scan atmospheric correction is widely applied to Martian near infrared CRISM and OMEGA spectra between 1000 and 2600 nanometers to remove prominent atmospheric gas absorptions with minimal computational investment. This correction method employs division by a scaled empirically-derived atmospheric transmission spectrum that is generated from observations of the Martian surface in which different path lengths through the atmosphere were measured and transmission calculated using the Beer-Lambert Law. Identifying and characterizing both artifacts and residual atmospheric features left by the volcano-scan correction is important for robust interpretation of CRISM and OMEGA volcano scan corrected spectra. In order to identify and determine the cause of spectral artifacts introduced by the volcano-scan correction, we simulated this correction using a multiple scattering radiative transfer algorithm (DISORT). Simulated transmission spectra that are similar to actual CRISM- and OMEGA-derived transmission spectra were generated from modeled Olympus Mons base and summit spectra. Results from the simulations were used to investigate the validity of assumptions inherent in the volcano-scan correction and to identify artifacts introduced by this method of atmospheric correction. We found that the most prominent artifact, a bowl-shaped feature centered near 2000 nanometers, is caused by the inaccurate assumption that absorption coefficients of CO2 in the Martian atmosphere are independent of column density. In addition, spectral albedo and slope are modified by atmospheric aerosols. Residual atmospheric contributions that are caused by variable amounts of dust aerosols, ice aerosols, and water vapor are characterized by the analysis of CRISM volcano-scan corrected spectra from the same location acquired at different times under variable atmospheric conditions.

We investigate an outcrop of ∼187 Ma lacustrine pillow basalts of the Talcott Formation exposed in Meriden, Connecticut, USA, focusing on coordinated analyses of one pillow lava to characterize the aqueous history of these basalts in the Hartford Basin. This work uses a suite of multidisciplinary measurements, including hyperspectral imaging, other spectroscopic techniques, and chemical and mineralogical analyses, from the microscopic scale up to the scale of an outcrop. The phases identified in the sample are albite, large iron oxides, and titanite throughout; calcite in vesicles; calcic clinopyroxene, aegirine, and Fe/Mg-bearing clay in the rind; and fine-grained hematite and pyroxenes in the interior. Using imaging spectroscopy, the chemistry and mineralogy results extend to the hand sample and larger outcrop. From all of the analyses, we suggest that the pillow basalts were altered initially after emplacement, either by heated lake water or magmatic fluids, at temperatures of at least 400–600 °C, and the calcic clinopyroxenes and aegirine identified in the rind are a preserved record of that alteration. As the hydrothermal system cooled to slightly lower temperatures, clays formed in the rind, and, during this alteration, the sample oxidized to form hematite in the matrix of the interior and Fe 3+ in the pyroxenes in the rind. During the waning stages of the hydrothermal system, calcite precipitated in vesicles within the rind. Later, diagenetic processes albitized the sample, with albite replacing plagioclase, lining vesicles, and accreting onto the exterior of the sample. This albitization or Na-metasomatism occurred when the lake within the Hartford Basin evaporated during a drier past climatic era, resulting in Na-rich brines. As Ca-rich plagioclase altered to albite, Ca was released into solution, eventually precipitating as calcite in previously-unfilled vesicles, dominantly in the interior of the pillow. Coordinated analyses of this sample permit identification of the alteration phases and help synthesize the aqueous history of pillow lavas of the Talcott Formation. These results are also relevant to Mars, where volcanically-resurfaced open basin lakes have been found, and this Hartford Basin outcrop may be a valuable analog for any potential volcano–lacustrine interactions. The results can also help to inform the utility and optimization of potentially complementary, synergistic, and uniquely-suited techniques for characterization of hydrothermally-altered terrains.

We present a new catalog of 205 candidate closed-basin lakes contained within impact craters across the surface of Mars. These basins have an inlet valley that incises the crater rim and flows into the basin but no visible outlet valley, and are considered candidate closed-basin lakes; the presence of a valley flowing into a basin does not necessitate the formation of a standing body of water. The major geomorphic distinction within our catalog of candidate paleolakes is the length of the inlet valley(s), with two major classes – basins with long (>20 km) inlet valleys (30 basins), and basins with short (

Dry tropical forests are experiencing some of the highest rates of change among the globe's forests. In sub-Saharan Africa, gross (loss, gain) and net changes in dry tropical forest areas are difficult to quantify at sub-national scales because of high spatio-temporal variability in land cover conditions due to vegetation phenology and land use practices. In this project, we developed new, field-validated remote sensing characterizations of dry season surface components to separate forest from non-forest land cover, and assessed forest changes from the 1990s–2010s in a Tanzanian Miombo Woodland landscape. Using a linear spectral mixture analysis (LSMA) approach with Landsat 5–8 data, we examined the hypothesis that higher proportions of substrate and non-photosynthetic vegetation (NPV) at non-forest regions distinguished them from forest cover against seasonally variable land cover conditions. Subsequently we evaluated the efficacy of multi-temporal classification and single-date image thresholding for identifying forest from non-forest cover. We found significantly greater proportions of substrate and NPV over non-forest compared to forest areas that enabled identification of forest cover across dry season images. Single-date, forest/non-forest maps based on an LSMA-derived metric attained overall accuracies of 81.0–85.3%, which approached multi-temporal unsupervised classifications (86.5% for forest/non-forest maps). Applying the LSMA-derived metric to study forest changes, our study region experienced a net 15.0% loss of 1995 forest area, and a 7.0% overall reduction in the total forest-occupied land cover from 1995–2011. Areas of gross forest gain were substantial, totaling 13.6% of the 1995 forest area. We found differing patterns in gross forest losses and gains among sub-regions and through time in our Tabora study area, which provide bases for testable hypotheses in future research on regional and localized drivers affecting forest cover. Our finding that non-green surface components distinguished forest from non-forest via an LSMA approach may be widely applicable to studying forest conversions in Miombo Woodlands and other dry tropical forests. This approach may also be useful for evaluating how land cover conditions change in response to potential land use or climate driving variables, or the impact of land changes for carbon balance and other ecosystem processes.

Northwest Africa (NWA) 7034 is the first breccia meteorite from Mars, and unlike the shergottite, nakhlite, and chassignite (SNC) martian meteorites, it matches the estimated chemical composition of martian crust. Here we show that the visible-infrared reflectance spectrum of NWA 7034 is unique compared to other SNCs and is more similar than them to remotely sensed data from Mars, suggesting the martian regolith may contain significant brecciated material produced during heavy bombardment of the crust.

