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  • 1.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Irrigation effects on hydro-climatic change: Basin-wise water balance-constrained quantification and cross-regional comparison2014In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 35, no 3, p. 879-895Article, review/survey (Refereed)
    Abstract [en]

    Hydro-climatic changes driven by human land and water use, including water use for irrigation, may be difficult to distinguish fromthe effects of global, natural and anthropogenic climate change. This paper quantifies and compares the hydro-climatic change effects ofirrigation using a data-driven, basin-wise quantification approach in two different irrigated world regions: the Aral Sea drainage basinin Central Asia, and the Indian Mahanadi River Basin draining into the Bay of Bengal. Results show that irrigation-driven changesin evapotranspiration and latent heat fluxes and associated temperature changes at the land surface may be greater in regions withsmall relative irrigation impacts on water availability in the landscape (here represented by the MRB) than in regions with severe suchimpacts (here represented by the Aral region). Different perspectives on the continental part of Earth’s hydrological cycle may thus implydifferent importance assessment of various drivers and impacts of hydro-climatic change. Regardless of perspective, however, actualbasin-wise water balance constraints should be accounted to realistically understand and accurately quantify continental water change.

  • 2.
    Baranov, Alexey
    et al.
    Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russian Federation; Institute of Earthquake Prediction Theory and Mathematical Geophysics, Russian Academy of Sciences, Moscow, Russian Federation.
    Tenzer, Robert
    Department of Land Surveying and Geo-Informatics, Hong Kong Polytechnic University, Kowloon, Hong Kong.
    Bagherbandi, Mohammad
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS. Division of Geodesy and Geoinformatics, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Combined Gravimetric–Seismic Crustal Model for Antarctica2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 1, p. 23-56Article in journal (Refereed)
    Abstract [en]

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz’s inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48–50 km) and the Kottas Mountains (48–50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34–38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24–28 km), while in West Antarctica the Moho depth minima are along the West Antarctic Rift System under the Bentley depression (20–22 km) and Ross Sea Ice Shelf (16–24 km). The gravimetric result confirmed a maximum extension of the Antarctic continental margins under the Ross Sea Embayment and the Weddell Sea Embayment with an extremely thin continental crust (10–20 km).

  • 3. Baranov, Alexey
    et al.
    Tenzer, Robert
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment. University of Gävle, Sweden.
    Combined Gravimetric-Seismic Crustal Model for Antarctica2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 1, p. 23-56Article, review/survey (Refereed)
    Abstract [en]

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24-28 km), while in West Antarctica the Moho depth minima are along the West Antarctic Rift System under the Bentley depression (20-22 km) and Ross Sea Ice Shelf (16-24 km). The gravimetric result confirmed a maximum extension of the Antarctic continental margins under the Ross Sea Embayment and the Weddell Sea Embayment with an extremely thin continental crust (10-20 km).

  • 4.
    Bring, Arvid
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arctic Climate and Water Change: Model and Observation Relevance for Assessment and Adaptation2014In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 35, no 3, p. 853-877Article, review/survey (Refereed)
    Abstract [en]

    The Arctic is subject to growing economic and political interest. Meanwhile, its climate and water systems are in rapid transformation. In this paper, we review and extend a set of studies on climate model results, hydro-climatic change, and hydrological monitoring systems. Results indicate that general circulation model (GCM) projections of drainage basin temperature and precipitation have improved between two model generations. However, some inaccuracies remain for precipitation projections. When considering geographical priorities for monitoring or adaptation efforts, our results indicate that future projections by GCMs and recent observations diverge regarding the basins where temperature and precipitation changes currently are the most pronounced and where they will be so in the future. Regarding late twentieth-century discharge changes in major Arctic rivers, data generally show excess of water relative to precipitation changes. This indicates a possible contribution to sea-level rise of river water that was previously stored in permafrost or groundwater. The river contribution to the increasing Arctic Ocean freshwater inflow is similar in magnitude to the separate contribution from glaciers, which underlines the importance of considering all possible sources of freshwater when assessing sea-level change. We further investigate monitoring systems and find a lack of harmonized water chemistry data, which limits the ability to understand the origin and transport of nutrients, carbon and sediment to the sea. To provide adequate information for research and policy, Arctic hydrological and hydrochemical monitoring needs to be extended, better integrated and made more accessible. Further water-focused data and modeling efforts are required to resolve the source of excess discharge in Arctic rivers. Finally, improvements in climate model parameterizations are needed, in particular for precipitation projections.

