WG 4.1.4: Imaging Techniques

Chair: M. Elhabiby (Canada)

Co-chair: J.-A. Paffenholz (Germany)

**Description**

This WG will focus on the investigation and development of imaging techniques for different navigation problems. Vision Based Navigation (VBN) systems research work will cover two different research streams: the non-inertial vision navigation and the inertial-aided vision navigation approaches. Real time efficient implementation with fast computations will extend the working group research activities to geo-computations, digital signal processing, non-linear optimization and image matching. The working group research work will be connected to the navigation industry in general and UAV industry in specific.

It has a major focus on:

* Evaluation of algorithms and methods for visually aiding inertial and non-inertial navigation systems.

* Evaluation of estimating aircraft position and velocity from sequential aerial images.

* Real-time implementation of a vision based navigation algorithm, which comprises both accuracy and effectiveness (meaning the cheapness of the sensors used, computational load and complexity). The new algorithm is composed of two sections: relative position estimation and absolute position estimation, which are connected with each other through a switching scheme.

* Assessment on the relative position estimation based on stereo modelling of two sequential images.

* Evaluation of the absolute position estimation techniques through matching schemes using reference images.

* Building an effective academic and industrial network worldwide that can help and promote the research activities of the working group.

* Establishing working links between this working group and similar national and international working groups such as ISPRS, ASPRS, CGU, AGU, IAG and FIG working groups.

Specific techniques include:

* Multi-resolution techniques: Curvelet and wavelet transform for image matching.

* Linear and non-linear optimization for position estimation.

* Implementation of Speeded Up Robust Features (SURF) Algorithms for interest point detection, image matching an object recognition.

* Extended Kalman filter update using position estimated from image matching techniques.

SC 4.2: Geodesy in Geospatial Mapping and Engineering

Chair: J. Wang (Australia)

Vice-Chair: G. Roberts (UK)

Secretary: H.-K. Lee (South Korea)

**Terms of Reference**

Geodesy provides foundations for geospatial mapping and engineering. Modern geospatial mapping as a massive point positioning process has been evolving towards automatic operations, and at the same time, various engineering areas are increasingly relying on highly developed geospatial technologies to deliver improved productivities and safety with minimised negative environment impact. This Sub-Commission (SC) 4.2 will therefore endeavour to coordinate research and other activities that address the broad areas of the theory and applications of geodesy tools in geospatial mapping and engineering, ranging from construction work, geotechnical and structural monitoring, precision farming, mining, to natural phenomena such as landslides and ground subsidence. The SC4.2 will carry out its work in close cooperation with other IAG Entities, as well as via linkages with relevant scientific and professional organizations such as ISPRS, FIG, IEEE, ION, ISM.

**Objectives**

* To develop and promote the use of new geospatial mobile mapping technologies for various applications.

* To develop and report the modelling and quality control framework for geo-referencing procedures.

* To monitor research and development into new technologies that are applicable to the general field of engineering geodesy, including hardware, software and analysis techniques.

* To study advances in geodetic methods for precision farming, mining operations, and large construction sites.

* To study advances in monitoring and alert systems for local geodynamic processes, such as landslides, ground subsidence, etc.

* To study advances in the application of artificial intelligence techniques in engineering geodesy.

* To document the body of knowledge in the field of geospatial mapping and engineering geodesy, and to present such knowledge in a consistent frame work at symposia and workshops.

* To promote research into several new technology areas or applications through the SC4.2 Working Groups.
# Working groups

## WG 4.2.1: Mobile Mapping Technologies and Applications

Chair: J. Skaloud (Switzerland)

Co-Chair: K.-W. Chiang (Taiwan)

### Description

Mobile mapping technologies have been widely used to collect geospatial data for a variety of applications, for example, navigation and online geospatial information services. As mobile mapping sensors are becoming cheaper and easier to access, modelling and quality control procedures for major steps of mobile mapping should be further developed to ensure the reliability of geospatial data from mobile mapping systems. This working group will conduct its work through coordinated activities among the members of the group as well as in collaborations with other professional organizations, such as ISPRS/FIG.

Major objectives of this WG are:

* To monitor new trends in mobile mapping technologies.

* To evaluate the performance of geo-referencing and mapping sensors, such as IMU, GNSS, 3D cameras, optical vision sensors.

* To develop realistic mathematical and functional models for geo-referencing procedures.

* To develop a framework to evaluate the quality of geo-referencing and mapping results.

* To promote the use of geospatial mapping systems for various applications.

## WG 4.2.2: Applications of Geodesy in Mining Engineering

Chair: A. Jarosz (Australia)

Co-Chair: J. Gao (China)

### Description

Geodesy has been playing an important role in mining operations from geospatial mapping, modern navigation and guidance technologies used in automation at various mine sites to special orientation and location procedures used in underground operations. This working group will conduct its activities in close collaborations with other relevant international professional organizations, such as the International Society of Mining Surveying (ISM) and FIG.

Major objectives of this WG are to study, and report the use of:

* Modern geodesy in various mining sites.

* 3D mapping for mining.

* Navigation and guidance of mining machinery.

* Miner location technologies in underground mining operations.

## WG 4.2.3: Geodetic technologies in Precision Farming

Chair: R. Bill (Germany)

Co-Chair: TBD

### Description

Modern precision farming operations are highly dependent on high precision positioning, orientation and geospatial mapping, which are based on modern geodetic theory, techniques and services. This working group will coordinate professional activities to look into major geodetic aspects in precision farming areas in various parts of the world.

Major objectives of this WG are to study, and report the use of geodetic tools in precision farming, in particular:

* Precise positioning and orientation of agricultural land-machinery and acquisition devices (such as geo-sensor networks, unmanned airborne vehicles, field robotics).

* Precise navigation and guidance for intelligent agricultural vehicles capable of automating tasks.

* Precise mapping, interpretation of space-time heterogeneities in the field, derivation of agricultural application maps.

* Web-based data infrastructures and services used in agricultural environment.

## WG 4.2.4: Monitoring of Landslides & System Analysis

Chair: G. Mentes (Hungary)

Co-Chair: J. Guo (China)

### Description

Landslides, as natural phenomena, have a local effect on structures and community infrastructure. Monitoring different types of landslides under various operational scenarios is a challenging task. The tools used in landslide monitoring range from conventional terrestrial measurement and alignment technology (optical, RF, etc.), Global Navigation Satellite Systems (GNSS), remote sensing, geotechnical instrumentation, and software systems such as GIS, decision support systems, etc. The WG will carry out its work in close cooperation with other related professional organizations such as ISPRS, FIG, ISM.
Major objectives of this WG are to study and report on:

* Development of new measuring methods.

* New dynamic and kinematic models of landslides.

* Integration of terrestrial and remote sensing measuring technology on multidisciplinary basis with the aim to develop an early alert system;

* Integrated workflow for landslide hazard management.

### WG 4.2.5: Applications of Artificial Intelligence in Geospatial Mapping and Engineering Geodesy

Chair: A. Reiterer (Germany)

Co-Chair: U. Egly (Austria)

#### Description

Artificial Intelligence (AI) has become an essential technique for solving complex problems in many applications. In the areas of geospatial mapping and engineering geodesy, knowledge-based systems are emerging. To develop reliable intelligent systems, this working group will focus on some critical issues ranging from the understanding of the nature of intelligence to the understanding of knowledge representation and deduction processes, eventually resulting in the construction of computer programs, which act intelligently.

Major objectives of this working group are to study and report on, the following major areas:

* Intelligent quality control procedures in geospatial mapping process.

* Robust control of measurement- and guidance-systems.

* Knowledge based deformation analysis.

* Intelligent control of deformation alert systems.

* Evaluation of various complex data streams in geospatial mapping and engineering geodesy with, e.g. knowledge-based systems, genetic algorithms, and artificial neural networks.

### SC 4.3: Remote sensing and modelling of the atmosphere

Chair: M. Santos (Canada)

Vice-Chair: J. Wickert (Germany)

Secretary: A. Krankowski (Poland)

#### Terms of Reference

The objective of this SC is to coordinate research dealing with the treatment, interpretation and modelling of measurements collected in the atmosphere for the purpose of improvements in geodetic positioning as well as for better understanding the atmosphere itself. Even though GNSS techniques are seen here as the primary research tools, other sensors also bring important information on the atmosphere and as such should be considered in the context of this Sub-Commission. Dedicated satellites, having on-board GNSS receivers, can also contribute to atmospheric studies by exploring the atmosphere-induced bending of GNSS signals while propagating through the atmosphere, to furnish round-the-clock weather data, monitor climate change, and improve space weather forecasts. Geodetic positioning can benefit and contribute to atmospheric models, such as Numerical Weather Prediction (NWP) models. Novel advancements in modelling the atmosphere as applied to positioning, error sources, instrumentation, dedicated missions, and real- or near real-time data access should also be contemplated. SC4.3 will foster linkages with sister scientific and professional organizations, such as IAG, ISPRS, FIG, IEEE and ION.

#### Objectives

* To explore the synergy that exists between Geodesy, meteorology and ionospheric sciences.

To encourage the processing of more and more LEO and also ground based data more and more also in near-real and/or real time.

* To study the application of readily available data from numerical weather prediction models (data provision, assimilation techniques).

* To study and suggest ways for homogenization of long term data set for climatologic investigations

* To investigate the development and enhancement of the GNSS-based sounding techniques, e.g. neutral atmosphere/ionosphere tomography, GNSS reflectometry/scatterometry for altimetry, meteorology, soil moisture.

* To exploit the potential of new GNSS signals' structures for GNSS based atmospheric remote sensing.

* To suggest additional platforms for GNSS based atmospheric remote sensing (buoys, aircrafts, balloons, more dense ground networks, LEO constellations).

* To follow, study and contribute towards the technical and scientific advances in atmospheric research.
* To suggest standard definitions and terminology as per appropriate in the context of Geodesy and atmospheric sciences.

## Program of activities

* To promote research collaboration among research groups worldwide.

* To organize and/or participate in scientific and professional meetings.

* To maintain a web page concatenating the Sub-Commission activities and reports.

* To encourage special issues of the Journal of Geodesy on atmospheric applications to Geodesy.

## Study groups

### SG 4.3.1: Ionosphere modelling and analysis

Chair: M. Schmidt (Germany)

Co-Chair: M. Karslioglu (Turkey)

#### Description

The general objective of this study group is the development of ionosphere models based on physics, mathematics and statistics. Within the next four years we will (1) focus on the development of appropriate parameter estimation and assimilation techniques based on the combination of different observation techniques. With respect to physical modelling we (2) will perform first steps by introducing physics-motivated functions such as the Chapman function into the parameter estimation process. Furthermore, we (3) will establish ionosphere models including near real-time applications by introducing Kalman filtering procedures. Other topics are the development of densification strategies of global models using regional approaches as well as applications, e.g. the study of the L3 GNSS frequency.

## Working groups

### WG 4.3.1: Standards for space weather products for geodetic and ionospheric studies

Chair: A. Krankowski (Poland)

#### Description

The objective of this WG is to suggest common international standards for the dissemination of space weather products used in geodesy and ionospheric studies. This WG will work in close scientific collaboration with IGS, URSI and COSPAR IRI group.

### SC 4.4: Applications of Satellite and Airborne Imaging Systems

Chair: Z. Li (UK)

Vice-Chair: T. Wright (UK)

Secretary: H. Lee (USA)

## Terms of Reference

The main objectives of this SC are to promote collaborative research in the development of satellite and airborne imaging systems, primarily including Synthetic Aperture Radar (SAR), Light Detection And Ranging (LiDAR) and Satellite Altimetry (SA) systems, for geodetic applications, and to facilitate communications and exchange of data, information and research results through coordinated efforts.

## Objectives

* Development of methods, models, algorithms and software for geodetic applications of satellite and airborne imaging systems.

* Integration of satellite and airborne imaging systems with other geodetic/geospatial technologies such as GPS and GIS.

* Investigation of effects of field and atmospheric conditions on satellite and airborne imaging systems.

* Development and promotion of new geodetic applications of satellite and airborne imaging systems.

* Development of collaboration with sister organisations such as FIG and ISPRS, and liaison with image data providers.

## Working groups

### WG 4.4.1: Quality Control Framework for InSAR Measurements

Chair: Z. Li (UK)

Co-Chair: S. Samsonov (Canada)

#### Description

To investigate quality measures and quality control procedures and formulate a quality control framework for InSAR measurements. In particular, the objectives are:

* To investigate the optimal procedure for InSAR measurements

* To demonstrate how accurately InSAR can measure surface movements

* To demonstrate how accurately InSAR can map atmospheric path delays
### WG 4.4.2: InSAR Observation and Modelling of Earthquakes, Volcanoes and Tectonics

Chair: T. Wright (UK)

Co-Chair: A. Hooper (Netherlands)

#### Description

To combine InSAR observations of Earth's surface movements, topography and terrestrial observations and modeling to advance understanding of the earthquake cycle, continental deformation and volcanic eruptions, and to quantify seismic and volcanic hazards.

### WG 4.4.3: Landslide Hazard Mitigation using InSAR Techniques

Chair: R. Jover (Spain)

Co-Chair: R. Furuta (Japan)

#### Description

The main objectives of this working group is to promote collaborative research in the application of InSAR techniques for landslide measurement, monitoring and modeling and to stimulate communications and exchange of data, information and research outcomes through coordinated efforts. In particular, the primary objectives are:

* Development/improvement of InSAR techniques, algorithms and software for landslide measurement and monitoring.

* Investigation of the spatio-temporal evolution of landslides.

* Integration of InSAR data with in-situ observations, aerial/ground-based remote sensing measurements and geoinformation to improve our understanding of landslide mechanisms.

* Development of landslide models using InSAR measurements.

### WG 4.4.4: Vertical land motion from Satellite Altimetry

Chair: H. Lee (USA)

Co-Chair: H. Wang (China)

#### Description

To develop optimal retracking and surface gradient correction algorithms for satellite altimeter measurements toward observing vertical crustal motion due to, e.g., glacial isostatic adjustment (GIA) and land subsidence. The primary

focus is to study the application of satellite altimetry for observing vertical crustal motion.

### WG 4.4.5: LiDAR and Laser Scanning

Chair: B. Yang (China)

Co-Chair: N. Tate (UK)

#### Description

To provide a focus for space-borne, airborne and terrestrial laser scanning activity internationally. There are currently four principal themes of research within the group: 3D modelling, data integration, mapping, and applications. In particular, the primary objectives are:

* To develop state-of-the-art laser scanning algorithms

* To collaborate with sister organizations (e.g. ISPRS and UK RSPSoc) to promote geodetic applications of laser scanning
# SC 4.5: High-Precision GNSS Algorithms and Applications

Chair: Y. Gao (Canada)

Vice-Chair: P. Wielgosz (Poland)

Secretary: G. Liu (Hong Kong)

## Terms of Reference

High-precision GNSS applications continue to grow, largely contributed to the rapid GNSS system developments currently underway including US's GPS modernization, the Russian GLONASS, European GALILEO and Chinese COMPASS systems. The increased number of satellites in view and improved system performance provide opportunities to create new high precision GNSS technologies and applications. Novel technologies are needed to address such opportunities and also challenges to further enhance the accuracy, availability and integrity of high precision GNSS applications, while the cost is to be dramatically reduced. SC4.5 will coordinate research efforts to identify important research problems in high precision GNSS and develop methods and technologies to support high precision GNSS applications. The research subjects include optimal use of signals from multiple GNSS systems, improved error modelling and mitigation methodologies, quality control and integrity monitoring, precise point positioning and RTK, low-cost precision GNSS, GNSS integration with enabling sensors, novel augmentation corrections and services, fast carrier phase ambiguity resolution. SC4.5 will also stimulate strong collaborations among researchers and international organizations, and develop strong linkage with the industry.

## Objectives

The major objective of SC4.5 is to promote collective research efforts on the development of high precision GNSS methods and technologies and their novel applications, to facilitate timely dissemination of scientific findings, to stimulate strong collaborations among researchers and international organizations, and to develop strong linkage with the industry.

## Program of activities:

* Identify and investigate important technical issues and problems in high precision GNSS.

* Identify and investigate emerging commercialization opportunities of high precision GNSS technologies.

* Publish white papers.

* Promote research collaboration among researchers.

* Develop strong linkage with the industry sector.

* Participate and organize international conferences and workshops.

* Collaborate with other international organizations.

## Working groups

### WG 4.5.1: Quality Measures for Network-based GNSS RTK

Chair: X. Meng (UK)

Co-Chair: H.-J. Euler (Switzerland)

#### Description

To study methods of quality control from both the end users and service providers' point of view. The research will focus on the assessment and improvement of the robustness and processing efficiency of Network-based GNSS RTK algorithms and software tools; the development of methods for integrity and completeness checking, time of arrival of corrections, impacts of incomplete and delayed messages; and the development of methods to increase the overall confidence and awareness of the positional accuracy.

### WG 4.5.2: Precise Point Positioning and Network RTK

Chair: Sunil Bisnath (Canada)

Co-Chair: Sue Lynn Choy, (Australia)

#### Description

To address and investigate issues related to the development of GNSS-based precise point positioning (PPP) and network RTK (Real-Time Kinematic) technology. The main research focus will include the development and integration of PPP and network RTK algorithms, high performance PPP and RTK in the context of multi-GNSSstellations, and methods and algorithms to improve the availability and reliability of PPP and RTK. Promoting innovative application development and increasing user adoption will be a continuous effort.
### WG 4.5.3: Integer Ambiguity Resolution for PPP and PPP-RTK

Chair: X. Zhang (China)

Co-Chair: P. Henkel (Germany)

#### Description

To study methods and algorithms of integer ambiguity resolution for precise point positioning and investigate issues and problems related to ambiguity initialization time, success rate and reliability etc. The research will focus on the following areas: the development of new augmentation corrections to mitigate fractional initial phase biases to recover the integer property of the undifferenced ambiguities; the development of methods and algorithms for integer ambiguity resolution in precise point positioning; and the real-time implementation and standardization of PPP-based RTK systems.

### WG 4.5.4: Multi-frequency, Multi-constellation Sub-cm RTK

Chair: B. Li (Australia)

Co-Chair: Y. Feng (Australia)

#### Description

To study efficient approaches for sub-cm RTK over longer baseline and high-precision large-scale network RTK solutions with multi-frequency, multi-constellation GNSS systems. The research task will focus on the following areas: the efficiency and reliability improvement of ambiguity resolution over longer baselines; new linear combinations for mitigating different error sources and improving the real time kinematic positioning solutions from the current centimeter level to sub-centimeter level; applications to geodesy, geodynamics, engineering and machine automations where sub-cm accuracy is of great interest.

### SC 4.6: GNSS-Reflectometry and Applications

Chair: S. Jin (China)

Vice-Chair: M. Martin-Neira (Netherlands)

Secretary: S. Gleason (Canada)

#### Terms of Reference

The Global Navigation Satellite System (GNSS) can be characterized as a highly precise, continuous, all-weather and near-real-time microwave (L-band) technique, which implies more and wider applications and potentials. Recently, the versatile reflected and scattered signals of GNSS have been successfully demonstrated to sound the land surfaces (including soil moisture), ocean, and the cryosphere as a new remote sensing tool. The GNSS reflected signals from the ocean and land surface could determine the ocean height, wind speed and wind direction of ocean surface, soil moisture, ice and snow thickness, which could supplement the traditional remote sensing techniques, e.g., radar altimetry and SAR. The focus of this Sub-Commission (SC4.6) is to facilitate collaboration and communication, and to support joint researches with promising GNSS-Reflectometry (GNSS-R) technique. Specific objectives will be achieved through closely collaborating with working groups and other IAG Commissions/Sub-Commissions. Meanwhile, close collaboration with the International GNSS Service (IGS), Institute of Navigation (ION) and IEEE Geoscience and Remote Sensing Society (IGRASS) will be promoted, such as joint sponsorship of international professional workshops and conferences.

#### Objectives:

* To promote and extend GNSS Reflectometry/Scatterometry developments and tests as well as environment remote sensing applications, including GNSS-R receiver, antenna, signals, system and experiments.

* To improve the existing estimation algorithms, inversion theory and temporal-spatial resolution in GNSS reflectometry from the ocean and land surface and supplement the traditional remote sensors, e.g., Satellite Altimetry and SAR.

* To coordinate data from GNSS-R campaign experiments and provide environment remote sensing products through fusing with other terrestrial and satellite observations.

