SECTION I

POSITIONING

DETERMINATION DE POSITION

President: F.K. Brunner (Austria)

Secretaries: Y. Bock (USA)

C. Boucher (France)

I. Terms of reference

Section I is concerned with the scientific aspects of the measurement and analysis of regional and global geodetic networks as well as satellite, inertial, kinematic and marine positioning. The practical results of this research work should be made available through recommendations to National Survey Organisations. Applications of geodesy in engineering is a recent new task of Section I.

Tremendous advances of GPS surveying have occured especially in precision and applicability. However, there are some remaining issues of accuracy and reliability of GPS surveying (hardware and software) which need to be addresses carefully. Recently, GPS measurements have shown the potential to be used as remote sensing tool of atmospheric parameters.

II. Structure

Commissions :

Commission X : Global and Regional Geodetic Networks

President : C. Boucher (France)

Special Commissions :

SC4 : Applications of Geodesy to Engineering

President :H. Kahmen (Austria)

Special Study Groups :

SSG 1.153 : Precise Marine Positioning : Surface and

Seafloor

Chairman : D. Egge (Germany)

SSG 1.154 : Quality Issues in Real Time GPS

Positioning

Chairman : C. Rizos (Australia)

SSG 1.155 : Active GPS Networks

H. Tsuji (Japan)

SSG 1.156 : Advanced GPS Analysis for Precise

Positioning

Chairman : G. Blewitt (UK)

SSG 1.157 : GPS Ambiguity Resolution and

Validation

Chairman : P.J. de Jonge (Netherlands)

SSG 1.158 : GPS Antenna and Site Effects

Chairman : J. Johansson (Sweden)

SSG 1.159 : Use of GPS Positioning for

Atmospheric Monitoring

Chairman : M. Bevis (USA)

Commission X

Global And Regional

Geodetic Networks

Réseaux Géodésiques

Globaux et Régionaux

President : C. Boucher (France)

Secretary : H. Fagard (France)

I) Purpose

The purpose is to focus on the variety of existing control networks (horizontal and vertical, national and continental, global from space techniques) as well as their connections and evolutions.

II) Charter

The Commission X has two types of subdivisions : Sub-Commissions and working groups.

(1) Sub-Commissions for large geographical areas :

Europe

North America

South America

Africa

South East Asia and Pacific

.......

Such Sub-Commissions will deal with all types of networks (horizontal, vertical and three-dimensional) and all related projects which belong to the geographical area. Such a Sub-Commission will be established only if sufficient active countries in the area want to participate.

(2) Working Groups for specific technical topics which are be relevant to the activities of the Commission X.

Such working groups should not substitute a SSG of IAG but rather look at technical and practical problems, in particular by establishing specifications for the countries and also possibly training seminars.

In addition Commission X will have a Steering Committee (SC) consisting of :

- president of the Commission

- presidents of the Sub-Commissions

- chairmen of the Working Groups

Each country member of IAG is allowed to appoint one representative to Commission X. If the country belongs to an area where a Sub-Commission has been already established, the representative will be a de facto member of the Sub-Commission. A Sub-Commission is free to have specific rules in addition to those of the whole commission. In particular they may ask for more than one representative for specific reasons.

Each country not yet being a full member of IAG is welcome to appoint an observer to the Commission. Members of Working Groups will be selected by the chairmen and approved by the SC after consultation of relevant people and representatives of countries.

Sub-Commission for Europe

(former EUREF and UELN/REUN)

President : E. Gubler (Switzerland)

Secretary : H. Hornik (Germany)

Sub-Commission for North America

President : TBD

Secretary : TBD

Sub-Commission for South America

President : TBD

Secretary : TBD

Sub-Commission for Africa

TBD

Sub-Commission for

South East Asia and Pacific

TBD

Working Group 1

Datums and Coordinate Systems

Chairman : J.P. Dufour (France)

The purpose of this group is to :

- establish standards and terminology about datums and coordinate systems (a preliminary work has been done in Europe and circulated in the EUREF Sub-Commission)

- participate to the worjk of the ISO TC 211 group on geographical information

- establish a catalogue of datum and coordinate systems existing over the World

Working Group 2

Use of GPS and IGS for ITRF densification

Chairman : W. Gürtner (Switzerland)

This group should establish specifications to process properly GPS campaigns using IGS products and to be if wished included rigorously into the densification of the ITRF/IGS network as a so called IGS regional network.

