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About this book

These proceedings contain 23 papers, which are the peer-reviewed versions of presentations made at the Joint Scientific Assembly of the International Association of Geodesy (IAG) and the International Association of Seismology and Physics of the Earth’s Interior (IASPEI). The assembly was held from 30 July to 4 August 2017 in Kobe, Japan. The scientific assembly included seven symposia organized by IAG, and nine joint symposia, along with additional symposia organized by IASPEI.

The IAG symposia were structured according to the four IAG Commissions and the three GGOS Focus Areas, and included reference frames, static and time-variable gravity field, Earth rotation and geodynamics, multi-signal positioning, geodetic remote sensing, and GGOS. The joint symposia included monitoring of the cryosphere, studies of earthquakes, earthquake source processes, and other types of fault slip, geohazard warning systems, deformation of the lithosphere, and seafloor geodesy. Together, the IAG and joint symposia spanned a broad range of work in geodesy and its applications.

Table of Contents

Frontmatter

Reference Frames

Frontmatter

DGFI-TUM Analysis and Scale Investigations of the Latest Terrestrial Reference Frame Realizations

Abstract
Solutions for the most recent realization of the International Terrestrial Reference System (ITRS) were computed by the three ITRS Combination Centers (CCs) of the International Earth Rotation and Reference Systems Service (IERS), namely the IGN in Paris (France), the JPL in Pasadena (USA), and the DGFI-TUM in Munich (Germany). Thereby, the solutions of IGN and DGFI-TUM comprise conventional parameters of the ITRS (station coordinates and velocities) at a reference epoch as defined in the IERS Conventions 2010. Although the two solutions are based on identical input data, there exist systematic differences between them.
Within all ITRS realizations, the scale is realized as a mean scale between SLR (satellite laser ranging) and VLBI (very long baseline interferometry). If the combined scale is compared to the scale realized by both techniques itself, the IGN solution reveals significant differences between SLR and VLBI whereas the DGFI-TUM solution shows much smaller differences.
When the combined solutions of IGN and DGFI-TUM as well as the single-technique solutions of both institutions are investigated and compared, a significant scale difference between SLR and VLBI is only visible in the IGN analysis but not in the results of the two other ITRS CCs. It is also found that the scale analysis via Helmert parameter is very difficult since the results are quite sensitive w.r.t. particular station networks. In addition, scale comparisons of the IVS and ILRS CCs also do not confirm a systematic scale offset.
Mathis Bloßfeld, Detlef Angermann, Manuela Seitz

Impact of Different ITRS Realizations on VLBI Combined EOP and Scale

Abstract
In this paper we investigate the impact of using the three ITRS realizations DTRF2014, ITRF2014, and JTRF2014 as a priori TRF for the VLBI combination on EOP and scale. The scale factor between the IVS routine combined solution and DTRF2014, ITRF2014, and JTRF2014 shows a significant offset of −0.59 ppb with respect to ITRF2014 and of 0.19 ppb with respect to JTRF2014. No significant offset was found for the DTRF2014-based solution. The investigation of the EOP of all four TRF-based solutions (DTRF2014-, ITRF2014-, JTRF2014- and VTRF2015q2-based) shows specific effects when comparing to the reference time series IERS 14C04, IGS, and ILRS. Relative to the VTRF2015q2-based solution, x-pole differences with respect to the DTRF2014-based solution (positive trend) and JTRF2014-based solution (scatter and negative trend), as well as an offset concerning the y-pole for all three TRF-based solutions with an additional scatter for the JTRF2014-based solution are recognized. No significant differences were found for pole rates, nutation, and LOD, but using ITRF2014 or JTRF2014 leads to marginal larger scatter with respect to the VTRF-based EOP series for LOD. In addition, a significant impact was found when comparing dUT1. All three TRF-based solutions show a significant offset comparing to IERS 14C04, whereas no offset is detected for the VTRF2015q2-based solution.
Sabine Bachmann, Daniela Thaller