* To address coastal ocean topography, ocean surface roughness characteristics (wind speed/direction and wave height), ice motion, wetland monitoring and surface soil moisture and snow/ice thickness as well as the condition of sea ice, glacial melting and the freezing/thaw state of frozen ground.
* To facilitate collaboration and communication with mutual Remote Sensing related communities (Oceanography, Hydrology, Cryosphere, Geodesy).

## Program of Activities:

This SC will establish WGs on relevant topics, and promote GNSS Reflectometry/Scatterometry developments and remote sensing applications. Chair/Co-Chair will work closely with members and other IAG Commissions/Sub-Commissions to obtain mutual goals. Also we will organize international workshops and symposiums to provide a platform for GNSS-R communication and collaboration and jointly sponsor special sessions at IAG Symposium and other workshop/conferences with IGARSS and ION.

## Working Groups

### WG 4.6.1: GNSS-R Development and Experiment

Chair: M. Martin-Neira (Netherlands)

Co-Chair: F. Fabra (Spain)

#### Description

The PARIS (PAssive Reflectometry Interferometric System, also called GNSS-Reflectometry) was successfully designed to use GNSS reflected signals from Earth's surface to act as multiple passive altimetric ranging signals and a bistatic scatterometer. This effort will be dedicated to GNSS-Reflectometry technique development, experiments and processing, e.g., GNSS-R test and applications in land and ocean surface. In particular, the WG goals are:

* To provide GNSS-R technique information and new developments, including GNSS-R receiver, antenna, signals, and simulations.

* To organize GNSS-R experiments in ocean coast, bridge, aircraft and LEO satellites and analyze and test the GNSS-R for land and ocean surface applications.

### WG 4.6.2: GNSS Scatterometry

Chair: S. Gleason (Canada)

Co-Chair: M. Clarizia (UK)

#### Description

This WG is primarily focused on the study of ocean wind and wave retrieval using scattered GNSS signals as well as ocean sensing applications, including looking into the

signal scattering statistics and analyzing the achievable surface resolution for different instrument configurations. The primary goals of this WG is:

* To improve the scattering signal quality and estimated theory for ocean wind and wave retrieval using different instrument and GNSS-R carrier configurations.

### WG 4.6.3: GNSS Ocean Altimetry

Chair: S. d'Addio (Netherlands)

Co-Chair: E. Cardellach (Spain)

#### Description

The ocean surface roughness characteristics can be detected in some cases using GNSS reflected signals comparable with other remote sensors. Further research is needed in detailed analysis of the electromagnetic field scattering theory, power and Delay-Doppler parameter retrieval methods and characterizing the L-band surface slopes' probability density function. The primary goal of this WG is:

* To improve GNSS Altimetry for all currently available GNSS signals and to demonstrate more applications in oceans through closely collaborating with Commission 2, e.g. Altimetry, Gravimetry, ICESat, etc.

### WG 4.6.4: Soil and Cryosphere detection by GNSS-R

Chair: M. Jacobson (USA)

Co-Chair: N. Floury (Netherlands)

#### Description

The soil moisture, ice and snow thickness are related to the amplitude of the reflected signal as a function of the incidence angle or relative amplitudes between different polarizations, which can be retrieved from the GNSS reflected signals. This effort is to develop GNSS reflectometry and multipath for land surface mapping, wetland monitoring and surface soil moisture and snow/ice thickness as well as the condition of sea ice, glacial melting and the frozen state. The primary goal of this WG is:

* To improve the estimate theory and sensitivity to soil moisture, snow and ice condition from the GNSS reflected signals and to precisely determine the soil moisture, ice status and features
# Inter-Commission Committee on Theory (ICCT)

http://icct.kma.zcu.cz

President: N. Sneeuw (Germany)

Vice President: P. Novák (Czech Republic)

## Terms of Reference

The Inter-Commission Committee on Theory (ICCT) was formally approved and established after the IUGG XXI Assembly in Sapporo, 2003, to succeed the former IAG Section IV on General Theory and Methodology and, more importantly, to interact actively and directly with other IAG entities. In accordance with the IAG by-laws, the first two 4-year periods were reviewed in 2011. IAG approved the continuation of ICCT at the IUGG XXIII Assembly in Melbourne, 2011.

Recognizing that observing systems in all branches of geodesy have advanced to such an extent that geodetic measurements (i) are now of unprecedented accuracy and quality, can readily cover a region of any scale up to tens of thousands of kilometres, yield non-conventional data types, and can be provided continuously; and (ii) consequently, demand advanced mathematical modelling in order to obtain the maximum benefit of such technological advance, the ICCT (1) strongly encourages frontier mathematical and physical research, directly motivated by geodetic need and practice, as a contribution to science and engineering in general and the theoretical foundations of geodesy in particular; (2) provides the channel of communication amongst the different IAG entities of commissions/services/projects on the ground of theory and methodology, and directly cooperates with and supports these entities in the topical work; (3) helps the IAG in articulating mathematical and physical challenges of geodesy as a subject of science and in attracting young talents to geodesy. The ICCT should strive to attract and serve as home to mathematically motivated/oriented geodesists and to applied mathematicians; and (4) encourages closer research ties with and gets directly involved in relevant areas of the Earth sciences, bearing in mind that geodesy has always been playing an important role in understanding the physics of the Earth.

## Objectives

The overall objectives of the ICCT are to act as international focus of theoretical geodesy, to encourage and initiate activities to advance geodetic theory in all branches of geodesy, to monitor developments in geodetic methodology.

To achieve these objectives, the ICCT interacts and collaborates with the IAG Commissions, GGOS and other IAG related entities (services, projects).

## Structure

### Joint Study Groups

**JSG 0.1:** Application of time series analysis in geodesy (joint with GGOS and all Commissions)
Chair: W. Kosek (Poland)

**JSG 0.2:** Gravity field modelling in support of height system realization (joint with Commissions 1, 2 and GGOS)
Chair: P. Novák (Czech Republic)

**JSG 0.3:** Comparison of current methodologies in regional gravity field modelling (joint with Commissions 2, 3)
Chairs: M. Schmidt, Ch. Gerlach (Germany)

**JSG 0.4:** Coordinate systems in numerical weather models (joint with all Commissions)
Chair: Th. Hobiger (Japan)

**JSG 0.5:** Multi-sensor combination for the separation of integral geodetic signals (joint with Commissions 2, 3 and GGOS)
Chair: F. Seitz (Germany)

**JSG 0.6:** Applicability of current GRACE solution strategies to the next generation of inter-satellite range observations (joint with Commission 2)
Chairs: M. Weigelt (Germany), A. Jäggi (Switzerland)

**JSG 0.7:** Computational methods for high-resolution gravity field modelling and nonlinear diffusion filtering (joint with Commissions 2, 3 and GGOS)
Chairs: R. Čunderlík, K. Mikula (Slovakia)

**JSG 0.8:** Earth system interaction from space geodesy (joint with all Commissions)
Chair: S. Jin (China)

**JSG 0.9:** Future developments of ITRF models and their geophysical interpretation (joint with Commission 1 and IERS)
Chair: A. Dermanis (Greece)
## Program of Activities

The ICCT's program of activities include

participation as (co-)conveners of geodesy sessions at major conferences (IAG, EGU, AGU, ...), organization of a Hotine-Marussi symposium, initiation of a summer school on theoretical geodesy, maintaining a website for dissemination of ICCT related information.

## Steering Committee

* President N. Sneeuw Germany

* Vice-President P. Novák Czech Rep.

* Representatives:

* Commission 1 T. van Dam Luxembourg

* Commission 2 U. Marti Switzerland

* Commission 3 R. Gross USA

* Commission 4 D. Brzezinska USA

* GGOS H. Kutterer Germany

# JSG 0.1: Application of Time-Series Analysis in Geodesy

Chair: W. Kosek (Poland)

Affiliation: GGOS, all commissions

## Introduction

Observations provided by modern space geodetic techniques (geometric and gravimetric) deliver a global picture of dynamics of the Earth. Such observations are usually represented as time series which describe (1) changes of surface geometry of the Earth due to horizontal and vertical deformations of the land, ocean and cryosphere, (2) fluctuations in the orientation of the Earth divided into precession, nutation, polar motion and spin rate, and (3) variations of the Earth's gravitational field and the centre of mass of the Earth. The vision and goal of GGOS is to understand the dynamic Earth's system by quantifying our planet's changes in space and time and integrate all observations and elements of the Earth's system into one unique physical and mathematical model. To meet the GGOS requirements, all temporal variations of the Earth's dynamics – which represent the total and hence integral effect of mass exchange between all elements of Earth's system including atmosphere, ocean and hydrology – should be properly described by time series methods.

Various time series methods have been applied to analyze such geodetic and related geophysical time series in order to better understand the relation between all elements of the Earth's system. The interactions between different components of the Earth's system are very complex, thus the nature of the considered signals in the geodetic time series is mostly wideband, irregular and non-stationary. Therefore, the application of time frequency analysis methods based on wavelet coefficients – e.g. time-frequency cross-spectra, coherence and semblance – is necessary to reliably detect the features of the temporal or spatial variability of signals included in various geodetic data, and other associated geophysical data.

Geodetic time series may include, for instance, temporal variations of site positions, tropospheric delay, ionospheric total electron content, masses in specific water storage compartments or estimated orbit parameters as well as surface data including gravity field, sea level and ionosphere maps. The main problems to be scrutinized concern the estimation of deterministic (including trend and periodic variations) and stochastic (non-periodic variations and random fluctuations) components of the time series along with the application of the appropriate digital filters for extracting specific components with a chosen frequency bandwidth. The application of semblance filtering enables to compute the common signals, understood in frame of
the time-frequency approach, which are embedded in various geodetic/geophysical time series.

Numerous methods of time series analysis may be employed for processing raw data from various geodetic measurements in order to promote the quality level of signal enhancement. The issue of improvement of the edge effects in time series analysis may also be considered. Indeed, they may either affect the reliability of long-range tendency (trends) estimated from data or the real-time processing and prediction.

The development of combination strategies for time- and space-dependent data processing, including multi-mission sensor data, is also very important. Numerous observation techniques, providing data with different spatial and temporal resolutions and scales, can be combined to compute the most reliable geodetic products. It is now known that incorporating space variables in the process of geodetic time series modelling and prediction can lead to a significant improvement of the prediction performance. Usually multi-sensor data comprises a large number of individual effects, e.g. oceanic, atmospheric and hydrological contributions. In Earth system analysis one key point at present and in the future will be the development of separation techniques. In this context principal component analysis and related techniques can be applied.

## Objectives

* To study geodetic time series and their geophysical causes in different frequency bands using time series analysis methods, mainly for better understanding of their causes and prediction improvement.

* The evaluation of appropriate covariance matrices corresponding to the time series by applying the law of error propagation, including weighting schemes, regularization, etc.

* Determining statistical significance levels of the results obtained by different time series analysis methods and algorithms applied to geodetic time series.

* The comparison of different time series analysis methods and their recommendation, with a particular emphasis put on solving problems concerning specific geodetic data.

* Developing and implementing the algorithms – aiming to seek and utilize spatio-temporal correlations – for geodetic time series modelling and prediction.

* Better understanding of how large-scale environmental processes, such as for instance oceanic and atmospheric oscillations and climate change, impact modelling strategies employed for numerous geodetic data.

* Developing combination strategies for time- and space-dependent data obtained from different geodetic observations.

* Developing separation techniques for integral measurements in individual contributions.

## Program of activities

Updating the webpage, so that the information on time series analysis and its application in geodesy (including relevant multidisciplinary publications and the unification of terminology applied in time series analysis) will be available.

Participating in working meetings at the international symposia and presenting scientific results at the appropriate sessions.

Collaboration with other working groups dealing with geodetic time-series e.g. Cost ES0701 Improved constraints on models of GIA or the Climate Change Working Group.

## Members

* W. Kosek (Poland), chair

* R. Abarca del Rio (Chile)

* O. Akyilmaz (Turkey)

* J. Böhm (Austria)

* L. Fernandez (Argentina)

* R. Gross (USA)

* M. Kalarus (Poland)

* M. O. Karslioglu (Turkey)

* H. Neuner (Germany)

* T. Niedzielski (Poland)

* S. Petrov (Russia)

* W. Popinski (Poland)

* M. Schmidt (Germany)

* M. van Camp (Belgium)

* O. de Viron (France)

* J. Vondrák (Czech Republic)

* D. Zheng (China)

* Y. Zhou (China)
# JSG 0.2: Gravity Field Modelling in Support of World Height System Realization

Chair: P. Novák (Czech Republic)

Affiliation: Comm. 2, 1 and GGOS

## Introduction

Description of the Earth's gravity field still remains a major research topic in geodesy. The main goal is to provide reliable global models covering all spatially-temporal frequencies of its scalar parameterization through the gravity potential. Detailed and accurate gravity field models are required for proper positioning and orientation of geodetic sensors (data geo-referencing). Geometric properties of the gravity field are then studied including those of its equipotential surfaces and their respective surface normals, since they play a fundamental role in definition and realization of geodetic reference systems. Gravity field models will be applied for definition and realization of a vertical reference system (currently under construction) that will support studies of the Earth system.

This study group is an entity of the Inter-Commission Committee on Theory. It is affiliated to Commissions 1 (Reference Frames) and 2 (Gravity Field); its close co-operation with GGOS Theme 1 "Unified Global Height System" is anticipated. It aims at bringing together scientists concerned namely with theoretical aspects in the areas of interest specified below.

## Objectives

* Considering different types and large amounts of gravity-related data available today, large variety of gravity field models and the ongoing IAG project of realizing a world height system (WHS), this study group shall focus on theoretical aspects related to the following (non-exhaustive to WHS) list of problems:

* To study available gravity field models in terms of their available resolution, accuracy and stability for the purpose of WHS realization.

* To define a role of a conventional model of the Earth's gravity field (EGM) to be used for WHS realization including its scale parameters.

* To study relations between an adopted conventional EGM and parameters of a geocentric reference ellipsoid of revolution approximating a time invariant equipotential surface of the adopted EGM aligned to reduced observables of mean sea level.

* To study theoretical aspects of various methods proposed for WHS definition and realization including investigations on tidal system effects.

* To investigate combination of heterogeneous gravity field observables by using spatial inversion, spherical radial functions, collocation, wavelets, etc. and by taking into account their sampling geometry, spectral and stochastic properties.

* To investigate methods of gravity field modelling based on combination of global gravitational models, ground and airborne gravity, GNSS/levelling height differences, altimetry data, deflections of the vertical, etc.

* To study stable, accurate and efficient methods for continuation of gravity field parameters including space-borne observables of type GRACE and GOCE.

* To advance theory and methods for solving various initial and boundary value problems (I/BVP) in geodesy.

* To study methods for gravity potential estimation based on its measured directional derivatives (gravity, gravity gradients) by exploiting advantages of simultaneous continuation and inversion of observations.

* To investigate requirements for gravity data (stochastic properties, spatially-temporal sampling, spectral content etc.) in terms of their specific geodetic applications.

## Program of activities

Active participation at major geodetic conferences and meetings.

Organizing a session at the Hotine-Marussi Symposium 2013.

Co-operation with affiliated IAG Commissions and GGOS. Electronic exchange of ideas and thoughts through a SG web page.

Monitoring activities of SG members and external individuals related to SG.

Compiling bibliography in the area of SG interest.

## Members

* Pavel Novák (Czech Republic), chair

* Hussein Abd-Elmotaal (Egypt)

* Robert Čunderlík (Slovakia)

* Heiner Denker (Germany)

* Will Featherstone (Australia)

* René Forsberg (Denmark)

* Bernhard Heck (Germany)

* Jianliang Huang (Canada)

* Christopher Jekeli (USA)

* Dan Roman (USA)

* Fernando Sansò (Italy)

* Michael G Sideris (Canada)

* Lars Sjöberg (Sweden)

* Robert Tenzer (New Zealand)

* Yan-Ming Wang (USA)
# JSG 0.3: Comparison of Current Methodologies in Regional Gravity Field Modelling

Chairs: M. Schmidt, Ch. Gerlach (Germany)

Affiliation: Comm. 2, 3

## Introduction

Traditionally the gravitational potential of the Earth and other celestial bodies is modelled as a series expansion in terms of spherical harmonics. Although this representation is technically possible for ultra-high expansions, it is well-known that spherical harmonic approaches cannot represent data of heterogeneous density and quality in a proper way. In order to overcome these and other deficiencies regional modelling comes into question.

In the last years many groups have developed sophisticated approaches for regional modelling, e.g. the expansion of the gravity field or functionals of the field in terms of spherical (radial) base functions. Analogously to spherical harmonic approaches, also in regional modelling the unknown model parameters, i.e. the coefficients of the series expansion, can be either determined by means of numerical integration or as the solution of a parameter estimation process. Numerical integration techniques are widely used in the mathematical community and provide efficient and stable solutions. However, numerical integration techniques suffer from important disadvantages. Among others these methods (1) require the input data to be given on a spherical integration grid, (2) cannot provide estimated error variances and covariances of the model parameters and (3) have difficulties to handle the combination of data from different measurement techniques. Due to these disadvantages, parameter estimation is the preferred strategy in the geodetic community. Although solutions in regional modelling based on parameter estimation are generated by several groups since many years, a large number of unsolved problems and open questions still remain. They mostly arise from the condition of the normal equation system and are therefore directly connected to the parametrization of the gravity field, the type and distribution of observation data, the choice and location of base functions, possible regularisation schemes, etc.

The aim of the proposed SG is to find guidelines on suitable strategies for setting up the parameter estimation of regional gravity field modelling. This includes appropriate strategies for the combination of satellite, airborne and terrestrial data. The focus of the SG is on the methodological foundation of regional gravity field modelling based on series expansions in terms of localizing base functions. Therefore numerical studies will be concentrated on simulations based on synthetic data. It is not the aim of the SG to process and compare solutions from real data.

## Objectives

The main objectives of this SG are:

* to collect information of available methodologies and strategies for regional modelling, including

- the type of base functions (splines, wavelets, Slepian function, Mascons, etc.),

- the point grids for placing the functions (standard grid, icosaeders, Reuter grid, etc. on a sphere, ellipsoid, etc.),

- the choice and establishment of an appropriate adjustment model (combination strategy, variance component estimation, rank deficiency problems, e.g., due to downward continuation, etc.),

- the consideration of model errors (truncation errors, edge effects, leakage, etc.),

- the specific field of application,

* to analyze the collected information in order to find specific properties of the different approaches and to find, why certain strategies have been chosen,

* to create a benchmark data set for comparative numerical studies,

* to carry out numerical comparisons between different solution strategies for estimating the model parameters and to validate the results with other approaches (spherical harmonic models, least-squares collocation, etc.),

* to quantify and interpret the differences of the comparisons with a focus on detection, explanation and treatment of inconsistencies and possible instabilities of the different approaches,

* to create guidelines for generating regional gravity solutions,

* to outline standards and conventions for future regional gravity products.

* Comparable work outside gravity field determination, e.g. in the mathematical communities and in geomagnetic field determination will be taken into account.

* To achieve the objectives, the SG interacts and collaborates with other ICCT SGs as well as IAG Commission 2. As a matter of fact the outcomes of the SG can be also used by other IAG commissions, especially in Commission 3.

* The SG's work will be distributed to IAG sister associations through respective members.

## Program of Activities

The SG's program of activities will include organization of SG meetings and of one or more scientific workshops on regional modelling participation in respective symposia (EGU, AGU, etc.), publication of important findings in proper journals, maintaining a website for general information as well as for internal exchange of data sets and results, supporting ICCT activities
## Members

* Michael Schmidt (Germany), chair

* Christian Gerlach (Germany); chair

* Katrin Bentel (Norway)

* Annette Eicker (Germany)

* Indridi Einarsson (Denmark)

* Junyi Guo (USA)

* Majid Naeimi (Germany)

* Isabelle Panet (France)

* Judith Schall (Germany)

* Uwe Schäfer (Germany)

* Frederick Simons (USA)

* C.K. Shum (USA)

* Matthias Weigelt (Germany)

* Gongyou Wu (China)

## Objectives

* Understand the horizontal coordinate systems of the different NWMs, ranging from global to small-scale regional models

* Understand the vertical coordinate systems of the different NWMs, ranging from global to small-scale regional models

* Formulate a clear mathematical description on how to transform between NWMs and a geodetic frame (in both directions)

* Summarize these findings in a peer-reviewed paper that will act as a standard for future use of NWM-produced fields.

