National Geochemical Survey of Australia:A Different Way of Thinking

Many countries around the world have carried out national-scale geochemical surveys,providing important information on the natural concentration of chemical elements and compounds in the near-surface regolith.Resultant data and information layers have been put to a multitude of uses:identifying targets for mineral exploration;improving land-use management and environmental policy development;and

Positioning Australia for the Future

1.Introduction In 2018,the Australian Commonwealth Government committed 224.9 million AUD(160 million USD)to the Positioning Australia program in order to provide 10 cm accurate and reliable positioning to all Australians and accelerate the adoption and development of positioning technology and applications.This is a significant improvement from the 5–10 m accuracy that can currently be achieved using consumer positioning devices.Geographically speaking,Australia is in the position to take advantage of highquality,accurate,and efficient space-based positioning constellations with view of all global and regional constellations,including those of the United States(Global Positioning System,GPS),Russia(Global Navigation Satellite System,GLONASS),the European Union(Galileo),China(BeiDou),Japan(Quasi-Zenith Satellite System,QZSS),and India(Indian Regional Navigation Satellite System,IRNSS).

基于多波束背向散射强度信号的海底表层沉积物粒度分类研究——以澳洲Joseph Bonaparte湾为例

近海海底地形探测与沉积物精确分类对涉海工程建设、生物栖息地反演以及海底资源勘查与开发具有重要的现实意义。以澳洲Joseph Bonaparte湾为例,利用多波束测深技术获取了该海湾约880 km^2水域的水深数据与背向散射强度信号,结合同步采集的54个海底表层沉积物样品,通过随机决策树模型对该海域海底表层沉积物进行了分类研究。结果表明:(1)利用随机决策树模型分析该海域沉积物类型与背向散射强度的关系时,当模型内部参数设置:树的总数为200,最小分裂节点为2,每棵树的最大分裂级数为5时,可提高预测准确率;(2)该参数设置下,利用13°和37°入射角的背向散射强度预测该海域沉积物类型时,准确率最高,其值为83.3%,且在研究海域,砂质砾和砾质砂分布在背向散射强度较强的深槽或海沟等地区,而砾质泥质砂和含砾泥质砂主要分布在背向散射强度较弱的浅水海域。分析还发现,当水深数据作为预测海底表层沉积物类型的特征变量时,有可能降低最终预测结果的准确率。

澳大利亚造山型金矿和侵入岩有关金矿系统流体包裹体资料和矿化过程的比较

We have examined the fluid inclusion data and fluid chemistry of Australian orogenic and intrusion-related gold deposits to determine if similar mineralization processes apply to both styles of deposits.The fluid inclusion data from the Yilgarn craton,the western subprovince of the Lachlan orogen,the Tanami,Tennant Creek and Pine Creek regions,and the Telfer gold mine show that mineralization involved fluids with broadly similar major chemical components(i.e.H_2O+NaCl+CO_2±CH_4±N_2).These deposits formed over a wide range of temperature-pressure conditions(<200 to>500℃,<100～400MPa).Low salinity, CO_2-bearing inclusions and low salinity aqueous inclusions occur in both systems but the main difference between these two types of deposits is that most intrusion-related gold deposits also contain at least one population of high-salinity aqueous brine.Oxygen and hydrogen isotope data for both styles of deposit usually cannot distinguish between a magmatic or metamorphic source for the ore-bearing fluids.However,sulfur and lead isotope data for the intrusion-related gold deposits generally indicate either a magmatic source or mixing between magmatic and sedimentary sources of fluid.The metamorphic geothermal gradients associated with intrusion-related gold deposits are characterized by low pressure,high temperature metamorphism and high crustal geothermal gradients of>30/km.Where amphibole breakdown occurs in a granite source region,the spatially related deposits are more commonly associated with Cu-Au deposits rather than Au-only deposits that are associated with lower temperature granites.The dominant processes thought to cause gold precipitation in both types of deposits are fluid-rock interaction(e.g.desulfidation)or phase separation.Consideration of the physical and chemical properties of the H_2O-NaCl-CO_2 system on the nature of gold precipitation mechanisms at different crustal levels infers different roles of chemical(fluid-rock interaction)versus rheological(phase separation and/or fluid mixing)host-rock controls on gold deposition.This also implies that at the site of deposition,similar precipitation mechanisms operate at similar crustal levels for both orogenic and intrusion-related gold deposits.