Testing Special Relativity with Geodetic VLBI

Abstract
Geodetic Very Long Baseline Interferometry (VLBI) measures the group delay in the barycentric reference frame. As the Earth is orbiting around the Solar system barycentre with the velocity V of 30 km/s, VLBI proves to be a handy tool to detect the subtle effects of the special and general relativity theory with a magnitude of (V∕c)2. The theoretical correction for the second order terms reaches up to 300 ps, and it is implemented in the geodetic VLBI group delay model. The total contribution of the second order terms splits into two effects – the variation of the Earth scale, and the deflection of the apparent position of the radio source. The Robertson-Mansouri-Sexl (RMS) generalization of the Lorenz transformation is used for many modern tests of the special relativity theory. We develop an alteration of the RMS formalism to probe the Lorenz invariance with the geodetic VLBI data. The kinematic approach implies three parameters (as a function of the moving reference frame velocity) and the standard Einstein synchronisation. A generalised relativistic model of geodetic VLBI data includes all three parameters that could be estimated. Though, since the modern laboratory Michelson-Morley and Kennedy-Thorndike experiments are more accurate than VLBI technique, the presented equations may be used to test the VLBI group delay model itself.
Oleg Titov, Hana Krásná

Development of Wideband Antennas

Abstract
Wideband antennas for VLBI have been under development in NICT Kashima and the status of the project was reported in the poster session. An aim of this wideband observing system is Time and Frequency Transfer, the comparison of atomic clocks separated by long distances of several hundred or thousand kilometers with VLBI, as reported in “Broadband VLBI System GALA-V” by M. Sekido et al. This report focuses on our wideband antenna systems.
H. Ujihara, K. Takefuji, M. Sekido, R. Ichikawa

Static Gravity Field

Frontmatter

Boundary Complexity and Kernel Functions in Classical and Variational Concepts of Solving Geodetic Boundary Value Problems

Abstract
In gravity field studies the complex structure of the Earth’s surface makes the solution of geodetic boundary value problems quite challenging. This equally concerns classical methods of potential theory as well as modern methods often based on a (variational or) weak solution concept. Aspects of this nature are reflected in the content of the paper. In case of a spherical Neumann problem the focus is on the classical Green’s function method and on the use of reproducing kernel and elementary potentials in generating function bases for Galerkin’s approximations. Similarly, the construction of Neumann’s function – Green’s function of the second kind and of entries in Galerkin’s matrix for basis functions generated by the reproducing kernel and by elementary potentials is also highlighted when solving Neumann’s problem in the exterior of an oblate ellipsoid of revolution. In this connection the role of elliptic integrals is pointed out. Finally, two concepts applied to the solution of the linear gravimetric boundary value problem are mentioned. They represent an approach based on variational methods and on the use of a transformation of coordinates offering an alternative between the boundary complexity and the complexity of the coefficients of the partial differential equation governing the solution. Successive approximations are involved in both the cases.
Petr Holota, Otakar Nesvadba

GEOMED2: High-Resolution Geoid of the Mediterranean

Abstract
Geoid models for the Mediterranean were computed using the remove-compute-restore method and Stokes-FFT, using shipborne gravity or altimetry inferred gravity data over sea and land gravity data. The remove step over sea does not include residual terrain correction (bathymetry), which leads to slightly worse results. The models were compared to an independent geoid constructed by subtracting the Mean Dynamic Topography from the Mean Sea Surface, and secondly to drifter-observed current speeds. Results revealed significant errors in the gravimetric geoid at smallest scales, and analysis of the results of this intermediate model showed that improvement is required in the gravity data preprocessing, specifically the de-biasing of marine data, as well as the gridding (interpolation) procedure. These issues will be addressed before the release of the final geoid model early 2018. Based on the drifter comparisons, the geoid based on altimeter data is the most accurate, more accurate than EIGEN6C4, and notably so at scales less than 50 km.
R. Barzaghi, D. Carrion, G. S. Vergos, I. N. Tziavos, V. N. Grigoriadis, D. A. Natsiopoulos, S. Bruinsma, F. Reinquin, L. Seoane, S. Bonvalot, M. F. Lequentrec-Lalancette, C. Salaün, O. Andersen, P. Knudsen, A. Abulaitijiang, M. H. Rio