# JSG 0.4: Coordinate Systems in Numerical Weather Models

Chair: T. Hobiger (Japan)

Affiliation: all Commissions

## Introduction

Numerical weather models (NWMs) contain valuable information that is relevant for a variety of geodetic models. Currently no clear description exists regarding how to deal with the NWM coordinate systems when carrying out the calculations in a geodetic reference frame. The problem can be split into two questions: First, how to relate the horizontal NWM coordinates, which are in most cases geocentric coordinates, derived initially from either Cartesian or spectral representations, properly into an ellipsoidal/geodetic frame? Second, how to transform the NWM height system into elliptical heights as used within geodesy? Although some work has been already done to answer these questions, still no procedures, guidelines or standards have been defined in order to consistently transform the meteorological information into a geodetic reference frame.

The study group will categorize the NWM coordinate systems, create mathematical models for transformation and summarize these findings in a peer-reviewed paper that will act as guidelines for those who intend to utilize NWM information. In addition, it will be necessary to define such transformations in both ways, in order to enable the assimilation of geodetic measurements into meteorological models as well. Moreover, the study group will deal with the issue of surface data contained in NWM and how this information can be consistently used.

## Program of activities

* Launch a web-page for dissemination of information, presentation, communication, outreach purposes; provide a bibliography

* Conduct working meetings in association with international conferences; present research results in appropriate sessions

* Organize workshops dedicated mainly to problem identification and to motivation of relevant scientific research

* Produce at least one peer-reviewed paper that presents a clear and consistent description of how to transform information from and to NWMs, and the relevance of different NWM structures, and, if possible, a second paper that deals with the uncertainty of the NWM related coordinate information will be considered.

## Members

* Thomas Hobiger (Japan), chair

* Johannes Boehm (Austria)

* Tonie van Dam (Luxembourg)

* Pascal Gegout (France)

* Rüdiger Haas (Sweden)

* Ryuichi Ichikawa (Japan)

* Arthur Niell (USA)

* Felipe Nievinski (USA)

* David Salstein (USA)

* Marcelo Santos (Canada)

* Michael Schindelegger (Austria)

* Henrik Vedel (Denmark)

* Jens Wickert (Germany)

* Florian Zus (Germany)
# JSG 0.5: Multi-Sensor Combination for the Separation of Integral Geodetic Signals

Chair: F. Seitz (Germany)

Affiliation: Comm. 2, 3 and GGOS

## Introduction

A large part of the geodetic parameters derived from space geodetic observation techniques are integral quantities of the Earth system. Among the most prominent ones are parameters related to Earth rotation and the gravity field. Variations of those parameters reflect the superposed effect of a multitude of dynamical processes and interactions in various subsystems of the Earth. The integral geodetic quantities provide fundamental and unique information for different balances in the Earth system, in particular for the balances of mass and angular momentum that are directly related to (variations of) the gravity field and Earth rotation. In respective balance equations the geodetic parameters describe the integral effect of exchange processes of mass and angular momentum in the Earth system. In contrast to many other disciplines of geosciences, geodesy is characterized by a very long observation history. Partly, the previously mentioned parameters have been determined over many decades with continuously improved space observation techniques. Thus geodesy provides an excellent data base for the analysis of long term changes in the Earth system and contributes fundamentally to an improved understanding of large-scale processes.

However, in general the integral parameter time series cannot be separated into contributions of specific processes without further information. Their separation and therewith their geophysical interpretation requires complementary data from observation techniques that are unequally sensitive for individual effects and/or from numerical models. Activities of the study group are focussed on the development of strategies for the separation of the integral geodetic signals on the basis of modern space-based Earth observation systems. A multitude of simultaneously operating satellite systems with different objectives is available today. They offer a broad spectrum of information on global and regional-scale processes at different temporal resolutions. Within the study group it shall be investigated in which way the combination of heterogeneous data sets allows for the quantification of individual contributors to the balances of mass and angular momentum.

The research activities shall be coordinated between the participating scientists and shall be conducted in interdisciplinary collaboration. At all times the group is open for new contacts and members in order to embed the activities in a wide context. The study group is primarily affiliated

with the IAG commissions 2 (Gravity field) and 3 (Earth rotation and geodynamics).

## Objectives

The primary objective of the study group is the development of strategies for multi-sensor combinations with the aim of separating time series of integral geodetic parameters related to Earth rotation and gravity field. The separation of the parameter time series into contributions of individual underlying effects fosters the understanding of dynamical processes and interactions in the Earth system. This is of particular interest in the view of global change.

Individual contributions from various subsystems of the Earth shall be quantified and balanced. In particular our investigations focus on the separation of the Earth rotation parameters (polar motion and variations of length-of-day) into contributions of atmospheric and hydroscopic angular momentum variations, and on the separation of GRACE gravity field observations over continents into the contributions of individual hydrological storage compartments, such as groundwater, surface water, soil moisture and snow.

Investigations in the frame of the study group will exploit the synergies of various observation systems (satellite altimetry, optical and radar remote sensing, SMOS, and others) for the separation of the signals and combine their output with numerical models. Among the most important steps are compilation and assessment of background information for individual observation systems and sensors (mode of operation, sensitivity, accuracy, deficiencies) as well as theoretical studies which (new) information on the Earth system can be gained from a combination of different observation methods.

In particular the research comprises the following topics:

* potential and usability of contemporary space-borne and terrestrial sensors for an improved understanding of processes within atmosphere and hydrosphere.

* analysis of accuracy, temporal and spatial resolution and coverage of different data sets

* theoretical and numerical studies on the combination of heterogeneous observation types. This comprehends investigations on appropriate methods for parameter estimation including error propagation, the analysis of linear dependencies between parameters and the solution of rank deficiency problems.

* mathematical methods for the enhancement of the information content (e.g. filters)

* quantification of variations of mass and angular momentum in different subsystems from multi-sensor analysis

* analysis of the consistencies of balances between individual effects and integral geodetic parameters on different spatial scales
* formulation of recommendations for future research and (if possible) for future satellite missions on the basis of balance inconsistencies

## Planned Activities

* Set-up of a SG webpage for dissemination of information (activities and a bibliographic list of references) and for presentation and communication of research results.

* Organization of conference sessions / workshops:
  * planned in 2013: Conference Session in the Hotine Marussi Symposium
  * planned in 2014: 2nd workshop on the Quality of Geodetic Observing and Monitoring Systems (QuGOMS' 14)

* Common publications of SG members

* Common fund raising activities (e.g. for PhD positions)

## Principal Scientific Outcome / Results

By the end of the 4-year period 2011-2015 the following outcome shall be achieved:

Mature experience in geodetic multi-sensor data combination including data availability, formats, combination strategies and accuracy aspects

Numerical results for separated hydrological contributions to integral mass variations observed by GRACE for selected study areas.

Numerical results for separated atmospheric/hydrospheric contributions Earth rotation parameters on seasonal to inter-annual time scales

Initiation of at least one common funded project with positions for PhD students working in the topical field of the study group

## Members

* Florian Seitz (Germany), chair

* Sarah Abelen (Germany)

* Rodrigo Abarca del Rio (Chile)

* Andreas Güntner (Germany)

* Karin Hedman (Germany)

* Franz Meyer (USA)

* Michael Schmidt (Germany)

* Manuela Seitz (Germany)

* Alka Singh (India)

# JSG 0.6: Applicability of Current GRACE Solution Strategies to the Next Generation of Inter-Satellite Range Observations

Chairs: M. Weigelt (Germany)
A. Jäggi (Switzerland)

Affiliation: Comm. 2

## Problem statement

The GRACE-mission (Tapley et al., 2004b) proved to be one of the most important satellite missions in recent times as it enabled the recovery of the static gravity field with unprecedented accuracy and, for the first time, the determination of temporal variations on a monthly (and shorter) basis. The key instrument is the K-band ranging system which continuously measures the changes of the distance between the two GRACE satellites with an accuracy of a few micrometer. Thanks to the success of this mission, proposals have been made for the development of a GRACE-follow-on mission and a next-generation GRACE satellite system, respectively. Apart from options for a multi-satellite mission, the major improvement will be the replacement of the microwave based K-band ranging system by laser interferometry (Bender et al., 2003). The expected improvement in the accuracy is in the range of a factor 10 to 1000.

Two types of solution strategies exist for the determination of gravity field quantities from kinematic observations (range, range-rate and range-acceleration). The first type is based on numerical integration. The most common ones are the classical integration of the variational equations (Reigber, 1989; Tapley et al., 2004a), the Celestial Mechanics Approach (Beutler et al., 2010) or the short-arc method (Mayer-Gürr, 2006). The second type of solution strategies tries to make use of in-situ (pseudo)-observations. The most typical ones are the energy balance approach (Jekeli, 1998; Han, 2003), the relative acceleration approach (Liu, 2008) or the line-of-sight gradiometry approach (Keller and Sharifi, 2005).

From a theoretical point of view all approaches are in one way or the other based on Newton's equation of motion and thus all of them should be applicable to the next generation of satellite missions as well. Practically, problems arise due to the necessity of approximations and linearizations, the accumulation of errors, the combination of highly-precise with less precise quantities, e.g. K-band with GPS, and the incorporation of auxiliary measurements, e.g. accelerometer data. These problems are often circumvented by introducing reference orbits, reducing the solution strategies to residual quantities, and by frequently
solving for initial conditions and/or additional empirical or
stochastic parameter. In the context of the next generation
of low-low satellite-to-satellite tracking systems, the
question is whether these methods are still sufficient to
fully exploit the potential of the improved range observa-
tions.

Objectives

Observations are related to gravity field quantities by
means of geometry, kinematics and dynamics. The gravity
field is then represented by global or local base functions.
The focus of this study group is primarily on the use of
spherical harmonics as base function with different
approaches to relate the observations to the gravity field.
However, since local methods also proofed to yield high-
quality solutions, this group will be affiliated with the pro-
posed study group on the "Methodology of Regional
Gravity Field Modelling" by M. Schmidt and Ch. Gerlach
in order to investigate the interplay with regional model-
ling. The usage of other global base functions is also wel-
come.

The objectives of the study group are therefore to:

* investigate each solution strategy, identify approximations and linearizations and test them for their permissionability to the next generation of inter-satellite range observations,

* identify limitations or the necessity for additional and/or more accurate measurements,

* quantify the sensitivity to error sources, e.g. in tidal or non-gravitational force modelling,

* investigate the interaction with global and local model-
ling,

* extend the applicability to planetary satellite mission, e.g. GRAIL,

* establish a platform for the discussion and in-depth understanding of each approach and provide documentation.

It will not be the objective of this study group to identify
the “best” approach as from a theoretical point of view all
approaches are able to yield a solution as long as the neces-
sary observations with sufficient accuracy have been made
and approximations and linearization errors remain below
the proposed accuracy of the new range observation. Fur-
ther, solutions need validation which is done best with
different and independent solution strategies in order to
identify possible systematic effects.

Methodology and Output

The investigation will be based on an in-depth analysis of
the theoretical foundations of each approach in combina-
tion with a simulation study with step-wise increasing

realism. The preparation of the simulated data set and each
approach will be assigned separate work packages with
subtasks, which include the above mentioned objectives.
Each member is supposed to assign himself to at least one
work package and contribute by adding to the discussion of
the principles of each approach, supplying simulated data
sets, carry out numerical investigations or develop solu-
tions to specific problems.

The primary output is the result of the collaborative
investigation of the different approaches aiming at the
identification of possible challenges and the development
of solutions ensuring their applicability to the next genera-
tion of inter-satellite range observations. These findings
are supposed to be well documented in journal paper,
possibly in a special issue of Journal of Geodesy or similar
by the end of 2014. A workshop is envisaged in the
vicinity of the Hotine-Marussi symposium in 2013.

Members

• Matthias Weigelt (Germany), chair

• Adrian Jäggi (Switzerland), chair

• Markus Antoni (Germany)

• Oliver Baur (Austria)

• Richard Biancale (France)

• Sean Bruinsma (France)

• Christoph Dahle (Germany)

• Christian Gerlach (Germany)

• Thomas Gruber (Germany)

• Shin-Chan Han (USA)

• Hassan Hashemi Farahani (The Netherlands)

• Wolfgang Keller (Germany)

• Jean-Michel Lemoine (France)

• Anno Löcher (Germany)

• Torsten Mayer-Gürr (Austria)

• Philip Moore (UK)

• Himanshu Save (USA)

• Mohammad Sharifi (Iran)

• Natthachet Tangdamrongsub (Taiwan)

• Pieter Visser (The Netherlands)

Corresponding members

• Christian Gruber (Germany)

• Majid Naeimi (Germany)

• Jean-Claude Raimondo (Germany)

• Michael Schmidt (Germany)
# JSG 0.7: Computational Methods for High-Resolution Gravity Field Modelling and Nonlinear Diffusion Filtering

Chairs: R. Čunderlík, K. Mikula (Slovakia)

Affiliation: Comm. 2, 3 and GGOS

## Introduction

Efficient numerical methods and HPC (High Performance Computing) facilities provide new opportunities in many applications in geodesy. The goal of the IC SG is to apply numerical methods like the finite element method (FEM), finite volume method (FVM), boundary element method (BEM) and others mostly for gravity field modelling and non-linear filtering of data on the Earth's surface. An advantage is that such numerical methods use finite elements as basis functions with local supports. Therefore a refinement of the discretization is very straightforward allowing adaptive refinement procedures as well.

In case of gravity field modelling, a parallelization of algorithms using the standard MPI (Message Passing Interface) procedures and computations on clusters with distributed memory allows to achieve global or local gravity field models of very high-resolution, where a level of the discretization practically depends on capacity of available HPC facilities. The aforementioned numerical methods allow a detailed discretization of the real Earth's surface considering its topography. To get precise numerical solution to the geodetic boundary-value problems (BVPs) on such complicated surface it is also necessary to handle problems like the oblique derivative.

Data filtering occurs in many applications of geosciences. A quality of filtering is essential for correct interpretations of obtained results. In geodesy we usually use methods based on the Gaussian filtering that corresponds to a linear diffusion. Such filtering has a uniform smoothing effect, which also blurs "edges" representing important structures in the filtered data. In contrary, a nonlinear diffusion allows adaptive smoothing that can preserve main structures in data, while a noise is effectively reduced. In image processing there are known at least two basic nonlinear diffusion models; (i) the regularized Perona-Malik model, where the diffusion coefficient depends on an edge detector, and (ii) the geodesic mean curvature flow model based on a geometrical diffusion of level-sets of the image intensity.

The aim of the SG is to investigate and develop nonlinear filtering methods that would be useful for a variety of geodetic data, e.g., from satellite missions, satellite altimetry and others. A choice of an appropriate numerical technique is open to members of the SG. An example of

the proposed approach is based on a numerical solution of partial differential equations using a surface finite volume method. It leads to a semi-implicit numerical scheme of the nonlinear diffusion equation on a closed surface.

## Objectives

* to develop numerical models for solving the geodetic BVPs using numerical methods like FEM, FVM, BEM and others,

* to investigate the problem of oblique derivative,

* to implement parallelization of numerical algorithms using the standard MPI procedures,

* to perform large-scale parallel computations on clusters with distributed memory,

* to investigate methods for nonlinear filtering of data on closed surfaces using the regularized Perona-Malik model or mean curvature flow model,

* to derive fully-implicit and semi-implicit numerical schemes for the linear and nonlinear diffusion equation on closed surfaces using the surface FVM,

* to develop algorithms for the nonlinear filtering of data on the Earth's surface,

* to summarize the developed methods and achieved numerical results in journal papers.

## Program of activities

active participation in major geodetic conferences, working meetings at international symposia, organization of a conference session.

## Membership

* Róbert Čunderlík (Slovakia), chair

* Karol Mikula (Slovakia), chair

* Ahmed Abdalla, New Zealand

* Michal Beneš (Czech Republic)

* Zuzana Fašková (Slovakia)

* Marek Macák (Slovakia)

* Otakar Nesvadba (Czech Republic)

* Róbert Špir (Slovakia)

* Róbert Tenzer (New Zealand)
# JSG 0.8: Earth System Interaction from Space Geodesy

Chair: S. Jin (China)

Affiliation: Comm. 2, 3 and 4

## Introduction

The gravity field and geodetic mass loading reflect mass redistribution and transport in the Earth's fluid envelope, and in particular interactions between atmosphere, hydro-sphere, cryosphere, land surface and the solid Earth due to climate change and tectonics activities, e.g., dynamic and kinematic processes and co-/post-seismic deformation. However, the traditional ground techniques are very difficult to obtain high temporal-spatial resolution information and processes, particularly in Tibet.

With the launch of the Gravity Recovery and Climate Experiment (GRACE) mission since 2002, it was very successful to monitor the Earth's time-variable gravity field by determining very accurately the relative position of a pair of Low Earth Orbit (LEO) satellites. Therefore, the new generation of the gravity field derived from terrestrial and space gravimetry, provides a unique opportunity to investigate gravity-solid earth coupling, physics and dynamics of the Earth's interior, and mass flux interaction within the Earth system, together with GPS/InSAR.

## Objectives

* To quantify mass transport within the Earth's fluid envelope and their interaction in the Earth system.

* To monitor tectonic motions using gravimetry/GPS, including India-Tibet collision, post-glacial uplift and the deformation associated with active tectonic events, such as earthquakes and volcanoes.

* To develop inversion algorithm and theories in a Spherical Earth on gravity field related deformation and gravity-solid Earth coupling, e.g. crust thickness, isostatic Moho undulations, mass loadings and geodynamics.

* To develop methods to extract a geodynamic signals related to Solid-Earth mantle and/or core and to understand the physical properties of the Earth interior and its dynamics from the joint use of gravity data and other geophysical measurements.

* To analyze and model geodynamic processes from isostatic modelling of gravity and topography data as well as density structure of the Earth's deep interior.

* To address mantle viscosity from analyzing post-seismic deformations of large earthquakes and post-glacial rebound (PGR) and to explain the physical relationships between deformation, seismicity, mantle dynamics, lithospheric rheology, isostatic response, etc.

* To achieve these objectives, the IC SG interacts and collaborates with the ICCT and all IAG Commissions.

## Program of Activities

* Organization of SG workshop and of conference sessions,

* Participation in related scientific conference and symposia,

* Supporting contributions to the ICCT activities.

## Membership

* Shuanggen Jin (China)

* David J. Crossley (USA)

* Carla Braitenberg (Italy)

* Isabelle Panet (France)

* Jacques Hinderer (France)

* Séverine Rosat (France)

* Tonie M. van Dam (Luxembour)

* Urs Marti (Switzerland)

* Patrick Wu (Canada)

* Isabella Velicogna (USA)

* Nico Sneeuw (Germany)
# JSG 0.9: Future Developments of ITRF Models and their Geophysical Interpretation

Chair: A. Dermanis (Greece)

Affiliation: Comm. 1 and IERS

## Terms of Reference

The realization of a reference system by means of a reference frame, in the form of coordinate time series or coordinate functions for a global set of control stations is a complicated procedure. It involves input data from various space techniques each one based on its own advanced modelling and observation analysis techniques, as well as, criteria for the optimal selection of the time evolution of the reference frame among all data compatible possibilities.

The relevant “observed” coordinate time series demonstrate significant signals of periodic, non-periodic variations and discontinuities, which pose the challenge of departing from the current ITRF model of linear time evolution, realized by reference epoch coordinates and constant velocities.

The remaining residual signal in coordinate variations is dominated by an almost periodic term with varying amplitude and phase, especially in the height component. The inclusion of additional terms in the ITRF model is an intricate problem that deserves further research and careful planning.

It is also important to understand the nature of these coordinate variations in order to adopt models that are meaningful from the geophysical point of view and not a simple fit to the observed data.

Since geophysical processes causing coordinate variations also cause variations in the gravity field, it is worthwhile to investigate the possibility of incorporating result results from space gravity missions in ITRF modelling.

The working group is primarily aiming in identification of new ITRF models, investigation of their performance and motivation of relevant scientific research.

## Objectives

* Geophysical interpretation of non-linear coordinate variations and sevelopement of relevant models

* Extension of ITRF beyond the current linear (constant velocity) model, treatment of periodic and discontinuous station coordinate time series and establishment of proper

procedures for estimation of extended ITRF parameters and quality assessment of the obtained results.