  • 5.
    Di Baldassarre, Giuliano
    et al.
    Department of Hydroinformatics and Knowledge Management, UNESCO-IHE, Delft, The Netherlands.
    Schumann, G
    Brandimarte, L
    Bates, P
    Timely Low Resolution SAR Imagery To Support Floodplain Modelling: a Case Study Review2011In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 32, no 3, p. 255-269Article in journal (Refereed)
  • 6.
    Kalscheuer, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhojuntti, Niklas
    Luossavaara Kiirunavaara AB, Kiruna, Sweden.
    Vaittinen, Katri
    Boliden Finnex Oy, Polvijarvi Explorat Off, Polvijarvi, Finland.
    Two-dimensional audiomagnetotelluric and magnetotelluric modelling of ore deposits: Improvements in model constraints by inclusion of borehole measurements2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 3, p. 467-507Article in journal (Refereed)
    Abstract [en]

    A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) an initial inversion model is computed from surface impedance measurements, (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of similar to 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and electric field sensors to be developed in a future project. Our results suggest that three-component SQUID and fluxgate magnetometers should be developed to facilitate borehole MT measurements at signal frequencies above and below 1 Hz, respectively.

  • 7.
    Leijon, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Danielsson, Oskar
    Gustafsson, Stefan
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Langhamer, Olivia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stålberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Energy from the North Sea: Experiences from the Lysekil Research Site2008In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed)
    Abstract [en]

    This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

  • 8.
    Radic, Valentina
    et al.
    Univ of British Columbia.
    Hock, Regine
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Glaciers in The Earth’s Hydrological Cycle: Assessments of Glacier Mass and Runoff Changes on Global and Regional Scales2014In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 35, no 3, p. 813-837Article in journal (Refereed)
    Abstract [en]

    Changes in mass contained by mountain glaciers and ice caps can modify theEarth’s hydrological cycle on multiple scales. On a global scale, the mass loss fromglaciers contributes to sea-level rise. On regional and local scales, glacier meltwater is animportant contributor to and modulator of river flow. In light of strongly acceleratedworldwide glacier retreat, the associated glacier mass losses raise concerns over the sus-tainability of water supplies in many parts of the world. Here, we review recent attempts toquantify glacier mass changes and their effect on river runoff on regional and global scales.We find that glacier runoff is defined ambiguously in the literature, hampering directcomparison of findings on the importance of glacier contribution to runoff. Despite con-sensus on the hydrological implications to be expected from projected future warming,there is a pressing need for quantifying the associated regional-scale changes in glacierrunoff and responses in different climate regimes.

  • 9.
    Rathnayake, Samurdhika
    et al.
    Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
    Tenzer, Robert
    Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Pitoňák, Martin
    New Technologies for the Information Society, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.
    Gravity Maps of the Lithospheric Structure Beneath the Indian Ocean2019In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 40, no 5, p. 1055-1093Article in journal (Refereed)
    Abstract [en]

    The lithospheric structure beneath the Indian Ocean is probably the most complicated, but at the same time, the least understood among world's oceans. Results of tomographic, geochemical, magnetic and other surveys provide the evidence of its complex geological history. Seismic surveys have been a primary source of information about the lithospheric structure beneath the Indian Ocean, but these experiments are mainly concentrated at locations of a high geophysical interest. Marine gravity data obtained from processing the satellite altimetry measurements, on the other hand, deliver a detailed image of the whole seafloor relief, advancing further the knowledge about its formation, tectonism and volcanism. In this study, we use gravitational, bathymetric, marine sediment and lithospheric density structure data to compile the Bouguer and mantle gravity maps. We then use both gravity maps to interpret the lithospheric structure beneath the Indian Ocean. The Bouguer gravity map reveals major tectonic and volcanic features that are spatially correlated with crustal thickness variations. The mantle gravity map exhibits mainly a thermal signature of the lithospheric mantle. Gravity lows in this gravity map mark distinctively active oceanic divergent tectonic margins along the Central, Southeast and Southwest Indian Ridges including also the Carlsberg Ridge. Gravity lows extend along the Red Sea-Gulf of Aden and East African Rift Systems, confirming a connection between mid-oceanic spreading ridges (in the Indian Ocean) and continental rift systems (in East Africa). The combined interpretation of the Bouguer and mantle gravity maps confirms a non-collisional origin of mountain ranges along continental rift systems in East Africa. The evidence of a southern extension of the East African Rift System and its link with the Southwest Indian Ridge in the mantle gravity map is absent. Similarly, the ongoing breakup of the composite Indo-Australian plate is not manifested. A missing thermal signature in the mantle gravity map at these two locations is explained by the fact that the southern Nubian-Somalian plate boundary (i.e., the Lwandle plate) and the Indo-Australian plate boundary (i.e., the Capricorn plate) are diffuse zones of convergence, characterized by low deformation and seismicity due to very slow rates of relative motions accommodated across these boundaries. The clear manifestation of the thermal signature of intraplate hot spots in the mantle gravity map is also absent. This finding agrees with the evidence from direct heat flow measurements that do not indicate the presence of a significant positive temperature anomaly compared to the oceanic lithosphere of a similar age. © 2019, Springer Nature B.V.

