09:00 〜 09:15
[SGD02-01] Updating Terrestrial Reference Frames
★Invited Papers
キーワード：terrestrial reference frame
The terrestrial reference frame is the foundation for virtually all space-based, airborne and ground-based Earth observations. Positions of objects are determined within an underlying TRF and the accuracy with which objects can be positioned ultimately depends on the accuracy of the reference frame. The TRF allows different spatial information, such as imagery from different space and airborne platforms, to be geo-referenced and aligned with each other. It plays a key role in modeling and estimating the motion of the Earth in space, in measuring change and deformation of all components of the Earth system, and in providing the ability to connect measurements made at the same place at different times, a critical requirement for understanding global, regional and local change. Providing an accurate, stable, homogeneous, and maintainable terrestrial reference frame to support numerous scientific and societal applications is one of the essential goals of the International Association of Geodesy (IAG).
The terrestrial reference frame is determined and maintained though a global network of ground sites with co-located SLR, VLBI, GNSS, and DORIS stations and is realized as the international standard through the ITRF (International Terrestrial Reference Frame). Requirements for the ITRF have increased dramatically since the 1980s. Today, the most stringent requirement comes from critical sea level programs: a global accuracy of 1.0 mm, and 0.1 mm/yr stability is required. This is a factor of 5 to 10 beyond current capability. Current and future satellites will have ever-increasing measurement capability and should lead to increasingly sophisticated models of the processes that they are observing. The accuracy and stability of the terrestrial reference frame needs to dramatically improve in order to fully realize the measurement potential of the current and future generation of Earth observing satellites.
One way of improving TRFs is to determine them more often. Recent ITRFs have been produced at intervals of 3-6 years (ITRF2000, ITRF2005, ITRF2008, ITRF2014, ITRF2020). Between these realizations, users must rely on predictions of the motions of the reference stations. However, these predictions degrade with time leading to errors in products that depend on the ITRF. Updating the TRF more frequently would eliminate the need for multi-year predictions and hence eliminate this source of error in the TRFs.
JPL is developing a sequential estimation approach to realizing TRFs. This approach, which was used at JPL to produce JTRF2014 and JTRF2020, is particularly well-suited to the task of updating the TRF in a timely manner. It is straightforward to save the state vector and its full covariance matrix at the end of a TRF solution. As more recent data become available, the filter can be re-started from the saved state and run forward in time, assimilating the new data until it ends, thereby updating the TRF. This process can then be repeated at regular intervals. JPL is currently planning on using this approach to update JTRF2020 at annual intervals.
The terrestrial reference frame is determined and maintained though a global network of ground sites with co-located SLR, VLBI, GNSS, and DORIS stations and is realized as the international standard through the ITRF (International Terrestrial Reference Frame). Requirements for the ITRF have increased dramatically since the 1980s. Today, the most stringent requirement comes from critical sea level programs: a global accuracy of 1.0 mm, and 0.1 mm/yr stability is required. This is a factor of 5 to 10 beyond current capability. Current and future satellites will have ever-increasing measurement capability and should lead to increasingly sophisticated models of the processes that they are observing. The accuracy and stability of the terrestrial reference frame needs to dramatically improve in order to fully realize the measurement potential of the current and future generation of Earth observing satellites.
One way of improving TRFs is to determine them more often. Recent ITRFs have been produced at intervals of 3-6 years (ITRF2000, ITRF2005, ITRF2008, ITRF2014, ITRF2020). Between these realizations, users must rely on predictions of the motions of the reference stations. However, these predictions degrade with time leading to errors in products that depend on the ITRF. Updating the TRF more frequently would eliminate the need for multi-year predictions and hence eliminate this source of error in the TRFs.
JPL is developing a sequential estimation approach to realizing TRFs. This approach, which was used at JPL to produce JTRF2014 and JTRF2020, is particularly well-suited to the task of updating the TRF in a timely manner. It is straightforward to save the state vector and its full covariance matrix at the end of a TRF solution. As more recent data become available, the filter can be re-started from the saved state and run forward in time, assimilating the new data until it ends, thereby updating the TRF. This process can then be repeated at regular intervals. JPL is currently planning on using this approach to update JTRF2020 at annual intervals.