## Program of Activities

* Launching of a web-page for dissemination of information, presentation, communication, outreach purposes, and providing a bibliography.

* Working meetings at international symposia and presentation of research results in appropriate sessions.

* Organization of workshops dedicated mainly to problem identification and motivation of relevant scientific research.

* Organization of a second IAG School on Reference Frames.

## Membership

* A. Dermanis (Greece), chair

* Z. Altamimi (France)

* X. Collilieux (France)

* H. Drewes (Germany)

* F. Sansò (Italy)

* T. van Dam (Luxembourg)
<figure><img src="image_8.png" /></figure>

# Global Geodetic Observing System (GGOS)

http://www.ggos.org

Chair of the GGOS Coordinating Board: **Hansjörg Kutterer** (Germany)
Acting Vice-Chair of the GGOS Coordinating Board: **Ruth Neilan** (USA)
Director of the GGOS Coordinating Office: **Guiseppe Bianco** (Italy)

## Preamble

The proposal for the Global Geodetic Observing System (GGOS) was developed by the GGOS planning group between 2001 and 2003 according to the Bylaws of the International Association of Geodesy (IAG). The proposal was accepted by the IAG Executive Committee and the IAG Council at their meetings during the XXIII IUGG General Assembly in Sapporo in July 2003. GGOS was endorsed by the IUGG through Resolution No. 3 at the same General Assembly.

Changes in the IAG Bylaws in 2007 resulted in GGOS being recognized as an integral component of IAG along with Services and Commissions. As a historical note, this transformed the status of GGOS from that of an IAG Project to an IAG component. Specific to the GGOS is IAG Bylaw numbers 1(d) and 15.

During 2009-2011, revisions to the structure of GGOS were discussed leading to these 2011 Terms of Reference, primarily to streamline the organizational structure of GGOS.

In February 2011, GGOS Executive Committee, with additional participants, conducted a strategic planning retreat that led to defining the vision, mission, goals and tasks of GGOS for the coming five years. In parallel, the GGOS Terms of Reference were being revised primarily to streamline the governance structure of GGOS. Both documents were approved by the GGOS Steering Committee at its meeting in Melbourne, Australia during the XXV General Assembly of IUGG, July 2011. The IAG Executive Committee then approved the new Terms of Reference (ToR) at its business meetings during IUGG. The ToR are located at http://www.ggos.org.

## Vision of GGOS

According to the IAG Bylaws 1(d) "*The Global Geodetic Observing System works with the IAG components to provide the geodetic infrastructure necessary for monitoring the Earth system and global change research*". The vision is "*Advancing our understanding of the dynamic Earth system by quantifying our planet's changes in space and time*".

## Mission of GGOS

*We live on a dynamic planet in constant motion that requires long-term continuous quantification of its changes in a truly stable frame of reference.*

The mission of GGOS is:

1. To provide the observations needed to monitor, map and understand changes in the Earth's shape, rotation and mass distribution.

2. To provide the global frame of reference that is the fundamental backbone for measuring and consistently interpreting key global change processes and for many other scientific and societal applications.

3. To benefit science and society by providing the foundation upon which advances in Earth and planetary system science and applications are built.

## Recent Activities

With the approval of the new GGOS ToR, we are in the process of implementing the new structure and establishing the necessary elements according to the ToR (Figure 1). As part of this transition, a GGOS retreat is planned for early 2012. One focus of this retreat will be to consider further the role of GGOS within IAG and how to develop the integration of IAG elements within GGOS.

The former GGOS Executive Committee is supporting the newly appointed Chair during this transition period until the GGOS Coordinating Board (CB) is fully established. This is expected to take another six months. During this time, the GGOS Consortium members are being identified. The GGOS consortium then will nominate and elect six open positions on the CB. Once these are filled, the CB will then elect three Members-at-Large to balance the CB for geography and expertise. Once the CB approves those members, then the election of the Vice-Chair can take place and the Chair will then propose the new GGOS Executive Committee.

The plan is to harmonize the GGOS structure and schedule with the IAG schedule of elections every four years. Note that the appointment of the GGOS Chair remains a responsibility of the IAG EC in consultation with the GGOS CB.

The three themes of GGOS: Unified Height System, Geo-hazards and Sea Level Variability will be a primary focus
for GGOS over the coming four years as these were identified in 2010 as themes that require cross-cutting disciplines and techniques with GGOS, as well as potentials for new partnerships.

The Committee on Earth Observation Satellites (CEOS) met during the week of November 7, 2011, in Lucca, Italy. GGOS made an application to become an associate member of CEOS and was unanimously accepted. GGOS principals are now exploring how best to engage with CEOS and what areas are of mutual benefit between CEOS and GGOS components.

GGOS is also looking towards establishing links with strategic partners and broadening the outreach and development of GGOS. This is demonstrated in one example through our participation and exhibit at the Group on Earth Observations VIII in Istanbul, Turkey Nov. 15-17, 2011. The Chair made a statement to the plenary on the recent activities and directions of GGOS, while a new GGOS exhibit was well received by the attendees.

## Key Goals and Tasks of GGOS

The goals of GGOS are:

1. To be the primary source for all global geodetic information and expertise serving society and Earth system science.

2. To actively promote, sustain, improve and evolve the global geodetic infrastructure needed to meeting Earth science and societal requirements.

3. To coordinate the international geodetic services that are the main source of key parameters needed to realize a stable global frame of reference and to observe and study changes in the dynamic Earth system.

4. To communicate and advocate the benefits of GGOS to user communities, policy makers, funding organizations, and society.

In order to accomplish its mission and goals, GGOS depends on the IAG Services and Commissions. The Services provide the infrastructure and products on which all contributions of GGOS are based. The IAG Commissions provide expertise and support for the scientific development within GGOS. In summary, GGOS is IAG's central interface to the scientific community and to society in general.

IAG is a Participating Organization of the Group on Earth Observations (GEO). GGOS acts on behalf of the IAG in GEO and actively contributes to the Global Earth Observation System of Systems (GEOSS).

GGOS addresses relevant science issues related to geodesy and geodynamics in the 21st century, but also issues relevant to society (including but not limited to management of

natural resources, natural hazards, global risk management, monitoring of climate change and related phenomena, ocean forecasting and sea level projections, early warning of severe storms, tsunamis, other hazards, and space weather). It is an ambitious program of a dimension that goes beyond IAG, requiring a strong cooperation within the geodetic and Earth science communities, and externally, to related endeavors and communities.

### Tasks of Goal 1:

To be the primary source for all global geodetic information and expertise serving society and Earth system science.

a. Identify the components and themes of GGOS needed to plan and meeting evolving user requirements and to provide crucial data and information to the user.

b. Define and implement internal and external interfaces needed for technical and organizational efficiency.

c. Evaluate and review the current GGOS organization and structure.

d. Develop mechanisms for regular review of GGOS quality and performance, including that of its data and products.

e. Expand and broaden user communities by conducting impact studies and organizing joint workshops and symposia.

f. Provide a unique point of access to the user community by creating and maintaining the GGOS portal.

### Tasks of Goal 2:

To actively promote, sustain, improve and evolve the global geodetic infrastructure needed to meeting Earth science and societal requirements.

a. Provide the scientific basis for the necessary global geodetic infrastructure, including establishing requirements for station distribution and data quality.

b. Provide a forum for inter-service communication and exchange of information about current activities, infrastructure performance and future plans.

c. Identify major infrastructure deficiencies and propose remedies to the geodetic and user communities and appropriate entitles including the GGOS Interagency Committee (GIAC).

d. Support requests of stations, agencies and other organizations for resources.

e. Advocate for the establishment of geodetic fundamental stations with potential sponsors.

f. Advocate for relevant space-based components including operational chains of geodetic missions like gravity, altimetry, and SAR missions to provide spatial and temporal coverage of continuous and episodic changes in the dynamic Earth system.

### Tasks of Goal 3:

To coordinate the international geodetic services that are the main source of key parameters needed to realize a
stable global frame of reference and to observe and study
changes in the dynamic Earth system.

a. Improve the interaction and communication amongst GGOS, and IAG Services and Commissions by defining appropriate linkages, organizing inter-Service workshops and, when appropriate, holding joint or co-located GGOS EC and Service GB/DB meetings.

b. Reform the GGOS governance structure in order to facilitate the execution of the Science Themes, manage the relationships between the IAG Executive, GGOS EC, the Services and the Commissions, fulfill GGOS's role in outreach, represent GGOS at forums such as GEO, and other activities as may be tasked.

c. Identify data and product gaps, integrated products, additional Service and Commission components and, if necessary, new Services and Commissions that are needed to fully address the requirements of the GGOS Science Themes.

d. Establish and promote the use of reference frames, common standards and models, open data access, geodetic expertise and information, and even methodologies where appropriate, so as to ensure reliable, consistent and high-quality data and products for the geoscientific community.

e. Promote combination analyses and integrated product generation across Services and Commissions, especially from co-located geodetic sites, in order to address the requirements of the GGOS Science Themes.

f. Promote a culture of continuous quality improvement of the geodetic infrastructure, analysis center operations, effectiveness of the GGOS structural components, and of the generated GGOS data and products.

## Tasks of Goal 4:

To communicate and advocate the benefits of GGOS to user communities, policy makers, funding organizations, and society.

a. Organize meetings about GGOS activities and participate in GEO meetings, user community events, conferences, workshops, symposia, etc.

b. Identify GGOS requirements in terms of infrastructure and workforce and interact with funding authorities, national and international and space agencies to advocate the importance of meeting these requirements.

c. Promote the development and submittal to funding agencies of proposals that advance the goals of GGOS.

d. Involve young scientists by means of GGOS scholarships and grants through national and international projects.

e. Foster geodetic educational programs within universities, schools and research organizations.

f. Strengthen outreach capabilities demonstrating GGOS benefits by means of case studies and success stories; release a short GGOS movie to be presented and distributed for educational purposes.

g. Review the respective roles of GGOS and the GIAC.

h. Improve the recognition and visibility of GGOS within GEO, ICSU, COPUOS, CEOS, COSPAR and other organizations.

## Overview of GGOS Structural Elements

The organizational structure of GGOS is comprised of the following key elements:

1. **GGOS Consortium** – is the collective voice for all GGOS matters. It will meet annually as possible. The elements of GGOS have the flexibility to determine and designate two representatives to the GGOS Consortium as each (Service, Commission, or other entity) decides. The Consortium is to be comprised of the Chairs of Services and the Directors of the Service's central offices or Central Bureaus; Presidents and Vice-Presidents of IAG Commissions, and other entities essential to GGOS as determined by the Consortium. The GGOS Consortium is the nominating and electing body of elected positions on the GGOS Coordinating Board as noted below. The Chair of GGOS shall act as the Chair of the GGOS Consortium.

2. **GGOS Coordinating Board** – is the central oversight and decision-making body and represents the IAG Services, Commissions and other entities (see below).

3. **GGOS Executive Committee** – serves at the direction of the Coordinating Board to accomplish day-to-day activities of GGOS tasks.

4. **GGOS Science Panel** – advises the Coordinating Board and represents the geodetic and geoscience community.

5. **IAG Services, Commissions and relevant Inter-Commission Committees** – are the fundamental elements comprising GGOS.

6. **GGOS Working Groups and Themes** – address overarching issues common to several or all IAG components, and are a mechanism to bring the various activities of the Services and Commissions together, or to link GGOS to external organizations. Themes are cross-disciplinary and address specific areas where GGOS contributors work together to address broader and critical issues.

7. **GGOS Coordinating Office** – coordinates the work within GGOS and supports the Chairs, the Executive Committee and the Coordinating Board.

8. **Bureau for Standards and Conventions** – tracks, reviews, examines, evaluates all actual standards, constants, resolutions and conventions adopted by IAG or its components and recommends their further use or proposes the necessary updates.

9. **Bureau for Networks and Communications** – develops a strategy to design, integrate and maintain the fundamental geodetic infrastructure including communication and data flow.
## Details of the Structure of GGOS

<figure><img src="image_9.png" /><figcaption>Figure 1: GGOS Organization Chart 2011</figcaption></figure>

### 1. GGOS Consortium

The GGOS Consortium is the voice and essentially the large steering committee of GGOS. It reviews the GGOS progress, activities, and nominates and votes for the candidates for the elected positions on the GGOS Coordinating Board.

The GGOS Consortium is comprised of two designated representatives from each IAG component, which designate their representatives. The Chair of the Service Governing or Directing Board, and the Director of the Central Bureau or Coordinating Office, the Commission Presidents and Vice Presidents may be those designated members, however, no person can represent two components (but no one may have more than one vote). The Chair of the GGOS Consortium is the presiding Chair of GGOS. GGOS Consortium decisions are based on consensus. Decisions requiring a vote are decided by simple majority of the votes cast. The quorum is when at least one half of members are present, but electronic voting is acceptable provided a quorum responds.

The process for elections to the GGOS Coordinating Board will coincide with IAG's schedule for elections, calling for nominations and elections 3 months prior to the four-year IAG General Assembly, which takes place during the IUGG General Assembly (see IAG Bylaws). Candidates nominated to serve on the CB must be members of the GGOS Consortium. However, the GGOS Chair is appointed by the IAG Executive Committee in consultation with the GGOS Coordinating Board, and is not appointed by the IAG Council (see IAG Bylaws: 15 (d) and 31-a-ii).

### 2. GGOS Coordinating Board

The Coordinating Board is the decision making body of GGOS. Decisions, to the extent possible, are based on consensus. Decisions requiring a vote are decided by simple majority of the votes cast. The quorum for a valid vote is participation of one half of the voting members of the Coordinating Board. Votes may be held at meetings or by appropriate electronic means at the discretion of the GGOS Executive Committee. The Coordinating Board will meet at least once yearly, although twice yearly is preferable.

Coordinating Board Members (voting members):

<table><tr><td>• GGOS Chair (ex-officio, votes in case of a tie)</td><td>1</td></tr><tr><td>• GGOS Vice-Chair (ex-officio)</td><td>1</td></tr><tr><td>• Chair of GGOS Science Panel (ex-officio)</td><td>1</td></tr><tr><td>• Head, Coordinating Office (ex-officio)</td><td>1</td></tr><tr><td>• Directors of GGOS Bureaus (ex-officio)</td><td>2</td></tr><tr><td>• IAG President or design. representative (ex-officio)</td><td>1</td></tr><tr><td>• Service Representatives (elected by Consortium)</td><td>4</td></tr><tr><td>• Commissions Representatives (elected by Consort.)</td><td>2</td></tr><tr><td>• Members-at-Large (elected by GGOS CB)</td><td>3</td></tr><tr><td>Total Voting Members</td><td>16</td></tr></table>

Coordinating Board Members (non-voting members):

<table><tr><td>• Chairs of GGOS Working Groups<br/>+ (or more, ex-officio)</td><td>1</td></tr><tr><td>• Theme Chairs (ex-officio)</td><td>3</td></tr><tr><td>• GGOS Portal Manager (ex-officio)</td><td>1</td></tr><tr><td>• Immediate Past Chair of the CB (ex-officio)</td><td>1</td></tr><tr><td>• Representative of the GIAC/GIC (ex-officio)</td><td>1</td></tr><tr><td>Total Non-Voting Members</td><td>7</td></tr></table>

<table><tr><td>Total Membership of the Coordinating Board<br/>(plus any approved observers)</td><td>23</td></tr></table>
The chair of the GGOS Coordinating Board is determined according to the IAG Bylaws (IAG Bylaw 15 (d)). The Chair of the GGOS CB is also known as the GGOS Chair. The CB elects the Vice-Chair of the GGOS CB.

The Members-at-large are to balance the Coordinating Board with regard to geographical region or unique capability. The Chair, with the assistance of the Coordinating Office, appoints an Election Committee to organize the voting process and to ensure availability of the nominated candidates. The Election Committee presents the final list of nominations for the Members-at-large to the CB for a vote.

### 3. GGOS Executive Committee

The GGOS Executive Committee (EC) is composed of the following members:

* GGOS Chair 1

* Vice-Chair 1

* Voting Members of the CB selected for the EC 3

Total 5

The GGOS Chair biennially submits his/her list of the three GGOS members for the EC to the GGOS CB for approval. EC candidates recommended by the Chair must be voting members of the CB.

The immediate Past Chair of GGOS, Director of the Coordinating Office, the Chair of the GGOS Science Panel, and the President of IAG are permanent guests at meetings of the Executive Committee. Other observers may be invited to attend EC meetings (usually teleconferences) as needed.

### 4. GGOS Science Panel

The GGOS Science Panel is an independent and multi-disciplinary advisory board that provides scientific support to the GGOS steering and coordination entities.

The GGOS Science Panel is composed of up to 7-12 members. Members are based on recommendations from the GGOS community and candidates are approved by the CB.

The Science Panel will elect its own Chair to be approved by the CB.

### 5. Services, Commissions, Inter-Commission Committees

GGOS works with these IAG components to provide the geodetic infrastructure necessary for monitoring the Earth system and global change research. GGOS respects the bylaws and terms of reference for these essential components. GGOS is built on the existing IAG Services and their products. GGOS is not taking over tasks of the existing, and well working IAG Services. GGOS will provide a framework for existing or future Services and strive to ensure their long-term stability.

### 6. GGOS Working Groups and Themes

GGOS Working Groups (WG) are established by the Coordinating Board as needed. The Coordinating Board appoints the chair of any WG. A charter for each WG will be prepared and approved by the GGOS Coordinating Board. The members of WGs are nominated by the WG Chair and confirmed by the Coordinating Board. GGOS Working Groups can be set up for limited periods of time or as standing Working Groups. Themes are cross-disciplinary and meant to consider gaps and needed future GGOS products. The GGOS CB approves the themes. The CB appoints theme chairs. Themes outline their purpose and propose a work plan to address any noted gap to be addressed by the particular theme focus.

### 7. GGOS Coordinating Office

The GGOS Coordinating Office (CO) performs the day-to-day activities in support of GGOS, the Executive Committee, the Coordinating Board and the Science Panel, and ensures coordination of the activities of the various components. The CO ensures information flow, maintains documentation of the GGOS activities and manages specific assistance functions that enhance the coordination across all areas of GGOS, including inter-services coordination and support for workshops. The CO in its long-term coordination role ensures that the GGOS components contribute to GGOS in a consistent and continuous manner and adhere to GGOS standards. The CO also maintains, manages and coordinates the GGOS Web presence.

The GGOS Portal is an important additional web presence that provides a unique access to all GGOS data sets and products.

### 8. Bureau for Standards and Conventions

The Bureau for Standards and Conventions keeps track of the strict observations of adopted geodetic standards, standardized units, fundamental physical constants, resolutions and conventions in all official products provided by the geodetic community. It reviews, examines and evaluates all actual standards, constants, resolutions and conventions adopted by IAG or its components, and recommends further use or proposes the necessary updates. It identifies eventual gaps in standards and conventions and initiates steps to close them with, e.g., resolutions by the IUGG and/or IAG Councils.

### 9. Bureau for Networks and Communications

The Bureau for Networks and Communications develops a strategy to design, integrate and maintain the fundamental infrastructure in a sustainable way to satisfy the long-term (10 - 20 years) requirements identified by the GGOS Science Panel. Primary emphasis must be on sustaining the
infrastructure needed to maintain the evolving global reference frames, while at the same time ensuring the broader support of the scientific applications of the collected data. Coordinating and implementing the GGOS co-located station network is a key focus for 2010-2020.

## 10. GGOS Inter-Agency Committee (GIAC)

The purpose of the GIAC is to provide a forum for coordination and support for the development, implementation and operation of those components of the GGOS, whose infrastructure is operated by governmental institutions.

The GIAC supports the IAG Services, particularly those involved in the establishment, maintenance and enhancement of the geodetic infrastructure, observing systems and the International Terrestrial Reference Frame (ITRF) in a sustainable and a cost-efficient way. Furthermore, GIAC members underpin geodetic research activities coordinated by the GGOS Science Committee by providing world class geodetic infrastructure.

The GIAC is a forum that seeks to generate a unified voice to communicate with Governments and Intergovernmental organisations (GEO, UN bodies) in all matters of global and regional spatial reference frames and GGOS research and applications.

According to its Terms of Reference the GIAC coordinates the common efforts of its governmental member organisations to meet the requirements of global geodetic programs, in particular, the terrestrial reference frame, IAG services and capacity building. It supports members to obtain the resources needed for their geodetic observing infrastructure and it maintains liaison with IAG/GGOS regarding GGOS application and research needs.