Evaluation of Altimetry Data in the Baltic Sea Region for Computation of New Quasigeoid Models over Poland

Abstract
The paper presents the comparison and validation of currently available gravity anomalies from the satellite altimetry models with the shipborne and airborne gravity anomalies along the Polish coast and in the Baltic Sea. The mean value of differences between the investigated DTU10 and GMG V24.1 altimetry-derived models is equal to 0.02 mGal. However, significant differences can be seen in the coastal areas. Shipborne and airborne marine gravity datasets, collected over the past 65 years by various institutions, were also compared.
Furthermore, the new gravimetric quasigeoid models for the territory of Poland were computed using the new gravity data from the satellite altimetry, the EIGEN-6C4 geopotential model, and the SRTM elevation model. The accuracy of these models, estimated using the ASG-EUPOS permanent GNSS stations, reaches 1.4 cm.
Joanna Kuczynska-Siehien, Adam Lyszkowicz, Michael G. Sideris

AFRGDB_V2.0: The Gravity Database for the Geoid Determination in Africa

Abstract
The available gravity data set for Africa consists of land point gravity data as well as shipborne and altimetry derived gravity anomalies data, but suffers from a lot of significant large gaps. The establishment of the AFRGDB_V2.0 gravity database for Africa has been carried out using a weighted least-squares prediction technique. The land gravity data got the highest precision, while the shipborne and altimetry gravity data got a moderate precision. The data gaps are filled by an underlying grid utilizing the GOCE Dir_R5 model, getting the lowest precision within the prediction technique. The window technique has been used to produce the best reduced anomalies before the interpolation process. The AFRGDB_V2.0 gravity database on a uniform 5× 5 grid has been established by the developed process and has been validated using real data. This validation proved that the established gravity database for Africa has an internal precision of about 5.5 mgal, and an external accuracy of about 7 mgal.
Hussein A. Abd-Elmotaal, Kurt Seitz, Norbert Kühtreiber, Bernhard Heck

Combined Use of a Superconducting Gravimeter and Scintrex Gravimeters for Hydrological Correction of Precise Gravity Measurements: A Superhybrid Gravimetry

Abstract
A variant of hybrid gravimetry using both a superconducting gravimeter and Scintrex gravimeters is proposed. One of the main factors limiting the accuracy of time lapse gravity measurements is the instrumental drift of spring-type gravimeters. Running the Scintrex CG-5 gravimeter in the nighttime on the same pier as the superconducting gravimeter allows us to model the long-term behavior of the former and to remove efficiently the effect of irregular drift on measured gravity. Initial tests performed at Ishigakijima, Japan, proved that accuracy of a few μGal level can be achieved with this method. This will help us precisely correct for the effect of underground water on superconducting gravimeters with 2-dimensional local gravity survey.
Yuichi Imanishi, Kazunari Nawa, Yoshiaki Tamura, Hiroshi Ikeda, Ryo Honda, Takashi Okuda, Makoto Okubo

Evaluation of the Global Altimetric Marine Gravity Field DTU15: Using Marine Gravity and GOCE Satellite Gravity

Abstract
Global marine gravity field modelling using satellite altimetry has been undergoing constant improvement since the launch of Cryosat-2 mission in 2010. With its 369 day-repeat Cryosat-2 provides one repeat of geodetic mission data with 8 km global resolution each year. Together with the completion of the Jason-1 end-of-life geodetic mission in 2011 and 2012, these new satellites has provided more than 4 times three times as much geodetic missions altimetric sea surface height observations than ever before. The higher precision of these new sea surface height observations compared with observations from ERS-1 and Geosat results in a dramatic improvement of the shorter wavelength of the gravity field (12–20 km) resulting in much favorable comparison with marine gravity. The pan-Arctic altimetric gravity field now surpassing 2008 Arctic Gravity Field project derived from multiple gravity field sources. A direct comparison between Arctic marine gravity fields and independent gravity field from the Gravity Field and Steady-State Ocean Circulation Explorer to degree and order 280 confirms this.
O. B. Andersen, P. Knudsen, S. Kenyon, S. Holmes, John K. Factor

