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New Report on Geodetic Infrastructure Highlights Needs to Measure Our Changing Planet into the Next Century

This Community Highlight features the work of UNAVCO community members' efforts to increase access to, use of, and innovation within geodesy. If there is an effort you would like to see highlighted here, please get in touch with us at communityunavco.org.

Provided by David T. Sandwell
Scripps Institution of Oceanography, UCSD
5 February 2020

Report author(s):
David T. Sandwell, Chair
Srinivas Bettadpur
Geoffrey Blewitt
John J. Braun
Anny Cazenave
Nancy Glenn
Kristine Larson
Anne Linn – NRC Staff
R. Steven Nerem
Michelle Sneed
Isabella Velicogna
Funding Source: NASA and the National Academy of Sciences’ Arthur L. Day Fund

The global geodetic infrastructure (GI) underlies our capabilities to make high-precision measurements of our Earth and its many processes. The GI provides the foundation for the geodesy data and tools provided by UNAVCO (e.g., GNSS, InSAR, lidar, etc.); moreover, many of NASA’s Earth Science missions planned for this decade (e.g., ICESat-2, GRACE-FO, SWOT, and NISAR) rely on the GI for computing the precise orbits needed for their basic observations. The extensive infrastructure consists of four global measurement systems (Figure 2) used to define the International Terrestrial Reference Frame (ITRF). Note that UNAVCO not only benefits from this infrastructure, but contributes to the maintenance of a subset of the global GNSS network on behalf of NASA.

The report Evolving the Geodetic Infrastructure to Meet New Scientific Needs highlights five science themes that rely on maintenance and enhancements to the geodetic infrastructure. The most stringent requirements for the accuracy and stability of the terrestrial reference frame are driven by science questions related to sea-level change, ice-mass loss, and land-surface deformation associated with the movement of water over the surface of the land, cryosphere, and oceans as well as the elastic and viscoelastic response of the solid Earth to water loading, earthquakes, and volcanic eruptions. These are all areas of interest to the UNAVCO science community.

Of course, as geodesists we know that the surface of the Earth is in constant motion due to these processes. How do we define a stable reference frame when all the components of the geodetic infrastructure are moving? The work is done by the international science community using algorithms developed over decades by teams of scientists and engineers. The raw data from the four geodetic measurements systems is sent to analysis and combination centers (IVS, ILRS, IGS, and IDS), where it is analyzed and refined to define the ITRF (Figure 3). No single country or agency is responsible for generating these products. Instead, all parties involved work in an open international collaborative environment to provide the most stable accurate reference frame for science and applications.

The report identifies three areas of improvement to the US component of the GI to meet the science needs into the next century:

  1. Finalize deployment and testing of next-generation VLBI and SLR systems and complete deployment of multi-GNSS receivers to achieve a balance of geodetic measurement techniques between the northern and southern hemispheres, document the errors in the systems, and improve the ability to estimate their positions accurately and automatically.
  2. Increase the capabilities for measuring the center of mass motions expected over the next 100 years, due to the melting of the Greenland and Antarctic ice sheets.
  3. Work with the international community to implement a fully time-dependent terrestrial reference frame that will accommodate sudden, annual, and long-term changes in the locations of the fundamental stations.

The report also identifies the need to increase the density of GNSS stations in high priority regions, including plate boundary zones to capture the earthquake cycle, coastlines to capture land motion that could affect sea level impacts and coastal ecosystems, and regions with substantial terrestrial water storage (Figure 4).

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Last modified: 2020-02-10  13:49:16  America/Denver