The CDDIS supports several NASA-sponsored and international scientific programs.

Current Programs:

• International GPS Service (IGS)
  • International GLONASS Service -- Pilot Project (IGLOS-PP)
  • Low Earth Orbiters (LEO) Pilot Project (LEO-PP)
  • GPS Tide Gauge Benchmark Monitoring Pilot Project (TIGA-PP)
• International Laser Ranging Service (ILRS)
• International VLBI Service for Geodesy and Astrometry (IVS)
• International DORIS Service (IDS)
• International Earth Rotation Service (IERS)
• NASA's Space Geodesy Program (SGP)
• Solid Earth and Natural Hazards Research and Applications NRA

Past Programs:

• Crustal Dynamics Project (CDP)
• NASA's Dynamics of the Solid Earth (DOSE) Investigation

International GPS Service (IGS)

The International GPS Service (IGS) was established by the International Association of Geodesy (IAG) in 1993 and began formal operation in January 1994. The IGS, with a multinational membership of organizations and agencies, provides GPS orbits, tracking data, and other data products in support of geodetic and geophysical research. The IGS also supports a variety of governmental and commercial activities and develops international GPS data standards and specificiations.

The IGS collects, archives, and distributes GPS observation data sets of sufficient accuracy to meet the objectives of a wide range of scientific and engineering applications and studies. The IGS has developed a worldwide system, comprising satellite tracking stations, data centers, and analysis centers, to put high-quality GPS data on-line withing one day and data products on-line withing two weeks of observations. The GPS data sets are used to generate the following products:

• GPS satellite ephemerides
• Earth rotation parameters
• IGS Tracking station coordinates and velocities
• GPS satellite and IGS tracking station clock information

From: IGS Brochure, June 1995

International GLONASS Service -- Pilot Project (IGLOS-PP)

The International GLONASS Service - Pilot Project (IGLOS-PP) is a pilot service of the International GPS Service (IGS) to track and analyze data from the Russian GLONASS satellite constellation. The primary products of the service are dual-frequency observations from the global tracking network and precise orbits computed for each satellite. These are made available to support and encourage other applications and studies. In particular, the products from the Service facilitate the use of combined GLONASS and GPS observations for scientific and engineering applications, and allow users to experiment with the combined systems as a prototype Global Navigation Satellite System. The pilot service will operate for a period of up to four years, from 2000-2003.

The goals and objectives of the IGLOS Pilot Service are as follows:

1. Establish and maintain a global GLONASS tracking network
   • Collocate dual-frequency, combined GPS/GLONASS receivers with dual-frequency GPS receivers or upgrade existing dual-frequency GPS receivers to dual-frequency, combined GPS/GLONASS receivers at existing IGS sites and at new sites
   • Apply International GPS Service (IGS) network operations standards
   • Calibrate and evaluate combined GPS/GLONASS receivers and antennas
   • Produce precise (10-cm level) orbits, satellite clock estimates, and station coordinates
2. Evaluate microwave-derived orbits using SLR observations and orbits
   • Incorporate SLR observations in routine orbit processing
   • Obtain initial operational capability of 20-50 cm orbits at Analysis Centers
   • Receive independent orbit/clock/station solutions from Analysis Centers within three weeks of observations
   • Monitor and assess GLONASS system performance
3. Investigate the use of GLONASS to improve Earth Orientation Parameters
4. Improve atmospheric products of the IGS
5. Fully integrate GLONASS into IGS products, operations and programs.

From: IGS IGLOS-PP web site, May 2000

Low Earth Orbiters (LEO) Pilot Project (LEO-PP)

A pilot project of the IGS

Recognizing the compelling climate and geodetic science possible with, and the rapid growth of, satellites carrying precise, geodetic-quality GPS receivers, the IGS Governing Board created the Low-Earth Orbit (LEO) Working Group with the charter of exploring the role of LEOs in the IGS, and suggesting possible activities for the IGS and its components in the world of spaceborne GPS. The activities of the working group led to the release of the IGS Call for Participation in support of Low Earth Orbiting Missions.

The establishment of a space network of orbiting GPS receivers could be developed as an extension of the ground network while utilizing many of the resources which the IGS currently has in place. Therefore with a Call for Participation the IGS solicited support in the establishment of an enhanced subset of IGS infrastructure targeted at supporting Low Earth Orbiting missions.

The IGS has a `de facto' role in the development and applications for orbiting GPS receivers and the stage is set for the IGS to now play a significant role in the development of spacebased GPS receiver applications. With this development, the IGS will serve the broader geoscience community as well as potentially provide services for commercial interests.