The rock alteration and rind formation in analog environments like Antarctica may provide clues to rock alteration and therefore paleoclimates on Mars. Clastic sedimentary rocks derived from basaltic sources have been studied in situ by martian rovers and are likely abundant on the surface of Mars. Moreover, how such rock types undergo alteration when exposed to different environmental conditions is poorly understood compared with alteration of intact basaltic flows. Here we characterize alteration in the chemically immature Carapace Sandstone from Antarctica, a terrestrial analog for martian sedimentary rocks. We employ a variety of measurements similar to those used on previous and current Mars missions. Laboratory techniques included bulk chemistry, powder X-ray diffraction (XRD), hyperspectral imaging and X-ray absorption spectroscopy. Through these methods we find that primary basaltic material in the Carapace Sandstone is pervasively altered to hydrated clay minerals and palagonite as a result of water–rock interaction. A thick orange rind is forming in current Antarctic conditions, superimposing this previous aqueous alteration signature. The rind exhibits a higher reflectance at visible-near infrared wavelengths than the rock interior, with an enhanced ferric absorption edge likely due to an increase in Fe3+ of existing phases or the formation of minor iron (oxy)hydroxides.more » This alteration sequence in the Carapace Sandstone results from decreased water–rock interaction over time, and weathering in a cold, dry environment, mimicking a similar transition early in martian history. This transition may be recorded in sedimentary rocks on Mars through a similar superimposition mechanism, capturing past climate changes at the hand sample scale. These results also suggest that basalt-derived sediments could have sourced significant volumes of hydrated minerals on early Mars due to their greater permeability compared with intact igneous rocks.« less

a b s t r a c t Molecular hydrogen produced through iron oxidation during formation of serpentine and magnetite can sustain terrestrial subsurface ecosystems. The Fe 3+ in serpentine partitions into octahedral and tetrahedral sites differently as serpentinization proceeds, and tetrahedral Fe 3+ is present toward the end of serpentinization. We map Fe oxidation states in a serpentinite to determine the degree to which serpentinization progressed and where hydrogen production has been maximized to assess habitability at an abandoned chrysotile mine in Norbestos, Quebec, in association with the Canadian Space Agency's Mars Methane Analogue Mission. We also analyzed stable isotopes of carbon and oxygen in carbonates to constrain the conditions of water-rock interaction during serpentinization. Iron oxidation and coordination was determined through field imaging of rock walls with a visible hyperspectral imager (420-720 nm), and samples collected from imaged rocks and elsewhere in the mine were imaged in the laboratory (420-1100 nm). Sample chemistry, mineralogy, and oxidation state were determined with laboratory measurements of visible through mid-infrared reflectance spectra, major element chemistry, mineralogy, and Mossbauer spectroscopy. Mapping with hyperspectral imaging of outcrops and hand samples shows that tetrahedral Fe 3+ is common in serpentinites at this site, and results are confirmed through other measurements. Major element chemistry and mineralogy are consistent with serpentine plus minor carbonate. Carbonate samples show an exceptional range in δ 13

Alteration of fresh rock surfaces proceeds very rapidly in most terrestrial environments so that initial stages of modification of newly exposed surfaces are quickly masked by subsequent aqueous weathering processes. The hyper-arid and hypo-thermal environment of Beacon Valley, Antarctica, is limited in terms of available liquid water and energy available for alteration, which severely slows weathering processes so that the initial stages of alteration can be studied in detail. We report on the nature of initial chemical alteration of the Ferrar Dolerite in Beacon Valley, Antarctica, using a multiplicity of approaches to characterize the process. We suggest that initial chemical alteration is primarily driven by cation migration in response to the oxidizing environment. Morphological studies of altered rock surfaces reveal evidence of small-scale leaching and dissolution patterns as well as physical erosion due to surface weakening. Within the alteration front, mineral structures are largely preserved and alteration is only indicated by discrete zones of discoloration. Mineralogical investigations expose the complexity of the alteration process; visible/near-infrared reflectance and mid-infrared emission spectroscopy reveal significant variations in mineralogical contributions that are consistent with the introduction of oxide and amorphous phases at the surfaces of the rocks, while X-ray diffraction analyses reveal no definitive changes in mineralogy or material properties. Chemical analyses reveal large-scale trends that are consistent with cation migration and leaching, while small-scale electron microprobe analyses indicate that chemical variations associated with magmatic processes are still largely preserved within the alteration rind. This work confirms the incomplete and immature chemical alteration processes at work in the McMurdo Dry Valleys. Liquid water is not a significant contributor to the alteration process at this early stage of rind development, but assists in the removal of alteration products and their local accumulation in the surrounding sediments. These results also suggest that the McMurdo Dry Valleys (and Beacon Valley, in particular) are relevant terrestrial analogs to hyper-arid and hypo-thermal alteration processes that may be dominant on the martian surface.

A large number of candidate open-basin lakes (low-lying regions with both inlet valleys and an outlet valley) have been identified and mapped on Mars and are fed by valley network systems that were active near the Noachian–Hesperian boundary. The nature of processes that modified the open-basin lake interiors subsequent to lacustrine activity, and how frequently sedimentary deposits related to lacustrine activity remain exposed, has not been extensively examined. An analysis of 226 open-basin lakes was undertaken to identify evidence for: (1) exposed deposits of possible lacustrine origin and (2) post-lacustrine-activity processes that may have modified or resurfaced open-basin lakes. Spectroscopic data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument were analyzed over identified exposed open-basin lake deposits to assess the mineralogy of these deposits. Particular attention was paid to the possible detection of any component of aqueous alteration minerals (e.g. phyllosilicates, hydrated silica, zeolites) or evaporites (e.g. carbonates, sulfates, chlorides) associated with these exposed deposits. The aim of this paper is to act as a broad survey and cataloguing of the types of lacustrine and post-lacustrine deposits that are present within these 226 paleolake basins. Results of the morphologic classification indicate that 79 open-basin lakes (∼35% of the population) contain exposed deposits of possible lacustrine origin, identified on the basis of fan/delta deposits, layered deposits and/or exposed floor material of apparent lacustrine origin. Additionally, all 226 open-basin lakes examined appear to have been at least partially resurfaced subsequent to their formation by several processes, including volcanism, glacial and periglacial activity, impact cratering and aeolian activity. Results from the analysis of CRISM data show that only 10 (∼29% of the 34 deposits with CRISM coverage) of the exposed open-basin lake deposits contain positively identified aqueous alteration minerals, with one deposit also containing evaporites. The identified hydrated and evaporite minerals include Fe/Mg-smectite, kaolinite, hydrated silica and carbonate, with Fe/Mg-smectite the most commonly identified mineral. These results indicate that hydrated and evaporite minerals are not as commonly associated with lacustrine deposits on Mars as they are on Earth. This suggests in situ alteration and mineral precipitation, a common source of such minerals in terrestrial lakes, was not a major process occurring in these paleo-lacustrine systems, and that the observed minerals are likely to be present as transported material within the lacustrine deposits. The lack of widespread in situ alteration also suggests that either the water chemistry in these paleolake systems was not conducive to aqueous alteration and mineral precipitation, or that the open-basin lake systems were relatively short-lived.