Time Variable Gravity Field

Frontmatter

Status of Development of the Future Accelerometers for Next Generation Gravity Missions

Abstract
The GRACE FO mission, led by the JPL (Jet Propulsion Laboratory) and GFZ (GeoForschungsZentrum), is an Earth-orbiting gravity mission, continuation of the GRACE mission, which will produce an accurate model of the Earth’s gravity field variation providing global climatic data during 5 years at least. Europe and US propose new gravity missions beyond GRACE-FO, with improved performance thanks to laser interferometry and better accelerometers. ONERA has procured the accelerometers for the previous geodetic mission (CHAMP, GRACE, GOCE and now GRACE-FO) and continues to improve the instruments to answer to the challenge of the future missions according to two main domains: Firstly, a new design of electrostatic accelerometer is proposed, based on MicroSTAR configuration, a 3-axes ultra-sensitive accelerometer, with a cubic proof-mass. Secondly, ONERA studies the hybridization of such electrostatic accelerometer with cold atom interferometer technology in order to take advantage of each instrument (high sensitivity for electrostatic accelerometer in short term, and absolute measurement for atom interferometer). A first result of the hybrid instrument, obtained on ground, is presented.
B. Christophe, B. Foulon, F. Liorzou, V. Lebat, D. Boulanger, P.-A. Huynh, N. Zahzam, Y. Bidel, A. Bresson

On Computation of Potential, Gravity and Gravity Gradient from GRACE Inter-Satellite Ranging Data: A Systematic Study

Abstract
In situ gravimetric observables are computed from GRACE inter-satellite K-band ranging (KBR) and GPS measurements, along with non-gravitational accelerations. For time-variable gravity field analysis, residual KBR data could be directly used to approximate gravimetric observables. We study the systematic errors in approximating potential difference, line-of-sight (LOS) gravity difference and LOS gravity gradient with residual KBR data. Based on a simulation study, we show that the approximation errors are significant at the low frequency part of the gravity spectrum for all three observable types. The approximation errors remain below 10% of the signal for the potential difference, LOS gravity difference, and LOS gravity gradient, at frequencies >1 cycle-per-revolution (CPR), >7 CPR, and 7–40 CPR, respectively. Considering the actual error of residual KBR data, it is feasible to accurately compute the gravimetric observables directly from band-pass filtered residual range-rate and range-acceleration data, and employ them for analyses concerning the regional time-variable gravity field of the Earth such as continental hydrology.
K. Ghobadi-Far, S.-C. Han, B. D. Loomis, S. B. Luthcke

Calibration of GRACE Accelerometers Using Two Types of Reference Accelerations

Abstract
Two approaches for the calibration of GRACE (Gravity Recovery And Climate Experiment) accelerometers are revisited. In the first approach, surface forces acting on the satellite are considered to derive the reference acceleration. In the second approach, the total acceleration consisting of a gravitational and a non-gravitational contribution is first determined from the reduced-dynamic orbits. The approximation of discrete satellite positions by a polynomial function allows the total acceleration to be obtained by a twofold derivative w.r.t. time. Calibration parameters (scale factor and bias) and statistical values are estimated for periods with a low and high solar activity. The quality of these two approaches shows dependencies on solar activity and consequent variations in the magnitude of the non-gravitational reference acceleration. Besides, the quality of the presented results is affected by the orientation of the orbital plane w.r.t. the Sun. The second approach is vitiated by a periodic disturbing signal on cross-track axis. This signal has been pointed out in earlier studies (Calabia et al., Aerosp Sci Technol 45, 2015; Calabia and Jin, Aerosp Sci Technol 49, 2016). We apply a moving window median filter to recover the underlying non-gravitational signal for accelerometer calibration. The calibration is accomplished by a direct comparison of reference accelerations and observed accelerometer measurements without introducing any a priori values or constraints. The focus of this work is more sensor oriented than gravity field recovery (GFR) related. Nevertheless, the results can be used as initial values for precise orbit determination (POD) or for pre-processing of accelerometer measurements in a multi step gravity field recovery approach (Klinger and Mayer-Gürr, Adv Space Res 58(9), 2016).
Igor Koch, Akbar Shabanloui, Jakob Flury