Working Group 3

Worldwide Unification of Vertical Datums

Chairman : W. Kearsley (Australia)

This group should investigate the possible actions to be undertaken to realize a global vertical datum and to determine its connection to the various existing vertical datums.

Steering Committee :

C. Boucher (France) President

J.P. Dufour (France) WG1

E. Gubler (Switzerland) Subcomm. for Europe

W. Gurtner (Switzerland) WG 2

W. Kearsley (Australia) WG3

Contact or liaisons with related activities :

IAG bodies

Commission XII : H. Sünkel (Austria)

IERS : C. Boucher (France)

IGS : G. Beutler (Switzerland)

Other organizations

Defense Mapping Agency: R. Smith (USA)

SCAR: J. Manning (Australia)

Projects

AFREF : TBD

SIRGAS : H. Drewes (Germany)

III) National Representatives

C. Bruyninx (Belgium)

M.R. Craymer (Canada)

Y. Zhang (China)

J. Kostelecky (Czech Rep.)

F. Madsen (Denmark)

A. Shaker (Egypt)

M. Le Pape (France)

E. Reinhart (Germany)

J. Adàm (Hungary)

H. Tsuji (Japan)

D. Grant (New Zealand)

O.M. Ostach (Russia)

R.T. Wonnacott (South Africa)

J.L. Caturla (Spain)

W. Gürtner (Switzerland)

W. Strange (USA)

Special Commission SC 4

Application of Geodesy to Engineering

President : H. Kahmen (Austria)

Rapid developments in engineering, microelectronics and the computer sciences have greatly changed both instrumentation and methodology in engineering geodesy. The objectives of the Special Commission are on the one hand to document the body of knowledge in this field and on the other hand to encourage new developments and present them in a consistent frame work.

To accomplish the first objective, a group of internationally well-known scientists have been asked to contribute (by communicating and cooperating) in this task. In addition, a series of symposia will be planned to document the current state of development in engineering applications of geodesy. This will be an ongoing task of the Special Commission and therefore requires long-term planning by a group of leading specialists.

The second objective will be accomplished by four working groups which will be established in areas of current research interest and which will have specific goals which can be accomplished in a four year period.

Members :

M. O. Altan (Turkey)

V. Ashkenazi (United Kingdom)

J. M. Becker (Sweden)

F. Brunner (Austria)

W. Caspary (Germany)

A. Chrzanowski (Canada)

A. Detreköi (Hungary)

H. Erwes (Brazil)

H. Haggren (Finland)

H. Henneberg (Venezuela)

H. Ingensand (Switzerland)

H. Kahmen (Austria) - President

K. Linkwitz (Germany)

G. Miler (Bulgaria)

H. Nakamura (Japan)

T. Oshima (Japan)

O. Remmer (Denmark)

M. Roic (Croatia)

J. M. Rüeger (Australia)

K. P. Schwarz (Canada)

H. Schlemmer (Germany)

B. Witte (Germany)

B. N. Yambaer (Russia)

P. Zazuliak (Ukraine)

The following four working groups are considered as challenging:

1) SC 4 WG 1: "Mobile Multi-Sensor Systems"

Chairman: Naser El-Sheimy (Canada)

Comments and context:

To fullfil the need for up-to-date inventory and geometric data along transportation routes (roads, railways, rivers, pipelines) mobile inventory systems are being operated. In general motion of a vehicle in three-dimensional space can be described by six parameters: they are normally chosen as three position and three orientation parameters.

Frequently GPS integrated with other sensors is proposed to fullfil these trajectory requirements. In addition inventory and geometric data can be collected with sensors, such as: CCD cameras, extensometers, tiltmeters, laser scanners, etc. Normally the multi-sensor systems need highly efficient software tools to adjust and store data.