The GIAC takes into account the special needs and interests of developing countries, including in particular the need to further the capabilities of these countries in geodetic observations for the realization and sustainability of global and regional spatial reference frames and related technology. In the perspective, the GIAC works on the creation of a GGOS Intergovernmental Committee and to explore possibilities to join existing international organisations to serve common interests.

# Program of Activities

## Working Groups

### WG 0.1 Satellite Missions

Chairs: Isabelle Panet (France), Roland Pail (Germany)

The GGOS Satellite Mission Working Group was established in December 2008 with its primary objectives to investigate rationale and interest from the geodetic community to establish a GGOS Bureau of Satellite Missions. An initial Terms of Reference has been drafted. Since early 2011, there are 20 members (see at the end of this section), including the Chairs, I. Panet and R. Pail.

### Key objectives

* To assess the satellite mission infrastructure at an international level relevant for achieving the goals of GGOS and make recommendations for needed missions,

* To advise and support proposed missions relevant to GGOS,

* To advocate new satellite mission proposals appropriate to advance GGOS objectives,

* To provide outreach for geodetic satellite missions,

* To facilitate the use of satellite products for users,

* To interface with the other entities, including IAG, GGOS, CEOS, GEO and space agencies, with regard to promoting satellite missions and their data products for scientific and public use.

The working group at present will address only Earth observation missions relevant for the GGOS goals.

### Actions 2011 – 2015

* Analysis of satellite infrastructure

- Identification of observational gaps for critical satellites

- Proposing needed concepts for future missions

* Focus particular types of satellite mission for advocacy

* Realization of the access to satellite products for users

- Historical data access

- Documentation, links to complementary datasets

- Thematic pages

- Provide Working Group information to GGOS portal

* Provide inputs on the scientific relevance of proposed missions in the context of GGOS goals

* Plan and continue to undertake setting up of interfaces to CEOS and other relevant organisations

* Rationalizing the possible establishment of the Bureau of Satellite Missions
## Members

* Bettadpur Srinivas (USA)

* Biancale Richard (France)

* Chao (Benjamin (Taiwan)

* Cho Sungki (Korea)

* Flechtner Frank (Germany)

* Fotopoulos Georgia (Canada)

* Fukuda Yoichi (Japan)

* Hwang, Cheinwey (Taiwan)

* Knudsen Per (Denmark)

* Matsumoto Koji (Japan)

* Müller Jürgen (Germany)

* Nerem R. Steve (USA)

* Pail Roland (Germany; co-chair)

* Panet Isabelle (France; co-chair)

* Ping Jinsong (China)

* Shum C.K. (USA)

* Sideris M. (Canada)

* Sneuuw Nico (Germany)

* Joong-Sun Won (Korea)

* Min Zhong (China)

## WG 0.2 Earth System Modelling

Chair: Maik Thomas (Germany)

The major goal of the Working Group is the preparation of a physically consistent unconstrained numerical Earth system model focussing on near-surface fluid dynamics. This modular model is expected to allow a homogeneous processing, interpretation, and prediction of geodetic parameters, i.e., Earth rotation, gravity field and deformation, and, thus, to finally contribute to a deeper understanding of dynamical processes in the Earth system reflected in geodetic observables.

### Tasks 2011 – 2015

* Selection of appropriate models for the representation of dynamics of the individual near-surface sub-systems, such as atmosphere, oceans, continental hydrosphere, cryosphere, and lithosphere;

* Development of a strategy to ensure physical consistency, in particular mass balance;

* Definition and implementation of standard modules to derive individual contributions to variations of geodetic quantities;

* Identification of relevant interactions among sub-systems as well as of appropriate parameterizations for their numerical consideration.

## Objectives 2011 – 2015

Within the period 2011-2015, the main objective is to prepare an unconstrained version of a modular Earth system model of near-surface dynamics. The system model approach has to be designed in such a way that it

* ensures consistent (passive) interactions and physical fluxes among sub-systems,

* is applicable to all geodetic quantities (rotation, gravity field, surface geometry),

* allows self-consistent predictions of geodetic parameters,

* can be used for interpretation and cross-validation of different data sets.

## WG 0.3 Data and Information Systems

Chair: Bernd Richter (Germany)

The tasks for data and information (D/I) handling, management and the GGOS Portal fall under the purview of the GGOS Data and Information Working Group. This action plan will address actions for populating and maintaining the portal and metadata standards for capturing information from contributing data centers.

### Objectives

The main objective of the D/I handling and management activity is to implement and maintain the GGOS Portal, the access point for all GGOS products.

### Actions 2011 – 2015

* Review the proposed portal structure and in particular the list of topics and their associated sub items. Provide text (both brief and long descriptive text) and illustrations for each topic. (GGOS Steering Committee, Science Panel);

* Identify key personnel to coordinate input for these sections of the portal. (GGOS Steering Committee, Science Panel, IAG Services);

* Complete draft of GGOS metadata catalog, review, and distribute to GGOS Steering Committee. (DIWG)

* Conduct monthly Data and Information Working Group telecons to coordinate activities and address actions. (DIWG);

* Implement metadata structures at GGOS contributing data centers (e.g., CDDIS, etc.) and fill the GGOS Portal metadata base for search and other applications. (IAG services);

* Ensure currency of GGOS Portal by continued review and update. (DIWG, SC, SP);

* Implement web features at the GGOS Portal when necessary, e.g. WMS, WFS (DIWG, Portal Manager).
## WG 0.4 Outreach and User Linkage

Chair: Guiseppe Bianco (Italy)

The GGOS Component “Outreach” [OR] is chaired by the GGOS Coordinating Office (CO) and managed by the Working Group on Outreach and Education (WG on O&E), approved during the GGOS Steering Committee meeting held in San Francisco on December 11th, 2010; its scope and duties have been discussed during the GGOS Retreat held in Zurich, February 2-4, 2011.

### Objectives

Objectives of the Outreach component must take into account GGOS 2020 Recommendation 1.3 (GGOS 2020, p. 283):

> "Recognizing that society to a large extent is not aware of the vital role played by geodesy for realizing a sustainable development, and that educational aspects are extremely important (because they have the greatest implication on societal behavior) in order to prepare future generations to make use of the full benefits of geodesy, it is recommended that IAG and GGOS make dedicated outreach efforts to science and society at large with the goal to promote geodesy's role in reaching sustainable development and to integrate this role of geodesy appropriately into education."

### Actions 2011 – 2015

#### Short term actions

* Finalization of the GGOS Outreach Document:

* Planning and design of GGOS Monographs, possibly finalizing the first prototype

* GGOS web site updating (continuous)

GGOS Monographs are short yet complete documents, targeted to non-specialized public, designed to clearly describe the role of geodesy in reaching sustainable development. Monographs may be devoted to specific earth science fields, such as oceanography, crustal deformations, and so on, or to societal issues such as hazard mitigation, water scarcity, global warming, and so on.

#### Mid-term actions:

* Multimedial monographs production

* Approach and collaboration with international science magazines, TV channels, to promote geodesy

* Approaching ministries of education/research to promote geodesy into curricula of all levels

## WG 0.5 ITRS Standard

Chair: Claude Boucher (France)

This Working Group develops a concept for a potential ISO Standard concerning the global geodetic reference system, with ITRS being a prime candidate. It also provides experts to its actual implementation within ISO

### Objectives 2011-2015

* Support to the drafting of an ISO standard related to ITRS

* Contribute to the report on geodetic references to be written within ISO TC211 "Geographic information/Geomatics" following a NWIP submitted by France

* Support of the formal NWIP related to the ITRS standard to be submitted to TC211 in due time.

## Bureau for Standards and Conventions

Chair: Detlef Angermann (Germany)

The Bureau for Standards and Conventions (BSC) supports GGOS in its goal to obtain products of highest accuracy, consistency, temporal and spatial resolutions, and referring to a unique reference frame stable over decades.

### Objectives

The overall goal is to ensure consistency between products generated by the different IAG services, especially between geometric and gravimetric products, by defining common standards and conventions and consistent modelling, parameterization and analysis strategies. Main objectives of the BSC are:

* Evaluate the geodetic standards and conventions currently in use by all the IAG Services for the generation of geodetic/geophysical products;

* Propagate all geodetic standards and conventions to geometric and general scientific communities and urge their common use;

* Maintain regular contact with all internal and external institutions involved in the adoption of standards, resolutions and conventions;

* Perform administrative tasks, communications and web support in cooperation with the GGOS Coordinating Office.

* Report regularly to the GGOS Coordinating Board and to the IAG Executive Committee, and – if necessary or appropriate – to the IUGG Executive Committee.
## Actions 2011 – 2015

* Numerical standards: Compilation of numerical and processing standards currently used.

* Inconsistencies: Removal of inconsistencies in the IAG/ IERS conventions.

* Metadata: Develop – together with the GGOS Portal – consistent metadata for all products describing underlying standards and conventions.

* Software routines: Make available a set of validated software routines for transformation between tide systems and time systems.

* Standards and Conventions: Development of homogeneous consistent models and standards for the integration of data to combine geometric positioning with physical heights and Earth gravity field parameters.

* IGSN: An extension of standardization activities to a new International Gravity Standardization Network (IGSN) shall be considered.

* Global Geophysical Fluids: Investigations regarding geophysical background models (e.g., loading, dealiasing) shall be carried out in cooperation with the GGFC.

**New GRS:** Development of a new Geodetic Reference System (GRS) based on a consistent system of best estimates of major parameters related to a geocentric equipotential ellipsoid.

## Bureau of Networks and Communication

Chair: Mike Pearlman (USA)

The Bureau provides oversight, coordination, and guidance for the development, implementation and operation of the GGOS Network of Core Sites. Elements of this role are:

* Promote communication and integration among Services;

* Develop and maintain a ground network station information base and data product directory;

* Monitor the development of prototype ground systems to understand performance and availability;

* Monitor network performance and advocate for maximum participation to maintain reference frame and other data product quality;

* Advocate the continued support and maintenance of the current geodetic networks and the implementation of upgraded and new field systems;

* Define the network requirements and scope the size and geometry of gravimetry and tide gauge ground networks; advocate for continued support, upgrade and expansion;

* Interface with upcoming missions to advocate for the best satellite technology to support the reference frame tasks;

* Advocate for reference frame connections through GNSS to other geodetic instruments including tide gauges, gravimeters, etc.

* Promote the formation of key partnerships to establish stations in present network gaps,

* Exploit synergistic opportunities to better integrate or co-locate stations with the infrastructure and communications networks of the many other Earth Observation disciplines.

## Actions 2011 – 2015

* Continue development by the Services (VLBI2010, NGSLR, new generation GNSS receivers, modern DORIS ground systems and new satellites; retro arrays on GPS, etc;

* Continue outreach

- Give presentations; meet with potential participants;

- Pursue the “American Networks Concept” in the first half of 2011 (1 year);

- Need to do something about Africa;

* Complete the simulation to scope the GNSS network (1 year);

* Develop Site Specification Document (1 year);

- Complicated by lack of configuration uniformity;

* Work on the technical and operational issues;

- Work with IERS WG on Inter-system vectors (co-location);

- Communications requirement;

- Multi-instrument control systems;

* Issue the CFP in concert with the GIAC (1 year);

* Strengthen our connection with the non-geometry geodesy techniques

* Characterize performance and trade-offs as the network builds up

* Implement the network

## Themes

### Theme 1: Unified Height System

Chairs: M. G. Sideris (Canada) and J. Ihde (Germany)

The objective of Theme 1 is the unification of the existing vertical reference systems around the world. This will be achieved through the definition and realization of a global vertical reference system that

* will support geometrical (ellipsoidal) and physical (normal, orthometric, geoidal) heights world-wide with centimetre precision ($10^{-9}$) in a global frame;

* will enable the unification of all existing physical height systems (i.e., all geopotential differences shall be referred to one and the same reference equipotential surface with potential $W_o$); and
* will provide high-accuracy and long-term stability of the temporal height changes (dh/dt, dH/dt, dN/dt) with 10⁻⁹ precision.

A World Height System (WHS) shall be realized with a global combined network, which will integrates at set of terrestrial reference stations high-precision absolute and relative gravity, leveling with gravity reductions, and GNSS and tide gauge observations. For this purpose, it will use contributions from all IAG Commissions, and the available databases, standards and infrastructure of the IAG/GGOS Services.

## Planned activities

### Short-Term:

Establish a global vertical reference surface and its geopotential value $W_o$.

1. Refinement of standards and conventions for the definition and realization of a WHS, including unification of standards and conventions that are used by the “geometric” and “gravity” Services of the IAG.

2. Establishment of a global vertical reference level. The work will be carried out by analysis centres for determining and monitoring the relationship between a conventional $W_o$ and the potential of the level surface closely approximating the mean sea surface.

### Medium-Term:

Develop GGOS products for the realization of a WHS.

3. Recommendation for a global vertical reference frame.

4. Guidelines/procedures for height system unification.

5. Development of a registry (metadata) containing the existing local/regional height systems and their connections to the global one.

### Long-Term:

Maintain and use in practice the WHS.

6. Determination and modeling of the temporal changes of the vertical reference frame.

7. Update the Unified Global Height System definition and realization as needed, based on future improvements in geodetic theory and observations.

8. Servicing the vertical datum needs of other geosciences such as, e.g., hydrography and oceanography.

Efforts are currently underway to establish working groups and processing centres that will focus on one or more of the action items above. One such group is the already established JWG 0.1.1, whose program of activities is outlined below.

# Joint Working Group of Theme 1

## JWG 0.1.1: Vertical Datum Standardization

(joint with Commissions 1 and 2, and IGFS)

Chair: L. Sánchez (Germany)

### Terms of Reference

During the last decades, many initiatives related to vertical datum unification have been developed in IAG. They are oriented to define and realize a global reference level and to determine the connection (transformation) of the local height datums to the global one, i.e. all physical heights (or geo-potential numbers) worldwide shall be referred to only one reference surface that is realized globally.

The main objective in the present period is to provide a reliable $W_0$ value to be introduced as the conventional reference level for the realization of the Global Height System. Although any $W_0$ value can arbitrarily be chosen, it is expected that this value is consistent with other defining parameters of geometric and physical models of the Earth. Activities will be based on the state-of-the-art data and methodologies, especially on the available representations of the Earth's surface and gravity field. Computations carried out will be documented in detail in order to guarantee the repeatability and reliability of the results. This documentation shall support the adoption of the obtained $W_0$ value as official IAG/GGOS convention. Another objective is to provide guidance on the usage of $W_0$ in practice, in particular for vertical datum unification.

### Program of activities

1. To coordinate all individual initiatives for a unified $W_0$ determination: Groups working on the estimation of a global $W_0$ value shall be brought together in order to elaborate an inventory describing the methodologies, conventions, standards, and models presently applied in $W_0$ computations.

2. To refine the $W_0$ estimation: Each group shall perform a new $W_0$ computation following its own methodologies, but applying recent models (e.g. GOCE/GRACE gravity models, sea surface models derived from calibrated and combined satellite altimetry observations, etc.). This analysis shall also include an investigation about the time-dependence of $W_0$.

3. To propose a IAG/GGOS convention on $W_0$: It is expected that results obtained after applying the different methodologies considered in the previous item are very similar. After a rigorous reliability evaluation, a best estimate of $W_0$ shall be recommended.

4. To provide a standard about the usage of $W_0$ in the vertical datum unification: Based on the interchange of experiences within the WG, it is expected to generate a document describing the most appropriate strategy to connect (unify, transform) any local height system with the global $W_0$ reference level.
## Members

* L. Sánchez (Germany), Chair

* J. Agreen (Sweden)

* R. Čunderlík (Slovakia)

* N. Dayoub (Syria)

* Z. Faskova (Slovakia)

* J. Huang (Canada).

* K. Mikula (Slovakia)

* P. Moore (United Kingdom)

* D. Roman (USA)

* Z. Šima (Czech Republic)

* V. Vatrt (Czech Republic)

* M. Vojtiskova (Czech Republic)

* Y. Wang (USA)

## Theme 2: Geohazards Monitoring

Mitigating the impact on human life and property of natural hazards such as earthquakes, volcanic eruptions, debris flows, landslides, land subsidence, tsunamis, floods, storm surges, hurricanes and extreme weather is an important scientific task to which GGOS can make fundamental contributions. GNSS and INSAR can be used to monitor the pre-eruptive deformation of volcanoes and the preseismic deformation of earthquake fault zones, aiding in the issuance of volcanic eruption and earthquake warnings. GNSS can also be used to rapidly estimate earthquake fault motion, aiding in the modeling of tsunami genesis and the issuance of tsunami warnings. Gravity measurements can be used to track mass motion within volcanic conduits; and gravity and altimetric measurements can be used to track floodwaters in river basins.

Geodetic observations are essential for understanding the processes causing the hazard, for assessing the risks of the hazard, for monitoring the development of the hazard, for deciding whether or not to issue an early warning, and to support rescue and damage assessment activities.

The objective of Theme 2 is to improve the effectiveness of the geodetic community in supporting natural hazard identification, assessment, prioritization, prediction, and early warning. As an international organization, GGOS can be very effective as an advocate for the role of geodesy in understanding and mitigating natural hazards. GGOS can be an effective advocate for improving the geodetic data needed for natural hazards research including better spatial coverage, higher sampling rate, lower latency, and wider data availability, particularly of SAR and GNSS data. Finally, improved public outreach is needed to better educate and inform the public about the benefits of geodesy for geohazards monitoring.

## Joint Working Group of Theme 2

### JWG 0.2.1: New technologies for disaster monitoring and management
(joint with Commission 4)

Chair: I.D. Doukas (Greece)

## Terms of Reference

United Nations International Strategy for Disaster Reduction (UNISDR) offers the following definition: "Disaster: A serious disruption of the functioning of a community or a society involving widespread human, material, economic or environmental losses and impacts, which exceeds the ability of the affected community or society to cope using its own resources".

These facts demand actions and therefore they make indispensable the existence of dedicated methodologies and practices that serve for the prevention of environmental risks (in terms of protecting the citizens against the effects resulting from a disaster). So, these facts trigger off the launch of many initiatives throughout the world. Many related serious undertakings have targets such as: the assessment and reduction of urban vulnerability, the boost of information and knowledge exchange concerning the numerous topics and parameters involved into the extremely complicated domain of disasters.

Consequently, there is a very wide and dynamic field for investigation, studying and testing of available technologies, sensors, geosensors, methods, information systems, techniques etc., with a lot of potential.

## Objectives

* To gather and register all kinds of disasters, either natural or man-made as a preparation to obtain a final reference base of study.

* To investigate, study and test any kind of available technologies, sensors, geosensors, methods, information systems (web-based or not), techniques etc. that could relate with Disaster Monitoring and risk management.

* To explore both the "Disaster Cycle" (Preparedness, Response, Recovery, Mitigation, Prevention) and the risk management domains, in order to detect where, how and what kind of the above mentioned new technologies could be infused to these domains.

* To dynamically record and register internationally existing disaster management systems, in order to have up-to-date information about the scene, the sophistication and the general advances in this field.

* To experiment with existing or new ideas, for ground based, water/marine based or airborne solutions, into
"standard fields" (Information Technology, Communica-
tion Technology, Space Technology).

* To experiment with new ideas into other fields that could appear as unconventional even as "exotic" (e.g. artificial intelligence, Simultaneous Localization and Mapping (SLAM), Simultaneous Localization, Mapping and Moving Object Tracking (SLAMMOT) etc.).

* To use Web-tools (web-site, social networks, blog etc.) in relation to the transmission, communication and propagation of information concerning risks, disasters.

* To attract most interesting cooperation with a variety of other scientific and/or professional institutes, organizations, groups.

Program of activities

* To use Web-tools (Web-site, social networks, blog etc.) in order to provide information about related bibliography, Web-links, events, and other activities of the group.

* To diffuse and promote research and collaboration (also by attracting interdisciplinary aspects), to disseminate of information, to organize and to participate in workshops, meetings, seminars, conferences, symposia (academic, public, professional domains).

• To support ICCT activities.

