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  • 51.
    Demšar, Urska
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    A strategy for observing soil moisture by remote sensing in the Murray-Darling basin2005In: Proceedings 2005: The 8th AGILE International Conference on Geographic Information Science, AGILE 2005, 2005Conference paper (Refereed)
    Abstract [en]

    The article presents a proposal for a strategy for integration of the data from the new environmental satellites, SMOS, HYDROS and ALOS in a system for monitoring soil moisture in the Murray-Darling basin in Australia. The proposal was developed as one of the results of the team project STREAM during the Summer Session Programme 2004 of the International Space University.

  • 52.
    Deng, Juan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Liu, Jinshuo
    Li, Li
    Niu, Xin
    Zou, Bin
    Hierarchical Segmentation of Multitemporal RADARSAT-2 SAR Data Using Stationary Wavelet Transform and Algebraic Multigrid Method2014In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 52, no 7, p. 4353-4363Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to develop a new effective method for hierarchical segmentation of multitemporal ultrafine-beam synthetic aperture radar (SAR) data in urban areas. Multitemporal RADARSAT-2 ultrafine-beam high-resolution horizontal transmit and horizontal receive-Synthetic Aperture Radar (HH-SAR) images acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008 are selected for this research. Stationary wavelet transform (SWT) and algebraic multigrid (AMG) method are proposed for segmentation of SAR data. SWT is applied for decomposition of multitemporal SAR images in image preprocessing. The hierarchical and matrix-based AMG method is applied for segmentation. A pyramid of fine-to-coarse grids is constructed by iteration of selecting representative pixels and calculating the interpolation matrix between a fine-level grid and a coarse-level grid. When the pyramid is completed, segments are determined by a top-down scanning based on the interpolation matrices. The AMG techniques provide a complete hierarchical segmentation of SAR data. The experimental results show that our method produces higher accuracy than eCognition.

  • 53.
    Dong, Fang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Moving Object Trajectory Based Spatio-Temporal Mobility Prediction.2012Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
  • 54.
    Ekström, Sofie
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Geografisk Tillgänglighet i Hälsovalet Gävleborg2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A method for redistricting in Health Choice Gävleborg are created and described in this thesis. Redistricting of areas in Health Choice should be objective and take into account the patient's best interest. This work aim to create alternative redistricting in the Health Choice Gävleborg and it also aims to explore the impact of different accessibility parameters. The results will then be used to compare with today's districts that are focused on the caregivers.

    Gävleborg is designated as the study area because they apply active revision of the districts as well as the uneven distribution of population in the cities and rural areas that can contribute to the redistricting becomes more complex.

    In this study, two different types of network analysis are applied, shortest path and route planning. The reference system used is SWEREF99. The municipal bus networks are integrated into the analysis in order to create areas from a patient perspective and emphasis is placed on walking distance and the availability of public transport. If residents of an area is not within walking distance to the health center but they are able to use public transportation they will be assigned to this health center instead. If bus transportation is also not possible to the residents they will be assigned to the clinic most accessible by car. Also travel time is a parameter included in this analysis as a criterion for a reasonable bus ride.

    A separate Python script designed to assign an area to a health center where walking distance, the distance to and from the bus and travel time by bus can be adapted to test the various parameters. In this thesis six alternative solutions to the redistricting in Health Choice Gävleborg are formed.

    Result is the new redistricting, transportation time and means of transportation. The method used in this work is designed to be applied to many different areas of society; an example can be school redistricting. With a possibility to change parameters in the analysis to obtain a custom classification based on individual restrictions can easily be customized to fulfill several functions.

  • 55.
    Ekström, Sofie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Isaksson, Camilla
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Dynamic Visualization of Spatio-Temporal Densities of Moving Objects: i2maps: integrated information maps2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    i2maps is an integrated information map and is designed as a web-based client-server structure that makes spatio-temporal data available on the Web in form of a map. The client-server structure consist of two components the HTML/JavaScript-component that manages the user interface and communication to the Python-component, which handles the data storage, access and processing. The developers of i2maps created i2maps as an open source software to make it flexible and usable for the public.

     

    To create an i2map several steps must be performed. First step is to create either a database where all spatio-temporal data is inserted or retrieve the data directly through a data crawler, i.e. live from the Web. Then, the code in both the Python and HTML/JavaScript component needs to be written, or if their example codes are reused, adjusted so that the data can be visualized (how much adjusting depends on the task and how well the code that is reused is compatible with the new application). If the code has been adapted the transformation and smoothening also must be changed to fit the area’s extent and the data preconditions, this is necessary to make it work.

     

    The purpose of this paper is to create an i2map to visualize the density in the Stockholm region over five days. In doing so, the flexibility and usefulness of i2maps is analysed. The result presented is primarily an i2map, which we created based on the data collected from GPS probes of taxis.