Geodetic Remote Sensing

Frontmatter

PPP Without Troposphere Estimation: Impact Assessment of Regional Versus Global Numerical Weather Models and Delay Parametrization

Abstract
Mapping functions based on global Numerical Weather Models (NWM) have been developed in recent years to model the tropospheric delay in space geodetic techniques such as the Global Navigation Satellite Systems (GNSS). However, the estimation of residual tropospheric delay is still a necessity when high accuracy is required. Additionally, correlation between the estimated tropospheric delay, the receiver clock offset and the station height component, prolongs the time required for the solution to converge and impacts directly the accuracy of the results. In this study, we applied tropospheric corrections from high resolution NWM in GPS processing, in an attempt to acquire rapid and accurate positioning results, waiving the need to estimate residual tropospheric delay. Although high resolution NWM have outperformed standard atmosphere parameters and global models, it is the first time they have been compared against NWM-derived corrections, such as the operational Vienna Mapping Function 1 (VMF1) parameters. The processing strategy employed utilizes different scenarios characterized by their (a) NWM temporal and spatial resolution (b) grid or site-specific domain and (c) delay parametrization. The results were assessed in terms of height components bias, convergence frequency and time as well as residuals of the GPS analysis. Results showed an overall scenarios agreement of about 20 cm for the height component. However, the site-specific domain and high resolution NWM scenarios outperformed the grid-based ones in most of the cases; centimeter compared to decimeter daily height time series bias along faster convergence time constituted their performance. The final height offset with respect to their ITRF14 values was almost three times larger for the grid-based scenarios compared to the site-specific ones. The iono-free least squares adjustment residuals analysis revealed similar patterns for all the scenarios while the estimated heights experienced a reduction on the days of heavy precipitation under most of the scenarios; for some of the stations the advantage of using direct ray-tracing became obvious during those days.
Thalia Nikolaidou, Felipe Nievinski, Kyriakos Balidakis, Harald Schuh, Marcelo Santos

Calibration of Empirical Models of Thermospheric Density Using Satellite Laser Ranging Observations to Near-Earth Orbiting Spherical Satellites

Abstract
The thermosphere causes by far the largest non-gravitational perturbing acceleration of near-Earth orbiting satellites. Especially between 80 km and 1,000 km, the thermospheric density distribution and variations are required to model accurately this acceleration for precise orbit determination (POD), ephemeris computation and re-entry prediction of the Low-Earth Orbiting (LEO) satellites. So far, mostly on-board accelerometers are used to measure the thermospheric density. However, such type of satellite is usually of complex shape and any error or mismodelling in the satellite drag coefficient and satellite effective cross-sectional area will directly propagate into the derived thermospheric density values. At GFZ, an empirical model of the thermospheric mass density denoted as “CH-Therm-2018” has been developed by using 9 years (2001–2009) of CHAMP observations.
A completely different approach for thermospheric density determination is based on using satellite laser ranging (SLR) measurements to LEO satellites equipped with retro-reflectors to determine an accurate satellite orbit. These measurements are sensitive to small perturbations acting on the satellite. In order to minimize the error induced by imprecise satellite macro-models, we use in our investigation SLR observations to satellites with a simple spherical shape and thus, relate estimated scaling factors to the thermospheric density.
In this paper, we use SLR observations to two ANDE-2 satellites – ANDE-Castor and ANDE-Pollux – as well as SpinSat with altitudes between 248 km and 425 km to calibrate the CH-Therm-2018 model, as well as four other empirical models of thermospheric density, namely CIRA86, NRLMSISE00, JB2008 and DTM2013. For our tests, we chose a period from 16 August 2009 to 26 March 2010 of low solar activity and a period from 29 December 2014 to 29 March 2015 of high solar activity. Using data of a few geodetic satellites obtained at the same and different time intervals allows us to investigate the reliability of the scaling factors of the thermospheric densities provided by the models. We have found that CIRA86 and NRLMSISE00 most significantly overestimate the thermospheric density at the period of low solar activity among the models tested. The JB2008 model is the least scaled model and provides reliable values of the thermospheric density for the periods of both low and high solar activity. The GFZ CH-Therm-2018 model, on the contrary, underestimates the thermospheric density at the time interval of low solar activity. Using SLR observations at longer time intervals should allow to investigate temporal evolution of the scaling factors of these models more precisely.
Sergei Rudenko, Michael Schmidt, Mathis Bloßfeld, Chao Xiong, Hermann Lühr

