ORCID Profile
0000-0003-4085-8725
Current Organisation
Dr Rob Hewson - Private Consultant
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Publisher: Elsevier BV
Date: 06-2015
Publisher: Springer Science and Business Media LLC
Date: 30-03-2016
DOI: 10.1038/SREP23702
Abstract: The Earth’s surface comprises minerals diagnostic of weathering, deposition and erosion. The first continental-scale mineral maps generated from an imaging satellite with spectral bands designed to measure clays, quartz and other minerals were released in 2012 for Australia. Here we show how these satellite mineral maps improve our understanding of weathering, erosional and depositional processes in the context of changing weather, climate and tectonics. The clay composition map shows how kaolinite has developed over tectonically stable continental crust in response to deep weathering during northwardly migrating tropical conditions from 45 to 10 Ma. The same clay composition map, in combination with one sensitive to water content, enables the discrimination of illite from montmorillonite clays that typically develop in large depositional environments over thin (sinking) continental crust such as the Lake Eyre Basin. Cutting across these clay patterns are sandy deserts that developed Ma and are well mapped using another satellite product sensitive to the particle size of silicate minerals. This product can also be used to measure temporal gains/losses of surface clay caused by periodic wind erosion (dust) and rainfall inundation (flood) events. The accuracy and information content of these satellite mineral maps are validated using published data.
Publisher: Informa UK Limited
Date: 08-2003
Publisher: Elsevier BV
Date: 03-2020
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2019JE006337
Publisher: Elsevier BV
Date: 11-2005
Publisher: Informa UK Limited
Date: 03-1991
DOI: 10.1071/EG991179
Publisher: Informa UK Limited
Date: 16-02-2015
Publisher: Unpublished
Date: 2008
Publisher: MDPI AG
Date: 13-12-2022
DOI: 10.3390/RS14246303
Abstract: Geologic remote sensing studies often targets surface cover that is supposed to be invariant or only changing on a geological timescale. In terms of surface material characteristics, this holds for rocks and minerals, but only to a lesser degree for soils (including alluvium, colluvium, regolith or weathered outcrop) and not for vegetation cover, for ex le. A view unobstructed by clouds, vegetation or fire scars is essential for a persistent observation of surface mineralogy. Sensors with a continuous multi-temporal operation (e.g., Landsat 8 OLI and Sentinel-2 MSI) can provide the data volume needed to come to an optimal seasonal acquisition and the application of data fusion approaches to create an unobstructed view. However, the acquisition environment always changes over time, driven by seasonal changes, illumination changes and the weather. Consequently, the creation of an unobstructed view does not necessarily lead to a repeatable measurement. In this paper, we evaluate the influence of weather and resulting soil moisture conditions over a 3-year period, with alternating dry and wet periods, on the variance of several “geological” spectral indices in a semi-arid area. Sentinel-2 MSI data are chosen to calculate band ratios for green vegetation, ferric and ferrous iron oxide mineralogy and hydroxyl bearing alteration (clay) mineralogy. The data were used “as provided”, meaning that the performance of the atmospheric correction and geometric accuracy is not changed. The results are shown as time-series for selected areas that include solid rock, beach sand, bare soil and natural vegetation surfaces. Results show that spectral index values vary not only between dry and wet periods, but also within dry periods longer than 45 days, as a result of changing soil moisture conditions long after a last rain event has passed. In terms of repeatability of measurements, an overall low soil-moisture level is more important for long-term stability of spectral index values than the occurrence of minor rain events. In terms of creating an unobstructed view, we found that thresholds for NDVI should not be higher than 0.1 when masking vegetation in geological remote sensing, which is lower than what usually is indicated in literature. In conclusion, multi-temporal data are not only important to study dynamic Earth processes, but also to improve mapping of surfaces that are seemingly invariant. As this work is based on a few selected pixels, the obtained results should be considered only indicative and not as a numerical truth. We conclude that multi-temporal data can be used to create an unobstructed view, but also to select the data that give the most repeatability of measurements. Images selection should not be based on a certain number of days without rain in the days preceding data acquisition but aim for the lowest soil moisture conditions. Consequently, weather data should be incorporated to come to an optimal selection of remote sensing imagery, and also when analyzing multi-temporal data.