  • 56.
    Engstrand, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Railway surveying - A case study of the GRP 50002011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The GRP 5000 is a track measuring trolley capable of collecting track geometry data and performing clearance analyses based on laser scanning technology. The obtained laser data can also be used for as-built documentation, and the track recording functionality makes applications such as surveying, tamping assistance and slab track construction possible. The accuracy, huge data amount and time efficiency by which the system operates sets a new standard in railway surveying, and outdates traditional methods of manual and visual inspection. This thesis is a case study of the GRP 5000 with several objectives: a functional and technical description of the system is given; the accuracy of the system is evaluated, showing overall good values except for one of the sensors used; comparisons are made to other railway surveying techniques, such as track recording vehicles, manual devices and other track recording trolleys; possible improvements are pointed out, both based on comparison results as well as testing results. Finally, new and innovative ways of using the trolley, such as offtrack usage, as well as for the obtained laser data, such as GIS, maintenance aspects and CFD aspects, are examined.

  • 57.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    A strategy towards an EGM08-based Fennoscandian geoid model2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 87, p. 53-59Article in journal (Refereed)
    Abstract [en]

    Today, the recent global Earth's gravity model, EGM08, is successfully utilised for different purposes in geosciences. Here, EGM08 is used to compute a geoid model for Fennoscandia and since it is restricted to degree and order 2160, the higher frequencies of the geoid, or the truncation bias, is recovered directly from terrestrial gravity anomalies using a simple formula. The total topographic and atmospheric effects are computed and added to the derived geoid as well. A very simple EGM08-based non-integral geoid estimator is developed and applied for computing the geoid of Fennoscandia. The outcome of the estimator is compared with the Global Positioning System (GPS)/levelling data of Sweden, Denmark, Finland and Norway. Numerical results show the successful performance of the presented estimator as the geoid become closer to GPS/levelling data than the one computed solely with EGM08. This study will show that considering the truncation bias of EGM08 will reduce the root mean square error (RMSE) of the differences between the geoid and GPS/levelling data by about 1.3 cm and the additive topographic and atmospheric corrections by 1 cm further. It is shown that the correlations among the data have no significant influence on the estimated geoid.

  • 58.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics. Department of Engineering Science, University West, Trollhättan, Sweden .
    An integral approach to regional gravity field refinement using earth gravity models2013In: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, Vol. 68, p. 18-28Article in journal (Refereed)
    Abstract [en]

    The idea of this paper is to refine the terrestrial gravimetric data with the Earth's gravity models (EGMs) and produce a high quality source of gravity data. For this purpose, biased and unbiased integral estimators are presented. These estimators are used to refine gravimetric data over Fennoscandia with the ITG-GRACE2010s and GO_CONS_GCF_2_DIR_R2 EGMs, which are the recent products of the gravity field and climate experiment (GRACE) and the gravity field and steady-state ocean circulation explorer (GOCE) satellite missions. Numerical results show that the biased integral estimator has smaller global root mean square error (RMSE) than the unbiased one. Also a simple strategy is presented to down-weight the low-frequencies the terrestrial data in spectral combination. The gravity anomalies, computed by EGM08, are compared to the refined anomalies for evaluation purpose. In the case of using a cap size of 1 degrees for integration the EGM08 gravity anomalies are more correlated with the refined ones. Also the band-limited kernels can simply be generated to maximum degree of the used EGMs for both estimators. Comparisons of the combined anomalies and those of EGM08 show insignificant differences between the biased and unbiased estimators in practice. However, the biased estimator seems to be proper one for gravity data refinement due to its smaller global RMSE.

  • 59.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Bi-Objective models of Geodetic Network Optimization2006Conference paper (Refereed)
  • 60.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Generalized Least Squares Adjustment of Gauss-Helmert Model2005Conference paper (Refereed)
  • 61.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Inversion of satellite gradiometry data using statistically modified integral formulas for local gravity field recovery2011In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 47, no 1, p. 74-85Article in journal (Refereed)
    Abstract [en]

    The satellite gravity gradiometric data can be used directly to recover the gravity anomaly at sea level using inversion of integral formulas. This approach suffers by the spatial truncation errors of the integrals, but these errors can be reduced by modifying the formulas. It allows us to consider smaller coverage of the satellite data over the region of recovery. In this study, we consider the second-order radial derivative (SORD) of disturbing potential (T-rr) and determine the gravity anomaly with a resolution of 1 degrees x 1 degrees at sea level by inverting the statistically modified version of SORD of extended Stokes' formula. Also we investigate the effect of the spatial truncation error on the quality of inversion considering noise of T-rr. The numerical investigations show satisfactory results when the area of T-rr coverage is the same with that of the gravity anomaly and the integral formula is modified by the biased least-squares modification. The error of recovery will be about 6 mGal after removing the regularization bias in the presence of 1 mE noise in T-rr measured on the orbit. (c) 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

  • 62.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Least-Squares Modification of Stokes' Formula with EGM082009In: Geodesy and Cartography, ISSN 1648-3502, Vol. 35, no 4, p. 111-117Article in journal (Refereed)
    Abstract [en]

    Least-squares modification is an optimal method of modifying Stokes' formula. This method can be categorized as a generalization of the spectral combination methods as it considers the truncation error of the integral formulas in its combination process. In short, this method involves the modification parameters based on minimizing the error of terrestrial gravimetric data, satellite data and the truncation error of the integral. In this respect, the choice of the geopotential model definitely plays an important role. This paper uses the recent combined geopotential model EGM08 for generating the spectra of gravity anomaly and its error. Numerical results show that EGM08 improves least-squares modification by about 10 cm comparing to the traditional way.

