Image Processing and Machine Learning for Hyperspectral Unmixing: An Overview and the HySUPP Python Package

Spectral pixels are often a mixture of the pure spectra of the materials, called endmembers, due to the low spatial resolution of hyperspectral sensors, double scattering, and intimate mixtures of materials in the scenes. Unmixing estimates the fractional abundances of the endmembers within the pixel. Depending on the prior knowledge of endmembers, linear unmixing can be divided into three main groups: supervised, semi-supervised, and unsupervised (blind) linear unmixing. Advances in Image processing and machine learning substantially affected unmixing. This paper provides an overview of advanced and conventional unmixing approaches. Additionally, we draw a critical comparison between advanced and conventional techniques from the three categories. We compare the performance of the unmixing techniques on three simulated and two real datasets. The experimental results reveal the advantages of different unmixing categories for different unmixing scenarios. Moreover, we provide an open-source Python-based package available at https://github.com/BehnoodRasti/HySUPP to reproduce the results

Vegetation Change and Water, Sediment and Carbon Dynamics in Semi-Arid Environments

This study develops understanding of vegetation change and water, sediment and carbon dynamics in semi-arid environments. Objectives were addressed using an integrated ecohydrological and biogeochemical approach. Fieldwork, over two contrasting grass-woody transitions at the Sevilleta National Wildlife Refuge, New Mexico, USA; quantified vegetation structure, soil structure and the spatial distribution of soil carbon resources. Over both transitions; woody sites showed a lower percentage vegetation cover and a greater heterogeneity in vegetation pattern, soil properties and soil carbon. Soil organic carbon differed in both quantity and source across the sites; with levels higher under vegetation, particularly at the woody sites. Biogeochemical analysis revealed soil organic carbon to be predominantly sourced from grass at the grassland sites. In contrast, at the woody sites soil organic carbon under vegetation patches was predominantly sourced from woody vegetation, whilst inter-patch areas exhibited a strong grass signature. Investigation of function focussed on the hydrological response to intense rainfall events. Rainfall-runoff monitoring showed woody sites to exhibit greater; runoff coefficients, event discharge, eroded sediment and event carbon yields. In contrast to grass sites, biogeochemical analysis showed the loss of organic carbon from woody sites to exhibit a mixed source signal, reflecting the loss of carbon originating from both patch and interpatch areas. To examine the linkages between vegetation structure and hydrological function, a flow length metric was developed to quantify hydrological connectivity; with woody sites shown to have longer mean flow pathways. Furthermore, in addition to rainfall event characteristics, flow pathway lengths were shown to be a significant variable for explaining the variance within fluxes of water, sediment and carbon. Results demonstrating increased event fluxes of sediment and carbon from woody sites have important implications for the quality of semi-arid landscapes and other degrading ecosystems globally. It is thus necessary to translate the understanding of carbon dynamics developed within this study to the landscape scale, so changing fluvial carbon fluxes can be incorporated into carbon budgets, research frameworks and land management strategies at policy-relevant scales.University of ExeterRothamsted Research at North Wyk

Gold mineralisation and tectonomagmatic evolution of the Yalgoo-Singleton Greenstone Belt, Western Australia

The Archaean Yalgoo-Singleton greenstone belt (YSGB) represents one of the most understudied supracrustal complexes in the well renowned Yilgarn Craton, Western Australia. Despite being highly prospective for various mineral deposit types and host to several gold deposits, the stratigraphy, structure, geochemistry and ages of rocks in the YSGB remains poorly understood. This study utilises a combination of mapping, petrography, geochemistry, and geochronology to better constrain the development of rocks in the YSGB. Drillcore logging, SEM analysis and stable isotope analysis has determined the style, paragenesis and controls on lode-gold mineralisation in the belt. Detailed mapping shows that the YSGB comprises a lower succession of mafic-ultramafic volcanic rocks, overlain by a sedimentary-dominated succession, and extensively intruded by layered, maficultramafic sills. Geochemical analysis has distinguished multiple distinct volcanic and intrusive subgroups within the stratigraphy, which exhibit geochemical evidence of variable degrees of crustal contamination and fractional crystallisation. U-Pb zircon geochronology has constrained the ages of several previously undated supracrustal units and demonstrates the rapid formation of the greenstone belt over a short interval of < 15 Ma, from ca. 2825-2810 Ma. Coupled geochronology and geochemistry has enabled the correlation of units within the YSGB across the region. This study has established a seven-stage deformational model for rocks in the YSGB, recording a progression from bulk extension that accommodated volcanism, sedimentation, and sill emplacement, to a period of extensive granitic diapirism, followed by bulk horizontal shortening and associated shearing, and successive brittle faulting episodes. Lode-gold deposits in the YSGB are invariably structurally-controlled and were emplaced along steeply-dipping shear zones associated with fluid overpressure, during horizontal shortening. The remarkable consistency of structural style, paragenesis and stable isotope signatures at lode-gold deposits is indicative of a single, widespread mineralising event. The age of lode-gold mineralisation in the belt has been constrained at ca. 2623 Ma