The region surrounding the Mawrth Vallis outflow channel on Mars hosts thick layered deposits containing diverse phyllosilicate minerals. Here we report detection of the Ca-sulfate bassanite on the outflow channel floor, requiring a more complex aqueous chemistry than previously inferred for this region. The sulfate-bearing materials underlie phyllosilicate-bearing strata, and provide an opportunity for testing proposed models of martian geochemical evolution with a future landed mission.

Previous orbital mapping of crystalline gray haematite, ferric oxides, and sulfates has shown an association of this mineralogy with light-toned, layered deposits on the floor of Valles Marineris, in chaos terrains in the canyon’s outflow channels, and in Meridiani Planum. The exact nature of the relationship between ferric oxides and sulfates within Valles Marineris is uncertain. The Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) spectrometer initially identified sulfate and ferric oxides in the layered deposits of Valles Marineris. The Thermal Emission Spectrometer (TES) has also mapped coarse (gray) haematite in or at the base of these deposits. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra and Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) imagery from the Mars Reconnaissance Orbiter (MRO) to explore the mineralogy and morphology of the large layered deposit in central Capri Chasma, part of the Valles Marineris canyon system that has large, clear exposures of sulfate and haematite. We find kieserite (MgSO 4 ·H 2 O) and ferric oxide (often crystalline red haematite) in the lower bedrock exposures and a polyhydrated sulfate without ferric oxides in the upper bedrock. This stratigraphy is duplicated in many other basinal chasmata, suggesting a common genesis. We propose the haematite and monohydrated sulfate formed by diagenetic alteration of a sulfate-rich sedimentary deposit, where the upper polyhydrated sulfate-rich, haematite-poor layers either were not buried sufficiently to convert to a monohydrated sulfate or were part of a later depositional phase. Based on the similarities between the Valles Marineris assemblages and the sulfate and haematite-rich deposits of Meridiani Planum, we hypothesize a common evaporite and diagenetic formation process for the Meridiani Planum sediments and the sulfate-bearing basinal Interior Layered Deposits.

New high-resolution spectral and morphologic imaging of deposits on walls and floor of Ius Chasma extend previous geomorphic mapping, and permit a new interpretation of aqueous processes that occurred during the development of Valles Marineris. We identify hydrated mineralogy based on visible-near infrared (VNIR) absorptions. We map the extents of these units with CRISM spectral data as well as morphologies in CTX and HiRISE imagery. Three cross-sections across Ius Chasma illustrate the interpreted mineral stratigraphy. Multiple episodes formed and transported hydrated minerals within Ius Chasma. Polyhydrated sulfate and kieserite are found within a closed basin at the lowest elevations in the chasma. They may have been precipitates in a closed basin or diagenetically altered after deposition. Fluvial or aeolian processes then deposited layered Fe/Mg smectite and hydrated silicate on the chasma floor, postdating the sulfates. The smectite apparently was weathered out of Noachian-age wallrock and transported to the depositional sites. The overlying hydrated silicate is interpreted to be an acid-leached phyllosilicate transformed from the underlying smectite unit, or a smectite/jarosite mixture. The finely layered smectite and massive hydrated silicate units have an erosional unconformity between them, that marks a change in surface water chemistry. Landslides transported large blocks of wallrock, some altered to contain Fe/Mg smectite, to the chasma floor. After the last episode of normal faulting and subsequent landslides, opal was transported short distances into the chasma from a few m-thick light-toned layer near the top of the wallrock, by sapping channels in Louros Valles. Alternatively, the material was transported into the chasma and then altered to opal. The superposition of different types of hydrated minerals and the different fluvial morphologies of the units containing them indicate sequential, distinct aqueous environments, characterized by alkaline, then circum-neutral, and finally very acidic surface or groundwater chemistry.

The observations of Mars by the CRISM and OMEGA hyperspectral imaging spectrometers require correction for photometric, atmospheric and thermal effects prior to the interpretation of possible mineralogical features in the spectra. Here, we report on a simple, yet non-trivial, adaptation to the commonly-used volcano-scan correction technique for atmospheric CO_2, which allows for the improved detection of minerals with intrinsic absorption bands at wavelengths between 1.9-2.1 $\mu$m. This volcano-scan technique removes the absorption bands of CO_2 by ensuring that the Lambert albedo is the same at two wavelengths: 1.890 $\mu$m and 2.011 $\mu$m, with the first wavelength outside the CO_2 gas bands and the second wavelength deep inside the CO_2 gas bands. Our adaptation to the volcano-scan technique moves the first wavelength from 1.890 $\mu$m to be instead within the gas bands at 1.980 $\mu$m, and for CRISM data, our adaptation shifts the second wavelength slightly, to 2.007 $\mu$m. We also report on our efforts to account for a slight ~0.001 $\mu$m shift in wavelengths due to thermal effects in the CRISM instrument., Comment: 17 pages, 6 figures, accepted for publication in 'Planetary and Space Science'