Geodetic Remote Sensing of Ionosphere in Relation to Space Weather and Seismic Activity in B&H

Abstract
Total electron content (TEC), along GNSS signal’s path in the ionosphere, is spatially and temporally highly variable. In addition, sudden disturbances in the ionosphere may occur on the global, regional or local level from external sources, such as space weather and seismic activity. Results of TEC investigation for mid-latitude ionosphere over B&H (Bosnia and Herzegovina) during seismic activity of medium intensity (4 < M < 5 Richter) and severe geomagnetic storm (St. Patrick’s Day in 2015) are presented. Analyses of relevant parameters such as solar wind, interplanetary magnetic field and geomagnetic activity are performed. Different analyses of TEC variations are carried out. Lower and upper bounds (LB and UB) are determined by 15-day running TEC median prior the day of consideration ± 2*standard deviation. TEC values which exceeded LB and UB are marked as anomalies. TECQUIET is calculated as mean TEC for five quietest days in a month regarding geomagnetic conditions to observe TEC residuals due to enhanced geomagnetic activity. Direct comparison of TEC values at different stations is also conducted. TEC deviations were in better agreement concerning GNSS stations located close to the epicentre. Both positive and negative anomalies were registered 2 weeks before the earthquake, with higher deviations during 7 days before, at stations located inside the earthquake preparation zone. The potential causes of these anomalies are discussed. Analysis of TEC response to the strongest geomagnetic storm in solar cycle 24 shows TEC deviations from 50% to even 150% compared to TECQUIET, where “positive ionospheric storm” is observed in the main phase and “negative ionospheric storm” in the recovery phase of the geomagnetic storm.
Randa Natras, Medzida Mulic

Comparing the Nigerian GNSS Reference Network’s Zenith Total Delays from Precise Point Positioning to a Numerical Weather Model

Abstract
As a pivotal infrastructure for the socio-economic development of Nigeria, the Nigerian Global Navigation Satellite Systems (GNSS) Reference Network – NIGNET – can serve as a tool for weather and climate monitoring, by obtaining and analyzing the neutral atmospheric Zenith Total Delays (ZTD) from processed GNSS data. With the use of surface meteorological measurements, the ZTD can be transformed to the integrated water vapor content in the neutral atmosphere, which is an essential parameter in weather forecasting, and climate change and variability analysis. The focus of this research is to assess the adaptability of the NIGNET for meteorological applications using the global positioning system precise point positioning (PPP) derived ZTD at the stations. ZTD estimates are derived from daily data obtained from the NIGNET and International GNSS Service (IGS) stations spanning the years 2011–2016. These estimates are compared with ray-traced delay estimates from the National Centre for Environmental Prediction Reanalysis II (NCEP II) global Numerical Weather Model (NWM) and the IGS zenith path delay products. A comprehensive analysis is performed to assess the level of agreement of the different ZTD estimates and to identify possible systematic effects from the different sources. Comparisons between the PPP and NCEP II NWM ZTD estimates show a range of mean offsets from −6.4 to 23.9 mm, and standard deviations from 33.1 to 44.9 mm. With the PPP and IGS ZTD estimates, mean offsets of −2.4 and −0.1 mm, and standard deviations of 9.9 and 13.8 mm are obtained.
A. O. Mayaki, T. Nikolaidou, M. Santos, C. J. Okolie

