Carey Noll

Current status of the doris pilot experiment and the future international doris service

Abstract The aim of the DORIS Pilot Experiment is to assess the need and feasibility of an International DORIS Service. A Call for Proposals was broadcasted in September 1999 to prompt qualified organizations to submit proposals for components of the future IDS. DORIS Days were held in Toulouse (May 2–3, 2000). This second version of these Doris days was in particular devoted to a review of the start-up of the Doris Pilot Experiment. This paper recalls the objectives of the future IDS, points out its components and structure, and gives information on the current and future activities.

IGEX: International GLONASS experiment — Scientific objectives and preparation

The GLONASS system is rapidly becoming of great interest for navigation, timing and geodetic applications, usually in combination with the GPS system. The goal of this paper is to describe the first world-wide campaign of observations of GLONASS satellites, organized with a large international participation. This first campaign, called IGEX98 will be organized in fall 1998. In this paper, we will focus on the scientific objectives and present the on-going preparation for this campaign. We will address several important scientific issues that could be solved in the short term by such a campaign. A large number of organizations have already answered positively to the IGEX98 International Call for Participation.

The future Global Geodetic Observing System

In this Chapter, we focus on the design of the geodetic observing system that will meet the specifications summarized in Section 7.7 and be able to sustain the products listed in Section 7.5. Thus, this Chapter treats GGOS as an observing system (see Section 1.3 for a discussion of the two different meanings of “GGOS”). In Chapter 10, the main focus will be on GGOS as an organization and the integration of GGOS in the global context of Earth observation. GGOS has been organized by the IAG to work with the established IAG Services in order to provide the geodetic contribution to global Earth monitoring, including the metrological and reference system basis for many other Earth observing systems. GGOS is therefore one of the basic observing systems comprising GEOSS. GGOS is complex, addressing relevant geodetic, geodynamic and geophysical problems, which have deep impact on vital issues for humankind, such as global change, sea level rise, global water circulation, water supply, natural disasters, risk reduction, etc.(see Chapter 5 for details). It is a visionary concept based on the requirements and specifications given in Chapter 7 and on the assessment of what components are needed to meet the very demanding goals. In order to address the ambitious GGOS goals, we will integrate a multitude of sensors into one global observing system. In the following sections the focus will be on the technical design and rationale for the proposed GGOS. The individual components of the system will be discussed and the interaction between the components will be outlined, from the geodetic observations and the interfaces to the products for the users.

The International DORIS Service (IDS): Recent Developments in Preparation for ITRF2013

The International DORIS Service (IDS) was created in 2003 under the umbrella of the International Association of Geodesy (IAG) to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). We first present some general background related to the DORIS system (current and planned satellites, current tracking network and expected evolution) and to the general IDS organization (from Data Centers, Analysis Centers and Combination Center). Then, we discuss some of the steps recently taken to prepare the IDS submission to ITRF2013 (combined weekly time series based on individual solutions from several Analysis Centers). In particular, recent results obtained from the Analysis Centers and the Combination Center show that improvements can still be made when updating physical models of some DORIS satellites, such as Envisat, Cryosat-2 or Jason-2. The DORIS contribution to ITRF2013 should also benefit from the larger number of ground observations collected by the last generation of DGXX receivers (first instrument being onboard Jason-2 satellite). In particular for polar motion, sub-milliarcsecond accuracy seems now to be achievable. Weekly station positioning internal consistency also seems to be improved with a larger DORIS constellation.

GGOS working group on ground networks and communications

Properly designed and structured ground-based geodetic networks materialize the reference systems to support sub-mm global change measurements over space, time and evolving technologies. Over this past year, the Ground Networks and Communications Working Group (GN&C WG) has been organized under the Global Geodetic Observing System (GGOS) to work with the IAG measurement services (the IGS, ILRS, IVS, IDS and IGFS) to develop a strategy for building, integrating, and maintaining the fundamental network of instruments and supporting infrastructure in a sustainable way to satisfy the long-term (10–20 year) requirements identified by the GGOS Science Council. Activities of this Working Group include the investigation of the status quo and the development of a plan for full network integration to support improvements in terrestrial reference frame establishment and maintenance, Earth orientation and gravity field monitoring, precision orbit determination, and other geodetic and gravimetric applications required for the long-term observation of global change. This integration process includes the development of a network of fundamental stations with as many co-located techniques as possible, with precisely determined intersystem vectors. This network would exploit the strengths of each technique and minimize the weaknesses where possible.