澳大利亚的巨大挑战与地球科学的作用

本文是澳大利亚地球科学局（Geoscience Australia，GA）首席执行官 Pigram 博士在2014年澳大利亚地球科学会议（2014 Aus-tralian Earth Sciences Convention）主题演讲的综述。引言澳大利亚独特的地质和地理特征使其成为了一个土地非常辽阔，但人口稀少的国家。为了帮助国家应对当前和未来的挑战，澳大利亚地球科学局重点聚焦6大主要挑战，并将其作为工作驱动力。本文结合实例，介绍澳大利亚地球科学局如何帮助应对这6大挑战。

Characterizing receiver clock behaviors onboard Low Earth Orbiters:A case study of GRACE satellites

Accurate estimation of clocks, for example for the Gravity Recovery And Climate Experiment(GRACE)twin-satellites, is a critical part of precise orbit determination(POD) that ensures temporal gravity inversion. Characterizing the periodic variations of the receiver clocks is critical for precise clock modeling and prediction. In this study, the receiver clock is estimated using two different POD procedure: kinematic and reduced-dynamic approaches. Choices and the number of orbital parameters estimated in POD process affect the clock estimates, e.g., there are 8895 and 34,560 total parameters in the reduced-dynamic and kinematic approaches, respectively. In the both cases, the periodic variations of GRACE receiver clock are mainly dominated by the GPS orbit period, as well as once-(1-pr) and twiceper-revolution(2-pr) effects. Here the 1-pr effect is coupled with the relativistic effect, resulting in a difficulty to separate both signals. The clock amplitudes caused by the GPS orbit period, 1-pr and 2-pr are about 0.1, 0.03 and 0.01 ns, respectively. The GPS orbit period is almost one order magnitude larger than the 1-and 2-pr effect. The 0.1-ns amplitude of the 12-h periodic variation is equivalent to a 3-cm error in range. Such a systematic error should be considered in the receiver clock modeling for both the improvement of positioning accuracy and the reduction of number of unknown parameters, if the precise point positioning(PPP) technique is used for the orbit determination of the GRACE.

East African topography and volcanism explained by a single,migrating plume

Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle plumes.Several models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east Africa.We devise paleogeographically constrained global models of mantle convection and,based on the evolution of flow in the deepest lower mantle,show that the Afar plume migrated southward throughout its lifetime.The models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system(EARS),which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone,over the last≈45 Myr.We further show that the age-progression of volcanism associated with the southward propagation of EARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African plate.The models suggest that the Afar plume became weaker as it migrated southwards,consistent with trends observed in the geochemical record.

Digital earth Australia-unlocking new value from earth observation data

Petascale archives of Earth observations from space(EOS)have the potential to characterise water resources at continental scales.For this data to be useful,it needs to be organised,converted from individual scenes as acquired by multiple sensors,converted into“analysis ready data”,and made available through high performance computing platforms.Moreover,converting this data into insights requires integration of non-EOS data-sets that can provide biophysical and climatic context for EOS.Digital Earth Australia has demonstrated its ability to link EOS to rainfall and stream gauge data to provide insight into surface water dynamics during the hydrological extremes of flood and drought.This information is supporting the characterisation of groundwater resources across Australia’s north and could potentially be used to gain an understanding of the vulnerability of transport infrastructure to floods in remote,sparsely gauged regions of northern and central Australia.

Operational continental-scale land cover mapping of Australia using the Open Data Cube

To comprehensively support national and international initiatives for sustainable development,land cover products need to be reliably and routinely generated within operational frameworks.Coupled with consistent semantics and taxonomies,ensuring confidence in mapping land cover for multiple time periods,facilitates informed decision-making at scales appropriate to multiple policy domains.The United Nations Food and Agriculture Organisation(FAO)Land Cover Classification System(LCCS)provides a taxonomy that comparable at different scales,level of detail and geographic location.The Open Data Cube(ODC)initiative offers a framework for operational continental-scale land cover mapping using analysis-ready Earth Observation data.This study utilised the FAO LCCS framework and the Landsat sensor data through Digital Earth Australia(DEA;Australia’s ODC instance)to generate consistent and continent-wide land cover mapping(DEA Land Cover)of the Australian continent.DEA Land Cover provides annual maps from 1988 to 2020 at 25 m resolution.Output maps were validated with∼12,000 independent validation points,giving an overall map accuracy of 80%.DEA Land Cover provides Australia with a nationally consistent picture of land cover,with an open-source software package using readily available global coverage data and demonstrates a pathway of adoption for national implementations across the world.