  • 63.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Long Wavelength Geoid Determination of Iran2006Conference paper (Refereed)
  • 64.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Multi-Objective Models of Geodetic Network Optimization2006Conference paper (Refereed)
  • 65.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Numerical aspects of EGM08-based geoid computations in Fennoscandia regarding the applied reference surface and error propagation2013In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 96, p. 28-32Article in journal (Refereed)
    Abstract [en]

    So far the recent Earth's gravity model, EGM08, has been successfully applied for different geophysical and geodetic purposes. In this paper, we show that the computation of geoid and gravity anomaly on the reference ellipsoid is of essential importance but error propagation of EGM08 on this surface is not successful due to downward continuation of the errors. Also we illustrate that some artefacts appear in the computed geoid and gravity anomaly to lower degree and order than 2190. This means that the role of higher degree harmonics than 2160 is to remove these artefacts from the results. Consequently, EGM08 must be always used to degree and order 2190 to avoid the numerical problems.

  • 66.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    On BQUE and BQUNE of variance-covariance components2005In: Proceedings of the Geomatics 84 Conference, National Cartographic Center, Tehran, Iran, Iranian National Cartographic Center, 2005Conference paper (Refereed)
  • 67.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    ON THE ESTIMATION OF VARIANCE IN UNSTABLE CONDITION ADJUSTMENT MODELS2011In: ACTA GEOD GEOPHYS HUNG, ISSN 1217-8977, Vol. 46, no 1, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Estimation of variance in an ordinary adjustment model is straightforward, but if the model becomes unstable or ill-conditioned its solution and the variance of the solution will be very sensitive to the errors of observations. This sensitivity can be controlled by stabilizing methods but the results will be distorted due to stabilization. In this paper, stabilizing an unstable condition model using Tikhonov regularization, the estimations of variance of unit weight and variance components are investigated. It will be theoretically proved that the estimator of variance or variance components has not the minimum variance property when the model is stabilized, but unbiased estimation of variance is possible. A simple numerical example is provided to show the performance of the theory.

  • 68.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    On the reliability and error calibration of some recent Earth's gravity models of GOCE with respect to EGM082013In: ACTA GEOD GEOPHYS, ISSN 2213-5812, Vol. 48, no 2, p. 199-208Article in journal (Refereed)
    Abstract [en]

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission is dedicated to recover spherical harmonic coefficients of the Earth's gravity field to degree and order of about 250 using its satellite gradiometric data. Since these data are contaminated with coloured noise, therefore, their inversion will not be straightforward. Unsuccessful modelling of this noise will lead to biases in the harmonic coefficients presented in the Earth's gravity models (EGMs). In this study, five of the recent EGMs of GOCE such as two direct, two time-wise and one space-wise solution are used to degree and order 240 and their reliability is investigated with respect to EGM08 which is assumed as a reliable EGM. The detected unreliable coefficients and their errors are replaced by the corresponding ones from EGM08 as a combination strategy. A condition adjustment model is organised for each two corresponding coefficients of GOCE EGMs and EGM08; and errors of the GOCE EGMs are calibrated based on a scaling factor, obtained from a posteriori variance factor. When the factor is less than 2.5 it will be multiplied to the error otherwise the error of EGM08 coefficient will be considered as the calibrated one. At the end, a simple geoid estimator is presented which considers the EGMs and their errors and its outcomes are compared with the corresponding geoid heights derived from the Global Positioning System (GPS) and the levelling data (GPS/levelling data), over Fennoscandia. This comparison shows that some of the combined-calibrated GOCE EGMs are closer to the GPS/levelling data than the original ones.

  • 69.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Orbit integration in non-inertial frame2009In: Journal of the Earth and Space Physics, ISSN 0378-1046, Vol. 35, no 1, p. 1-8Article in journal (Refereed)
  • 70.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Robust maximum Likelihood Estimation of Huber in geodetic Networks2006Conference paper (Refereed)
  • 71.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Scalar Risk functions as Criteria for datum Definition of Geodetic Networks2006Conference paper (Refereed)
  • 72.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Semi-stochastic modification of second-order radial derivative of Abel-Poisson's formula for validating satellite gravity gradiometry data2011In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 47, no 4, p. 757-767Article in journal (Refereed)
    Abstract [en]

    The geoid can be used to validate the satellite gravity gradiometry data. Validation of such data is important prior to their downward continuation because of amplification of the data errors through this process. In this paper, the second-order radial derivative of Abel-Poisson's formula is modified stochastically to reduce the effect of the far-zone geoid and generate the second-order radial derivative of geopotential at 250 km level. The numerical studies over Fennoscandia show that this method yields the gradients with an error of 10 mE and when the long wavelength of geoid is removed from the estimator and restored after the computations (remove compute restore) the error will be in 1 mE level. We name this method semi-stochastic modification. The best case scenario is found when the degree of modification of the integral formula is 200 and the long wavelength geoid to degree 100 is removed and restored. In this case the geoid should have a resolution of 15' x 15' and the integration should be performed over a cap size of 3 degrees.