Members

* Ioannis (John) D. Doukas (Greece), chair

* Günther Retscher (Austria)

* Cheng Wang (China)

* Allison Kealy (Australia)

* Gyula Mentes (Hungary)

* Mikhail Kanevski (Switzerland)

* Melinda Laituri (USA)

* Jonathan Li (USA)

* Beniamino Murgante (Italy)

* Clement A. Ogaja (USA)

* Urbano Fra Paleo (Spain)

Theme 3: Sea-Level Change, Variability and
Forecasting

Sea level rise and its impact on human habitats and economic well being have received considerable attention in recent years by the general public, engineers, and policy makers. A GGOS retreat in 2010 has identified sea level change as one of the cross-cutting themes for geodesy. The primary focus is to demonstrate the value of geodetic techniques to mitigation of sea level rise including studies of the impacts of its change over the world's coastal regions and islands, and to support practical applications such as sustainability. Theme 3 interacts with the other two Themes as well as with related GGOS Working Groups.

Close cooperation will also be established with groups and
organizations working in related fields. One major topic is
the identification of gaps in geodetic observing techniques
and to advocate additions in the GGOS monitoring
network and Services where necessary.

Activities

Through a Call for Participation Theme 3 will progress
with the following tasks:

* Identification or (re)-definition of the requirements for a proper understanding of global and regional/local sea-level rise and its variability especially in so far as they relate to geodetic monitoring provided by the GGOS infrastructure, and their current links to external organizations (e.g., GEO, CEOS, and other observing systems).

* Identification of organizations or individuals who can take forward each requirement, or act as points of contact for each requirement where they are primarily the responsibility of bodies not related to GGOS.

* Identification of a preliminary set of practical (as opposed to scientific) pilot projects, which will demonstrate the viability, and the importance of geodetic measurements to mitigation of sea-level rise at a local or regional level. This identification will be followed by construction of proposals for pilot projects and their undertaking.

* The immediate action and pending on the outcomes of the Call for Participation, will be to identify, establish or reaffirm leadership and members of the Theme.

* In the long-term, the aim is to support forecasting of global and regional sea level for the 21st century. Special emphasis will be given to local and regional projects which are relevant to coastal communities, and which depend on the global perspective of GGOS.

Members

* T. Schöne (Germany)

* M. Tamisea (UK)

* C.K. Shum (USA)

* P. Woodworth (UK)
IAG Scientific Services

<figure><img src="image_10.png" /></figure>

IAG Bibliographic Service (IBS)

http://www.bkg.bund.de

Chair: **Annekathrin Michlenz** (Germany)

**Overview**

The service is based on the literature database geodesy, photogrammetry and cartography (GEOPHOKA), which is maintained by the Federal Agency for Cartography and Geodesy, Branch Office Leipzig. Since 1984 there are stored literature entries. They cover the whole subject of geodesy, cartography and photogrammetry and the neighbouring files. Every year 1000 new entries are included into the database. In July 2011 the database comprises about 63 930 entries.

In addition to the Fast Bibliography within the IAG Newsletter of the Journal of Geodesy the IAG Bibliographic Service serves mainly to inform the geodesists who are associated in the IAG about current geodetic literature from all over the world.

For the IAG Bibliographic Service geodetic journals and other periodicals, publications of research institutes, manuals und text books as well as congress papers are analyzed. The documentalists choose such sources for the service which are relevant to the activities of the Sections, Commissions, Special Commissions und Special Study Groups.

These literature sources are available in the library of the Bundesamt für Kartographie und Geodäsie (BKG) (library symbols F128 and L191).

The topicality of the sources recorded in the IAG Bibliographic Service is dependent on the date of their arriving at the library of the BKG. German-language literature und conference proceedings on geodesy are processes as a rule within 3 weeks after receipt.

Each literature record contains:

- The bibliographic description of the source according to the commonly known rules.

- The descriptors in German. They inform about the content of the recorded source.

- In most cases an abstract, if possible in English. The abstracts are often taken from the source or are processes by the documentalist on the basis of the summary, the conclusions, or the list of contents of the source.
**International Altimetry Service (IAS)**

http://iag.dgfi.badw.de

Chair: **Wolfgang Bosch** (Germany)

**Preamble**

In the past two decades satellite altimetry has evolved to an operational remote sensing technique with important inter-disciplinary applications. For geodesy, the precise and near global mapping and monitoring of the ocean surface is of particular importance. As the ocean surface is nearly co-inciding with an equipotential surface of the Earth gravity field satellite altimetry contributes to essential improvements of the Earth gravity field. Even with the dedicated gravity field missions GRACE and GOCE, satellite altimetry will remain the basic source for the determination of the high resolution marine gravity field. The sampling of short-term tidal variations is possible by sufficient long altimetry time series and allows the empirically estimate ocean tide models which in turn are required to correct any geodetic space techniques. Mapping and monitoring of seasonal and secular changes of the mean sea level helps to understand fundamental processes of the System Earth: the ocean water mass redistribution, one component of the global hydrological cycle, has impact to the Earth centre-of-gravity, to Earth rotation by the ocean angular momentum functions, the temporal variations of the Earth gravity field, as well as to studies on regional sea level changes and the global sea level rise. Finally the discrimination between the ocean surface and the geoid leads to improved knowledge on the dynamic ocean topography which does not only allow to infer mass and heat transfer in the ocean but also helps to globally unify height reference systems. In summary satellite altimetry is a space technique with fundamental application to geodesy and other geosciences. It has to be a basic component of the Global Geodetic Observing System.

Following endorsements by GLOSS, IAPSO and IAG the **International Altimetry Service** was established as IAG initiative. IAS recognizes that there are already many organisations providing altimeter data and value-added products of geophysical and geodetic relevance. The IAS initiative is meant to be non-competitive, but open to identify and pool together all efforts which contribute to geodetic applications of satellite altimetry. Moreover, IAS will try to initiate projects completing or gradually improving existing services for the benefit of geodetic and geophysical applications at large.

**IAS General Objectives**

The general objectives of IAS shall be:

* to provide general information on satellite altimetry necessary to promote and support geodetic applications;

* to communicate with, and interface to, providers of altimeter mission data, centres which process, archive, and analyse altimeter data, and other related services and organizations;

* to promote satellite altimetry as a core element of Global Geodetic Observing Systems;

* to support the generation, comparison and validation of altimetry based products which are of particular impact to the geodetic user community and

* to help compile and analyse altimeter data, and respond to specific requirements of geodetic users.

The IAS accomplishes its mission by:

* collaborating as appropriate with space agencies, processing centres, research institutes and altimetry experts;

* establishing a web site compiling basic information on satellite altimetry, its data, products and applications as given by data providers, archive and product centres, research laboratories and experienced users;

* supporting users to read, transform, and apply data and products, to assess data and product quality and to compare similar products generated by different organisations.

* establishing pilot projects which will solve, enhance or expand various needs of geodetic users on altimetry data and products,

* considering consolidated procedures for generating value-added altimeter products which may become permanent components of the International Altimeter Service; and

* reporting to IAG, IAPSO, GLOSS, GOOS, GGOS, GEOSS and other bodies related to satellite altimetry on the status, achievements and plans of the altimetry service.
The Time Department is one of the five scientific depart-
ments of the BIPM. The activities at the Time Department
are focused on the maintenance of the SI second and the
formation of the international reference time scales.

The International Committee for Weights and Measures (CIPM) decided in October 2009 to discontinue the activities on gravimetry. Consequence of these decisions, the BIPM time, frequency and gravimetry (TFG) section became since 1 January 2011 the BIPM Time Department.

The BIPM provides, together with the US Naval Observa-
tory, the IERS Conventions Centre, with the responsibility
of the establishment and publication of the IERS Conven-
tions, providing standards and models for applications in
the fields of geodesy, geophysics and astronomy.

The establishment and maintenance of the International
System of Units (SI) at the BIPM constitutes a funda-
mental contribution to the activities relating to the IAG.

**International Time Scales at the BIPM**

The international time scales International Atomic Time (TAI) and Coordinated Universal Time (UTC) are regularly computed and published in monthly *BIPM Circular T*. The frequency stability of UTC, expressed in terms of an Allan deviation, is estimated to $3 \times 10^{-16}$ for averaging times of one month. About 400 industrial clocks located in almost 70 national laboratories contribute to the calculation of TAI. Some of these laboratories develop and maintain primary frequency standards – among them caesium fountains – that contribute to the improvement of the accuracy of TAI. The scale unit of TAI has been estimated to match the SI second to about $5 \times 10^{-16}$.

The laboratories contributing to the formation of UTC maintain representations of the international time scale named UTC(k). Routine UTC(k) comparison is undertaken using different techniques and methods of time transfer. All laboratories contributing to the calculation of UTC at the BIPM are equipped for GNSS reception. GPS C/A observations from time and geodetic-type receivers are used with different methods, depending on the characteristics of the receivers. Dual-frequency receivers allow performing iono-free solutions. Since October 2009 a

combination of code and phase measurements of geodetic-
type receivers is used in the computation of TAI. Also at
the end of 2009 observations of GLONASS are used for
the computation of TAI. Thanks to this evolution, the
statistical uncertainty of time comparisons is at the sub-
nanosecond level for the best GNSS time links. Some
laboratories are equipped of two-way satellite time and
frequency transfer (TWSTFT) devices allowing time com-
parisons independent from GNSS through geostationary
communication satellites. The uncertainty of time com-
parison by GNSS is still limited by the hardware to 5 ns for
the calibrated links whilst in the case of TWSTFT it is at
the nanosecond order.

The algorithm used for the calculation of time scales is an
iterative process that starts by producing a free atomic
scale (Échelle atomique libre or EAL) from which TAI and
UTC are derived. Research into time scale algorithms is
conducted in the section with the aim of improving the
long-term stability of EAL and the accuracy of TAI.

Because TAI is computed on a monthly basis and has
operational constraints, it does not provide an optimal
realization of Terrestrial Time (TT), the time coordinate of
the geocentric reference system. The BIPM therefore com-
putes an additional realization TT(BIPM) in post-pro-
cessing, which is based on a weighted average of the
evaluation of the TAI frequency by the primary frequency
standards. The last updated computation of TT(BIPM),
named TT(BIPM10), valid until December 2010, has an
estimated accuracy of order $0.3 \times 10^{-15}$. Starting with
TT(BIPM09), an extrapolation for the current year of the
latest realization TT(BIPMYY) is provided and is updated
each month after the TAI computation.

Radiations other than the caesium 133, most in the optical
wavelengths, have been recommended by the International
Committee for Weights and Measures (CIPM) as
secondary representations of the second. These frequency
standards are at least one order of magnitude more accurate
than the caesium. Their use for time metrology is still
limited by the state of the art of frequency transfer, still
unable to compare these standards at the level of their
performances. Studies on the use of optical fibres show
excellent results. The time community is engaged in a
collective effort for solving this issue, since one of the
interests is the possibility of redefining the SI second.
The computation of TAI is carried out every month and the results are published monthly in *BIPM Circular T*. When preparing the *Annual Report*, the results shown in *Circular T* may be revised taking into account any subsequent improvements made to the data. Results are also available from the BIPM website (www.bipm.org), as well as all data used for the calculation. The broad real-time dissemination of UTC through broadcast and satellite time signals is a responsibility of the national metrology laboratories and some observatories, following the recommendations of the International Telecommunication Union (ITU-R).

## Interruption of activities on gravimetry

The 8th International Comparison of Absolute Gravimetres in 2009 (ICAG 2009) was the last organized by the BIPM. The task of the BIPM on the ICAGs had concluded with the calculation of results of this last comparison and its subsequent publication. As agreed with the IAG, the future ICAGs will be organized at national institutes under a regional scheme. The Consultative Committee for the Mass and Related Quantities (CCM) continues organizing the Working Group on Gravimetry (WGG), and thus co-operating with the IAG in providing support to the future ICAGs.

## Conventions and references

Research work is also dedicated to space-time reference systems. The BIPM provides, in partnership with the US Naval Observatory, the Conventions Product Centre of the IERS. A new version of the IERS Conventions (2010) has been published in the IERS Technical Note N°36, also available in electronic version at (http://www.iers.org/nn_11216/IERS/EN/Publications/TechnicalNotes/tn36.html). Updates to the last published version are made whenever necessary and available on the internet at http://tai.bipm.org/iers/conv2010/conv2010.html, http://maia.usno.navy.mil/conv2010/convupdt.html.

Activities in cooperation with Paris Observatory within the IERS International Celestial Reference System Centre on the realization of reference frames for astrogeodynamics, contribute to the maintenance of the international celestial reference frame in the scope of the activities of the International Astronomical Union and International VLBI Service.

## International validation of the International Terrestrial Reference System (ITRS)

Thanks to the actions of the BIPM and the Consultative Committee for Time and Frequency (CCTF), the 24rd General Conference on Weight and Measures adopted in October 2011 by unanimity a resolution that recommends the adoption of the International Terrestrial Reference System, as defined by the IUGG and realized by the IERS, for all metrological applications. The full text of the recommendation is annexed to this report. This resolution, adopted in the frame of an international diplomatic treaty (The Metre Convention), and of an intergovernmental organization (the BIPM) gives world-wide validity to the ITRS, putting it at the level of other international standards as, for example, UTC. This resolution reinforces the Resolution 2 of the IUGG, adopted at the XXIV IUGG General Assembly in 2007 on the Geocentric and International Terrestrial Reference Systems (GTRS and ITRS).

## Activities planned for 2012-2015

* Calculation and dissemination of UTC through the monthly publication of *BIPM Circular T*;

* Improvement of techniques of time and frequency transfer for

* Clock comparison for UTC;

* Comparison of optical frequency standards requiring an accuracy at the level of $10^{-17} - 10^{-18}$;

* Improvement of the algorithms for calculation of time-scales;

* Calculation of TT(BIPM) annually, and of its monthly extrapolation;

* Calculation and dissemination of a “rapid UTC” on a weekly basis for providing a reference to the UTC(k) available on a short delay;

* Supporting with expert advice the organization of the future international comparisons of absolute gravimeters;

* Continuing operating in cooperation with the USNO the IERS Conventions Centre;

* Continuing the cooperation with the IERS for the establishment of space references;

* Liaising with the relevant organizations, such as: IUGG, IAG and GGOS, IERS, IAU, ITU-R, IGS, and the International Committee for GNSS (ICG).
<figure><img src="image_11.png" /></figure>

**International Centre for Earth Tides (ICET)**

http://www.bim-icet.org

Director: **Jean-Pierre Barriot** (France, French Polynesia)

**Activities:**

The centralized Internet gateway to ICET services is:
http://www.bim-icet.org.

* **Summary of Data Held:**

Data from about 360 worldwide tidal gravity stations including GGP stations (hourly values, main tidal waves obtained by least squares analyses, residual vectors, oceanic attraction and loading vectors). The online Data Bank

(http://www.bim-icet.org) contains GGP superconducting gravimeters one minute data files, the off-line data bank contains also data from tiltmeters and extensometers worldwide.

* **Data Products, Publications, Catalogues:**

A "Bulletin d'Informations des Marées Terrestres" is published electronically once per year with a large number of translations of Russian and Chinese papers (also on

(http://www.bim-icet.org, 146 Bulletins are currently online as pdf files).

A General Bibliography is also regularly kept up to date and published online.

* **User Services:**

The Center provides assistance for the setup of new stations, calibrations of the instruments, data processing as well as for tidal analysis. The assistance is accomplished either by a stay at the Centre or by providing computers programs. ICET is validating on a month-to-month basis one minute data files from the network of superconducting gravimeters of the GGP project.

ICET makes also available tidal predictions for any place and time, which are needed for field gravimetry, absolute gravity measurements and for tilt measurements. These predictions can be computed either on the basis of elastic Earth models and oceanic co-tidal maps, or on basis of the results of direct measurements.
## Terms of Reference

The determination of the Earth's global gravity field is one of the main tasks of Geodesy: it serves as a reference for geodesy itself, and it provides important information about the Earth, its interior and its fluid envelope for all geosciences. Thus, it is important to make the models of the global gravity field available to the public as products of geodesy. This becomes increasingly important as time variations of the global gravity field can be measured with better and better spatial and temporal resolution.

The calculation of the different functionals of the geo-potential (e.g.: geoid, gravity anomaly, gravity disturbance, equivalent water height) from a defined global model, on a specified grid and with respect to a defined reference system, is far from being trivial and a responsibility of geodesy too.

Additionally, it is important to make the spatial structure and temporal variability of the global gravity field available to the general public in a graphic vivid manner. In particular for temporal gravity models, aspects of consistency in processing, reference frame, and parameterization are becoming more and more important.

ICGEM has been established in 2003 as a new service under the umbrella of the new International Gravity Field Service (IGFS) as one of six centres.

## Objectives

* collecting and long-term archiving of existing global gravity field models

* making them available on the web

* use of standardised format (self-explanatory)

* interactive visualisation of the models

* solutions from dedicated time periods (e.g. monthly GRACE models) included

* web-interface to calculate gravity functionals from the spherical harmonic models on freely selectable grids (filtering)

* evaluation of the models

## Services

### The Models

Currently, 122 models are listed with their references and, apart from 17 older models, all are available in form of spherical harmonic coefficients. If available, the link to the original model web site has been added. Models from dedicated time periods (e.g. monthly solutions from GRACE) of CSR, JPL, CNES/GRGS and GFZ are also available.

### The Format

The spherical harmonic coefficients are available in a standardised self-explanatory format which has been accepted by ESA as the official format for the GOCE project.

### The Visualisation

<figure><img src="image_12.png" /><figcaption>Fig. 1: Visualisation (geoid) of a global gravity field model</figcaption></figure>

An online interactive visualisation of the models (height anomalies and gravity anomalies) as illuminated projection on a freely rotatable sphere is available (see fig. 1). Differences of two models, arbitrary degree windows, zooming in and out, are possible. Additionally, an animation over time of the monthly solutions from GRACE is also included. The visualisation of single spherical harmonics is possible for tutorial purposes.
## The Calculation Service

A web-interface to calculate gravity functionals from the spherical harmonic models on freely selectable grids, with respect to a reference system of the user's choice, is provided (see figs. 2 and 3). The following functionals are available:

* pseudo height anomaly on the ellipsoid (or at arbitrary height over the ellipsoid)

* height anomaly (on the Earth's surface as defined)

* geoid height (height anomaly plus spherical shell approximation of the topography)

* gravity disturbance

* gravity disturbance in spherical approximation (at arbitrary height over the ellipsoid)

* gravity anomaly (classical and modern definition)

* gravity anomaly (in spherical approximation, at arbitrary height over the ellipsoid)

* simple Bouguer gravity anomaly

* gravity on the Earth's surface (including the centrifugal acceleration)

* gravity on the ellipsoid (or at arbitrary height over the ellipsoid, including the centrifugal acceleration)

* gravitation on the ellipsoid (or at arbitrary height over the ellipsoid, without centrifugal acceleration)

* second derivative in spherical radius direction (at arbitrary height over the ellipsoid)

* equivalent water height (water column)

<figure><img src="image_13.png" /><figcaption>Fig. 2: Input mask of the calculation service</figcaption></figure>

Filtering is possible by selecting the range of used coefficients or the filter length of a Gaussian averaging filter. The calculated grids (self-explanatory format) and corresponding plots (postscript) are available for download after some seconds.

<figure><img src="image_14.png" /><figcaption>Fig. 3: Example of grid and plot generation by the calculation service: gravity disturbances of the Chicxulub crater region from the model EGM2008</figcaption></figure>

## Evaluation

For a concise evaluation of the models, comparisons with GPS-levelling data (see fig. 4) and with the most recent combination model in the spectral domain (see figs. 5 and 6) are provided.