Members:

W. Benning (Germany)

J. B. Bullock (USA)

W. Caspary (Germany)

I. Colomina (Spain)

D. Cosandier (Canada)

H. Döller (Austria)

Naser El-Sheimy (Canada) - Chairman

A. Hasan (Canada)

W. Niemeier (Germany)

G. Presle (Austria)

G. Retscher (Austria)

2) SC 4 WG 2: "Building Structures as Kinematic Systems"

Chairman: G. Mentes (Hungary)

Comments and context:

Many tasks in engineering geodesy require monitoring the motion of objects, such as bridges and towers affected by wind, buildings and industrial establishments affected by recent crustal movements, land slides, etc. Instruments used to observe the motion are often fixed to the moving object or are moved with respect to the object. Consequently, the system parameters change. The aim of the working group is to develop mathematical and physical models as well as experimental methods for the determination of such parameter changes.

Members:

M. O. Altan (Turkey)

A. Bilajbegovic (Croatia)

F. Brunner (Austria)

B. Crippa (Italy)

E.-N. Dietz (Germany)

X. Ding (Australia)

T. Egeltoft (Sweden)

H. Heister (Germany)

O. Heunecke (Germany)

J. Kalmar (Hungary)

A. Kopacik (Slowakia)

G. Lachapelle (Canada)

G. Mentes (Hungary) - Chairman

H.-J. Mönicke (Germany)

H. Papo (Israel)

A. Pfeufer (Germany)

J. Piechocinski (Sweden)

W. Proszynski (Poland)

J. M. Rüeger (Australia)

3) SC 4 WG 3: "High Precision Alignment Systems"

Chairman: R. Ruland (USA)

Comments and context:

The development and application of high precision alignment systems has become increasingly important for the fields of civil engineering and manufacturing. Typical examples of applications are: high speed trains, dams, particle accelerators, aero-space industry, etc. The working group will summarize the state-of-the-art for these applications in algorithm development, instrumentation and special equipment, by analysing recent examples of challenging projects.

Members:

M. Mayoud (Switzerland)

Oren (USA)

R. Ruland (USA) - Chairman

Schauerte (Germany)

Schwarz (Germany)

A. Sprent (Australia)

(Additional members will be nominated by the chairman.)

4) SC 4 WG 4: "Geometrical Investigation of Spatial Geodetic Problems"

Chairman: Th. A. Wunderlich (Austria)

Comments and context:

The task of the proposed working group is to study, to describe and to develop the pure geometrical foundations and properties pertinent to new sophisticated geodetic techniques and to demanding architectural design. Modern geodetic measurement techniques, sometimes based on novel measurement quantities (like e.g. pseudoranges in GPS), have their own specific geometrical properties. Research is needed to gain insight into the geometrical behaviour and to isolate optimum and critical configurations.

The investigations have to be accompanied by the development of instructive software to visualize the findings for training purposes. Modern architectural designs, often in connection with precise prefab-manufacturing of plastic construction parts, demand geodetic conversion of the artistic idea into consistent geometric parameters and coordinates. Investigations are needed as an essential part of TQM on the major steps leading to the realization of the design, such as the geometrical elements and on-site assembly.

Members :

T. Ayan (Turkey)

A. Geiger (Switzerland)

R. Finsterwalder (Germany)

R. Heer (Germany)

M. Husty (Austria)

W. Rath (Austria)

R. Santerre (Canada)

P. Savvaidis (Greece)

Th. A. Wunderlich (Austria) - Chairman

Special Study Group 1.153

Precise Marine Positioning,

Surface and Seafloor

Chairman : D. Egge (Germany)

Terms of Reference :

Precise marine positioning is an important subset of marine geodesy. As such, it is in close vicinity to the sciences of navigation and hydrography. Coordinates of stationary points on the continents have to be transported to points on the sea surface and on the seafloor, thereby extending geodetic control to these points. This is accomplished by measurements that involve moving interfaces such as satellites and surface vessels. In general, marine positioning is a multisensor effort in a dynamic environment with partly specialized instrumentation. This, in turn, leads to related modelling, estimation, and optimization problems. The rapid evolution of computer and networking technology adds another dimension of complexity to the subject.