The mineralogical composition of the Martian surface is investigated by a Multiple-Endmember Linear Spectral Unmixing Model (MELSUM) of the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) imaging spectrometer onboard Mars Express. OMEGA has fully covered the surface of the red planet at medium to low resolution (2–4 km per pixel). Several areas have been imaged at a resolution up to 300 m per pixel. One difficulty in the data processing is to extract the mineralogical composition, since rocks are mixtures of several components. MELSUM is an algorithm that selects the best linear combination of spectra among the families of minerals available in a reference library. The best fit of the observed spectrum on each pixel is calculated by the same unmixing equation used in the classical Spectral Mixture Analysis (SMA). This study shows the importance of the choice of the input library, which contains in our case 24 laboratory spectra (endmembers) of minerals that cover the diversity of the mineral families that may be found on the Martian surface. The analysis is restricted to the 1.0–2.5 μm wavelength range. Grain size variations and atmospheric scattering by aerosols induce changes in overall albedo level and continuum slopes. Synthetic flat and pure slope spectra have therefore been included in the input mineral spectral endmembers library in order to take these effects into account. The selection process for the endmembers is a systematic exploration of whole set of combinations of four components plus the straight line spectra. When negative coefficients occur, the results are discarded. This strategy is successfully tested on the terrestrial Cuprite site (Nevada, USA), for which extensive ground observations exist. It is then applied to different areas on Mars including Syrtis Major, Aram Chaos and Olympia Undae near the North Polar Cap. MELSUM on Syrtis Major reveals a region dominated by mafic minerals, with the oldest crustal regions composed of a mixing between low-calcium pyroxenes (LCPs) (orthopyroxenes (OPx)) and high-calcium pyroxenes (HCPs) (clinopyroxenes (CPx)). The Syrtis volcanic edifice appears depleted in LCP (OPx) and enriched in HCP (CPx), which is consistent with materials produced with a lower partial fusion degree at an age younger to the surrounding crust. Strong olivine signatures are found between the two calderas Nili Patera and Meroe Patera and in Nili Fossae. A strong signature of iron oxides is found within Aram Chaos, with a spatial distribution also consistent with thermal emission spectrometer (TES). Gypsum is unambiguously detected in the northern polar region, in agreement with the study of Langevin et al. [2005. Sulfates in the north polar region of Mars detected by OMEGA/Mars Express. Science 307(5715), 1584–1586]. Our results show that the linear spectral unmixing provides good first order results in a variety of mineralogical contexts, and can therefore confidently be used on a wider scale to analyze the complete archive of OMEGA data.

Since 2000, the southwestern Brazilian Amazon has undergone a rapid transformation from natural vegetation and pastures to row-crop agricultural with the potential to affect regional biogeochemistry. The goals of this research are to assess wavelet algorithms applied to MODIS time series to determine expansion of row-crops and intensification of the number of crops grown. MODIS provides data from February 2000 to present, a period of agricultural expansion and intensification in the southwestern Brazilian Amazon. We have selected a study area near Comodoro, Mato Grosso because of the rapid growth of row-crop agriculture and availability of ground truth data of agricultural land-use history. We used a 90% power wavelet transform to create a wavelet-smoothed time series for five years of MODIS EVI data. From this wavelet-smoothed time series we determine characteristic phenology of single and double crops. We estimate that over 3200 km 2 were converted from native vegetation and pasture to row-crop agriculture from 2000 to 2005 in our study area encompassing 40,000 km 2 . We observe an increase of 2000 km 2 of agricultural intensification, where areas of single crops were converted to double crops during the study period.

Phenological records constructed from global mapping satellite platforms (e.g. AVHRR and MODIS) hold the potential to be valuable tools for monitoring vegetation response to global climate change. However, most satellite phenology products are not validated, and field checking coarse scale (≥500 m) data with confidence is a difficult endeavor. In this research, we compare phenology from Landsat (field scale, 30 m) to MODIS (500 m), and compare datasets derived from each instrument. Landsat and MODIS yield similar estimates of the start of greenness (r 2 =0.60), although we find that a high degree of spatial phenological variability within coarser-scale MODIS pixels may be the cause of the remaining uncertainty. In addition, spatial variability is smoothed in MODIS, a potential source of error when comparing in situ or climate data to satellite phenology. We show that our method for deriving phenology from satellite data generates spatially coherent interannual phenology departures in MODIS data. We test these estimates from 2000 to 2005 against long-term records from Harvard Forest (Massachusetts) and Hubbard Brook (New Hampshire)ExperimentalForests.MODISsuccessfullypredicts86%ofthevarianceatHarvardforestand70%ofthevarianceatHubbardBrook;the more extreme topography of the later is inferred to be a significant source of error. In both analyses, the satellite estimate is significantly dampened from the ground-based observations, suggesting systematic error (slopes of 0.56 and 0.63, respectively). The satellite data effectively estimates interannual phenology at two relatively simple deciduous forest sites and is internally consistent, even with changing spatial scale. We propose that continued analyses of interannual phenology will be an effective tool for monitoring native forest responses to global-scale climate variability.

The apparent strength of absorptions due to H 2 O near 1.9 and 3 μm in reflectance spectra is strongly affected by sample albedo. This study uses experimental and analytical approaches to quantify the effects of albedo on estimating the water content of hydrated minerals using various band parameters. We compare spectral band parameters for a series of low-albedo physical and numerical mixtures to measured water contents. Physical experiments consist of montmorillonite, clinoptilolite, and palagonite mixed with lesser amounts of carbon black and ilmenite, whereas numerical mixtures are composed of these host minerals mixed with a material of constant, low albedo. We find the effective single-particle absorption-thickness parameter provides the best correlation to water content, independent of composition and albedo, when derived from continuum-removed single scattering albedo spectra. Uncertainties in estimated water content are on the order of ±1 wt% using this method. The normalized optical path length parameter provides the best correlation to water content when using reflectance spectra, yielding estimates within ±1.6 wt% H 2 O. The accuracy of these models is related to the physical nature of the darkening material. Scattering and absorption efficiencies are easier to model for intimate mixtures containing relatively large, dark grains than mixtures dominated by coatings of a fine-grained, strongly absorbing material. This suggests the physical properties that give rise to the albedo of a material are an important factor for accurate estimates of absolute water content.