Publisher: CSIRO Publishing
Date: 2000
DOI: 10.1071/RJ0000105
Abstract: This study summarises the application of several remote sensing techniques to investigate various components of a land surface in the semi-arid environment of Fowlers Gap. These remote sensing techniques included NASA's Thermal Infrared Multispectral Scanner (TIMS) and CSIRO's Mid-Infrared Airborne CO, Laser Spectrometer (MIRACO,LAS), NASA's AIRSAR radar and geophysical airborne radiometrics. Linear spectral unmixing of extracted emissivities from the TIMS data produced four endmembers: quartz, clay minerals, dry vegetation (cellulose) in fine soils, and green vegetation/moisture. MIRAC0,LAS data identified spectral signatures similar to the spectra of endmembers derived from TIMS data. The sensitivity of both thermal infrared remote sensing techniques to the quartzklay contents and textures of the soils and sediments was confirmed by detailed laboratory spectral measurements. Surface roughness information from AIRSAR's band C radar backscatter assisted the discrimination of alluvial and colluvial quartz and clay-rich deposits from the outcropping geological units. In particular the C band AIRSAR radar discriminated the coarse grained sandstone and quartzite scree within the colluvial pediments, from the finer grained quartz-rich 'radar smooth' alluvium in the scalds. Airborne radiometrics were also found useful for further discriminating potassium and thorium- bearing phyllosilicate/clay minerals, within shales and ghyllites, from the kaolinite and montmorillonite- rich alluvium. This study found that TIMS data could identify some of the geomorphological features at Fowlers Gap, such as colluvial pediments, depositional scalds and gilgai landforms, that characterise some of the land systems in the Lowlands and Plains relief class of the Fowlers Gap land system classification. Thermal infrared remote sensing techniques also proved capable of discriminating areas of cellulose-rich dry vegetation and fine grained soils within the Plains relief class. The sensitivity of AIRSAR radar for topographic relief and surface roughness suggests that it is useful for distinguishing land systems in the Ranges relief class. Radiometrics appeared useful for land system definition when outcropping argillaceous units and alluvium assisted their classification. Key words: remote sensing, Fowlers Gap, thermal infrared, land system, spectral unmixing
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2019
Publisher: IEEE
Date: 2008
Publisher: Hindawi Limited
Date: 2012
DOI: 10.1155/2012/535646
Abstract: The ability of thermal and shortwave infrared spectroscopy to characterise composition and texture was evaluated using both particle size separated soil s les and natural soils. Particle size analysis and separation into clay, silt, and sand-sized soil fractions was undertaken to examine possible relationships between quartz and clay mineral spectral signatures and soil texture. Spectral indices, based on thermal infrared specular and volume scattering features, were found to discriminate clay mineral-rich soil from mostly coarser quartz-rich sandy soil and to a lesser extent from the silty quartz-rich soil. Further investigations were undertaken using spectra and information on 51 USDA and other soils within the ASTER spectral library to test the application of shortwave, mid- and thermal infrared spectral indices for the derivation of clay mineral, quartz, and organic carbon content. A nonlinear correlation between quartz content and a TIR spectral index based on the 8.62 μ m was observed. Preliminary efforts at deriving a spectral index for the soil organic carbon content, based on 3.4–3.5 μ m fundamental H–C stretching vibration bands, were also undertaken with limited results.
Publisher: Informa UK Limited
Date: 06-2001
DOI: 10.1071/EG01102
Publisher: IEEE
Date: 2009
Publisher: IEEE
Date: 07-2013
Publisher: MDPI AG
Date: 19-10-2021
DOI: 10.3390/S21206924
Abstract: Mineral composition can be determined using different methods such as reflectance spectroscopy and X-ray diffraction (XRD). However, in some cases, the composition of mineral maps obtained from reflectance spectroscopy with XRD shows inconsistencies in the mineral composition interpretation and the estimation of (semi-)quantitative mineral abundances. We show why these discrepancies exist and how should they be interpreted. Part of the explanation is related to the s le choice and preparation another part is related to the fact that clay minerals are active in the short-wave infrared, whereas other elements in the composition are not. Together, this might lead to distinctly different interpretations for the same material, depending on the methods used. The main conclusion is that both methods can be useful, but care should be given to the limitations of the interpretation process. For infrared reflectance spectroscopy, the lack of an actual threshold value for the H–OH absorption feature at 1900 nm and the poorly defined Al–OH absorption feature at 2443 nm, as well as for XRD, detection limit, powder homogenizing, and the small amount of montmorillonite below 1 wt.%, was the source of discrepancies.
Publisher: IEEE
Date: 11-07-2021
Publisher: Informa UK Limited
Date: 2017
Publisher: Copernicus GmbH
Date: 03-06-2016
DOI: 10.5194/ISPRS-ANNALS-III-4-49-2016
Abstract: Abstract. Field spectroscopic metadata is a central component in the quality assurance, reliability, and discoverability of hyperspectral data and the products derived from it. Cataloguing, mining, and interoperability of these datasets rely upon the robustness of metadata protocols for field spectroscopy, and on the software architecture to support the exchange of these datasets. Currently no standard for in situ spectroscopy data or metadata protocols exist. This inhibits the effective sharing of growing volumes of in situ spectroscopy datasets, to exploit the benefits of integrating with the evolving range of data sharing platforms. A core metadataset for field spectroscopy was introduced by Rasaiah et al., (2011-2015) with extended support for specific applications. This paper presents a prototype model for an OGC and ISO compliant platform-independent metadata discovery service aligned to the specific requirements of field spectroscopy. In this study, a proof-of-concept metadata catalogue has been described and deployed in a cloud-based architecture as a demonstration of an operationalized field spectroscopy metadata standard and web-based discovery service.