The IGS Global Data Center at the CDDIS: An Update

Abstract The Crustal Dynamics Data Information System (CDDIS) has served as a global data center for the International GPS Service (IGS) since its start in June 1992, providing on-line access to data from over 175 sites on a daily basis. This paper will present information about the GPS and GLONASS data and products archive at the CDDIS. General information about the system and its support of other international space geodesy services (the ILRS, IVS, IGLOS-PP, and DPE) will also be discussed.

The goals, achievements, and tools of modern geodesy

Friedrich Robert Helmert (1843-1917) defined geodesy as the science “of measurements and mappings of the Earth’s surface”. Over time, this definition of geodesy has been extended, mainly as a consequence of technological developments allowing geodesy to observe the Earth on global scales with high accuracy. Today, geodesy is the science of determining the geometry, gravity field, and rotation of the Earth and their evolution in time. This understanding of modern geodesy has led to the definition of the “three pillars of geodesy”, namely (1) Geokinematics, (2) Earth Rotation and (3) the Gravity Field (see Figure 1.1 on page 4). These three pillars are intrinsically linked to each other, and they jointly change as a consequence of dynamical processes in the Earth system as a whole. The changes in Earth’s shape (including the surface of the water and ice bodies), i.e. the geokinematics, are the result of dynamic processes in the solid Earth and its fluid envelope, affecting mass distribution and angular momentum, and thus changing the gravity field and Earth rotation. Traditionally, geodesy has been a service science, providing an important utility to other sciences and many applications. This aspect has remained unchanged, and a principal tool and output of geodesy is a reference frame allowing the determination of the position of points relative to each other. But geodesy has developed into a science that can no longer satisfy this service aspect without encompassing and monitoring the whole Earth system, its kinematic and dynamics. As an additional benefit, geodesy is increasingly forced not only to “measure” the geokinematics, gravity field, and rotation, but also to “model” these quantities on the basis of mass transport and dynamics. The instruments (or measurement tools) are of crucial importance in geodesy. They in essence define the scope of the problems, which may be addressed by geodesy. Before the advent of the space age the geometrical aspects were studied mainly by measuring angles and time (time-tagging of the observations). In the best

The proposed International DORIS Service

In 1999, an International DORIS Experiment was initiated under the aegis of the International Association of Geodesy. Since then, 3 new DORIS satellites have been launched carrying improved Doppler receivers. In addition, the DORIS tracking network has also been steadily improved. In 2001, a DORIS analysis campaign was launched. Several groups participated using different software and providing weekly and monthly time series of results, making them available on Internet. The goal of this paper is to discuss the status of the DORIS Pilot experiment, to analyze the progress made during the past 2 years and to propose the official creation within the IAG of an International DORIS Service (IDS). Such a service would operate in conjunction with the already existing IGS, IVS and ILRS as part of the proposed International Global Geodetic Observing System (IGGOS).

The IGEX-98- campaign: Highlights and perspective

Starting in October 1998, a large international campaign of GLONASS observations, called IGEX-98, has been conducted during a 6 month period. This campaign has involved a large international cooperation worldwide, including GLONASS, GPS and Laser observations and data processing. The goal of this paper is to present the scientific goals of the IGEX-98 campaign, to describe briefly its organization and also to present the preliminary results obtained for precise orbit determination, terrestrial reference frame and timing issues.

Global GPS Data Flow from Station to User within the IGS

The International GPS Service for Geodynamics (IGS) has been operational since January, 1994. This service was formed to provide GPS data and highly accurate ephemerides in a timely fashion to the global science community to aid in geophysical research. The GPS data flows from the global network of IGS sites through a hierarchy of data centers before they are available to the user at the global and regional data centers. A majority of these data flow from the receiver to global data centers within 24 hours of the end of the observation day. IGS analysis centers retrieve these data daily to produce IGS products (orbits, clocks, Earth rotation parameters, etc.). These products are then forwarded to the global data centers by the analysts for access by the IGS Analysis Coordinator for generation of the rapid and final IGS orbit product and for access by the geodynamics community in general. A discussion of the network data flow, from station to global data center to users, will be presented. Statistics on data quantity, volume, latency, and user access will be given.