  • 10.
    Ren, Zhengyong
    et al.
    Cent S Univ, Key Lab Metallogen Predict Nonferrous Met & Geol, Minist Educ, Changsha 410083, Hunan, Peoples R China.;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China..
    Chen, Chaojian
    Cent S Univ, Key Lab Metallogen Predict Nonferrous Met & Geol, Minist Educ, Changsha 410083, Hunan, Peoples R China.;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China..
    Pan, Kejia
    Cent S Univ, Sch Math & Stat, Changsha 410083, Hunan, Peoples R China..
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Maurer, Hansruedi
    Swiss Fed Inst Technol, Inst Geophys, Dept Earth Sci, CH-8092 Zurich, Switzerland..
    Tang, Jingtian
    Cent S Univ, Key Lab Metallogen Predict Nonferrous Met & Geol, Minist Educ, Changsha 410083, Hunan, Peoples R China.;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China..
    Gravity Anomalies of Arbitrary 3D Polyhedral Bodies with Horizontal and Vertical Mass Contrasts2017In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 38, no 2, p. 479-502Article, review/survey (Refereed)
    Abstract [en]

    During the last 15 years, more attention has been paid to derive analytic formulae for the gravitational potential and field of polyhedral mass bodies with complicated polynomial density contrasts, because such formulae can be more suitable to approximate the true mass density variations of the earth (e.g., sedimentary basins and bedrock topography) than methods that use finer volume discretization and constant density contrasts. In this study, we derive analytic formulae for gravity anomalies of arbitrary polyhedral bodies with complicated polynomial density contrasts in 3D space. The anomalous mass density is allowed to vary in both horizontal and vertical directions in a polynomial form of , where m, n, t are nonnegative integers and a, b, c are coefficients of mass density. First, the singular volume integrals of the gravity anomalies are transformed to regular or weakly singular surface integrals over each polygon of the polyhedral body. Then, in terms of the derived singularity-free analytic formulae of these surface integrals, singularity-free analytic formulae for gravity anomalies of arbitrary polyhedral bodies with horizontal and vertical polynomial density contrasts are obtained. For an arbitrary polyhedron, we successfully derived analytic formulae of the gravity potential and the gravity field in the case of , , , and an analytic formula of the gravity potential in the case of . For a rectangular prism, we derive an analytic formula of the gravity potential for , and and closed forms of the gravity field are presented for , and . Besides generalizing previously published closed-form solutions for cases of constant and linear mass density contrasts to higher polynomial order, to our best knowledge, this is the first time that closed-form solutions are presented for the gravitational potential of a general polyhedral body with quadratic density contrast in all spatial directions and for the vertical gravitational field of a prismatic body with quartic density contrast along the vertical direction. To verify our new analytic formulae, a prismatic model with depth-dependent polynomial density contrast and a polyhedral body in the form of a triangular prism with constant contrast are tested. Excellent agreements between results of published analytic formulae and our results are achieved. Our new analytic formulae are useful tools to compute gravity anomalies of complicated mass density contrasts in the earth, when the observation sites are close to the surface or within mass bodies.

  • 11.
    Ren, Zhengyong
    et al.
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Peoples R China.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Uncertainty and Resolution Analysis of 2D and 3D Inversion Models Computed from Geophysical Electromagnetic Data2020In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 41, no 1, p. 47-112Article in journal (Refereed)
    Abstract [en]