We investigate the ability to refine pyroxene composition and modal abundance from laboratory and remotely acquired spectra. Laboratory data including the martian meteorites, Shergotty, Zagami, MIL03346, and ALH84001 as well as additional pyroxene-rich spectra obtained from the OMEGA (Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite) spectrometer for Mars are characterized using the Modified Gaussian Model (MGM), a spectral deconvolution method developed by Sunshine et al. [Sunshine, J.M., Pieters, C.M., Pratt, S., 1990. J. Geophys. Res. 95, 6955–6966]. We develop two sensitivity tests to assess the extent to which the MGM can consistently predict (1) pyroxene composition and (2) modal abundance for a compositionally diverse suite of pyroxene spectra. Results of the sensitivity tests indicate that the MGM can be appropriately applied to remote spectroscopic measurements of extraterrestrial surfaces and can estimate pyroxene composition and relative abundance within a derived uncertainty. Deconvolved band positions for laboratory spectra of the meteorites Shergotty and Zagami are determined within ±17 nm while remotely acquired OMEGA spectra are defined within ±50 nm. These results suggest that absolute compositions can be uniquely derived from laboratory pyroxene-rich spectra and non-uniquely derived from the remote measurements of OMEGA at this time. While relative pyroxene chemistries are not assessed from OMEGA measurements at this time, relative pyroxene abundances are estimated using a normalized band strength ratio between the low-calcium (LCP) and high-calcium (HCP) endmember components and are constrained to ± 10 % . The fraction of LCP in a two-pyroxene mixture is the derived value from the normalized band strength ratio, LCP/(LCP + HCP). This calculation for relative abundance is robust in the presence of up to 10–15% olivine. Deconvolution results from the OMEGA spectra indicate that the ancient terrain in the Syrtis Major region is uniquely enriched in LCP ( 59 ± 10 % LCP) relative to HCP while the volcanics of Syrtis Major are uniquely enriched in HCP ( 39 ± 10 % LCP).

Annual, inter-annual and long-term trends in time series derived from remote sensing can be used to distinguish between natural land cover variability and land cover change. However, the utility of using NDVI-derived phenology to detect change is often limited by poor quality data resulting from atmospheric and other effects. Here, we present a curve fitting methodology useful for time series of remotely sensed data that is minimally affected by atmospheric and sensor effects and requires neither spatial nor temporal averaging. A two-step technique is employed: first, a harmonic approach models the average annual phenology; second, a spline-based approach models inter-annual phenology. The principal attributes of the time series (e.g., amplitude, timing of onset of greenness, intrinsic smoothness or roughness) are captured while the effects of data drop-outs and gaps are minimized. A recursive, least squares approach captures the upper envelope of NDVI values by upweighting data values above an average annual curve. We test this methodology on several land cover types in the western U.S., and find that onset of greenness in an average year varied by less than 8 days within land cover types, indicating that the curve fit is consistent within similar systems. Between 1990 and 2002, temporal variability in onset of greenness was between 17 and 35 days depending on the land cover type, indicating that the inter-annual curve fit captures substantial inter-annual variability. Employing this curve fitting procedure enhances our ability to measure inter-annual phenology and could lead to better understanding of local and regional land cover trends.

Spectroscopic studies of analog terrestrial mineral assemblages are necessary to develop criteria to identify similar environments on Mars. We use visible/near infrared (VNIR) laboratory, field, and remotely acquired spectral data to identify the iron-bearing and hydrous minerals of Rio Tinto, Spain, an astrobiological analog. Mineralogy evolves from iron sulfate- and oxide-rich (jarosite, rozenite, gypsum, schwertmannite, copiapite, goethite, and hematite assemblages) in young sediments to hydrated iron oxides in preserved terraces. Using spectra from the Rio Tinto, we examine one of the key challenges of extraterrestrial exploration: how to identify promising targets from spatially coarse data for in situ investigation. We apply an index to quantify the expression of spectral diversity as a function of spatial scale from hand sample to landscape. To validate this method for use at the decimeter orbital scale, we apply the index to cm-scale point spectra and meter-scale gridded spectra collected in the field. This exercise in spatial scaling gives increased confidence in the ability of the Spectral Variance Index (SVI) method to locate regions with increased mineral diversity from remotely sensed data. We divide the remotely sensed data into 25 × 25 pixel (200 m × 200 m) cells and calculate the average mean (albedo) and spectral variance over all wavelengths for each cell. We next calculate the expected variance for each cell with a linear regression between mean and spectral variance. The number of standard deviations of each cell's spectral variance is from the expected variance is the SVI value. We locate ∼ 20 areas with high SVI values within the tailing piles and along wide riverbanks downstream of the active mine. This method uses spatially coarse VNIR spectra to recognize areas in Rio Tinto that would be ideal targets for future field exploration, and could also be applied to Mars orbital spectral datasets, such as OMEGA and CRISM.

A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance–compositional–structural relations for this group of minerals. Sulfates exhibit diverse spectral properties, and absorption-band assignments have been developed for the 0.3–26 μm range. Sulfate absorption features can be related to the presence of transition elements, OH, H2O, and SO4 groups. The number, wavelength position, and intensity of these bands are a function of both composition and structure. Cation substitutions can affect the wavelength positions of all major absorption bands. Hydroxo-bridged Fe3+ results in absorption bands in the 0.43, 0.5, and 0.9 μm regions, while the presence of Fe2+ results in absorption features in the 0.9–1.2 μm interval. Fundamental S O bending and stretching vibration absorption bands occur in the 8–10, 13–18, and 19–24 μm regions (1000–1250, 550–770, and 420–530 cm−1). The most intense combinations and overtones of these fundamentals are found in the 4–5 μm (2000–2500 cm−1) region. Absorption features seen in the 1.7–1.85 μm interval are attributable to H O H/O H bending and translation/rotation combinations, while bands in the 2.1–2.7 μm regions can be attributed to H2O- and OH-combinations as well as overtones of S O bending fundamentals. OH- and H2O-bearing sulfate spectra are fundamentally different from each other at wavelengths below ∼6 μm. Changes in H2O/OH content can shift S O band positions due to change in bond lengths and structural rearrangement. Differences in absorption band wavelength positions enable discrimination of all the sulfate minerals used in this study in a number of wavelength intervals. Of the major absorption band regions, the 4–5 μm region seems best for identifying and discriminating sulfates in the presence of other major rock-forming minerals.