<table><caption>Fig. 4: Table (truncated) of comparison of the models with GPS-levelling: Root mean square (rms) about mean of GPS / levelling minus gravity field model derived geoid heights [m]</caption><thead><tr><th>Model</th><th>Nmax</th><th>USA 6169 points</th><th>Canada 1930 points</th><th>Europe 1235 points</th><th>Australia 201 points</th></tr></thead><tbody><tr><td>EIGEN-6C</td><td>1420</td><td>0.247 m</td><td>0.136 m</td><td>0.214 m</td><td>0.219 m</td></tr><tr><td>EIGEN-6S</td><td>240</td><td>0.446 m</td><td>0.373 m</td><td>0.449 m</td><td>0.397 m</td></tr><tr><td>GOCO02S</td><td>250</td><td>0.435 m</td><td>0.352 m</td><td>0.434 m</td><td>0.372 m</td></tr><tr><td>AIUB-GRACE03S</td><td>160</td><td>0.650 m</td><td>0.514 m</td><td>0.713 m</td><td>0.486 m</td></tr><tr><td>GO_CONS_GCF_2_DIR_R2</td><td>240</td><td>0.443 m</td><td>0.374 m</td><td>0.449 m</td><td>0.391 m</td></tr><tr><td>GO_CONS_GCF_2_TIM_R2</td><td>250</td><td>0.436 m</td><td>0.356 m</td><td>0.434 m</td><td>0.376 m</td></tr><tr><td>GO_CONS_GCF_2_SPW_R2</td><td>240</td><td>0.457 m</td><td>0.376 m</td><td>0.473 m</td><td>0.376 m</td></tr><tr><td>GO_CONS_GCF_2_DIR_R1</td><td>240</td><td>0.407 m</td><td>0.319 m</td><td>0.402 m</td><td>0.319 m</td></tr><tr><td>GO_CONS_GCF_2_TIM_R1</td><td>224</td><td>0.455 m</td><td>0.378 m</td><td>0.474 m</td><td>0.371 m</td></tr><tr><td>GO_CONS_GCF_2_SPW_R1</td><td>210</td><td>0.471 m</td><td>0.399 m</td><td>0.498 m</td><td>0.384 m</td></tr><tr><td>GOCO01S</td><td>224</td><td>0.451 m</td><td>0.374 m</td><td>0.473 m</td><td>0.370 m</td></tr><tr><td>EIGEN-51C</td><td>359</td><td>0.335 m</td><td>0.245 m</td><td>0.289 m</td><td>0.234 m</td></tr><tr><td>EIGEN-5C</td><td>360</td><td>0.341 m</td><td>0.251 m</td><td>0.303 m</td><td>0.244 m</td></tr><tr><td>AIUB-CHAMP03S</td><td>100</td><td>0.755 m</td><td>0.743 m</td><td>1.148 m</td><td>1.148 m</td></tr><tr><td>EIGEN-CHAMP05S</td><td>150</td><td>0.784 m</td><td>0.763 m</td><td>1.216 m</td><td>0.661 m</td></tr><tr><td>ITG-GRACE2010S</td><td>180</td><td>0.548 m</td><td>0.459 m</td><td>0.595 m</td><td>0.523 m</td></tr><tr><td>AIUB-GRACE02S</td><td>150</td><td>0.630 m</td><td>0.571 m</td><td>0.701 m</td><td>0.495 m</td></tr><tr><td>GGM03C</td><td>360</td><td>0.346 m</td><td>0.279 m</td><td>0.334 m</td><td>0.259 m</td></tr><tr><td>GGM03S-UPTO150</td><td>150</td><td>0.641 m</td><td>0.521 m</td><td>0.710 m</td><td>0.494 m</td></tr><tr><td>AIUB-GRACE01S</td><td>120</td><td>0.724 m</td><td>0.628 m</td><td>0.930 m</td><td>0.563 m</td></tr><tr><td>EGM2008</td><td>2190</td><td>0.248 m</td><td>0.126 m</td><td>0.208 m</td><td>0.217 m</td></tr><tr><td>EIGEN-5S</td><td>150</td><td>0.630 m</td><td>0.547 m</td><td>0.737 m</td><td>0.475 m</td></tr><tr><td>ITG-GRACE03</td><td>180</td><td>0.633 m</td><td>0.557 m</td><td>0.658 m</td><td>0.603 m</td></tr><tr><td>AIUB-CHAMP01S</td><td>70</td><td>0.843 m</td><td>0.906 m</td><td>1.513 m</td><td>0.893 m</td></tr><tr><td>ITG-GRACE02S</td><td>170</td><td>0.623 m</td><td>0.511 m</td><td>0.639 m</td><td>0.489 m</td></tr><tr><td>EIGEN-GL04C</td><td>360</td><td>0.339 m</td><td>0.253 m</td><td>0.336 m</td><td>0.244 m</td></tr><tr><td>EIGEN-GL04S1</td><td>150</td><td>0.630 m</td><td>0.576 m</td><td>0.748 m</td><td>0.464 m</td></tr><tr><td>EIGEN-CG03C</td><td>360</td><td>0.346 m</td><td>0.306 m</td><td>0.355 m</td><td>0.260 m</td></tr><tr><td>GGM02C</td><td>200</td><td>0.473 m</td><td>0.378 m</td><td>0.515 m</td><td>0.376 m</td></tr><tr><td>GGM02S</td><td>160</td><td>0.977 m</td><td>1.116 m</td><td>1.416 m</td><td>1.356 m</td></tr><tr><td>EIGEN-CG01C</td><td>360</td><td>0.351 m</td><td>0.270 m</td><td>0.370 m</td><td>0.263 m</td></tr><tr><td>EIGEN-CHAMP03S</td><td>140</td><td>0.816 m</td><td>0.842 m</td><td>1.451 m</td><td>0.849 m</td></tr><tr><td>EIGEN-GRACE02S</td><td>150</td><td>0.739 m</td><td>0.643 m</td><td>0.828 m</td><td>0.538 m</td></tr><tr><td>TIM03S</td><td>80</td><td>0.964 m</td><td>0.963 m</td><td>1.630 m</td><td>1.494 m</td></tr></tbody></table>
<figure><img src="image_15.png" /><figcaption>Fig. 5: Comparison of the models in the spectral domain (e.g.: GO_CONS_GCF_2_TIM_R2) with one of the most recent combination models (e.g. EIGEN-6C)</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Fig. 6: Visualisation of the improvement of satellite-only models over the past decades: Geoiddifferences to the model EIGEN-6C as a function of spatial resolution</figcaption></figure>

## Models of other Celestial Bodies

Although it is not the main purpose of ICGEM, the calculation and visualisation service for some gravity field models of the celestial bodies Moon, Mars and Venus are also offered (see fig. 7).

<figure><img src="image_17.png" /><figcaption>Fig. 7: Visualisation of the “Geoid” of the Moon</figcaption></figure>

## Data Policy

Access to global gravity models, derived products and tutorials, once offered by the centre, shall be unrestricted for any external user.

## Staff

ICGEM is hosted by GFZ Potsdam. Its staff consists of

- Franz Barthelmes

- Wolfgang Köhler

## Point of Contact

Franz Barthelmes

GeoForschungsZentrum Potsdam

Telegrafenberg

D-14473 Potsdam

Germany

E-mail: bar@gfz-potsdam.de
<figure><img src="image_18.png" /></figure>

INTERNATIONAL
DORIS
SERVICE

# International DORIS Service (IDS)

web: http://ids.doris.org

Chair: Pascal Willis (France)

## Terms of Reference

### Introduction

The DORIS (Doppler Orbit determination and Radio-positioning Integrated on Satellite) system for satellite orbit determination and precise positioning was developed by the Centre National d'Etudes Spatiales (CNES) in conjunction with the Institut Géographique National (IGN) and the Groupe de Recherche de Géodesie Spatiale (GRGS).

A proof of concept for the International DORIS Service (IDS) was conducted through a pilot phase prior to the establishment of the International DORIS Experiment in 1999 by the International Association of Geodesy (IAG). The IDS formally began on July 1, 2003 after the IAG official approval at the IUGG General Assembly in Sapporo. The IDS is an IAG Service and operates in close cooperation with the International Earth rotation and Reference frames Service (IERS).

### The IDS Mission

The primary objective of the IDS is to provide a service to support geodetic and geophysical research activities through DORIS data and derived products.

The IDS collects, archives and distributes DORIS observation data sets of sufficient accuracy to satisfy the objectives of a wide range of applications and experimentations. From these data sets the following products are derived:

* Coordinates and velocities of the IDS tracking stations

* Geocenter and scale of the Terrestrial Reference Frame

* High accuracy ephemerides of the DORIS satellites

* Earth orientation parameters (EOPs)

The accuracies of these products are sufficient to support current scientific objectives including:

* Realization of global accessibility to and the improvement of the International Terrestrial Reference Frame (ITRF)

* Monitoring deformations of the solid Earth

* Monitoring crustal deformation at tide gauges

* Monitoring variations in the hydrosphere (sea level, ice-sheets, etc.)

* Orbit determination for scientific satellites

<figure><img src="image_19.png" /></figure>

### The IDS Organization

The IDS accomplishes its mission through the following components:

* Satellites carrying a DORIS receiver

* Network of tracking stations

* Data Centers

* Analysis centers and Analysis Coordinator

* Combination Center

* Working Groups

* Central Bureau

* Governing Board

## Satellites Carrying a DORIS Receiver

Since July 2003, the CNES and the European Space Agency (ESA) have provided DORIS data to the IDS. Data from additional agencies are expected and welcome. DORIS receivers are flown on LEO satellites for precise orbit determination as well as for geodetic applications. Satellites with DORIS receivers are listed on the IDS website at http://ids-doris.org/.

A representative of the DORIS system serves as a voting member of the Governing Board.

## Network of Tracking Stations

The IDS network is composed of DORIS permanent tracking stations located at host institutions and maintained by the IGN. A list of the sites (past and present) is included on the IDS website at http://ids-doris.org/.

The network also includes additional DORIS stations proposed by the IDS to observe during specific campaigns of scientific interest.

A representative of the Network serves as a voting member of the Governing Board.
## Data Centers

The Data Centers are in direct contact with the CNES, which provides the DORIS data. The Data Centers archive the DORIS data, derived products, and ancillary information required to process these data.

A representative of the Data Centers serves as a voting member of the Governing Board.

## Analysis Centers and Analysis Coordinator

The Analysis Centers (ACs) are committed to provide at least one of the above IDS products on a regular basis. Expertise in DORIS data analysis and operational capability are essential factors in the selection of Analysis Centers.

The Analysis Coordinator assists the Analysis Centers and monitors their activities to ensure that the IDS objectives are carried out. The Analysis Coordinator, working with the Analysis Centers, is expected to provide quality control, performance evaluation, and continued development of appropriate analysis standards. The Analysis Coordinator, with the support of the Combination Center, is also responsible for the appropriate combination of the Analysis Centers products into a single set of prescribed data products.

The Analysis Coordinator and a representative of the Analysis Centers serve as voting members of the Governing Board.

## Combination Center

The IDS appoints a Combination Center (CC) to combine individual AC solutions and to generate IDS data products for submission to the IERS for the formulation of the periodic update of the ITRF and other geodetic products. The CC is selected by the Governing Board every four years through a Call for Participation initiated six months prior to the end of the current CC term. Interested centers submit proposals outlining their plan for operation of the CC and the resources that they will commit.

A representative of the Combination Center serves as a voting member of the Governing Board.

## Working Groups

IDS Working Groups provide expertise on particular topics related to the IDS components and on development of particular IDS product(s) or service(s) relying on the IDS infrastructure.

All Working Groups are created when needed and retired by the IDS Governing Board when their work has been completed or they are no longer needed. Each Working Group must develop a charter that includes a mandate, a list of specific tasks, a schedule, and an identified Chairperson.

The Chairpersons of the Working Groups are non-voting members of the IDS Governing Board (see below).

## Central Bureau

The Central Bureau (CB) is the executive arm of the IDS Governing Board and as such is responsible for the general management of the IDS consistent with the directives, policies and priorities set by the Governing Board.

In this role the CB, within available resources, coordinates IDS activities, facilitates communications, maintains documentation, and organizes reports, meetings, and workshops. The CB responds to external inquiries about the IDS, promotes the use of IDS data and products, and coordinates interactions with other services, including the IERS.

The CB supports the Combination Center in combining the various Analysis Centers products and providing all information necessary to validate the final combined products.

The CB operates the information system for the IDS and produces the IDS Annual Reports and IDS Associates directory. The CB coordinates the publication of other documents required for the satisfactory planning and day-to-day operation of the Service, including standards and specifications regarding the performance, functionality and configuration requirements of all Service elements.

Although the Chairperson of the Governing Board is the official representative of the IDS to external organizations, the CB, consistent with the directives established by the Governing Board, is responsible for the day-to-day liaison with such organizations.

The long-term function of the IDS is assured through redundancy and emergency contingency plan for all of its components except for the CB. The Central Bureau serves for a term of four years. One year prior to the end of each term, the GB formally reviews the performance of the Central Bureau. At the behest of the GB, the CB may be asked to reconfirm its commitment to serve another four years. If the CB agrees, it submits a proposal for GB approval. If the CB declines or if the GB chooses to change CB operators, the GB announces a Call for Proposals for a new IDS Central Bureau to take over responsibilities including a six-month transition phase with the outgoing Central Bureau.
In summary, the Central Bureau performs primarily a long-term coordination role to ensure that IDS participants contribute to the Service in a consistent and harmonious manner and adhere to IDS standards.

The Director of the Central Bureau serves as a voting member of the Governing Board.

## Governing Board

The principal role of the Governing Board (GB) is to set policy and to exercise broad oversight of all IDS functions and components. It also controls general activities of the Service, including restructuring, when appropriate, to maintain Service efficiency and reliability.

The Governing Board (GB) consists of eleven voting members and a number of non-voting members. The membership is chosen to try to strike the right balance between project specialists and the general community. The voting membership of the GB is distributed as follows:

### Elected by IDS Associates (see below):

<table><tr><td>Analysis Centers' representative:</td><td>1</td></tr><tr><td>Data Centers' representative:</td><td>1</td></tr><tr><td>Analysis Coordinator:</td><td>1</td></tr><tr><td>Members-at-Large:</td><td>2</td></tr></table>

### Appointed members:

<table><tr><td>Director of the Central Bureau:</td><td>1</td></tr><tr><td>IERS representative to IDS:</td><td>1</td></tr><tr><td>IAG representative to IDS:</td><td>1</td></tr><tr><td>Combination Center representative:</td><td>1</td></tr><tr><td>DORIS System representative (CNES):</td><td>1</td></tr><tr><td>Network representative (IGN):</td><td>1</td></tr></table>

### Total number of voting members: 11

During their mandate, the Working Group chairpersons are GB members with voice but without vote.

The elected members have staggered four-year terms, with elections every two years. There is no limit to the number of terms that a person may serve, however he or she may serve only two term consecutively as an elected member. The Analysis Centers' representative, the Data Centers' representative, and one Member-at-Large are elected during the first two-year election. The Analysis Coordinator and the other Member-at-Large are elected in the second two-year election. Although no formula is prescribed, efforts should be made to keep the GB membership properly balanced with regard to supporting organizations and geographic representation.

Members of the GB become IAG Fellows with the appropriate rights and privileges, as described on the IAG website, after an initial two-year period.

### GB Elections
The GB elects a Chairperson from its members to serve a term of four years with the possibility of re-election for one additional term. The Chairperson does not vote on GB decisions, except in the case of a tie. The Chairperson is the official representative of the IDS to external organizations.

Five members of the GB are elected by the IDS Associates. A nominating committee conducts the elections for membership on the IDS Governing Board. The nominating committee consists of three members. The Chair of the nominating committee is appointed by the Chair of the GB, and must be a member of the GB not currently up for re-election. The GB chooses the remaining two members of the nominating committee from the list of IDS Associates.

The nominating committee solicits nominations from the IDS Associates for each position to be filled; at least two candidates are required for each position. The Central Bureau runs the election. All IDS Associates are eligible to vote. Election is by a simple majority of votes received for each position. The two Member-at-Large positions are filled by the two candidates receiving the most votes; a vote by the GB will resolve any situation of a tie.

### Appointed Members
The IAG and IERS representatives to the IDS Governing Board are appointed respectively by the IAG Executive Committee and by the IERS Directing Board for a maximum of two four-year terms. The DORIS System representative and the Network representative are appointed by CNES and IGN, respectively, for four-year terms without limitation. The Director of the Central Bureau and the Combination Center representative are the two other appointed members.

In case of a resignation from the Governing Board, the CB, after consulting with the appropriate IDS components, nominates a replacement candidate for election by the GB. The replacement will serve until the end of the term of the resigned Board member.

### GB Decisions
Most decisions at GB meetings are to be made by consensus or by a simple majority vote of the voting members present, provided that there is a quorum consisting of at least six voting members of the GB. GB decisions can be made through email or other correspondence by a majority vote of the GB voting membership. Changes in the IDS Terms of Reference and Chairperson of the GB can only be made by a 2/3 majority of the members of the GB, i.e., by seven or more votes.

### GB Meetings
The Board shall meet at least annually and at such other times as shall be considered appropriate by the Chairperson or at the request of three members. The Central Bureau provides the secretariat of the GB.
## IDS representatives to the IERS and the IAG

Through the existing reciprocity agreement between the IDS and the IERS, the IDS Analysis Coordinator serves as the DORIS Technique Center representative to IERS, and as such, subject to Governing Board approval, is a member of the IERS Directing Board (together with another person selected by the IDS Governing Board). This arrangement ensures full cooperation between the two services.

The IDS Governing Board will select the IDS representative to the IAG Executive Committee.

## IDS Associates

IDS Associates are persons representing organizations that participate in any of the IDS components. A participating institution can submit a person's name, email, and primary IDS function in its organization to the Central Bureau for application to become an IDS Associate. The Governing Board approves all memberships. The Central Bureau maintains the current list of IDS Associates and makes the list available on the IDS website.

IDS Associates vote for the incoming Analysis Centers' representative, the Data Centers' representative, the Analysis Coordinator, and the Members-at-Large representatives as members of the GB.

The GB must approve the list of IDS Associates eligible for voting in the elections at least three months prior to the election process. For the purposes of the election, current and former GB members are also considered IDS Associates. are considered IAG Affiliates.
<figure><img src="image_20.png" /></figure>

# International Earth Rotation and Reference Systems Service (IERS)

web: www.iers.org

Chair of the Directing Board: **Chopo Ma** USA

Director of the Central Bureau: **Bernd Richter** (Germany)

## Development

The IERS was established as the International Earth Rotation Service in 1987 by the International Astronomical Union and the International Union of Geodesy and Geophysics, and it began operation on 1 January 1988. Since 2001, the IERS works in a new organizational structure; in 2003, the new name of the Service, without changing its abbreviation, was adopted. The IERS is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS).

## Objectives

The primary objectives of the IERS are to serve the astronomical, geodetic and geophysical communities by providing the following:

* The International Celestial Reference System (ICRS) and its realization, the International Celestial Reference

* Frame (ICRF)

* The International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial

* Reference Frame (ITRF)

* Earth orientation parameters required to study earth orientation variations and to transform between the

* ICRF and the ITRF

* Geophysical data to interpret time/space variations in the ICRF, ITRF or earth orientation parameters, and model such variations

* Standards, constants and models (i.e., conventions) encouraging international adherence

## Products

IERS collects, archives and distributes products to satisfy the objectives of a wide range of applications, research and experimentation. These products include the following:

* International Celestial Reference Frame

* International Terrestrial Reference Frame

* Monthly earth orientation data

* Daily rapid service estimates of near real-time earth orientation data and their predictions

* Announcements of the differences between astronomical and civil time for time distribution by radio stations

* Leap second announcements

* Products related to global geophysical fluids such as mass and angular momentum distribution

* Annual report and technical notes on conventions and other topics

* Long-term earth orientation information

The accuracies of these products are sufficient to support current scientific and technical objectives including the following:

* Fundamental astronomical and geodetic reference systems

* Monitoring and modeling earth rotation/orientation

* Monitoring and modeling deformations of the solid earth

* Monitoring mass variations in the geophysical fluids, including the atmosphere and the hydrosphere

* Artificial satellite orbit determination

* Geophysical and atmospheric research, studies of dynamical interactions between geophysical fluids and

* the solid earth

* Space navigation.

## Structure

The IERS accomplishes its mission through the following components:

* **Technique Centers:** International GNSS Service, International Laser Ranging Service, International VLBI Service, and International DORIS Service

* **Product Centers:** Earth Orientation Center, Rapid Service/Prediction Center, Conventions Center, ICRS Center, ITRS Center, and Global Geophysical Fluids Center with Special Bureaus for the Atmosphere,

* for the Oceans, for Hydrology, and for Combination

* **ITRS Combination Centers** at Deutsches Geodätisches Forschungsinstitut (DGFI), Geomatics Canada/Geodetic Survey Division, Institut Géographique National (IGN)

* **Analysis Coordinator**

* **Central Bureau**

* **Directing Board**

* **Working Groups:** WG on Site Survey and Co-location, WG on Combination at the Observation Level, IERS/IVS WG on the Second Realization of the ICRF, WG on SINEX Format.
Some of these components (e.g., Technique Centers) may be autonomous operations, structurally independent from IERS, but which cooperate with the IERS. A participating organization may also function as one or several of these components (except as a Directing Board).