    A meaningful solution to an inversion problem should be composed of the preferred inversion model and its uncertainty and resolution estimates. The model uncertainty estimate describes an equivalent model domain in which each model generates responses which fit the observed data to within a threshold value. The model resolution matrix measures to what extent the unknown true solution maps into the preferred solution. However, most current geophysical electromagnetic (also gravity, magnetic and seismic) inversion studies only offer the preferred inversion model and ignore model uncertainty and resolution estimates, which makes the reliability of the preferred inversion model questionable. This may be caused by the fact that the computation and analysis of an inversion model depend on multiple factors, such as the misfit or objective function, the accuracy of the forward solvers, data coverage and noise, values of trade-off parameters, the initial model, the reference model and the model constraints. Depending on the particular method selected, large computational costs ensue. In this review, we first try to cover linearised model analysis tools such as the sensitivity matrix, the model resolution matrix and the model covariance matrix also providing a partially nonlinear description of the equivalent model domain based on pseudo-hyperellipsoids. Linearised model analysis tools can offer quantitative measures. In particular, the model resolution and covariance matrices measure how far the preferred inversion model is from the true model and how uncertainty in the measurements maps into model uncertainty. We also cover nonlinear model analysis tools including changes to the preferred inversion model (nonlinear sensitivity tests), modifications of the data set (using bootstrap re-sampling and generalised cross-validation), modifications of data uncertainty, variations of model constraints (including changes to the trade-off parameter, reference model and matrix regularisation operator), the edgehog method, most-squares inversion and global searching algorithms. These nonlinear model analysis tools try to explore larger parts of the model domain than linearised model analysis and, hence, may assemble a more comprehensive equivalent model domain. Then, to overcome the bottleneck of computational cost in model analysis, we present several practical algorithms to accelerate the computation. Here, we emphasise linearised model analysis, as efficient computation of nonlinear model uncertainty and resolution estimates is mainly determined by fast forward and inversion solvers. In the last part of our review, we present applications of model analysis to models computed from individual and joint inversions of electromagnetic data; we also describe optimal survey design and inversion grid design as important applications of model analysis. The currently available model uncertainty and resolution analyses are mainly for 1D and 2D problems due to the limitations in computational cost. With significant enhancements of computing power, 3D model analyses are expected to be increasingly used and to help analyse and establish confidence in 3D inversion models.

  • 12.
    Ren, Zhengyong
    et al.
    Cent S Univ, Minist Educ, Key Lab Metallogen Predict Nonferrous Met & Geol, Changsha 410083, Hunan, Peoples R China;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Zhong, Yiyuan
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Chen, Chaojian
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Tang, Jingtian
    Cent S Univ, Minist Educ, Key Lab Metallogen Predict Nonferrous Met & Geol, Changsha 410083, Hunan, Peoples R China;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Maurer, Hansruedi
    Swiss Fed Inst Technol, Inst Geophys, Dept Earth Sci, CH-8092 Zurich, Switzerland.
    Li, Yang
    Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing 100029, Peoples R China.
    Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 5, p. 901-935Article, review/survey (Refereed)
    Abstract [en]

    During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets.

  • 13.
    Smirnov, Maxim
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Baba, Kiyoshi
    Earthquake Research Institute, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, Japan.
    Guest Editorial: Special Issue on “The 24th Electromagnetic Induction Workshop, Helsingor, Denmark”2020In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 41, no 1, p. 1-3Article in journal (Refereed)
  • 14. Tenzer, Robert
    et al.
    Chen, Wenjin
    Tsoulis, Dimitrios
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Novak, Pavel
    Jin, Shuanggen
    Analysis of the Refined CRUST1.0 Crustal Model and its Gravity Field2015In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 36, no 1, p. 139-165Article, review/survey (Refereed)
    Abstract [en]

    The global crustal model CRUST1.0 (refined using additional global datasets of the solid topography, polar ice sheets and geoid) is used in this study to estimate the average densities of major crustal structures. We further use this refined model to compile the gravity field quantities generated by the Earth's crustal structures and to investigate their spatial and spectral characteristics and their correlation with the crustal geometry in context of the gravimetric Moho determination. The analysis shows that the average crustal density is 2,830 kg/m(3), while it decreases to 2,490 kg/m(3) when including the seawater. The average density of the oceanic crust (without the seawater) is 2,860 kg/m(3), and the average continental crustal density (including the continental shelves) is 2,790 kg/m(3). The correlation analysis reveals that the gravity field corrected for major known anomalous crustal density structures has a maximum (absolute) correlation with the Moho geometry. The Moho signature in these gravity data is seen mainly at the long-to-medium wavelengths. At higher frequencies, the Moho signature is weakening due to a noise in gravity data, which is mainly attributed to crustal model uncertainties. The Moho determination thus requires a combination of gravity and seismic data. In global studies, gravimetric methods can help improving seismic results, because (1) large parts of the world are not yet sufficiently covered by seismic surveys and (2) global gravity models have a relatively high accuracy and resolution. In regional and local studies, the gravimetric Moho determination requires either a detailed crustal density model or seismic data (for a combined gravity and seismic data inversion). We also demonstrate that the Earth's long-wavelength gravity spectrum comprises not only the gravitational signal of deep mantle heterogeneities (including the core-mantle boundary zone), but also shallow crustal structures. Consequently, the application of spectral filtering in the gravimetric Moho determination will remove not only the gravitational signal of (unknown) mantle heterogeneities, but also the Moho signature at the long-wavelength gravity spectrum.