  • 73.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Sequential Tikhonov Regularization: an alternative way for inverting satellite gradiometric data2011In: Zfv, ISSN 1618-8950, Vol. 136, no 2, p. 113-121Article in journal (Refereed)
    Abstract [en]

    Numerous regularization methods exist for solving the ill-posed problem of downward continuation of satellite gravity gradiometry (SGG) data to gravity anomaly at sea level. Generally, the use of a dense set of data is recommended in the downward continuation. However, when such dense data are used some of the regularization methods are not efficient and applicable. In this paper, a sequential way of using the Tikhonov regularization is developed for solving large systems and compared to methods of direct truncated singular value decomposition and iterative methods of range restricted minimum residual, algebraic reconstruction technique,  and conjugate gradient for recovering gravity anomaly at sea level from the SGG data. Numerical studies show that the sequential Tikhonov regularization is comparable to the conjugate gradient and yields similar result.

     

  • 74.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Single-Objective Models of Geodetic Network Optimization2006Conference paper (Refereed)
  • 75.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Spatially Restricted Integrals in Gradiometric Boundary Value Problems2010In: Artificial Satellites, ISSN 2083-6104, Vol. 44, no 4, p. 131-148Article in journal (Refereed)
    Abstract [en]

    The spherical Slepian functions can be used to localize the solutions of the gradiometric boundary value problems on a sphere. These functions involve spatially restricted integral products of scalar, vector and tensor spherical harmonics. This paper formulates these integrals in terms of combinations of the Gaunt coefficients and integrals of associated Legendre functions. The presented formulas for these integrals are useful in recovering the Earth's gravity field locally from the satellite gravity gradiometry data.

  • 76.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Spectral Combination of Spherical Gradiometric Boundary-Value Problems: A Theoretical Study2012In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 169, no 12, p. 2201-2215Article in journal (Refereed)
    Abstract [en]

    The Earth's gravity potential can be determined from its second-order partial derivatives using the spherical gradiometric boundary-value problems which have three integral solutions. The problem of merging these solutions by spectral combination is the main subject of this paper. Integral estimators of biased- and unbiased-types are presented for recovering the disturbing gravity potential from gravity gradients. It is shown that only kernels of the biased-type integral estimators are suitable for simultaneous downward continuation and combination of gravity gradients. Numerical results show insignificant practical difference between the biased and unbiased estimators at sea level and the contribution of far-zone gravity gradients remains significant for integration. These contributions depend on the noise level of the gravity gradients at higher levels than sea. In the cases of combining the gravity gradients, contaminated with Gaussian noise, at sea and 250 km levels the errors of the estimated geoid heights are about 10 and 3 times smaller than those obtained by each integral.

  • 77.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Spectral combination of vector gravimetric boundary value problems2011In: Engineering Journal of Geospatial Information system, Vol. 1, no 3, p. 23-50Article in journal (Refereed)
    Abstract [en]

    f there are more than a unique type of boundary value problem, so there may not be just one solution for problem. The vector gravimetric boundary value problem is one of the types of such problems which include two integral solutions. In this paper, this problem is solved in spectral domain, and then the solutions will be converted to integrals in spatial domain. The kernels of these integrals are divergent but by using spectral combination they become convergent and even they will have the downward continuation property. To do so, different stochastic estimators for recovering the disturbing potential at sea level are presented, and for each one of them the spectral coefficients are derived. Numerical computations show that the convergent kernels have the property of modifying the integral formulas in addition to the downward continuation and Wiener filtering, so that the kernels are well-behaved and reduce the contributions of far-zone data easily. The method presented in this paper can be applied for combination of satellite or air-borne vector gravimetric data.

  • 78.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Spherical harmonics expansion of the atmospheric gravitational potential based on exponential and power models of atmosphere2008In: Artificial Satellites, ISSN 0208-841X, Vol. 43, no 1, p. 26-43Article in journal (Refereed)
  • 79.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    The effect of spatial truncation error on integral inversion of satellite gravity gradiometry data2011In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 47, no 7, p. 1238-1247Article in journal (Refereed)
    Abstract [en]

    The satellite gravity gradiometry (SGG) data can be used for local modelling of the Earth's gravity field. In this study, the SGG data in the local north-oriented and orbital frames are inverted to the gravity anomaly at sea level using the second-order partial derivatives of the extended Stokes formula. The emphasis is on the spatial truncation error and the kernel behaviour of the integral formulas in the aforementioned frames. The paper will show that only the diagonal elements of gravitational tensor at satellite level are suitable for recovering the gravity anomaly at sea level. Numerical studies show that the gravity anomaly can be recovered in Fennoscandia with an accuracy of about 6 mGal directly from on-orbit SGG data.

  • 80.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Towards Validation of Satellite Gradiometric Data Using Modified Version of 2nd Order Partial Derivatives of Extended Stokes' Formula2010In: Artificial Satellites, ISSN 2083-6104, Vol. 44, no 4, p. 103-129Article in journal (Refereed)
    Abstract [en]

    The satellite gradiometric data should be validated prior to being used. One way of such a validation process is to use some integral estimators which are the second-order partial derivatives of the extended Stokes formula to regenerate the data from the gravity anomaly at the topographic surface. In this paper, we present how least-squares modification methods are used to modify such integral estimators. Our concentration will be on validation of the vertical-horizontal and horizontal-horizontal elements of the gravitational tensor at satellite level. The paper will formulate the elements of the system of equations from which the modification parameters are derived based on all types of least-squares modification. The truncation and Paul's coefficients will also be modelled.