Overview of legal traceability of GPS positioning in Australia

Global Positioning System(GPS)position verification and legal traceability in Australia supports industry,trade,science and innovation and is trusted and recognized domestically and internationally.At the end of 2017,the Australia’s national datum was transitioned from the Geocentric Datum of Australia 1994(GDA94)to the Geocentric Datum of Australia 2020(GDA2020).As such,the datum for the legal traceability of GPS positions in Australia has also moved to GDA2020.This paper highlights the importance of legal metrology and measurement in terms of GPS positions in accordance with the National Measurement Act 1960(Commonwealth of Australia).Here we provide an overview of the process of issuing the so-called‘Regulation 13 Certificates’for Continuously Operating Reference Stations(CORS)across Australia.The position verification methodology is detailed,including the quality control,metadata assurance,and dynamic management of the certificates as well as positional uncertainty determination of CORS with varying quality.A quality monitoring system of positions is also discussed along with how measurement traceability is ensured including short-term and long-term position monitoring schemes.

FAIR Data and Metadata:GNSS Precise Positioning User Perspective

The FAIR principles of Wilkinson et al.[1]are finding their way from research into application domains,one of which is the precise positioning with global satellite navigation systems(GNSS).Current GNSS users demand that data and services are findable online,accessible via open protocols(by both,machines and humans),interoperable with their legacy systems and reusable in various settings.Comprehensive metadata are essential in seamless communication between GNSS data and service providers and their users,and,for decades,geodetic and geospatial standards are efficiently implemented to support this.However,GNSS user community is transforming from precise positioning by highly specialised use by geodetic professionals to every-day precise positioning by autonomous vehicles or wellness obsessed citizens.Moreover,rapid technological developments allow alternative ways of offering data and services to their users.These transforming circumstances warrant a review whether metadata defined in generic geospatial and geodetic standards in use still support FAIR use of modern GNSS data and services across its novel user spectrum.This paper reports the results of current GNSS users'requirements in various application sectors on the way data,metadata and services are provided.We engaged with GNSS stakeholders to validate our findings and to gain understanding on their perception of the FAIR principles.Our results confirm that offering FAIR GNSS data and services is fundamental,but for a confident use of these,there is a need to review the way metadata are offered to the community.Defining standard compliant GNSS community metadata profile and providing relevant metadata with data on-demand,the approach outlined in this paper,is a way to manage current GNSS users'expectations and the way to improve FAIR GNSS data and service delivery for both humans and the machines.

Think global,cube local:an Earth Observation Data Cube’s contribution to the Digital Earth vision

The technological landscape for managing big Earth observation(EO)data ranges from global solutions on large cloud infrastructures with web-based access to self-hosted implementations.EO data cubes are a leading technology for facilitating big EO data analysis and can be deployed on different spatial scales:local,national,regional,or global.Several EO data cubes with a geographic focus(“local EO data cubes”)have been implemented.However,their alignment with the Digital Earth(DE)vision and the benefits and trade-offs in creating and maintaining them ought to be further examined.We investigate local EO data cubes from five perspectives(science,business and industry,government and policy,education,communities and citizens)and illustrate four examples covering three continents at different geographic scales(Swiss Data Cube,semantic EO data cube for Austria,DE Africa,Virginia Data Cube).A local EO data cube can benefit many stakeholders and players but requires several technical developments.These developments include enabling local EO data cubes based on public,global,and cloud-native EO data streaming and interoperability between local EO data cubes.We argue that blurring the dichotomy between global and local aligns with the DE vision to access the world’s knowledge and explore information about the planet.