Despite the large number of in situ, plot-level phenological measurements and satellite-derived phenological studies, there has been little success to date in merging these records temporally or spatially. In this research, we bridge this scale gap through higher resolution satellite records (Landsat) and quantify the accuracy of satellite-derived metrics with direct field measurements. We compiled fifty-seven Landsat scenes from southern New England (P12 R51) from 1984 to 2002. Green vegetation areal abundance for each scene was derived from spectral mixture analysis and a single set of endmembers. The leaf area signal was fit with a logistic-growth simulating sigmoid curve to derive phenological markers (half-maximum leafonset and offset). Spring leaf-onset dates in homogenous stands of deciduous forests displayed significant and persistent local variability. The local variability was validated with multiple springtime ground observations (r 2 =0.91). The highest degree of verified small-scale variation occurred where contiguous forests displayed leaf-onset gradients of 10–14 days over short distances (

An understanding of land use/land cover change at local, regional, and global scales is important in an increasingly human-dominated biosphere. Here, we report on an under-appreciated complexity in the analysis of land cover change important in arid and semi-arid environments. In these environments, some land cover types show a high degree of inter-annual variability in productivity. In this study, we show that ecosystems dominated by non-native cheatgrass ( Bromus tectorum ) show an inter-annual amplified response to rainfall distinct from native shrub/bunch grass in the Great Basin, US. This response is apparent in time series of Landsat and Advanced Very High Resolution Radiometer (AVHRR) that encompass enough time to include years with high and low rainfall. Based on areas showing a similar amplified response elsewhere in the Great Basin, 20,000 km 2 , or 7% of land cover, are currently dominated by cheatgrass. Inter-annual patterns, like the high variability seen in cheatgrass-dominated areas, should be considered for more accurate land cover classification. Land cover change science should be aware that high inter-annual variability is inherent in annual dominated ecosystems and does not necessarily correspond to active land cover change.

High spatial and temporal resolution maps of sea surface temperature (SST) have numerous applications in coastal and estuarine systems. A climatology map, tracking SST as a function of year-day, was produced at Southern New England using 53 Landsat TM and ETM+ thermal infrared data. A recursive curve-fitting algorithm was used to fit these data and eliminate cloud contamination, resulting in an average daily temperature at every 60-m pixel. The climatology was validated against long-term in situ records that were analyzed with the same techniques. The results show, as expected, that isolated and shallow water bodies undergo more extreme temperature variation (−2 to 25 °C) than deeper, well-connected embayments (1 to 21 °C) or the coastal ocean (4 to 18 °C). The coastal ocean is shown to lag insolation and shallow lakes by up to 44 days, with embayments showing a gradation between these extremes. Despite the subtle temperature range variation, there is rich detail in the spatial patterns which are relevant to the applied sciences of coastal and estuarine systems. The spatial pattern of the climatology reveals anomalous patterns, such as occur where anthropogenic forcing alters climatological patterns. The heat budget of Mount Hope Bay in northeast Narragansett Bay has anthropogenic thermal input from a large power plant, and this input is reflected in the climatology. From the results, it is seen that Narragansett Bay has, on average, a mean annual temperature of 11.86±0.41 °C, while the Mount Hope Bay system is consistently warmer at 12.30±0.21 °C and shows a delayed response to autumn cooling. The long history of Landsat data acquisition can be used to create a climatology of coastal and estuarine scale dynamics at an order of magnitude finer scale resolution than AVHRR climatologies.

The goal of this work is to determine the spectroscopic properties of sulfate in martian soil analogs over the wavelength range 0.3 to 25 μm (which is relevant to existing and planned remotely sensed data sets for Mars). Sulfate is an abundant component of martian soil (up to 9% SO3 by weight) and apparently exists as a particulate in the soil but also as a cement. Although previous studies have addressed the spectroscopic identity of sulfates on Mars, none have used laboratory mixtures of materials with sulfates at the abundances measured by landed spacecraft, nor have any works considered the effect of salt-cementation on spectral properties of soil materials. For this work we created mixtures of a palagonitic soil (JSC Mars-1) and sulfates (MgSO4 and CaSO4·2H2O). The effects of cementation were determined and separated from the effects of packing and hydration by measuring the samples as loose powders, packed powders, cemented materials, and disaggregated materials. The results show that the presence of particulate sulfate is best observed in the 4–5 μm region. Soils cemented with sulfate exhibit a pronounced restrahlen band between 8 and 9 μm as well as well-defined absorptions in the 4–5 μm region. Cementation effects are distinct from packing effects and disaggregation of cemented samples rapidly diminishes the strength of the restrahlen bands. The results of this study show that sulfate in loose materials is more detectable in the near infrared (4–5 μm) than in the thermal infrared (8–9 μm). However, cemented materials are easily distinguished from loose mixtures in the thermal infrared because of the high values of their absorption coefficient in this region. Together these results suggest that both wavelength regions are important for determining the spatial extent and physical form of sulfates on the surface of Mars.

Calibration of at-sensor radiance to reflectance is a critical step for the use of remotely sensed hyperspectral data of water to determine the concentrations of optically active components. Because water has such a low reflectance, sources of radiance other than the water-leaving radiance contribute significantly to the at-sensor radiance and vary with wavelength and spatially. While radiative transfer models have improved significantly, there are still large uncertainties in prescribing the spatial and spectral properties of aerosol scattering. In addition, errors in the sensor calibration of radiance can lead to additional uncertainty. An atmospheric correction method based entirely on scene information, but not in situ data, is described. This approach accounts for nonuniform aerosol scattering, glint from the water surface, and reflected skylight. Normalization by an estimate of the direct solar irradiance reaching the surface, also derived from scene information, then provides an estimate of reflectance. This method is applied to AVIRIS data acquired over a temperate estuary. The resultant reflectance estimates are shown to be consistent with field observations. While the method is empirical, it is based on physical principles that allow it to be applied under a wide range of conditions.

IRMA (the acronym stands for InfraRed Microscope Analysis) is a hyperspectral imaging spectrometer which is capable, in its present design, to achieve a spatial resolution of 38 μm in the 0.8–5 μm infrared spectral range. IRMA has the goal to first ever quantitatively characterize the mineralogy and the microphysical structure of the materials of the Martian soils and rocks down to the depth available to a lander sampling mechanism. The experiment has been selected by the Italian Space Agency (ASI), in the framework of the Italian participation to the NASA's Mars Surveyor Programme, to be part of the Italian Package for Scientific Experiments (IPSE). IPSE was to fly on-board the ill-fated MARS2003 MARS SAMPLE RETURN Mission, postponed during the early months of 2000 to a later date (possibly 2007). IRMA present state of development is compatible with a flight readiness in 2007. IPSE is a small laboratory devoted to the analysis of in situ collected samples of rock and soil of Martian material. Details on IPSE are given in a paper in this same journal issue. IRMA will provide detailed information on: • texture, habit and microphysical properties of the grains and particulates of the Martian soil as well as the petrography of Martian rocks, with a spatial resolution of the order of the tens of micron. • Mineralogical composition and relative mineral abundances of the rocks and soils, with a relative accuracy of the order of 1%. A Signal to Noise Ratio of at least 100 shall be required to achieve this goal IRMA measurements shall provide essential contributions to the understanding of outstanding scientific issues such as the history of water and other volatiles, e.g., CO2, the role of physical and chemical weathering in the past and present day Mars and hence the assessment of the environmental conditions present on the martian surface throughout its history.