Global Geodetic Observing System (GGOS) and Earth Monitoring Services

Frontmatter

GGOS Bureau of Products and Standards: Recent Activities and Future Plans

Abstract
This paper presents a summary of the activities of the Bureau of Products and Standards (BPS) to support IAG’s Global Geodetic Observing System (GGOS) in its goal to provide observations and consistent geodetic products needed to monitor, map, and understand changes in the Earth’s shape, rotation, and mass distribution. As a key activity the BPS has compiled an inventory of the standards and conventions currently adopted and used by the IAG and its components for the processing of geometric and gravimetric observations as the basis for the generation of IAG products. The outcome of the BPS inventory concerning numerical standards and the product-based review is summarized and recommendations for future improvements are provided. Finally, an overview about the ongoing and planned activities of the BPS is given.
Detlef Angermann, Thomas Gruber, Michael Gerstl, Robert Heinkelmann, Urs Hugentobler, Laura Sánchez, Peter Steigenberger

Recent Activities of the GGOS Standing Committee on Performance Simulations and Architectural Trade-Offs (PLATO)

Abstract
The Standing Committee on Performance Simulations and Architectural Trade-Offs (PLATO) was established by the Bureau of Networks and Observations of the Global Geodetic Observing System (GGOS) in order to support – by prior performance analysis – activities to reach the GGOS requirements for the accuracy and stability of the terrestrial reference frame. Based on available data sets and simulated observations for further stations and satellite missions the committee studies the impact of technique-specific improvements, new stations, and additional co-locations in space on reference frame products. Simulation studies carried out so far show the importance of the individual station performance and additional stations for satellite laser ranging, the perspectives for lunar laser ranging assuming additional stations and reflectors, and the significant impact of the new VGOS antennas. Significant progress is achieved in processing VLBI satellite tracking data. New insights in technique-specific error sources were derived based on real data from short baselines. Regarding co-location in space PLATO members confirmed that E-GRASP could fulfill the GGOS requirements with reaching a geocenter and scale accuracy and stability of 1 mm and 0.1 mm/year, respectively.
Benjamin Männel, Daniela Thaller, Markus Rothacher, Johannes Böhm, Jürgen Müller, Susanne Glaser, Rolf Dach, Richard Biancale, Mathis Bloßfeld, Alexander Kehm, Iván Herrera Pinzón, Franz Hofmann, Florian Andritsch, David Coulot, Arnaud Pollet

IGFS Metadata for Gravity. Structure, Build-up and Application Module

Abstract
Gravity field related products have been the focus of almost all geosciences in the sense that they give a realistic representation of the physical properties of system Earth. The rigorous documentation and archiving of gravity field related data (e.g., absolute gravity, gravity anomalies etc.), either irregularly distributed and on a grid, has become mandatory in order to ensure coherent and unambiguous utilization by users and archiving in related data management servers and services. Given the above, the International Gravity Field Service (IGFS) has taken steps in order to generate metadata for gravity field related data so that fragmentation of databases at national and international level as well as user needs can be addressed. To that respect, a new ISO19115-1 profile for gravity field metadata has been prepared, describing all necessary fields that the metadata should have, while an online PHP-based (PHP: Hypertext Preprocessor) web application (XML generator) has been developed and became available as an IGFS product to assist users to generate compliant metadata. In this work, we describe the main characteristics of the metadata structure and give details on the developed web application. Finally, the dedicated IGFS application server, igfsapps.topo.auth.gr, is described and details on the incorporation of the gravity metadata application as an online IGFS service are provided.
G. S. Vergos, V. N. Grigoriadis, R. Barzaghi, D. Carrion

Multi-signal Positioning: Theory and Applications

Frontmatter

Assessment of GNSS and Map Integration for Lane-Level Applications in the Scope of Intelligent Transportation Location Based Services (ITLBS)