  • 15. Tenzer, Robert
    et al.
    Chen, Wenjin
    Tsoulis, Dimitrios
    Bagherbandi, Mohammad
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS. Royal Institute of Technology (KTH), Stockholm, Sweden .
    Sjöberg, Lars E.
    Novák, Pavel
    Jin, Shuanggen
    Analysis of the Refined CRUST1.0 Crustal Model and its Gravity Field2015In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 36, no 1, p. 139-165Article, review/survey (Refereed)
    Abstract [en]

    The global crustal model CRUST1.0 (refined using additional global datasets of the solid topography, polar ice sheets and geoid) is used in this study to estimate the average densities of major crustal structures. We further use this refined model to compile the gravity field quantities generated by the Earth's crustal structures and to investigate their spatial and spectral characteristics and their correlation with the crustal geometry in context of the gravimetric Moho determination. The analysis shows that the average crustal density is 2,830 kg/m3, while it decreases to 2,490 kg/m3 when including the seawater. The average density of the oceanic crust (without the seawater) is 2,860 kg/m3, and the average continental crustal density (including the continental shelves) is 2,790 kg/m3. The correlation analysis reveals that the gravity field corrected for major known anomalous crustal density structures has a maximum (absolute) correlation with the Moho geometry. The Moho signature in these gravity data is seen mainly at the long-to-medium wavelengths. At higher frequencies, the Moho signature is weakening due to a noise in gravity data, which is mainly attributed to crustal model uncertainties. The Moho determination thus requires a combination of gravity and seismic data. In global studies, gravimetric methods can help improving seismic results, because (1) large parts of the world are not yet sufficiently covered by seismic surveys and (2) global gravity models have a relatively high accuracy and resolution. In regional and local studies, the gravimetric Moho determination requires either a detailed crustal density model or seismic data (for a combined gravity and seismic data inversion). We also demonstrate that the Earth's long-wavelength gravity spectrum comprises not only the gravitational signal of deep mantle heterogeneities (including the core-mantle boundary zone), but also shallow crustal structures. Consequently, the application of spectral filtering in the gravimetric Moho determination will remove not only the gravitational signal of (unknown) mantle heterogeneities, but also the Moho signature at the long-wavelength gravity spectrum. 

  • 16.
    Tenzer, Robert
    et al.
    Hong Kong Polytech Univ, Dept Land Surveying & Geoinformat, Room ZS621,6-F,South Wing,Block Z,Phase 8, Kowloon, Hong Kong, Peoples R China..
    Foroughi, Ismael
    Univ New Brunswick, Dept Geodesy & Geomat, Fredericton, NB E3B 5A3, Canada..
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. University of Gävle, Sweden.
    Hirt, Christian
    Tech Univ Munich, Inst Astron & Phys Geodesy, D-80333 Munich, Germany.;Tech Univ Munich, Inst Adv Study, D-80333 Munich, Germany..
    Pitonak, Martin
    Univ West Bohemia, Fac Sci Appl, NTIS, Plzen 30100, Czech Republic..
    Definition of Physical Height Systems for Telluric Planets and Moons2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 3, p. 313-335Article, review/survey (Refereed)
    Abstract [en]