The purpose of this Special Study Group is to promote comprehensive research for precise geodetic positioning in the marine environment. The overall objectives are

- to help to improve our understanding of current

capabilities and applications,

- to analyze remaining limitations,

- and to explore the possibilities of achieving

future improvements.

Program of Activities :

1. This IAG Special Study Group (SSG) will attempt to focus on the relevant marine positioning aspects of the IAG Special Commission on Marine Positioning (ISCOMAP, 1991 - 1995).

2. The members of this SSG are invited to contribute their ideas and findings (copies of publications) to a central information pool maintained by the SSG Chairman.

Preferred study areas are:

a. Seafloor positioning.

b. Seafloor spreading.

c. Height systems and bathymetry.

d. Surface positioning.

e. Instrumentation / measurement techniques.

f. Modeling of observations and errors.

g. Geoid and mean sea level.

h. Estimation techniques.

i. Applications.

3. Participation in related symposia and meetings is encouraged.

4. It is planned to continue the very successful quadrennial symposia series known as "International Symposium on Marine Positioning" (INSMAP).

Special Study Group 1.154

Quality Issues in Real time

GPS Positioning

Chairman : C. Rizos (Australia)

Main objectives :

Concerns about GPS positioning quality are shared by all users, from those engaged in the most precise geodetic applications through to the casual navigator. The quality of GPS positioning, however, is dependent on a number of factors. Experience with precise geodetic applications of GPS has shown that sophisticated mathematical modelling, careful field procedures and top-of-the-line GPS hardware are all necessary prerequisites. However great care still has to be applied to ensure that data quality is uniformly high. The procedure of data screening, position computations, result evaluation and quality assurance has generally been an off-line (as well as iterative) process. With the development of precise "on-the-fly" GPS positioning techniques it is no longer possible to process (and re-process) GPS data in post-mission mode until positioning quality is assured. The challenge therefore is to develop quality control and quality assurance procedures that can be applied in "real-time" (or "near-real-time") GPS positioning.

The work of the SSG on "Quality Issues in Real-Time GPS Positioning" will focus on identifying practical procedures, as well as mathematical techniques, that can be applied to assure the quality of positioning results obtained from this distinct class of GPS applications. The objectives of the SSG are to :

(a) IDENTIFY the main issues impacting on the "quality" of real-time GPS positioning - including those due to instrumental effects, environmental sources, site-dependent effects, communcations-dependent, etc.

(b) COMPILE a set of procedures, algorithms and guidelines that can be implemented within real-time GPS positioning software - this is the practical outcome.

(c) DEFINE areas for further research and development - as derived from practical experience on the one hand, and a study of the literature and research trends in the development of mathematical and/or empirical tools for "quality control".

Program of activities :

1. Compile and document the QC procedures and algorithms as implemented in scientific GPS geodesy software.

2. Investigate which of these procedures are adaptable for "real-time" operation - for example, for the detection of faulty navigation messages, data spikes, etc.

3. Compile a bibliography of QC literature specifically applicable to precise kinematic GPS positioning.

4. Research fault detection algorithms for real-time GPS applications.

5. Encourage discussion and critical evaluation of such algorithms.

6. Monitor the activity taking place in the development of quality control (QC) and quality assurance (QA) for standard pseudo-range based DGPS.

7. Determine the appropriate "mix" of QC/QA procedures that can be recommended for real-time precise GPS positioning - as it is likely that a "cocktail" of procedures will be necessary to give greatest assurance on quality.

8. Prepare a comprehensive report on the SSG's activities and recommendations.

Members :

C. Rizos (Australia) Chairman

E. Cannon (Canada)

R. Galas (Germany)

Y. Hatanaka (Japan)

X. Jin (The Netherlands)

H. Kutterer (Germany)

S. Mertikas (Greece)

P. Morgan (Australia)

S. Oszczak (Poland)

W. Roberts (United Kingdom)

G. Seeber (Germany)

M. Stewart (Australia)

Special Study Group 1.155

Active GPS Networks

Chairman : H. Tsuji (Japan)

Terms of Reference

"Active GPS networks" originally referred to permanent GPS arrays which automatically collect continuous data from GPS satellites for the primary purpose of monitoring crustal deformations. However, it is clear that such GPS network data are useful for surveying and navigation. Currently, many national GPS networks allow a public access to their data (RINEX or RTCM) to support static/kinematic/RTK/DGPS applications of GPS. Compared to conventional geodetic networks, such GPS arrays are "active" because they transmit products through electronic media on a continuous basis.