  • 81.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Abdollahzadeh, Makan
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Software for generating gravity gradients using a geopotential model based on an irregular semivectorization algorithm2012In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 39, p. 152-160Article in journal (Refereed)
    Abstract [en]

    The spherical harmonic synthesis of second-order derivatives of geopotential is a task of major concern when the spatial resolution of synthesis is high and/or a high-resolution Earth's gravity model is used. Here, a computational technique is presented for such a process. The irregular semivectorization is introduced as a vectorization technique in which one loop is excluded from matrix-vector products of mathematical models in order to speed up the computation and manage the computer memory. The proposed technique has the capability of considering heights of computation points on a regular grid. MATLAB-based software is developed, which can be used for generating gravity gradients on an ordinary personal computer. The numerical results show that irregular semivectorization significantly reduces the computation time to 1 h for synthesis of these data with global coverage and resolution of 5′×5′ on an elevation model. In addition, a numerical example is presented for testing satellite gravity gradiometry data of the recent European Space Agency satellite mission, the gravity field and steady-state ocean circulation explorer (GOCE), using an Earth's gravity model.

  • 82.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Abdollahzadeh, Makan
    Geodesy, KNToosi University of Technology.
    Najai-Alamdari, Mehdi
    Geodesy, KNToosi University of Technology.
    Simplification of geopotential perturbing force acting on a satellite2008In: Artificial Satellites, ISSN 0208-841X, Vol. 43, no 2, p. 45-64Article in journal (Refereed)
  • 83.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Alishahi, Reza
    Islamic Azad University.
    Investigation of Behavior of Net points during variance components estimation process2005Conference paper (Refereed)
  • 84.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Quality Description For Gravimetric And Seismic Moho Models Of Fennoscandia Through A Combined Adjustment2012In: Acta Geodaetica et Geophysica Hungarica, ISSN 1217-8977, E-ISSN 1587-1037, Vol. 47, no 4, p. 388-401Article in journal (Refereed)
    Abstract [en]

    The gravimetric model of the Moho discontinuity is usually derived based on isostatic adjustment theories considering floating crust on the viscous mantle. In computation of such a model some a priori information about the density contrast between the crust and mantle and the mean Moho depth are required. Due to our poor knowledge about them they are assumed unrealistically constant. In this paper, our idea is to improve a computed gravimetric Moho model, by the Vening Meinesz-Moritz theory, using the seismic model in Fennoscandia and estimate the error of each model through a combined adjustment with variance component estimation process. Corrective surfaces of bi-linear, bi-quadratic, bi-cubic and multi-quadric radial based function are used to model the discrepancies between the models and estimating the errors of the models. Numerical studies show that in the case of using the bi-linear surface negative variance components were come out, the bi-quadratic can model the difference better and delivers errors of 2.7 km and 1.5 km for the gravimetric and seismic models, respectively. These errors are 2.1 km and 1.6 km in the case of using the bi-cubic surface and 1 km and 1.5 km when the multi-quadric radial base function is used. The combined gravimetric models will be computed based on the estimated errors and each corrective surface.

  • 85. Eshagh, Mehdi
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Smoothing impact of isostatic crustal thickness models on local integral inversion of satellite gravity gradiometry data2011In: ACTA GEOPHYSICA, ISSN 1895-6572, Vol. 59, no 5, p. 891-906Article in journal (Refereed)
    Abstract [en]

    The effects of topographic masses on satellite gradiometric data are large and in order to reduce the magnitude of these effects some compensation mechanisms should be considered. Here we use the isostatic hypotheses of Airy-Heiskanen and the recent Vening Meinesz-Moritz for compensating these effects and to smooth the data prior to their downward continuation to gravity anomaly. The second-order partial derivatives of extended Stokes' formula are used for the continuations over a topographically rough territory like Persia. The inversions are performed and compared based on two schemes of the remove-compute-restore technique and direct downward continuation. Numerical results show that the topographic-isostatic effect based on Vening Meinesz-Mortiz's hypothesis smoothes the data better than that based on Airy-Heiskanen's hypothesis. Also the quality of inversions of the smoothed data by this mechanism is twice better than that of the nonsmoothed ones.

  • 86.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    A COMBINED GLOBAL MOHO MODEL BASED ON SEISMIC AND GRAVIMETRIC DATA2011In: ACTA GEOD GEOPHYS HUNG, ISSN 1217-8977, Vol. 46, no 1, p. 25-38Article in journal (Refereed)
    Abstract [en]

    The Moho depth can be determined using seismic and/or gravimetric methods. These methods will not yield the same result as they are based on different hypotheses as well as different types, qualities and distributions of data. Here we present a new global model for the Moho computed based on a stochastic combination of seismic and gravimetric Moho models. This method employs condition equations in the spectral domain for the seismic and gravimetric models as well as degree-order variance component estimation to optimally weight the corresponding harmonics in the combination. The preliminary data for the modelling are the seismic model CRUST2.0 and a new gravimetric Moho model based on the inverse solution of the Vening Meinez-Moritz isostatic hypothesis and the global Earth Gravitational Model EGM08. Numerical results show that this method of stochastic combination agrees better with the seismic Moho model (3.6 km rms difference) than the gravimetric one. The model should be a candidate for dandifying the frequently sparsely data CRUST2.0. We expect that this way of combining seismic and gravimetric data would be even more fruitful in a regional study.