    In planetary sciences, the geodetic (geometric) heights defined with respect to the reference surface (the sphere or the ellipsoid) or with respect to the center of the planet/moon are typically used for mapping topographic surface, compilation of global topographic models, detailed mapping of potential landing sites, and other space science and engineering purposes. Nevertheless, certain applications, such as studies of gravity-driven mass movements, require the physical heights to be defined with respect to the equipotential surface. Taking the analogy with terrestrial height systems, the realization of height systems for telluric planets and moons could be done by means of defining the orthometric and geoidal heights. In this case, however, the definition of the orthometric heights in principle differs. Whereas the terrestrial geoid is described as an equipotential surface that best approximates the mean sea level, such a definition for planets/moons is irrelevant in the absence of (liquid) global oceans. A more natural choice for planets and moons is to adopt the geoidal equipotential surface that closely approximates the geometric reference surface (the sphere or the ellipsoid). In this study, we address these aspects by proposing a more accurate approach for defining the orthometric heights for telluric planets and moons from available topographic and gravity models, while adopting the average crustal density in the absence of reliable crustal density models. In particular, we discuss a proper treatment of topographic masses in the context of gravimetric geoid determination. In numerical studies, we investigate differences between the geodetic and orthometric heights, represented by the geoidal heights, on Mercury, Venus, Mars, and Moon. Our results reveal that these differences are significant. The geoidal heights on Mercury vary from - 132 to 166 m. On Venus, the geoidal heights are between - 51 and 137 m with maxima on this planet at Atla Regio and Beta Regio. The largest geoid undulations between - 747 and 1685 m were found on Mars, with the extreme positive geoidal heights under Olympus Mons in Tharsis region. Large variations in the geoidal geometry are also confirmed on the Moon, with the geoidal heights ranging from - 298 to 461 m. For comparison, the terrestrial geoid undulations are mostly within +/- 100 m. We also demonstrate that a commonly used method for computing the geoidal heights that disregards the differences between the gravity field outside and inside topographic masses yields relatively large errors. According to our estimates, these errors are - 0.3/+ 3.4 m for Mercury, 0.0/+ 13.3 m for Venus, - 1.4/+ 125.6 m for Mars, and - 5.6/+ 45.2 m for the Moon.

  • 17.
    Tenzer, Robert
    et al.
    The Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
    Foroughi, Ismael
    Department of Geodesy and Geomatics, University of New Brunswick, Canada.
    Sjöberg, Lars E.
    Division of Geodesy and Satellite Positioning, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Bagherbandi, Mohammad
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS. Division of Geodesy and Satellite Positioning, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Hirt, Christian
    Institute for Astronomical and Physical Geodesy and Institute for Advanced Study, Munich, Germany.
    Pitoňák, Martin
    New Technologies for the Information Society (NTIS), Faculty of Applied Sciences, University of West Bohemia, 301, Czech Republic.
    Definition of Physical Height Systems for Telluric Planets and Moons2018In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, no 3, p. 313-335Article, review/survey (Refereed)
    Abstract [en]

    In planetary sciences, the geodetic (geometric) heights defined with respect to the reference surface (the sphere or the ellipsoid) or with respect to the center of the planet/moon are typically used for mapping topographic surface, compilation of global topographic models, detailed mapping of potential landing sites, and other space science and engineering purposes. Nevertheless, certain applications, such as studies of gravity-driven mass movements, require the physical heights to be defined with respect to the equipotential surface. Taking the analogy with terrestrial height systems, the realization of height systems for telluric planets and moons could be done by means of defining the orthometric and geoidal heights. In this case, however, the definition of the orthometric heights in principle differs. Whereas the terrestrial geoid is described as an equipotential surface that best approximates the mean sea level, such a definition for planets/moons is irrelevant in the absence of (liquid) global oceans. A more natural choice for planets and moons is to adopt the geoidal equipotential surface that closely approximates the geometric reference surface (the sphere or the ellipsoid). In this study, we address these aspects by proposing a more accurate approach for defining the orthometric heights for telluric planets and moons from available topographic and gravity models, while adopting the average crustal density in the absence of reliable crustal density models. In particular, we discuss a proper treatment of topographic masses in the context of gravimetric geoid determination. In numerical studies, we investigate differences between the geodetic and orthometric heights, represented by the geoidal heights, on Mercury, Venus, Mars, and Moon. Our results reveal that these differences are significant. The geoidal heights on Mercury vary from − 132 to 166 m. On Venus, the geoidal heights are between − 51 and 137 m with maxima on this planet at Atla Regio and Beta Regio. The largest geoid undulations between − 747 and 1685 m were found on Mars, with the extreme positive geoidal heights under Olympus Mons in Tharsis region. Large variations in the geoidal geometry are also confirmed on the Moon, with the geoidal heights ranging from − 298 to 461 m. For comparison, the terrestrial geoid undulations are mostly within ± 100 m. We also demonstrate that a commonly used method for computing the geoidal heights that disregards the differences between the gravity field outside and inside topographic masses yields relatively large errors. According to our estimates, these errors are − 0.3/+ 3.4 m for Mercury, 0.0/+ 13.3 m for Venus, − 1.4/+ 125.6 m for Mars, and − 5.6/+ 45.2 m for the Moon.

1 - 17 of 17
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