The goal of our SSG is to exchange and maintain descriptive information on these active GPS networks of the world and provide a forum to discuss common issues in making full use of such networks in close relationship

with IGS.

Objectives

To achieve the goal, the SSG will maintain a WWW home page on the internet, and provide information on active GPS networks of the world. It is planned that members will provide linked pages giving details of their own regional networks. The SSG will also investigate and discuss the common issues in making full use of active GPS networks such as:

- technical innovations in network operations (e.g. communications, high-density storage devices, receiver automated status reports);

- technical requirements for better user interface (e.g. efficient compression of observation data, addition of ancillary data, integrated user interface for baseline analysis);

- new application of active GPS networks (e.g. possibility of ionospheric monitoring, GPS meteorology, and GPS seismology).

Members

Members

H. Tsuji (Japan) - Chairman

B.C. Ambrosius (Netherlands)

H. Dragert (Canada)

P. Fang (USA)

L.P.S. Fortes (Brazil)

R. Galas (Germany)

J. K ahar (Indonesia)

J-T.Lee (Taiwan)

J. Manning (Australia)

M.A. Marsella (Italy)

M. Murray (USA)

B.R. Pettersen (Norway)

W.E. Strange (USA)

S. Tatevian (Russia)

A. Tealeb (Egypt)

F. Webb (USA)

U. Wild (Switzerland)

R. Wonnacott (South Africa)

W. Zhu (China)

Corresponding members

C. Boucher (France)

J.M. Johansson (Sweden)

C. Rizos (Australia)

Special Study Group 1.156

Advanced GPS Analysis for

Precise Positioning

Chairman : G. Blewitt (United Kingdom)

I- Terms of Reference

The goal of SSG 1.156 is to improve high precision GPS static positioning over regional to global scales. This will be achieved by providing a forum for experts in today's high precision GPS software and analysis techniques, with the aim of improving the software's models, algorithms, recommended processing procedure, and recommended estimation strategies. This will be achieved by conducting a comparative study of the state-of-the-art in models and methodology.

II- Objectives

The specific objectives of SSG 1.156 are to :

(i) investigate how best to compare models and solutions from high precision GPS positioning software, and determine methods and measures for the assessment of solution quality;

(ii) comparatively assess current models and algorithms that are embodied in high precision GPS positioning software;

(iii) comparatively assess current processing procedures and estimation strategies employed by experienced analysts who demand the highest positioning accuracy over regional to global scales;

(iii) assess new models, algorithms, and strategies which are proposed by the SSG members.

The outcome of these activities will be a final report which contains :

(i) a comparative description and assessment of current high precision analysis software and methodology;

(ii) recommendations (wherever possible) for GPS analysis methods which are most appropriate for specific types of situations (ranging from epoch regional campaigns, to global network analysis );

(iii) proposed modifications to the IERS standards for GPS analysis.

III-Members

G. Blewitt (United Kingdom) Chairman Y. Bar-Sever (USA)

G. Dick (Germany)

P. Fang (USA)

J. Johansson (Sweden)

J. Kouba (Canada)

K. Larson (USA)

T. Martin-Mur (Germany)

M. Rothacher (Switzerland)

M. Schenewerk (USA)

T. Springer (Switzerland)

H. Tsuji (Japan)

T. vanDam (USA)

J. Zumberge (USA)

Special Study Group 1.157

GPS Ambiguity Resolution

and Validation

Chairman : P.J. de Jonge (The Netherlands)

Terms of reference

Ambiguity resolution has been a `hot' topic for the last five years or so. Starting from relative simple rounding schemes, sophisticated and sometimes time consuming algorithms have been devised. Despite the large effort spent by many groups from all over the world in devising various schemes, knowledge about their theoretical foundation, and how the schemes are related to each other, is still lacking. Different terminology is used and comparisons between methods are rare.