  • 87.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ghorbannia, Morteza
    The use of Gaussian equations of motions of a satellite for local gravity anomaly recovery2013In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 52, no 1, p. 30-38Article in journal (Refereed)
    Abstract [en]

    The orbital elements of a low Earth orbiting satellite and their velocities can be used for local determination of gravity anomaly. The important issue is to find direct relations among the anomalies and these parameters. Here, a primary theoretical study is presented for this purpose. The Gaussian equations of motion of a satellite are used to develop integral formulas for recovering the gravity anomalies. The behaviour of kernels of the integrals are investigated for a two-month simulated orbit similar to that of the Gravity field and steady-state ocean circulation explorer (GOCE) mission over Fennoscandia. Numerical investigations show that the integral formulas have neither isotropic nor well-behaved kernels. In such a case, gravity anomaly recovery is not successful due to large spatial truncation error of the integral formulas. Reformulation of the problem by combining the orbital elements and their velocities leads to an integral with a well-behaved kernel which is suitable for our purpose. Also based on these combinations some general relations among the orbital elements and their velocities are obtained which can be used for validation of orbital parameters and their velocities. (C) 2013 COSPAR.

  • 88.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Lemoine, Jean-Michel
    Gegout, Pascal
    Biancale, Richard
    On regularized time varying gravity field models based on grace data and their comparison with hydrological models2013In: Acta Geophysica, ISSN 1895-6572, Vol. 61, no 1, p. 1-17Article in journal (Refereed)
    Abstract [en]

    Determination of spherical harmonic coefficients of the Earth's gravity field is often an ill-posed problem and leads to solving an ill-conditioned system of equations. Inversion of such a system is critical, as small errors of data will yield large variations in the result. Regularization is a method to solve such an unstable system of equations. In this study, direct methods of Tikhonov, truncated and damped singular value decomposition and iterative methods of nu, algebraic reconstruction technique, range restricted generalized minimum residual and conjugate gradient are used to solve the normal equations constructed based on range rate data of the gravity field and climate experiment (GRACE) for specific periods. Numerical studies show that the Tikhonov regularization and damped singular value decomposition methods for which the regularization parameter is estimated using quasioptimal criterion deliver the smoothest solutions. Each regularized solution is compared to the global land data assimilation system (GLDAS) hydrological model. The Tikhonov regularization with L-curve delivers a solution with high correlation with this model and a relatively small standard deviation over oceans. Among iterative methods, conjugate gradient is the most suited one for the same reasons and it has the shortest computation time.

  • 89.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Najafi-Alamdari, Mehdi
    Investigation of Orbital Perturbations of a Low Earth Orbiting (LEO) Satellite2005Conference paper (Refereed)
  • 90.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Najafi-Alamdari, Mehdi
    KNToosi University of Technology.
    Numerical Orbit Integration of a Low earth Orbiting satellite2005Conference paper (Other academic)
  • 91.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Najafi-Alamdari, Mehdi
    KNToosi University of Technology.
    Farnin, Ahmed
    Islamic Azad University.
    Investigation of long wavelength EIGEN spheroids of Iran2006Conference paper (Refereed)
  • 92.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Romeshkani, Mohsen
    Department of Geodesy, KNToosi Uni. Tech..
    Generation of vertical–horizontal and horizontal–horizontal gravity gradients using stochastically modified integral estimators2011In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 48, no 8, p. 1341-1358Article in journal (Refereed)
    Abstract [en]

    The Earth’s gravity field modelling is an ill-posed problem having a sensitive solution to the error of data. Satellite gravity gradiometry (SGG) is a space technique to measure the second-order derivatives of geopotential for modelling this field, but the measurements should be validated prior to use. The existing terrestrial gravity anomalies and Earth gravity models can be used for this purpose. In this paper, the second-order vertical–horizontal (VH) and horizontal–horizontal (HH) derivatives of the extended Stokes formula in the local north-oriented frame are modified using biased, unbiased and optimum types of least-squares modification. These modified integral estimators are used to generate the VH and HH gradients at 250 km level for validation purpose of the SGG data. It is shown that, unlike the integral estimator for generating the second-order radial derivative of geopotential, the system of equations from which the modification parameters are obtained is unstable for all types of modification, with large cap size and high degree, and regularization is strongly required for solving the system. Numerical studies in Fennoscandia show that the SGG data can be estimated with an accuracy of 1 mE using an integral estimator modified by a biased type least-squares modification. In this case an integration cap size of 2.5° and a degree of modification of 100 for integrating 30′ × 30′ gravity anomalies are required.

