CDDIS

The International Association of Geodesy (IAG)

The International Association of Geodesy (IAG) is a scientific organization in the field of geodesy. The mission of the IAG is the advancement of geodesy and thus the association promotes scientific cooperation and research in geodesy on a global scale and contributes to it through its various research bodies. It is an active member of the International Association of Geodesy and Geophysics (IUGG) which itself is a member of the International Council for Science (ICSU). Key components of the IAG are its Services. In particular, the geometric services are dedicated to providing data and products relevant for geodesy and broader scientific applications:

• International GNSS Service (IGS)
• International Laser Ranging Service (ILRS)
• International VLBI Service for Geodesy and Astrometry (IVS)
• International DORIS Service (IDS)

Services function as cooperating federations dedicated to a particular type of data. They provide data and products on an operational basis to geodesy analysts as well as a broader scientific community. The services are examples of a successful model of community management where they develop standards, are self-regulating, monitor performance, and define and deliver products using pre-determined schedules. The IAG services are a excellent example of successful operation through cooperation of many international organizations who leverage their respective limited resources to all levels of service functionality.

The CDDIS is the principle data center supporting four geometric services created under the IAG and make up the primary user community for CDDIS archive.

Space Geodesy Project (SGP)

NASA's Space Geodesy Project (SGP) is an initiative that started in the fall of 2011. SGP is part of the Earth Science Decadal and the National Research Council study "Precise Geodetic Infrastructure." It is a Goddard/JPL partnership with participation from the Smithsonian Astrophysical Observatory and the University of Maryland.

The long-range goal of the Space Geodesy Project is to build, deploy and operate a next generation NASA Space Geodetic Network (NSGN) of integrated, multi-technique next generation space geodetic observing systems, along with a system that provides for accurate vector ties between them. This new NSGN will serve as NASA’s core contribution to a global network designed to produce the higher quality observational data required to maintain the Terrestrial Reference Frame and provide other data necessary for fully realizing the measurement potential of the current and coming generation of Earth Observing spacecraft.

The primary goals of the SGP are to:

• Contribute to the maintenance and improvement of a stable Terrestrial Reference Frame (TRF) that meets the needs of NASA's Earth orbiting missions, Earth Surface and Interior Focus Area, and deep space navigation
• Contribute to measurements of Earth orientation parameters (EOP) that meet the needs of NASA's Earth orbiting missions, Earth Surface and Interior Focus Area, and deep space navigation
• Contribute to determining accurate precision orbits to meet the needs of NASA's geodetic, Earth observation, navigation and space science missions

From: SGP website

International Earth Rotation and Reference Systems Service (IERS)

The International Earth Rotation and Reference Systems 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.

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 Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR) and satellite-geodetic techniques such as Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radio-Positioning by Integrated Satellite (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

Global Geodetic Observing System (GGOS)

In mid-2003, the IAG established the Global Geodetic Observing System (GGOS) as a project to foster cooperation among the geometric services of the IAG and to promote outreach and education to a broad user community on the importance of the geodetic infrastructure to many Earth science applications. GGOS, a component of the IAG, works to integrate the geodetic techniques to ensure long-term monitoring of Earth processes, including global change research. Distribution of data and products for the generation of GGOS combination products will be accomplished through the data flow paths developed by the IAG services forming the underlying structure of GGOS. Access to data and products generated by these services will continue to be provided through the services, either directly or via a GGOS portal. This portal will facilitate access to GGOS products and provide a way to view the underlying, dedicated information systems developed by the IAG’s contributing services.

The CDDIS supports GGOS as an essential archive for the geometric services and will contribute to the GGOS portal by implementing systems to provide uniform access to a combined set of geodetic services’ information as well as technique-specific information systems.

From: GGOS web site

Earth Observing System Data and Information System (EOSDIS)

In late 2007, funding support for the CDDIS transitioned from the science research area within NASA to the Earth Observing System Data and Information System (EOSDIS). EOSDIS is a key core capability in NASA's Earth Science Data Systems Program. EOSDIS provides end-to-end capabilities for managing NASA’s Earth science data from various sources – satellites, aircraft, field measurements, and other programs. EOSDIS is responsible for the processing, archiving, and distribution of Earth science data sets, providing tools to facilitate use of these data, and ensuring that these data are available to the public to study Earth processes from space in order to meet the needs of the global community. In addition to managing the science systems, EOSDIS supports 12 Distributed Active Archive Centers (DAACs) in the U.S., each of which serves a specific Earth system science discipline. As one of these EOSDIS data centers, the CDDIS cooperates with other groups in support of NASA’s Earth science goals. This activity includes implementation of metadata standards that will eventually permit discovery of CDDIS archive content by researchers outside the existing user base. Thus, the CDDIS will have the opportunity to promote use of its data and products to a broader scientific community.

Solid Earth and Natural Hazards Research and Applications NRA

The Solid Earth and Natural Hazards Research and Applications NASA Research Announcement (NRA) presented 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 scientific 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
• 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 1970s 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 1970s, 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 1980s, 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 unprecedented 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 1990s 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.

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

From: DOSE NRA, December 1990

EGM96 is a spherical harmonic model of the Earth's gravitational potential complete to degree and order 360 developed by NASA's Goddard Space Flight Center (GSFC) and NIMA.

The major reference for this model is NASA/TP-1998-206861.

Please use the following citation when referencing EGM96:

The Development of the Joint NASA GSFC and NIMA Geopotential Model EGM96, F. G. Lemoine, S. C. Kenyon, J. K. Factor, R.G. Trimmer, N. K. Pavlis, D. S. Chinn, C. M. Cox, S. M. Klosko, S. B. Luthcke, M. H. Torrence, Y. M. Wang, R. G. Williamson, E. C. Pavlis, R. H. Rapp and T. R. Olson, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA, July 1998.