Due to a lack of knowledge about the various methods, the implementations used in the comparisons are not always complete, thereby making the test results unreliable. Moreover, results reported of one particular method, are often difficult to relate to the results of another method, due to lacking knowledge of the characteristics of the data and the type of computer that was used.

It is important to note that ambiguity resolution is applied in different fields (navigation, rapid static surveying, ambiguity resolution in regional networks), and that every application has its own special needs. The validation of the results is another important topic that needs more attention (especially for the navigation and rapid-static applications).

Objectives

The outcome of this Special Study Group should be

1. A further understanding of the problem of ambiguity resolution.

2. Understanding how the various algorithms work, and how they are related to each other.

3. Advantages and disadvantages of each class of methods.

These goals can be met by

1. A formulation of a consistent terminology, or at least a translation between the terms that are used.

2. A classification and description of the various methods, using a standard terminology to clearly see the differences and similarities of the methods. This will lead to a better understanding of the concepts of the existing methods, and possibly to improvements.

3. Collection of test sets, consisting of data, a detailed description of it, and a ground truth for the integer ambiguities. The test sets should be exemplary for what is encountered in practice.

4. Comparisons of the various algorithms with the help of the test sets of (3).

Members :

P. de Jonge (The Netherlands) - Chairman

H. Abidin (Indonesia)

B. Betti (Italy)

S. Corbett (United Kingdom)

M. Crespi (Italy)

H.-J. Euler (Switzerland)

S. Han (Australia)

H. Kutterer (Germany)

H. Landau (Germany)

B. Marana (Italy)

M. Martin-Neira (the Netherlands)

D. Marujoao (Portugal)

J. Galera Monico (Brasil)

S. Schaer (Switzerland)

B. Remondi (USA)

W. Werner (Germany)

P. Willis (France)

G. Wuebbena (Germany)

M. Yang (Taiwan)

Z. Li (Canada)

Special Study Group 1.158

GPS Antenna and Site Effects

Chairman : J. Johansson (Sweden)

I- Terms of Reference

The improvement in precision obtained from GPS observations over recent years has revealed problems related to the local conditions at the GPS sites. In order to further improve high precision GPS positioning, orbit determination, and the estimates of atmospheric parameters, investigations of site dependent effects are required. The establishment of large numbers of permanent GPS stations on global, regional, and local scales has also raised concerns regarding the monuments used and the long- and short-term mechanical and electromagnetic stability of the sites.

The goal of SSG 1.158 is to provide information and recommendations regarding the reduction of site dependent effects such as those related to GPS antennas, radomes, electromagnetic scattering, monuments and local stability, radio interference, and local atmospheric conditions.

This goal will be achieved by providing a forum for discussions and for the exchange of ideas and literature. Interaction with the IGS community, regional and national GPS networks, and other study groups in Section I are essential to achieving the goals of the SSG.

II- Objectives

The objectives of SSG 1.158 are to :

(I) investigate the characteristics of different GPS antennas (mainly those used in high-precision applications) based on measurements in anechoic chambers, field experiments, and numerical evaluation; study the effects of "antenna mixing;" design and evaluate new space GPS antennas;

(II) study the influence of electromagnetic scattering (including multipath) and provide information on how to minimize these effects;

(III) investigate and formulate recommendations regarding establishment of new GPS sites, including the design and construction of pillars (monuments) and the monitoring of their long-term stability; evaluate radomes used to protect permanently installed antennas;

(IV) study and minimize the influence of snow, rain, and local atmospheric conditions on the final estimates;

(V) provide information and recommendations on how to eliminate (or minimize) the effects of radio interference.

The outcome of these activities will be summarized in a final report which contains information regarding site dependent effects and how to minimize them, recommendations (wherever possible) of appropriate solutions for the establishment of new GPS sites, and proposed modifications to GPS processing standards.