  • 93.
    Eshagh, Mehdi
    et al.
    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.
    Satellite Gravity Gradiometry: An approch to high resolution gravity field modelling from space2009Book (Other academic)
  • 94.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Determination of gravity anomaly at sea level from inversion of satellite gravity gradiometric data2011In: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, Vol. 51, no 5, p. 366-377Article in journal (Refereed)
    Abstract [en]

    Gravity gradients can be used to determine the local gravity field of the Earth. This paper investigates downward continuation of all elements of the disturbing gravitational tensor at satellite level using the second-order partial derivatives of the extended Stokes formula in the local-north oriented frame to determine the gravity anomaly at sea level. It considers the inversion of each gradient separately as well as their joint inversion. Numerical studies show that the gradients T-zz, T-xx, T-yy and T-xz have similar capability of being continued downward to sea level in the presence of white noise, while the gradient T-yz is considerably worse than the others. The bias-corrected joint inversion process shows the possibility of recovering the gravity anomaly with 1 mGal accuracy. Variance component estimation is also tested to update the observation weights in the joint inversion.

  • 95.
    Fan, Hongchao
    et al.
    Department of Cartography, Technical University of Munich.
    Mao, Bo
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Meng, Liqiu
    Department of Cartography, Technical University of Munich.
    An automatic approach for the typification of façade structuresIn: ISPRS journal of photogrammetry and remote sensing (Print), ISSN 0924-2716, E-ISSN 1872-8235Article in journal (Other academic)
    Abstract [en]

    Typification is a well-established operator of map generalization. Although it is widely used in many existing research fields, less discussion has been devoted to the quality of typification. This paper presents a user survey for the evaluation of different typification results of façade structures under different constraints. The survey shows that preservation of the shape of the features is the most important constraint for a reasonable typification process, which has also been quantitatively verified by calculating the similarities between the typified façades and the original façade using attributed relational graph (ARG) and nested earth mover’s distance (NEMD) algorithms. Based on that, an algorithm is developed to generate perceivably reasonable representation from the original facade with decreasing map scale. The algorithm is implemented and tested on a number of façades. Experiments reveal that the typification can be automatically conducted and can create results which are well associated with the original façades.

  • 96.
    Fan, Hongchao
    et al.
    Department of Cartography, Technical University of Munich.
    Mao, Bo
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Shen, Jie
    Nanjing Normal University.
    Meng, Liqiu
    Department of Cartography, Technical University of Munich.
    Shell model representation as a substitute of LOD3 for 3D modeling in CityGML2011In: Geo-spatial Information Science, ISSN 1009-5020, Vol. 14, no 2, p. 78-84Article in journal (Refereed)
    Abstract [en]

    The OGC standard for 3D city modeling is widely used in an increasing number of applications. It defines five consecutive Levels of Detail (LoD0 to LoD4 with increasing accuracy and structural complexity), in which LoD3 includes all exterior appearances and geometrical details and subsequently requires much storage space. A new LoD is introduced as shell model with the exterior shell of the LoD3 model and the opening objects like windows, doors as well as smaller façade objects are projected onto walls. In this paper, a user survey is presented. The results of this survey show that the shell model can give users almost the same visual impression as the LoD3 model. Furthermroe, algorithms are developed to extract the shell model from LoD3 model. Experiments show that this shell model can reduce up to 90% storage of the original LoD3 model. Therefore, on one hand it can be used as a substitute for a LoD3 model for the visualization on small displays. On the other hand, it can be treated as a sub-level of detail (SLoD3) in CityGML, since it retains almost the same amount of information but requires much less storage space.

  • 97.
    Fombuena Valero, Arnau
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    3D Augmented Reality Mobile Application Prototype for Visual Planning Support2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to implement a prototype of a 3D Augmented Reality mobile application.

    Using 3D is becoming more and more common for professionals as well as users. A good example of that is Google Earth and its 3D view. Implementing a mobile application that takes advantage of 3D and Augmented Reality may be very useful for planning new constructions in both urban and non-urban areas allowing to visualize how the construction will be in the future and how it will interact with its surrounding environment. There is a great potential for such kind of applications. An example could be the modification of a certain area of a city; allowing the inhabitants of that city to preview the project and, hopefully, avoiding unnecessary conflicts related to that project. In non-urban areas this application is also very useful for helping decision making by visualizing, on site, how the project will be and its impact on the environment.

    In order to preview a future construction there is the need to have a 3D model. Therefore, a 3D format for that model is necessary. Since COLLADA is a 3D standard interexchange format it is used in this thesis. Together with COLLADA, the computer graphics imagery and gaming technology called OpenGL ES 2.0 is used. Using COLLADA and OpenGL ES 2.0 combined with the properties of the views’ layers, the camera input, the sensors in the mobile device and the positioning technologies permit obtaining successful results displaying a 3D object in an Augmented Reality mobile prototype application. Interface elements are implemented as well in order to bring basic usability tools. The results show the advantages of combining technologies in a mobile device and the problems derived from the low accuracy in positioning in such kind of devices. Thus, ideas for improving the positioning accuracy are discussed as well. 