Publisher: Society of Exploration Geophysicists, Australian Society of Exploration Geophysicists, Chinese Geophysical Society, Korean Society of Earth and Exploration Geophysicists, and Society of Exploration Geophysicists of Japan
Date: 10-07-2015
Publisher: Informa UK Limited
Date: 12-2013
Publisher: Informa UK Limited
Date: 02-1996
Publisher: Geological Society of London
Date: 02-2011
Publisher: Springer New York
Date: 2010
Publisher: Unpublished
Date: 2014
Publisher: IEEE
Date: 07-2018
Publisher: Unpublished
Date: 2011
Publisher: Elsevier BV
Date: 09-1996
Publisher: MDPI AG
Date: 26-06-2021
DOI: 10.3390/RS13132499
Abstract: An accuracy assessment of a classified thematic map is critical for the success of a remote sensing project. The identification and quantification of accuracy sources for classified mineral maps derived from satellite images enable confident decisions to be made for further exploration operations. Nineteen rock s les were collected from the different lithological units of the hydrothermally altered Kuh Panj Cu porphyry occurrence within the south-eastern part of Iran. SPECIM hyperspectral imaging was applied to the rock s les, followed by X-ray diffraction (XRD) analysis to compare the SPECIM mineral maps. The SPECIM results were then interpreted for mineralogy and compositional mapping extracted from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images. The spectral angle mapper (SAM) and real value−area (RV−A) fractal methods were applied on SPECIM and ASTER images to interpret the mineralogy and derived classified map products. Two methods, including confusion matrix and one minus standard deviation over mean, were used to assess the accuracy of the classified SPECIM and ASTER derived mineral maps. Performing sensitivity studies were investigated, including the effect of spatially displacing ASTER mineral mapping and changing the SAM-derived threshold values on the accuracy of the ASTER mineral map. The sensitivity analyses demonstrated that selecting an optimum SAM-derived threshold value is more important than spatial displacement. Finally, accuracy sources were summarized in an accuracy budget table. The results demonstrated 89 and 88% accuracy for SPECIM and 88 and 92% accuracy for ASTER mineral maps via the confusion matrix and one minus standard deviation over mean methods, respectively. The accuracy budget helped to evaluate and compare all sources of accuracy with their accuracy values.
Publisher: Elsevier BV
Date: 10-2022
Publisher: MDPI AG
Date: 21-09-2018
DOI: 10.3390/RS10101518
Abstract: Remote sensing systems are largely used in geology for regional mapping of mineralogy and lithology mainly from airborne or spaceborne platforms. Earth observers such as Landsat, ASTER or SPOT are equipped with multispectral sensors, but suffer from relatively poor spectral resolution. By comparison, the existing airborne and spaceborne hyperspectral systems are capable of acquiring imagery from relatively narrow spectral bands, beneficial for detailed analysis of geological remote sensing data. However, for vertical exposures, those platforms are inadequate options since their poor spatial resolutions (metres to tens of metres) and NADIR viewing perspective are unsuitable for detailed field studies. Here, we have demonstrated that field-based approaches that incorporate thermal infrared hyperspectral technology with about a 40-nm bandwidth spectral resolution and tens of centimetres of spatial resolution allow for efficient mapping of the mineralogy and lithology of vertical cliff sections. We used the Telops lightweight and compact passive thermal infrared hyperspectral research instrument for field measurements in the Jura Cement carbonate quarry, Switzerland. The obtained hyperspectral data were analysed using temperature emissivity separation algorithms to isolate the different contributions of self-emission and reflection associated with different carbonate minerals. The mineralogical maps derived from measurements were found to be consistent with the expected carbonate results of the quarry mineralogy. Our proposed approach highlights the benefits of this type of field-based lightweight hyperspectral instruments for routine field applications such as in mining, engineering, forestry or archaeology.
Publisher: IEEE
Date: 07-2018
Publisher: Informa UK Limited
Date: 02-2018
DOI: 10.1071/EG16056
Publisher: MDPI AG
Date: 24-10-2012
DOI: 10.3390/RS4113265
Location: Netherlands
No related grants have been discovered for Robert Hewson.