From: LEO-PP web site, January 2000.

GPS Tide Gauge Benchmark Monitoring Pilot Project

A pilot project of the IGS

The GPS Tide Gauge Benchmark Monitoring - Pilot Project (TIGA-PP) is a pilot study of the International GPS Service (IGS) for establishing a service to analyze GPS data from stations at or near tide gauges (TG) on a continuous basis (CGPS @ TG). The primary product of the service is time series of coordinates for analyzing vertical motions of Tide Gauges and Tide Gauge Benchmarks (TGBM). All products are made public to support and encourage other applications, e.g. sea level studies. In particular, the products of the service facilitate the distinction between absolute and relative sea level changes by accounting for the vertical uplift of the station, and are, therefore, an important contribution to climate change studies. The service may further contribute to the calibration of satellite altimeters and other oceanographic activities. The pilot project will operate for a period up to three years, from 2001 to 2004. After this period the IGS Governing Board will evaluate the project and decide whether or not this activity should become a regular IGS service function.

The goals of the TIGA-PP are identified as follows:

1. Establish, maintain and expand a global CGPS @ TG network
2. Contribute to the procedures in which IGS realizes a global reference frame in order to improve its utility for global vertical geodesy
3. Compute precise station coordinates and velocities for the CGPS @ TG stations using a processing stream that runs months behind real-time in order to include the largest possible number of stations.
4. Establish a secondary processing stream with much reduced latency in order to support operational activities that cannot tolerate large processing delays.
5. Monitor the stability of the network.

From: TIGA-PP web site, June 2001

International Laser Ranging Service (ILRS)

The primary objective of the International Laser Ranging Service (ILRS) is to provide a service to support, through Satellite and Lunar Laser Ranging data and related products, geodetic and geophysical research activities as well as IERS products important to the maintenance of an accurate International Terrestrial Reference Frame (ITRF). The service also develops the necessary standards/specifications and encourages international adherence to its conventions.

The ILRS collects, merges, archives and distributes Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) observation datasets of sufficient accuracy to satisfy the objectives of a wide range of scientific, engineering, and operational applications and experimentation. These datasets are used by the ILRS to generate a number of scientific and operational data products including but not limited to:

• Earth orientation parameters (polar motion and length of day)
• Three-dimensional coordinates and velocities of the ILRS tracking stations
• Time-varying geocenter coordinates
• Static and time-varying coefficients of the Earth's gravity field
• Centimeter accuracy satellite ephemerides
• Fundamental physical constants
• Lunar ephemerides and librations
• Lunar orientation parameters

The accuracy of SLR/LLR data products is sufficient to support a variety of scientific and operational applications including:

• Realization of global accessibility to and the improvement of the International Terrestrial Reference Frame (ITRF)
• Monitoring three dimensional deformations of the solid Earth
• Monitoring Earth rotation and polar motion
• Support the monitoring of variations in the topography and volume of the liquid Earth (ocean circulation, mean sea level, ice sheet thickness, wave heights, etc.)
• Tidally generated variations in atmospheric mass distribution
• Calibration of microwave tracking techniques
• Picosecond global time transfer experiments
• Astrometric observations including determination of the dynamic equinox, obliquity of the ecliptic, and the precession constant
• Gravitational and general relativistic studies including Einstein's Equivalence Principle, the Robertson-Walker b parameter, and time rate of change of the gravitational constant
• Lunar physics including the dissipation of rotational energy, shape of the core-mantle boundary (Love Number k2), and free librations and stimulating mechanisms
• Solar System ties to the International Celestial Reference Frame (ICRF)

From: ILRS Terms of Reference, 1998

International VLBI Service for Geodesy and Astrometry (IVS)

IVS is the International VLBI Service for Geodesy and Astrometry. IVS groups geodesy and astrometry together because they use the same observations and the same analysis gives both types of results. IVS is established under the International Association of Geodesy's (IAG) Commission VIII - the International Coordination of Space Techniques for Geodesy and Geodynamics, or CSTG, chaired by Gerhard Beutler of the University of Berne, Switzerland. IVS is the third of this type of service to be established. The first was the IGS (International GPS Service) which has been highly successful as a service for GPS. The second service was the ILRS (International Laser Ranging Service) which started in late 1998.

The objectives of IVS are

1. to provide a service to support geodetic, geophysical, and astrometric research and operational activities;
2. to promote research and development for VLBI; and
3. to interact with users of VLBI products.