Abstract
To enable safe and robust Intelligent Transportation Systems (ITS) applications, the integration of different sensors and techniques will certainly be a common reality. One application in this context is the lane-keeping techniques for autonomous driving systems. These systems normally use imagery sensors for lane identification, however imagery systems always depend on light and well-structured roads. One potential worldwide autonomous driving technique without any other lane and road detection/identification sensor would be GNSS positions along with accurate map information. However, this fusion depends on the accuracy and reliability of both GNSS positions and map information. The positioning accuracy that Intelligent Transportation Location Based Services (ITLBS) requires for where-in-lane and active control applications are 0.5 m and 0.1 m, respectively. To evaluate the potential of fusion, this work proposes an integration of GNSS and map information in the attempt to address the lane-keeping problem. This integration is performed by merging a GNSS solutions and lane centerline positions, acquired from aerial orthophotos, into a Kalman Filter and a simple map matching approach. To measure the positioning error, or off-track performance, a conversion of positions to the road space is necessary. To evaluate the results, a positioning accuracy limit, considering the road, vehicle dimensions, and the requirements for ITLBS is also proposed. The results showed that 95% of the time the proposed methodology off-track performances were within 1.89 m, in an average of 4 runs. Half of the runs were within 0.75 m, in average, at 95% of the time. Compared to an accurate GNSS Post Processed Kinematic (PPK) mode, an improvement of 10% was achieved.
Emerson Pereira Cavalheri, Marcelo Carvalho dos Santos

Improving Low-Cost GNSS Navigation in Urban Areas by Integrating a Kinect Device

Abstract
In the last decades, low-cost GNSS receivers have been widely used for navigation purposes. Some of them deliver also raw data, allowing for a more sophisticated processing, such as the double-difference approach, and therefore a more accurate positioning, typically at the decimeter level. However, these accuracies can be generally achieved only with a good sky visibility, that is a critical issue in urban areas even using low-cost receivers equipped with a high-sensitive antenna. In this respect, a significant contribution comes from the use of digital images or dense point clouds which provides an estimate of the sensor kinematic position. To maintain the low-cost target, the Kinect device, endowed with RGB and depth cameras, can be used. In this work, we have first processed the GNSS raw data from a u-blox receiver by using the free and open source goGPS software. Then, we have studied the integration of the Kinect device by a proper Kalman filter. An outdoor experiment has been arranged with the aim of testing the hardware and software system.
C. I. De Gaetani, D. Pagliari, E. Realini, M. Reguzzoni, L. Rossi, L. Pinto

Geodesy and Seismology General Contributions

Frontmatter

Crustal Deformation and Fault Models of the 2016 Kumamoto Earthquake Sequence: Foreshocks and Main Shock

Abstract
We explored crustal deformation associated with the foreshocks and the main shock of the 2016 Kumamoto earthquake sequence. We conducted kinematic-Global Navigation Satellite System analysis for the foreshocks, and succeeded in separately retrieving the coseismic crustal deformation for the two M6-class events that occurred nearly contemporaneously (within 3 h). Our fault model shows that the first seismic event occurred in the northern part of the Takano-Shirahata segment of the Hinagu Fault, while the second occurred in the southern part of the segment. For the main shock, we mapped the widely distributed ground displacements in and around the Futagawa Fault zone by conducting an Interferometric Synthetic Aperture Radar analysis. The obtained displacement field shows clear displacement boundaries linearly along the Futagawa and the Hinagu faults, across which the sign of the displacement component turns to the opposite, suggesting that the two faults were intimately involved with the main shock. The previously known fault trace of the Futagawa Fault terminates at the western edge of the Aso Caldera, but the intense deformation implying fault ruptures clearly appears within the caldera. Our fault model suggests that the main rupture occurred on the Futagawa Fault in a right-lateral fashion with normal faulting. The rupture on the Futagawa Fault extends into the Aso Caldera, and the fault plane dips oppositely toward the southeast, suggesting that the rupture propagates eastward on a conjugate fault against the main fault. The rupture on the Hinagu Fault shows a right-lateral fault motion on a plane dipping west.
Tomokazu Kobayashi, Hiroshi Yarai, Satoshi Kawamoto, Yu Morishita, Satoshi Fujiwara, Yohei Hiyama

Backmatter

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