Imaging spectrometer data from the ISM instrument on Phobos 2 were used to characterize spatial variations in near-infrared spectral properties of the martian surface, to determine the correspondence between near-infrared and visible-wavelength spectral variations, and to assess lithologic variations in the surface materials. All data were radiometrically calibrated and corrected for effects of atmospheric gases using previously described methods. The data were also corrected photometrically to a standard geometry, and the estimated contribution of light backscattered by atmospheric aerosols was removed to isolate the reflectance properties of surface materials. At shorter near-infrared wavelengths, the surface varies between three major spectral types which correspond to known visible color units. Dark gray materials have 1- and 2-μm absorptions consistent with a pyroxene-containing lithology, and bright red dust has a shallow 0.9-μm absorption consistent with a poorly crystalline ferric mineralogy. Dark red soils are spectrally similar to dust although lower in albedo. In some cases their 0.9-μm ferric iron absorption is deeper and offset toward longer wavelengths than in dust. These attributes agree well with those determined in situ for comparable materials at the Mars Pathfinder landing site. At longer wavelengths, significant regional heterogeneities are observed in the slope of the spectral continuum and the depth of the 3-μm H2O absorption. The 3-μm band is stronger in bright red soils than in most dark gray soils, but the strongest absorptions are found in intermediate-albedo dark red soils. Observed spectral variations suggest the presence of at least four surface components, dust, pyroxene-containing rock and sand, one or more crystalline ferric minerals, and a water-bearing phase. These are broadly consistent with four surface components that have been inferred from ground-based, orbital, and landed spectral studies and from in situ compositional measurements. We also conclude from our analysis that most albedo and spectral variations result from the coating of dark mafic rock materials by bright ferric dust. Dark red regions, however, are inferred to have dust-like compositions but lower albedos, due in part to intermixture of a dark, crystalline ferric mineral. Both of these major conclusions are strongly supported by landed investigations by Mars Pathfinder. The layered materials in Valles Marineris are the only geologic formation with distinctive spectral properties, including an enhanced 3-μm H2O band and pyroxene absorptions which imply a mineralogy distinct from materials in the surrounding highlands. These properties provide important evidence for the layered materials' origins and are most consistent with mechanisms that involve volcanism restricted to the interiors of the chasmata.

Because in situ techniques for determining vegetation abundance in semiarid regions are labor intensive, they usually are not feasible for regional analyses. Remotely sensed data provide the large spatial scale necessary, but their precision and accuracy in determining vegetation abundance and its change through time have not been quantitatively determined. In this paper, the precision and accuracy of two techniques, Spectral Mixture Analysis (SMA) and Normalized Difference Vegetation Index (NDVI) applied to Landsat TM data, are assessed quantitatively using high-precision in situ data. In Owens Valley, California we have 6 years of continuous field data (1991-1996) for 33 sites acquired concurrently with six cloudless Landsat TM images. The multitemporal remotely sensed data were coregistered to within 1 pixel, radiometrically intercalibrated using temporally invariante surface features and geolocated to within 30 m. These procedures facilitated the accurate location of field-monitoring sites within the remotely sensed data. Formal uncertainties in the registration, radiometric alignment, and modeling were determined. Results show that SMA absolute percent live cover (%LC) estimates are accurate to within ?4.0%LC and estimates of change in live cover have a precision of +/-3.8%LC. Furthermore, even when applied to areas of low vegetation cover, the SMA approach correctly determined the sense of clump, (i.e., positive or negative) in 87% of the samples. SMA results are superior to NDVI, which, although correlated with live cover, is not a quantitative measure and showed the correct sense of change in only 67%, of the samples.

A montmorillonite clay and a palagonitic soil sample were sieved to produce a series of size fractions in order to investigate the role that extremely fine particle sizes play on absorption strengths in martian analog materials. Significant decreases in band strength for both samples were observed as particle size decreased. The less than 5-μm fractions had 1.4-, 1.9-, and 2.2-μm bands that were approximately half the strength of the absorptions from the 45- to 75-μm size fractions. X-ray diffraction and loss on ignition measurements indicate that there are no significant changes in crystallinity, composition, or water content with particle size. Thus the reduction in spectral contrast is dominated by changes in the ratio of scattering to absorption with particle size. Furthermore, larger particles of montmorillonite clay are not individual crystals but are aggregates of much smaller particles. Nevertheless, the aggregate particles exhibit spectral properties consistent with the size of the aggregate, not the individual particles in the aggregate. This has important implications for the spectroscopic determination of the composition of the extremely fine martian dust. The abundance of very fine grained mineral phases such as phyllosilicates will be underestimated if comparisons to coarser or clumped laboratory samples are made.

Thermal effluent from a large coal-fired electric generating facility located on Mt. Hope Bay in the Narragansett Bay (Rhode Island, U.S.A.) has been implicated in a large decline in fish populations in this region. Detailed information on the spatial and temporal properties of this thermal input (approximately 5 million m 3 day −1 of thermal effluent 7 °C above ambient) is, however, lacking. In this paper it is shown that the spatial extent and magnitude of the thermal impacts can be quantitatively determined by exploiting the strengths of remotely sensed data. Seasonal trends of surface temperature in the Narragansett Bay estuary were derived from a composite of 14 thermal infrared satellite images (Landsat TM Band 6) with a spatial resolution of 120 m. The derived temperatures were validated against independent measures of surface temperature for a number of sites within the bay, and it was shown that the satellite measures were within 1 °C of the in situ temperatures. Relationships among thermal properties and physical characteristics were identified through a comparison of the seasonal temperature patterns of 12 regions within the bay. As expected, depth was the primary factor in determining the magnitude of seasonal temperature variation in the estuary, while advective exchange with the coast ocean was the second most important factor. Although the behaviour of Mount Hope Bay was significantly correlated with the other upper estuarine regions, the bay did not experience autumn cooling, which is characteristic of upper estuarine waters. From late summer through to autumn, the average temperature difference between Mount Hope Bay and Upper Narragansett Bay was 0·8 °C, which can be attributed to warming from the thermal effluent of the Brayton Point Power Station in Mount Hope Bay. An unsupervised (statistical) classification of temperature as a function of season revealed the natural boundaries between areas with different seasonal temperature signals, and statistically identified Mount Hope Bay as a unique area in the upper estuary which had anomalously high temperatures throughout the year. Among the scenes included in the unsupervised analysis, Mount Hope Bay was on average 0·8 °C warmer than the rest of the upper estuary, and the total area affected is 36 km 2 .