The service aspect of IVS is meant to serve both outside users and the geodetic and astrometric community itself. Both the contributors and users of data will be served.

IVS provides data and products for the scientific community. Some of the products are

• a terrestrial reference frame (TRF),
• the international celestial reference frame (ICRF), and
• Earth orientation parameters (EOP).

All IVS data and products are archived and are publically available. IVS products contribute to research in many areas, including areas such as the solid Earth, tides, studies of the vertical, and VLBI technique improvement.

From: IVS web site, April 1999

International DORIS Service (IDS)

The International DORIS Service (IDS) is a project for an international service to provide a support, through DORIS data and products, to geodetic, geophysical, and other research and operational activities. The creation of the IDS is initiated by the DORIS Pilot Experiment in order to assess the need and the feasibility of such a service.

After a decade of fully operational functioning, the DORIS space geodesy system has demonstrated its capabilities for orbitography and navigation of the satellites and also ground location. It plays a key rule in the Topex/Poseidon altimetric mission for oceanography providing in association with the Laser technique a 2 cm accuracy in the radial component of the orbit. DORIS and Laser are renewed as the nominal orbitographic system for the Jason mission (end of 2000).

DORIS also provides with Diode navigator on Spot-4 (1993), an orbit in real time within a few meters. It's a world first at this level of precision.

Since 1994 and thanks to its more than fifty permanent beacon network, DORIS contributes to the IERS activities for the realization and maintenance of the ITRS (International Terrestrial Reference System). 3D positions and velocities of the reference sites at a cm and mm/y accuracy lead to scientific studies (investigations) in the fields of global and regional tectonics. Two recent DORIS results appear very encouraging for the future. One concerns a seasonal effect of earth surface fluid mass redistribution (oceanic water, atmospheric masses, snow, etc.) on the relative positions of the earth mass and earth figure centers. Another concerns vertical displacement of the crust monitored near tides-gages. This information is of major interest for the topic of sea level variations and correlation to the Global Change.

Such as the other space geodesy techniques GPS, VLBI, SLR, there is a strong demand among the scientific community to create an International DORIS Service, so called IDS. The CSTG, commission for international co-ordination of space techniques for geodesy of the International Association Geodesy (IAG)and the IERS directing board decided last July to initiate a DORIS Pilot Experiment. Its objective is to assess the need and feasibility of an International DORIS Service.

From: IDS web site, July 2000

International Earth Rotation Service (IERS)

The International Earth Rotation Service (IERS) was created in 1988 by the International Union of Geodesy and Geophysics (IUGG) and the International Astronomical Union (IAU). It replaced the Earth rotation section of the Bureau International de l'Heure ( BIH , ) and the International Polar Motion Service (IPMS). It is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS).

According to its Terms of Reference , the mission of the IERS is to provide timely and accurate data on the Earth's rotation for current use and long-term studies. For this purpose it has established and maintains an international terrestrial reference frame and an international celestial reference frame and it regularly monitors the relative motion of these two frames by analysing observational data from a variety of techniques, including radio interferometry (VLBI), Lunar Laser Ranging ( LLR ) and satellite-geodetic techniques such as GPS , SLR , DORIS .

The IERS techniques have strengths that are used in a complementary way, keeping enough redundancy for ensuring the permanence of the service over decades and maintaining close operational interaction with other global astronomical and geophysical programs. The maintenance of the consistency and accuracy of IERS products requires a careful organisation and management of the contributions of the major techniques used in space navigation, space geodesy and astrometry.

The IERS is an interdisciplinary , service that maintains key connections between astronomy, geodesy and geophysics.

From: IERS web site

Space Geodesy Program (SGP)

The space geodesy program at NASA uses several space-age techniques to study the Earth, including laser ranging to an artificial satellite or the Moon, the Global Positioning System (GPS), and Very Long Baseline Interferometry (VLBI). A network of laser, GPS, and VLBI stations has been established worldwide to gather data and derive three-dimensional station positions as a function of time, baseline distances, velocities, and orientations as a function of time, and Earth rotation and polar motion values. Frequent highly accurate measurements of baselines between stations in active areas near plate boundaries are underway to determine regional deformation and strain accumulation. Baseline distances between a global set of stations are measured repeatedly to determine relative plate motions. Measurements between several stations on the same plate are conducted to determine internal deformation of the plate. At this time, the precision of the space geodetic techniques is about one centimeter on baselines of several thousand kilometers in length. Variations in the motion of the Earth's pole and rotation of its axis are determined from regular measurements.

