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•Spectra of savanna understorey vegetation species over phenological seasons.•Separability of functional groups, and species, depended on season.•Informs species separation and timing ...for drone-based hyperspectral captures.•VNIR drone spectral range excludes foliar traits such as cellular water absorption.
The relationship between species phenology and spectral separability is essential to determine the optimal remote sensing sampling period to maximise spectral separability of vegetation species. However, this relationship in many native grasses, introduced grasses and herbs, shrubs, and vine species in tropical savannas is unknown. We measured the in-situ hyperspectral response of monospecific vegetation stands of several understorey species representing different functional groups over phenological stages (throughout dry and wet seasons) using a non-imaging spectrometer. We present a spectral library of both native and introduced species of a tropical savanna environment. We analysed the data using continuum removal to highlight absorption features. Most understorey species displayed a photosynthetic spectral response with increased greenness at the end of the wet season that progressively declined as vegetation dried out. For some species, there were seasonally dependent differences in absorption features with spectral differences between the late wet and early dry season, and late dry and early wet seasons. We resampled the data to the spectral range typical of drone-mounted hyperspectral sensors (i.e., 150 bands between 400 and 1000 nm), which omits the water absorption features of the SWIR. These findings suggest an ideal sampling period for measuring outdoor canopy reflectance of understorey species, which will promote methodological improvements of hyperspectral data capture. The use of a VNIR only hyperspectral sensor will exclude the important regions of the spectrum for plant spectral identification including non-pigment bands for water, nitrogen and cellulose. The results have implications for determining the completeness of rehabilitation assessing reestablishment among indigenous species across mine sites under rehabilitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The miniaturisation of hyperspectral sensors for use on drones has provided an opportunity to obtain hyper temporal data that may be used to identify and monitor non-native grass species. However, a ...good understanding of variation in spectra for species over time is required to target such data collections. Five taxological and morphologically similar non-native grass species were hyper spectrally characterised from multitemporal spectra (17 samples over 14 months) over phenological seasons to determine their temporal spectral response. The grasses were sampled from maintained plots of homogenous non-native grass cover. A robust in situ standardised sampling method using a non-imaging field spectrometer measuring reflectance across the 350–2500 nm wavelength range was used to obtain reliable spectral replicates both within and between plots. The visible-near infrared (VNIR) to shortwave infrared (SWIR) and continuum removed spectra were utilised. The spectra were then resampled to the VNIR only range to simulate the spectral response from more affordable VNIR only hyperspectral scanners suitable to be mounted on drones. We found that species were separable compared to similar but different species. The spectral patterns were similar over time, but the spectral shape and absorption features differed between species, indicating these subtle characteristics could be used to distinguish between species. It was the late dry season and the end of the wet season that provided maximum separability of the non-native grass species sampled. Overall the VNIR-SWIR results highlighted more dissimilarity for unlike species when compared to the VNIR results alone. The SWIR is useful for discriminating species, particularly around water absorption.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Managing saline water discharges from mining operations is a global environmental challenge. Measuring the location and extent of surface efflorescence can indicate solute movement before changes in ...electrical conductivity (EC) are detected in waterways. We hypothesised through the use of a case study that ground-based reflectance spectrometry and airborne hyperspectral (450–2500 nm) analysis of surface efflorescence could be a rapid method for monitoring large regions of the surrounding environment, including downstream of remote mines. X-ray diffraction and X-ray fluorescence were used to determine mineralogy and elemental composition of surface salts around a uranium mine. Salt samples were found to be mixtures of magnesium sulfate. The reflectance of field spectra varied depending on the hydration of the mineral, mainly hexahydrite and starkeyite. A constrained energy minimisation technique was used to match the field reflectance spectra to the airborne data. Airborne matches were confirmed at the field sampling sites and surrounds. Salts were also detected at lower matches at mine water irrigation areas where excess mine water had previously been applied. Hence, hyperspectral remote sensing is a potentially rapid and sensitive method for mapping magnesium sulfates over large areas in operating and rehabilitated mines. It was successfully demonstrated as a tool for monitoring and assessment of efflorescence as a result of saline processes.