Forecasting tropical cyclone wind hazards and impacts:Summary from the Tenth International Workshop on Tropical Cyclones(IWTC-10)

In this paper,we summarizefindings from the Tenth International Workshop on Tropical Cyclones(IWTC-10)subgroup on forecasting wind hazards and impacts.We found that new approaches to TC wind hazard forecasts continue to be developed and are becoming an increasingly common product offered by operational centres.To add greater context to wind risk information for users,many operational and research centres are also working to develop impact-based forecasts that incorporate hazard,vulnerability,and exposure data.Efforts to develop tropical cyclone wind impact forecasts present resourcing challenges,and when compared to wind hazard forecasting,are generally still in their infancy.Overall,both operational and research centres are extending significant efforts to meet the strong public need for accurate predictions of TC wind hazards and impacts around the world.

Living Earth:Implementing national standardised land cover classification systems for Earth Observation in support of sustainable development

Earth Observation(EO)has been recognised as a key data source for supporting the United Nations Sustainable Development Goals(SDGs).Advances in data availability and analytical capabilities have provided a wide range of users access to global coverage analysis-ready data(ARD).However,ARD does not provide the information required by national agencies tasked with coordinating the implementation of SDGs.Reliable,standardised,scalable mapping of land cover and its change over time and space facilitates informed deci-sion making,providing cohesive methods for target setting and reporting of SDGs.The aim of this study was to implement a global framework for classifying land cover.The Food and Agriculture Organisation’s Land Cover Classification System(FAO LCCS)provides a global land cover taxonomy suitable to comprehensively support SDG target setting and reporting.We present a fully implemented FAO LCCS optimised for EO data;Living Earth,an open-source software package that can be readily applied using existing national EO infrastructure and satellite data.We resolve several semantic challenges of LCCS for consistent EO implementation,including modifications to environmental descriptors,inter-dependency within the mod-ular-hierarchical framework,and increased flexibility associated with limited data availability.To ensure easy adoption of Living Earth for SDG reporting,we identified key environmental descriptors to provide resource allocation recommendations for generating routinely retrieved input parameters.Living Earth provides an optimal platform for global adoption of EO4SDGs ensuring a transparent methodology that allows monitoring to be standardised for all countries.

Rapid,high-resolution detection of environmental change over continental scales from satellite data–the Earth Observation Data Cube

The effort and cost required to convert satellite Earth Observation(EO)data into meaningful geophysical variables has prevented the systematic analysis of all available observations.To overcome these problems,we utilise an integrated High Performance Computing and Data environment to rapidly process,restructure and analyse the Australian Landsat data archive.In this approach,the EO data are assigned to a common grid framework that spans the full geospatial and temporal extent of the observations–the EO Data Cube.This approach is pixel-based and incorporates geometric and spectral calibration and quality assurance of each Earth surface reflectance measurement.We demonstrate the utility of the approach with rapid time-series mapping of surface water across the entire Australian continent using 27 years of continuous,25 m resolution observations.Our preliminary analysis of the Landsat archive shows how the EO Data Cube can effectively liberate high-resolution EO data from their complex sensor-specific data structures and revolutionise our ability to measure environmental change.

Issues in the application of Digital Surface Model data to correct the terrain illumination effects in Landsat images

The accuracy of topographic correction of Landsat data based on a Digital Surface Model(DSM)depends on the quality,scale and spatial resolution of the DSM data used and the co-registration between the DSM and the satellite image.A physics-based bidirectional reflectance distribution function(BRDF)and atmospheric correction model in conjunction with a 1-second DSM was used to conduct the analysis in this paper.The results show that for the examples used from Australia,the 1-second DSM,can provide an effective product for this task.However,it was found that some remaining artefacts in the DSM data,originally due to radar shadow,can still cause significant local errors in the correction.Where they occur,false shadows and over-corrected surface reflectance factors can be observed.More generally,accurate co-registration between satellite images and DSM data was found to be critical for effective correction.Mis-registration by one or two pixels could lead to large errors of retrieved surface reflectance factors in gully and ridge areas.Using low-resolution DSM data in conjunction with high-resolution satellite images will also fail to correct significant terrain components where they occur at the finer scales of the satellite images.DSM resolution appropriate to the resolution of satellite image and the roughness of the terrain is needed for effective results,and the rougher the terrain,the more critical will be the accurate registration.