Solid Earth and Natural Hazards Research and Applications NRA

The Solid Earth and Natural Hazards Research and Applications NASA Research Announcement (NRA) presents an opportunity for researchers to participate in the NASA research and development themes of Solid Earth and Natural Hazards Research and Applications. The research themes aim to develop and use NASA space geodetic and remote sensing technology to improve our understanding of the physical dynamics of the solid earth (including the interaction with atmosphere, ocean and fluid core) and to improve and demonstrate the capability of this technology in the assessment and mitigation of natural hazards.

From: Solid Earth and Natural Hazards Research and Applications NRA, August 1996

Crustal Dynamics Project (CDP)

The scientifc objectives of the Crustal Dynamics Project (CDP) developed by the science community and NASA in the late 1970's were to improve our knowledge and understanding of:

• Regional deformation and strain accumulation related to earthquakes at the plate boundary in the western United States;
• Contemporary relative plate tectonic motions of the North American, Pacific, South American, Eurasian, Australian, Nazca, and Caribbean plates;
• Internal deformation of lithospheric plates away from plate boundaries, with particular emphasis on North America;
• Polar motion and variations in Earth rotation and their possible correlation with earthquakes and other geophysical phenomena; and
• Crustal motion and deformation occuring in other regions of high earthquake activity.

These objectives required the development of global geodetic systems that could measure distances with high accuracy. As a consequence, a major goal of NASA and solid Earth science in the 1970's was the development of satellite laser ranging (SLR) and very long baseline interferometry (VLBI) techniques to accuracy levels that would enable the scientific problems to be addressed. By the late 1970's, confidence in the viability of these measurement techniques justified initiation of an international, global program. This led to the formation of the NASA Crustal Dynamics Project (CDP) in 1979.

During the 1980's, the CDP and its international partners have made measurements of crustal motion between numerous sites around the world. One of the primary results of this work was to show that the current day motion of the major plates is close to the million year average motion vectors developed from geology. In addition, our knowledge of the distribution of crustal deformation occurring at both transform and subduction plate boundaries was significantly increased; and a new international effort was spawned to monitor the rotational dynamics of the Earth with unprecendented accuracy.

Through improvements in the tracking of satellites, our models of the Earth's gravity field and the ocean tides were dramatically improved.

From: Contributions of Space Geodesy to Geodynamics: Crustal Dynamics, Introduction. D.E. Smith and M. Baltuck

Dynamics of the Solid Earth (DOSE) Investigation

NASA's Solid Earth Sciences Branch has identified broad scientific research objectives which require:

• the improvement of our understanding of the interactions of the solid Earth with the oceans, ground water and atmosphere on time scales of hours to millions of years
• the local changes in sea level resulting from changes in the Earth's climatic, hydrologic, and tectonic systems
• the response of the lithosphere to local regional strain and loading and unloading phenomena such as post-seismic and glacial rebound; the evolving landscape as a record of tectonics, volcanism, and climate change during the last two million years
• the motions and deformations of the lithosphere within the plates and across plate boundaries; the evolution of continents and the structure of the lithosphere
• the dynamics of the mantle including the driving mechanisms of plate motion ; the dynamics of the core and the origin of the magnetic field
• the origins and variability of the Earth's gravity field, and
• the rotational dynamics and reference frames of the planet.

A major emphasis in Dynamics of the Solid Earth (DOSE) for the 1990's will be NASA's contribution to the implementation and operation of an international global geophysical network for integrated, comprehensive measurements of many geophysical parameters. This fiducial network incorporates VLBI, SLR, and GPS systems which are operated on a permanent, continuous basis, and which will provide reference geodetic data to which regional studies occupying many sites on a short-term, temporary basis can anchor. Two or more different systems will be co-located at many sites to provide strong reference frame ties, strengthen fiducial control, and allow intercomparison of the techniques. The two components of the system can be briefly characterized:

• Fiducial Laboratories for an International Natural Science Network (FLINN) -- a global permanent network of space geodetic stations with approximately 1000 km spacing which integrate GPS, VLBI, SLR, and LLR technology to monitor plate motion and deformation, to monitor Earth rotation, and to define and maintain a terrestrial reference frame.
• Densely Spaced Geodetic Systems (DSGS) -- temporary or permanent regional and local monitoring networks deployed across tectonically active regions to measure and analyze motion and deformation over a broad range of spatial and temporal scales.

From: DOSE NRA, December 1990

A total of 54 investigations where selected in response to the DOSE NRA.