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•Composition and extent of MgSO4 efflorescence mapped with hyperspectral data•Hexahydrite and starkeyite were the dominant salt mineralogy identified by XRD.•Elevated uranium detected by a spectral absorption at 0.44 μm confirmed by XRD•A constrained energy minimisation technique matched field data to airborne survey•Remote method detected known locations of efflorescence from saline drainage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Knowing the baseline level of radioactivity in areas naturally enriched in radionuclides is important in the uranium mining context to assess radiation doses to humans and the environment both during ...and after mining. This information is particularly useful in rehabilitation planning and developing closure criteria for uranium mines as only radiation doses additional to the natural background are usually considered ‘controllable’ for radiation protection purposes. In this case study we have tested whether the method of contemporary groundtruthing of a historic airborne gamma survey could be used to determine the pre-mining radiological conditions at the Ranger mine in northern Australia. The airborne gamma survey was flown in 1976 before mining started and groundtruthed using ground gamma dose rate measurements made between 2007 and 2009 at an undisturbed area naturally enriched in uranium (Anomaly 2) located nearby the Ranger mine. Measurements of 226Ra soil activity concentration and 222Rn exhalation flux density at Anomaly 2 were made concurrent with the ground gamma dose rate measurements. Algorithms were developed to upscale the ground gamma data to the same spatial resolution as the historic airborne gamma survey data using a geographic information system, allowing comparison of the datasets. Linear correlation models were developed to estimate the pre-mining gamma dose rates, 226Ra soil activity concentrations, and 222Rn exhalation flux densities at selected areas in the greater Ranger region. The modelled levels agreed with measurements made at the Ranger Orebodies 1 and 3 before mining started, and at environmental sites in the region. The conclusion is that our approach can be used to determine baseline radiation levels, and provide a benchmark for rehabilitation of uranium mines or industrial sites where historical airborne gamma survey data are available and an undisturbed radiological analogue exists to groundtruth the data.
•Data from a historic airborne gamma survey at a uranium mine were groundtruthed.•Algorithms were developed to upscale the ground gamma data in ArcGIS.•Correlation models allow estimation of pre-mining radiological conditions.•Pre-mining γ-dose rates, Rn flux, and soil 226Ra activity concentrations determined•Approach can be used at mines where historical airborne gamma survey data exist.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Obtaining accurate quantitative spectral information from raw multispectral satellite imagery requires the conversion of raw digital numbers (DNs) to units of radiance or reflectance. In this ...article, an empirical line method is used to calibrate WorldView-2 satellite imagery to surface reflectance. Prediction equations for the eight multispectral bands were developed using a non-linear relationship between sensor top-of-atmosphere spectral radiance (LTOA) and surface reflectance values obtained from seven field targets. An accuracy assessment was undertaken by comparing image reflectance values against the surface reflectance values of 19 independent field targets. The overall accuracy based on the root mean square error (RMSE) for the eight bands ranged between 0.94% and 2.14% with the greatest variance in the near-infrared (NIR) bands. The results of this study show that empirical line methods can be used to successfully calibrate WorldView-2 satellite imagery to reflectance data.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Pixel-based image classification has been used to capture various components of vegetation for a number of applications and at a range of spatial scales across the world. The few studies that have ...attempted to capture the floristic composition of vegetation communities in tropical savanna environments, at fine spatial scales (1:25000 or less) using these methods, have found minimal success. To address this gap, we evaluated a supervised image classification process using the Maximum Likelihood Classifier and 50% of a floristic and structural (strata, cover, height, and growth form) field dataset applied to SPOT5 and Landsat5 Thematic Mapper multispectral data. Two approaches were conducted to evaluate the influence of ancillary data on classification results: (i) "image-only" (image and field data) and (ii) "integrated" (various combinations of ancillary data with the image and field data). Multivariate analysis and intuitive classification were employed to identify 22 vegetation communities within the 530 km
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study area situated on Bullo River Station, Northern Territory, Australia. Class (vegetation community) separability averaged 1.94 and 1.42 for Landsat5 Thematic Mapper and SPOT5, respectively. A standard accuracy assessment was based on the remaining 50% of the field data. Overall accuracy ranged from 30%-53% for 1:25000 and 1:100000 spatial scale products. The inclusion of ancillary data was superior to the image and field data alone. The results of this study emphasize the need for finer spatial scale maps for property management planning (≤ 1:25000) and coarser scales for regional applications (≥ 1:100000).
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
This article describes an airborne gamma survey of a 7 x 5 km region around the rehabilitated Nabarlek uranium mine in northern Australia. An unusually tight line spacing (100 m) and low aircraft ...height (50 m) were used, enabling the survey to distinguish man-made structures such as ponds and accommodation areas, as well as creek lines. Positive correlations between airborne data and ground-based readings enabled an estimation of the average absorbed dose rate arising from terrestrial gamma radiation over large areas of the site to be derived. For the fenced minesite area this estimate was 0.31 micro Gy hr(- 1). The airborne survey data were found to be invaluable in helping to plan further ground-level investigations and showed promise as an assessment tool for rehabilitated minesites.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This article describes an airborne g survey of a 7 5 km region around the rehabilitated Nabarlek uranium mine in northern Australia. An unusually tight line spacing (100 m) and low aircraft height ...(50 m) were used, enabling the survey to distinguish man-made structures such as ponds and accommodation areas, as well as creek lines. Positive correlations between airborne data and ground-based readings enabled an estimation of the average absorbed dose rate arising from terrestrial g radiation over large areas of the site to be derived. For the fenced minesite area this estimate was 0.31 k Gy hr super(- 1). The airborne survey data were found to be invaluable in helping to plan further ground-level investigations and showed promise as an assessment tool for rehabilitated minesites.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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