Fine grained particles ,50 mm in size dominate particle size changes in the volume scattering region, the Christiansen feadistributions of many planetary surfaces. Despite the predomi- ture, restrahlen bands, and transparency features. The quartz nance of fine particles in planetary regoliths, there have been particle size series were less well modeled, with the greatest few investigations of the systematic effects of the finest particles discrepancies in the restrahlen bands and the overall spectral on reflectance spectra, and on the ability of quantitative models contrast. © 1997 Academic Press to extract compositional and/or textural information from remote observations. The effects of fine particles that are approximately the same size as the wavelength of light on reflectance

Imaging sprectroscopic measurements (ISM) of Mars acquired by the ISM instrument on Phobos-2 are used to investigate the NIR spectral properties of aerosols and the effects of atmospheric scattering on inferred mineralogy of the surface. Estimates of aerosols spectra between 0.77 and 2.6 micrometers are derived above Tharsis and Ophir Planum. The spectral continua are consistent with the particle size distribution derived using data from the solar occultation experiment on-board the spacecraft (effective radius approximately = 1.2 micrometers, with an effective variance approximately = 0.2). The aerosols spectra contain water-ice absorption features and possibly absorptions due to clay and/or sulfates. The largest effect of the aerosols on surface spectra is in dark regions, where the continuum spectral slope becomes more negative and the 1-micrometers absorption due to Fe in pyroxene is shifted toward longer wavelengths. The effects of aerosols on spectra of bright regions are insufficiently large to change mineralogic interpretations based on ISM data, i.e., that bright regions in Tharsis are dominated spectrally by hematite, but that additional ferric minerals are probably present in other areas including Arabia.

Previous spectroscopic studies of the lunar crater Bullialdus, located in the Nubium Basin, indicated an unusual stratigraphy of two gabbroic layers overlying a noritic unit. The possible existence of a layered mafic pluton at Bullialdus was suggested. To investigate the geologic context with more detailed spatial information, charge-coupled device (CCD) images of Bullialdus were obtained using eight filters. A linear mixing model was used to investigate the fractional abundances of spectral end-members chosen from within the multispectral image. Since the reflectance properties of lunar materials over this wavelength range are sensitive to variations in composition and soil maturity, fractional abundance images were used to create a new geologic map of the crater. The spatial relationships of the surface materials confirm the previously inferred stratigraphy, and further reveal the central peaks to exhibit two distinct compositional units: noritic anorthosite and anorthositic norite. Three models for the origin of the observed stratigraphy are considered: Bullialdus has excavated stratigraphic units containing (1) early mare basalt overlying anorthositic-noritic crustal material, (2) part of a layered mafic pluton, and/or (3) part of an impact melt sheet formed by the Nubium Basin impact event.

High spatial-resolution observations made by orbiting spacecraft from the Viking and Phobos missions suggest the local development of crystalline ferric oxides in a small area in Mars' Valles Marineris canyon system. Quantitative color analysis of Viking Orbiter multispectral images identifies two spatially coherent regions of unique hue among the interior layered deposits in western Candor Chasma. The anomalous color indicates a local compositional difference between these regions and the surrounding high-albedo materials. The unusual appearance of the unit in the Viking color observations could be explained by a small increase in the degree of crystallinity or abundance of hematite. Near-infrared spectra obtained by the ISM imaging spectrometer aboard Phobos 2 confirm a local enrichment in ferric oxides or oxyhydroxides in the region and suggest the presence of another phase in addition to hematite. In high resolution, the spectral unit can be seen to occur within two 20-km-long depressions on the margins of an Hesperian-aged layered deposit which forms a plateau on the chasma floor. Water is implicated in the formation of the iron oxides, since the same sedimentary layers seen in the depressions are exposed on steep surfaces elsewhere on the plateau but show no evidence of unusual coloration. This suggests that the mineralization occurred through secondary alteration of preexisting rocks and developed locally in association with the depressions, which could have ponded surface runoff or groundwater seepage.

Much of the surface of Mars is covered by material that is bright and reddish at visible wavelengths and which is interpreted as chemically altered soil. High spatial resolution data from the ISM near-infrared imaging spectrometer on the Phobos 2 spacecraft have provided new information about the composition and compositional heterogeneity of this soil. Most bright soil exhibits a weak, narrow absorption feature near 2.2 micron, suggesting the presence of poorly crystalline phyllosilicate. The strength of the 3.0-micron H2O absorption exhibits spatially coherent variations, with stronger absorptions occurring in specific geologic units. These variations may result from differences in the content of molecular water in soils developed on different deposits. Additionally, the position and shape of the 0.9-micron Fe(3+) absorption indicate hematite to be present in bright soils covering many areas, including Tharsis. However, other large areas covered by bright soil, including much of Arabia, exhibit a deeper absorption at a longer wavelength, suggesting occurrence of ferric minerals other than hematite. These spectral heterogeneities indicate that bright martian soil is compositionally diverse and not completely homogenized by eolian activity. The compositional differences may result from different histories of chemical alteration of parent materials and their resulting soils, possibly including local effects of liquid water.

A linear mixing model is used to model the spectral variability of an AVIRIS scene from the western foothills of the Sierra Nevada and calibrate these radiance data to reflectance. Five spectral endmembers from the AVIRIS data, plus an ideal 'shade' endmember were required to model the continuum reflectance of each pixel in the image. Three of the endmembers were interpreted to model the surface constituents green vegetation, dry grass, and illumination. These are the main transient surface constituents that are expected to change with shifts in land use or climatic influences and viewing conditions ('shade' only). The spectral distinction between the other three endmembers is very small, yet the spatial distributions are coherent and interpretable. These distributions cross anthropogenic and vegetation boundaries and are best interpreted as different soil types. Comparison of the fraction images to the bedrock geology maps indicates that substrate composition must be a factor contributing to the spectral properties of these endmembers. Detailed examination of the reflectance spectra of the three soil endmembers reveals that differences in the amount of ferric and ferrous iron and/or organic constituents in the soils is largely responsible for the differences in spectral properties of these endmembers.