  • 98.
    Fröjse, Linda
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Multitemporal Satellite Images for Urban Change Detection2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The objective of this research is to detect change in urban areas using two satellite images (from 2001 and 2010) covering the city of Shanghai, China. These satellite images were acquired by Landsat-7 and HJ-1B, two satellites with different sensors. Two change detection algorithms were tested: image differencing and post-classification comparison. For image differencing the difference image was classified using unsupervised k-means classification, the classes were then aggregated into change and no change by visual inspection. For post-classification comparison the images were classified using supervised maximum likelihood classification and then the difference image of the two classifications were classified into change and no change also by visual inspection. Image differencing produced result with poor overall accuracy (band 2: 24.07%, band 3: 25.96%, band 4: 46.93%), while post-classification comparison produced result with better overall accuracy (90.96%). Post-classification comparison works well with images from different sensors, but it relies heavily on the accuracy of the classification. The major downside of the methodology of both algorithms was the large amount of visual inspection.

  • 99.
    Fröjse, Linda
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Unsupervised Change Detection Using Multi-Temporal SAR Data: A Case Study of Arctic Sea Ice2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The extent of Arctic sea ice has decreased over the years and the importance of sea ice monitoring is expected to increase. Remote sensing change detection compares images acquired over the same geographic area at different times in order to identify changes that might have occurred in the area of interest. Change detection methods have been developed for cryospheric topics. The Kittler-Illingworth thresholding algorithm has proven to be an effective change detection tool, but has not been used for sea ice. Here it is applied to Arctic sea ice data. The objective is to investigate the unsupervised detection of changes in Arctic sea ice using multi-temporal SAR images. The well-known Kittler-Illingworth algorithm is tested using two density function models, i.e., the generalized Gaussian and the log-normal model.

    The difference image is obtained using the modified ratio operator. The histogram of the change image, which approximates its probability distribution, is considered to be a combination of two classes, i.e., the changed and unchanged classes. Histogram fitting techniques are used to estimate the unknown density functions and the prior probabilities. The optimum threshold is selected using a criterion function directly related to classification error.

    In this thesis three datasets were used covering parts of the Beaufort Sea from the years 1992, 2002, 2007 and 2009. The SAR and ASAR C-band data came from satellites ERS and ENVISAT respectively. All three were interpreted visually. For all three datasets, the generalized Gaussian detected a lot of change, whereas the log-normal detected less.

    Only one small subset of a dataset was validated against reference data. The log-normal distribution then obtained 0% false alarm rate through all trials. The generalized Gaussian obtained false alarm rates around 4% for most of the trials. The generalized Gaussian achieved detection accuracies around 95%, whereas the log-normal achieved detection accuracies around 70%. The overall accuracies for the generalized Gaussian were about 95% in most trials. The log-normal achieved overall accuracies at around 85%. The KHAT for the generalized Gaussian was in the range of 0.66-0.93. The KHAT for log-normal was in the range of 0.68-0.77. Using one additional speckle filter iteration increased the accuracy for the log-normal distribution. Generally, the detection of positive change has been accomplished with higher level of accuracy compared with negative change detection.

    A visual inspection shows that the generalized Gaussian distribution probably over-estimates the change. The log-normal distribution consistently detects less change than the generalized Gaussian.

    Lack of validation data made validation of the results difficult. The performed validation might not be reliable since the available validation data was only SAR imagery and differentiating change and no-change is difficult in the area. Further due to the lack of reference data it could not be decided, with certainty, which distribution performed the best. 

  • 100. Fujita, S.
    et al.
    Holmlund, P.
    Andersson, I.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Brown, I.
    Enomoto, H.
    Fujii, Y.
    Fujita, K.
    Fukui, K.
    Furukawa, T.
    Hansson, M.
    Hara, K.
    Hoshina, Y.
    Igarashi, M.
    Iizuka, Y.
    Imura, S.
    Ingvander, S.
    Karlin, T.
    Motoyama, H.
    Nakazawa, F.
    Oerter, H.
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Sugiyama, S.
    Surdyk, S.
    Strom, J.
    Uemura, R.
    Wilhelms, F.
    Spatial and temporal variability of snow accumulation rate on the East Antarctic ice divide between Dome Fuji and EPICA DML2011In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 5, no 4, p. 1057-1081Article in journal (Refereed)
    Abstract [en]

    To better understand the spatio-temporal variability of the glaciological environment in Dronning Maud Land (DML), East Antarctica, a 2800-km-long Japanese-Swedish traverse was carried out. The route includes ice divides between two ice-coring sites at Dome Fuji and EPICA DML. We determined the surface mass balance (SMB) averaged over various time scales in the late Holocene based on studies of snow pits and firn cores, in addition to radar data. We find that the large-scale distribution of the SMB depends on the surface elevation and continentality, and that the SMB differs between the windward and leeward sides of ice divides for strong-wind events. We suggest that the SMB is highly influenced by interactions between the large-scale surface topography of ice divides and the wind field of strong-wind events that are often associated with high-precipitation events. Local variations in the SMB are governed by the local surface topography, which is influenced by the bedrock topography. In the eastern part of DML, the accumulation rate in the second half of the 20th century is found to be higher by similar to 15% than averages over longer periods of 722 a or 7.9 ka before AD 2008. A similar increasing trend has been reported for many inland plateau sites in Antarctica with the exception of several sites on the leeward side of the ice divides.

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