## IERS Directing Board 2011

Zuheir Altamimi (France), ITRS Center Representative

Aleksander Brzezinski (Poland), IAU Representative

Daniel Gambis (France), Earth Orientation Center Representative

Rüdiger Haas (Sweden), IVS Representative

Thomas Herring (USA), Analysis Coordinator

Urs Hugentobler (Germany), IGS Representative

Frank Lemoine (USA), IDS Representative

Brian J. Luzum (USA), Rapid Service/Prediction Center Representative

Chopo Ma (USA), IVS Representative, Chair

Jürgen Müller (Germany), ILRS Representative

Erricos C. Pavlis (USA), ILRS Representative

Gérard Petit (France), Conventions Center Representative

Bernd Richter (Germany), Director of the Central Bureau

Jean Souchay (France), ICRS Center Representative

Tonie van Dam (Luxembourg), GGFC Representative

Clark R. Wilson (USA), IAG/IUGG Representative
<figure><img src="image_21.png" /></figure>

# International Geoid Service (IGeS)

web: http://www.iges.polimi.it

President and Director: **R. Barzaghi** (Italy)

## Mission / Objectives

The main tasks of IGeS are

* to collect geoid estimates worldwide, when possible to validate them and to disseminate them upon request among the scientific community: other auxiliary data can also be collected by IGeS, when useful for the geoid determination, and might be made available with the sharp exclusion of gravity anomalies data,

* to collect, test and, when allowed, to distribute software for the geoid determination,

* to conduct researches on methods for the geoid determination, particularly trying to define optimal procedures for merging all the available data, including satellite gravity.

* to organize schools on geoid determination where both theoretical and practical aspects are illustrated. During the schools students are trained in the use of the relevant software used for geoid computation,

* to issue, at least once per year, the Newton's Bulletin, collecting papers on gravity and geoid. Also, news and results from the other IGFS Centers are welcome,

* to disseminate special publications on geoid computations, e.g. lecture notes of the schools,

* to establish and update a web page and a forum for discussing practical and theoretical aspects on geoid computation,

* to support Agencies or scientists in computing regional geoids.

The Newton's Bulletin has a technical and applied nature and will not accept papers that could be published on the International Journal of Geodesy.

Data and software given to IGeS remain property of the source, which can dictate the conditions of use and restrict their distribution. IGeS itself can indeed perform geoid computations within different projects, but not in economic competition with Firms or Public Organizations institutionally devoted to that.

## Products

* SW for handling global models

* SW for the local geoid estimation

* SW for the evaluation of different functionals of the Gravity Field

* Grids, for specified areas, of local and regional geoid estimates

* Documentation of the SW and of the data sources

* Newton's Bulletin

* Lecture notes and special publications

* International Schools on geoid computation

## Future Programs/Development

Beyond institutional activities of IGeS, the following programs are worth of specific mention:

* participation to the International ESA Gradiometric Mission (GOCE);

* computation of improved geoids for Italy and the Mediterranean area;

* participation within GGOS to the study of the height datum unification problem;

* study of improved methodologies for the determination of the geoid at global and local level;

* organization of International Geoid School, possibly one school every two years;

* participation to the GOCE Global Models validation.

## Structure

The Service is for the moment provided by two Centres, one at the Politecnico of Milano, and the other at NIMA (contact person S. Kenyon, steve.c.kenyon@nga.mil) and by individual scientists, called advisors.

IGeS is an official IAG Service which is related to IAG through the International Gravity Field Service and is one of the operative arms of the International Commission for the Gravity Field. The IGeS Milano Centre is supported by
Italian authorities, which nominate upon recommendation of the IGFS, a President, for its international representation and a Director for the operative management.

Its structure, tools and activities are illustrated in the IGeS reports to the Advisory Board of IGFS. In addition the IGeS advisors are individual members of IGeS, which have had an outstanding activity in the field of geoid determination and also can represent IGeS in both research and teaching activities.

At present the following distinguished scientists are IGeS advisors:

* R. Forsberg (Denmark)

* C.C. Tscherning (Denmark)

* M. Sideris (Canada)

* W. Kearsley (Australia)

* S. Kenyon (USA)

* N. Pavlis (USA)

* H. Denker (Germany)

* U. Marti (Switzerland)

* I. Tziavos (Greece)

* A. J. Gil (Spain)

* D. Blitzkow (Brasil)

Finally, within the structure of IGeS, Working Groups can be established for specific purposes, limited in time.
# International GNSS Service (IGS)

Web: http://www.igs.org/

Chair of the Governing Board: **Urs Hugentobler** (Germany)

Director of the Central Bureau: **Ruth Neilan** (USA)

## Overview

Planning for the years 2011-2014, the International GNSS Service (IGS) has a number of activities and tasks to pursue, both externally and internal to the organization. The mission of the IGS is to provide the highest-quality GNSS data and products in support of the terrestrial reference frame, Earth rotation, Earth observation and research, positioning, navigation and timing and other applications that benefit society.

Key activities are the extension of the IGS' tracking and analysis capabilities to new GNSS and new signals as well as of its real-time capabilities. Basis of the work of the IGS is its global tracking network which requires continuous

maintenance and extension in close interaction with the operating agencies and institutions.

A key undertaking through 2012 will be the development of the IGS Strategic Plan for the period 2013-2017. The IGS Strategic Plan 2008-2012 is located here:

http://igs.org/overview/pubs.html

The IGS develops annually a strategic implementation plan with which the progress of the organization is measured. The IGS Implementation plan for 2011 may be found at

ftp://www.igs.org/pub/resource/pubs/IGSImpPlan2011_GB_37.pdf

Figure 1 displays the organizational structure of the IGS and includes the list of Pilot Projects and Working Groups.

<figure><img src="image_22.png" /><figcaption>Figure 1. IGS Organization Chart 2011</figcaption></figure>
## Key Activities

The global tracking network and the quality of the acquired GNSS data is the basis for the generation of highest-quality products. Fostering of the network, quality monitoring of the station data and facilitating of its extension are high priority tasks also in the coming years. This includes planning for the transition to a GNSS tracking network without disruption of the existing long station coordinate time series required for the maintenance of the reference frame.

The quality of the IGS products are continuously monitored and improved. After the termination of a first complete reanalysis of GPS tracking data from 1994 to 2007 the IGS plans a next reanalysis effort based on the most up-to-date models, standards and conventions as input for the next ITRF frame.

IGS fully supports IAG's Global Geodetic Observing System (GGOS) and considers its products as GGOS products.

It works with other IAG components towards the realization of GGOS Mission, Vision and Goals, see:

http://www.ggos.org

In 2011, IGS released a Call for Participation in the IGS Multi-GNSS Global Experiment – IGS M-GEX. The CfP is posted at the IGS website and calls for multi-GNSS observing stations, data centers, analysis centers and cooperative networks and organizations. Main objective of the experiment is to gather experience with new signals and new navigation satellite systems. The experiment will expand the IGS tracking network, currently tracking GPS and GLONASS (Figure 2), to include GNSS observations of new constellations: Galileo (European Union), Compass (China), QZSS (Japan), as well as laying the foundation for tracking the modernized signal of the GPS and GLONASS. Coordinated analysis of the observations and generation of reliable products will be a challenge as the IGS strives to incorporate all GNSS. IGS M-GEX will begin in February 2012 and operate through August 2012, with first discussion of results at the IGS workshop in July 2012 (see below).

<figure><img src="image_23.png" /><figcaption>Figure 2. IGS Tracking Network, all stations.</figcaption></figure>

IGS is operating a real-time network as part of the IGS Real-Time Pilot Project (Figure 3). Currently data are available to project participants and real-time analysis is coordinated by the European Space Operations Center in Darmstadt (ESOC), Germany. IGS plans to make real-time products available within the next few years. For more information, visit the project pages:

http://www.rtigs.net/index.php

IGS is an active associate member of the United Nations Office for Outer Space Affairs' (UNOOSA) International Committee on GNSS (ICG). One of the ICG's four Working Groups, the Working Group on Reference Frame, Timing and Applications, is co-chaired by IGS, IAG and the International Federation of Surveyors (FIG). IGS is recently also named co-chair of a new ICG sub-committee on GNSS Monitoring. The sub-committee will be co-chaired by government representatives of China and Japan, and the IGS. This is recognition that IGS, due to multi-GNSS ob-
servations and analysis, may potentially be able to take on
a greater service role for system providers by providing in-
dependent monitoring of the available GNSS constella-
tions.

A challenge for the IGS in both the IGS M-GEX and Real-
time Pilot Project is data format issues. The IGS has for-
malized its efforts towards standardization of multi-GNSS
batch and real time observation and product formats and

protocols through cooperation with the Radio Technical
Commission for Maritime Services (RTCM). RTCM Spe-
cial Committees are chartered to address in-depth radio-
communication and radio-navigation areas of concern to
the RTCM membership. The output documents and reports
prepared by these Committees are usually published as
RTCM Recommended Standards and include standards for
GNSS.

<figure><img src="image_24.png" /><figcaption>Figure 3. IGS Real-Time Tracking Network 2011</figcaption></figure>

The IGS is applying for membership with the new Inter-
national Council for Science (ICSU) World Data System
(WDS). This is a new interdisciplinary body of ICSU, an
integration of the former Federation of Astronomical and
Geophysical Data Analysis Services (FAGS) and World
Data Center System. See:

http://www.icsu-wds.org/

IGS continues to support other IAG elements, with focus
on lesser economically developed countries (LEDC). For
the past ten years, IGS has been actively supporting efforts
within Africa to realize the Unification of African Refer-
ence Frames – AFREF. This is progressing, but continued
engagement is needed.

Internally, the IGS Central Bureau (CB) is in the process of
a complete redesign and implementation of the IGS web-
site. A top goal of the design is to have a state-of-the-art
website that has shared administration with other principal
people within the IGS. A ‘Site Log Manager (SLM)’ is be-
ing jointly developed with the University NAVSTAR Con-
sortium (UNAVCO), and will permit station operators to
manage and updated their own information. The infor-
mation within the website, and the SLM, will have auto-

matic validation procedures built in, so that managing the
400+ stations and networks within the IGS can be done ef-
ficiently. The website, once adequate resources are identi-
fied, can be extended to other scientific services within the
IAG and specifically to GGOS. Social networking options
for the IGS will also be explored and implemented where
value can be identified.

The IGS 2012 Workshop will be held in Poland, July 23-
27, 2012, and will be hosted by the Geodynamics Research
Laboratory of the University of Warmia and Mazury in Ol-
sztyn, Poland. Foci of the workshop are the first results of
the M-GEX experiment and progress in IGS real time de-
velopments.

Summary

The IGS remains a vital organization that continues to
evolve with challenging opportunities. The IGS is prepar-
ing for a future with new additional GNSS signals and new
constellations to eventually generate highest-quality prod-
ucts for all available GNSS for the benefit of science and
society.
## Terms of Reference

The Bureau Gravimétrique International (BGI) has been created in 1951 as a service of IAG during the IUGG (International Union in Geophysics and Geodesy) General Assembly. The initial task of BGI was to collect, on a world-wide basis, all gravity measurements to generate a global digital database of gravity data for any public or private user. The technological and scientific evolutions which occurred over the last 50 years in the area of gravimetry (improvements in field, airborne and seaborne gravity meters, development of absolute gravity meters, space gravity missions, etc.) provided significant increases of the number, diversity and accuracy of the gravity field observables. Following these evolutions, the BGI has contributed to provide original databases and services for a wide international community concerned by the studies of the Earth gravity field.

The BGI is an official service of the International Association of Geodesy (IAG) and is coordinated since 2003, with others IAG services (IGES, ICET, ICGEM, IDEMS) by the International Gravity Field Service (IGFS). It also directly contributes to the activities of the IAG Commission 2 “Gravity Field” and of the IAG Global Geodetic Observing System (GGOS). It is recognized by the International Council for Science (ICSU) successively as one of the services of the Federation of Astronomical and Geophysical Services (FAGS) and of the World Data System (WDS) created in 2008.

## Mission and objectives

The main task of BGI is to collect, on a world-wide basis, all gravity measurements (relative or absolute) and pertinent information about the gravity field of the Earth, to compile them and store them in a computerized data base in order to redistribute them on request to a large variety of users for scientific purposes.

The database of relative measurements contains over 12 millions of observations compiled and computerized from land, marine and airborne gravity surveys. It has been extensively used for the definition of Earth gravity field models and for many applications in geodesy, satellite orbit computation, oceanography, geophysics, etc.

More recently, a database for absolute gravity measurements was set up and put into operation in joint cooperation between BGI and BKG (Bundesamt für Kartographie und Geodäsie, Germany). The database is capable to store information about stations, instruments, observations and involved institutions. By this, it allows the exchange of meta data and the provision of contact details of the responsible institutions on the one hand and the storage and long term availability of gravity data and processing details on the other hand. The database can be accessed by a web based interface which provides publicly available meta-data as well as complete datasets for community of users contributing to the archive. A simple exchange format was selected which includes all relevant information and is known by the majority of users avoiding additional effort. In this way the upload of data to the database is possible, using a web based upload form.

In addition, BGI develops other additional services in the area of gravimetry (data validation for regional or global projects, online access to reference gravity stations, expertise, bibliography database, etc.). It also contributes to research & development activities (software developments, interpretation) and to educational activities (summer schools on gravity data acquisition and processing, provision of tutorials and educational materials in gravimetry).

## Programs / Activities

The current and future activities are dedicated (i) to consolidate the terrestrial gravity databases (relative and absolute measurements) and (ii) to ease the consultation and retrieval of gravity data and products by end-users. BGI will also continue operating with its supporting organizations, in educational, research and development activities with the aim to maintain a high level of competence and to improve the efficiency and the quality of its services.

* Gravity databases: The main achievements consist in maintaining and developing the three BGI databases (relative measurements, absolute measurements, reference gravity stations). Collection of new dataset (from field, marine or airborne surveys) will be encouraged in order to improve the global data coverage and accuracy. Incoming datasets are carefully evaluated and validated using protocols and software already developed at BGI. Global data and products derived from satellite altimetry
and gravity missions are to be more and more frequently used to validate land and sea measurements.

* Realization and diffusion of data and products: New functionalities are currently implemented in relation with the database management to improve the BGI services (direct requests and downloads of open-file data or products from the BGI webpage, inter-operability between other sites hosting gravity-related databases). BGI also contributes to the release of updated gravity products (digital maps and grids...) for educational and research purposes. The release of the first global spherical gravity anomaly maps and grids (World Gravity Map) realized for the Geological Commission for the Geological Map of the World (CGMW) and UNESCO

has been achieved in late 2011. It includes complete Bouguer and Isostatic anomaly maps corrected from the topography (1'x1' resolution) and based on the EGM2008 model. Updated versions will be done as soon as new global gravity model will be available.

* Other activities: Publication of the Newton's Bulletin jointly with the International Geoid Service (IGeS) ; Contribution within the IAG commission “Gravity Field” to the definition of a new global absolute reference gravity network; Contribution to research projects involving gravity data acquisition or validation and combination of surface and satellite gravity observations ; Contribution to summer schools and to dissemination of educative materials related to gravimetry.

<figure><img src="image_25.png" /></figure>

## Services

The most frequent service BGI can provide is data retrieval over a limited area or over a limited number of observations. Data requests are issued through the BGI website and are processed electronically (email, ftp transfer or direct download).

Data, products or software available at BGI are mostly dedicated to support scientific and academic activities. Digital gravity data or products are usually distributed free of charge to research or academic institutions or to data contributors according to the conditions given below. Other users, individual or private companies, are invited to
specify in their request the expected use of the data and products. See BGI website for diffusion and charging policies.

* Access to non-confidential or non-proprietary relative gravity measurements is provided free of charge to public institutions or data contributors over geographic areas limited to 20°x20° or on the base of a maximum number of 10000 data points (land data) and/or 100000 data points (marine data). Retrieval of full data coverage for a whole country is not included in that case. All other requests (for larger datasets, for extended geographic area or for a whole country) as well as massive data retrieval will be subject to an evaluation by BGI who might require a specific protocol of use of the data or ask authorization of the proprietary Institutions. Charges might be applied

* Access to the Absolute gravity database is provided free of charge without any restriction. Data retrieval is done through the Web interfaces at BGI and BKG mirror sites. Confidential data or proprietary data may appear with restricted information (metadata only).

* Access to the Reference gravity stations database is provided free of charge without any restriction. Please note that reference gravity stations (especially those determined and described decades ago) may have been destroyed or modified.

Other services include: Access to global or regional gravity anomaly grids and maps ; Prediction of gravity value on Earth ; Software ; Documentation, etc.

## Structure and membership

Since 2003, the BGI is one of the services of the International Gravity Field Service (IGFS) which coordinates within the IAG, the servicing of the geodetic and geophysical community with gravity field-related data, software and information.

The BGI central office (management, secretariat and technical staff) is located in Toulouse, France, in the premises of the Observatoire Midi-Pyrénées. Since 1998, BGI is supported by French Institutions, Universities and Laboratories (see below) whose contributions to BGI over four year renewable periods are defined by a covenant. The supporting French organizations are:

* the Centre National d'Etudes Spatiales (CNES),

* the Bureau de Recherches Géologiques et Minières (BRGM),

* the Institut National des Sciences de l'Univers (INSU/CNRS),

* the Institut National de l'Information Géographique et Forestière (IGN),

* the Institut de Recherche pour le Développement (IRD),

* the Service Hydrographique et Océanographique de la Marine (SHOM),

* the Groupe de Recherches en Géodésie Spatiale (GRGS)

* the Institut de Physique du Globe de Paris (IPGP),

* the Ecole et Observatoire des Sciences de la Terre (EOST)

* the Ecole Supérieure des Géomètres et Topographes (ESGT),

* the Université de Montpellier 2 (UM2)

Each supporting organization has a representative member in the BGI Advisory Board. The Advisory Board (who also includes a representative member of IAG) contributes once a year to the orientation and evaluation of the BGI activities. The program of BGI activities is also evaluated and discussed by the IGFS Advisory Board at each IGFS meetings and IUGG General Assemblies. A new partnership has been also established in 2008 between BGI and the Bundesamt für Kartographie und Geodäsie (BKG), Germany, for the realization and the maintenance of the global database of absolute gravity measurements (AGRAV).

## Providing data to BGI

As a service of IAG/IGFS, the final task of BGI is to give access to the largest scientific community to relative and absolute measurements of the Earth gravity field and related information. The permanent archiving of new incoming gravity data sets is crucial to improve the coverage and accuracy of the global gravity database and to improve our knowledge of the Earth gravity field. It also enables BGI to validate the gravity observations in a global reference frame and restore them in standard and unified formats useful for various users.

BGI currently collect & provides information on:

* Relative gravity measurements from land, marine & airborne surveys

* Absolute gravity measurements

* Reference gravity base stations

* Software for gravimetric applications (data processing, modeling, etc.)

* Other gravimetry-related information (printed or digital maps, bibliography, etc.)

The contribution of scientists, agencies or institutions involved in these fields is welcome to ensure the best service to the community. Contributors interested in archiving their gravity observations as non-confidential or as proprietary data (to be defined by the contributors themselves) are invited to contact BGI. For relative gravity observations, all kind of data from land, marine or airborne surveys can be sent to BGI. ASCII data files containing all necessary information and quantities are preferred (station coordinates, gravity measurements and accuracies; gravity corrections; reference geographic, height and gravity systems, etc.). For absolute gravity observations, the data-
base is maintained on two mirror sites located in Toulouse
(France), at BGI and in Frankfurt/Main (Germany), at the
Federal Agency for Cartography and Geodesy (BKG).
Scientists interested to upload their observations or meta-
data only (site positions and approximated values for
instance) in the international Absolute Gravity database
AGRAV are invited to contact either BGI (http://bgi.
ompobs-mip.fr) or BKG (http://agrav.bkg.bund). For any
contribution (relative or absolute gravity data), it is
reminded that BGI will keep the status of diffusion (with
or without restrictions of redistribution) as specified by the
proprietary institution.

BGI address:
Bureau Gravimétrique International
Observatoire Midi-Pyrénées
14, Avenue Edouard Belin
31401 Toulouse Cedex 9, France
Phone: 33-5 61 33 29 80
E-mail: bgi@cnes.fr, sylvain.bonvalot@ird.fr