III- List of Members

Members

J. Johansson (Sweden) - Chairman

J. Campbell (Germany)

T. Clark (USA)

J. Davis (USA)

C. Dunn (USA)

A. Geiger (Switzerland)

K. Jaldehag (Sweden)

H. Koivula (Finland)

R. Langley (Canada)

K. Larson (USA)

G. Mader (USA)

C. Meertens (USA)

P. Morgan (Australia)

A. Rius (Spain)

M. Rothacher (Switzerland)

B. Schupler (USA)

J. Tranquilla (Canada)

D. Van Loon (The Netherlands)

L. Vittuari (Italy)

R. Warnant (Belgium)

Corresponding Members

G. Blewitt (UK)

B. Burki (Switzerland)

U. Lindqwister (USA)

S.Musyoka (Germany/Kenya)

C. Rizos (Australia)

W. Schlueter (Germany)

H. Tsuji (Japan)

Special Study Group 1.159

Use of GPS Positioning for Atmospheric Monitoring

Chairman : M. Bevis (USA)

I. Main Objectives

In recent years is has become clear that continuous GPS networks can support a variety of meteorological applications. These applications include the study of climate and climate change, operational weather analysis and prediction, and basic research into tropospheric phenomena.

The main objectives of this SSG are :

(i) to identify the range of measurements that may be useful to the meteorological community,

(ii) to explore the many technical issues associated with optimizing such measurements in real-time and non-real-time settings,

(iii) to provide an interface between the geodetic and the meteorological communities, and

(iv) to advise the IGS on how the global tracking network can optimize its support of GPS meteorology, (v) to investigate possible synergies between GPS meteorology and similar measurements made with VLBI or other geodetic techniques.

This SSG will not focus on characterization of the ionosphere, nor on space-based GPS meteorology, except to the extent that these areas intersect ground-based GPS characterization of the neutral atmosphere.

II. Program of Activities

1. Promote Discussions between Meteorologists and Geodesists about Goals and Priorities

Identify the various classes of measurements that can be made by GPS networks and specific meteorological applications in which each class of measurement might be useful. For example, numerical weather models could assimilate geodetic estimates of total column estimates such as precipitable water (PW), but also estimates of lateral gradients in these quantities at each GPS station, and even pointed measurements in which quantities are gauged along a specific station-satellite raypath. It may be that the computational burden associated with assimilating pointed measurements (and ray tracing) so greatly exceeds that associated with assimilation of total column variables such as PW, that operational meteorologists may assign these GPS measurements very different priorities on purely practical grounds. Geodesists need to understand these nuances as they explore new estimation strategies.

2. Discuss New or Improved Approaches to Measurement of Delay and Water Vapor Structure

Topics include

(i) optimizing mapping functions, including anisotropic mapping functions,

(ii) prior versus posterior decomposition of the total neutral delay into its hydrostatic and wet components,

(iii) antenna-related noise sources,

(iv) the role of ephemerides, including predicted ephemerides for nearly-real-time estimation,

(v) software architectures for real-time analysis, etc.

3. Promote and Discuss External Comparisons

There is considerable interest in comparing GPS-derived estimates of delay and PW, and of lateral gradients in these quantities with those derived from other classes of geodetic system (such as VLBI and DORIS) and from instruments more routinely employed by atmospheric scientists (such as water vapor radiometers, radiosondes, LIDAR, etc.).

4. Identification and Distribution of Standard Datasets

A few 'standard' regional and global datasets would greatly facilitate the intercomparison of GPS-derived quantities such as PW, by groups using different hardware, algorithms, software packages, and orbital solutions. The various GPS-derived time series might also be useful for meteorologists examining the impact of these data products on numerical weather prediction, climate models, etc. Of course, datasets that include some basis for external comparison are likely to prove the most useful.

III. Membership

Members

J. Beavan (New Zealand)

M. Bevis (USA) - Chairman

B. Bürki (Switzerland)

S. Businger (USA)

J. Davis (USA)

A. Dodson (UK)

G. Elgered (Sweden)

G. Gendt (Germany)

R. Ichikawa (Japan)

S. Keihm (USA)

G. Kirchengast (Austria)

R. Langley (Canada)

V. Mendes (Portugal)

I. Naito (Japan)

A. Rius (Spain)

B. Sierk (Switzerland)

P. Willis (France)

Correspondin,g Members

H. Tsuji (Japan)