SCEC Award Number 22037 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title NASA Collaborative Research: Three-dimensional displacement and strain rates from the integration of GNSS and InSAR for the Community Geodetic Model
Investigator(s)
Name Organization
Michael Floyd Massachusetts Institute of Technology Ekaterina Tymofyeyeva National Aeronautics and Space Administration
Other Participants
SCEC Priorities 1a, 2a, 3e SCEC Groups Geodesy, CXM, SDOT
Report Due Date 03/15/2023 Date Report Submitted 12/08/2023
Project Abstract
 We present two results from contributions to the Community Geodetic Model (CGM), which were identified during this award as being important initial steps to combine InSAR with GNSS products (time series and velocities) ultimately and successfully. We have quantified uncertainties for both InSAR time series and InSAR velocities, based on the variance of contributing solutions and time series analysis similar to standard approaches for GNSS, respectively. We have also shown that a plate rotation beneath the SAR satellite orbits, nominally in the International Terrestrial Reference Frame 2014 (ITRF2014), produces a measureable velocity gradient, which must be accounted for when producing InSAR time series and velocities over a significant portion of the Earth’s surface. The latter has also been demonstrated, and published, by Stephenson et al. (2022). Finally, we have both continued to lead and coordinate the Working Groups of the CGM, with PI Tymofyeyeva chairing online meetings of the CGM (InSAR) Working Group once every two weeks and PI Floyd overseeing the CGM as a whole, in particular the GNSS component. Much of the work and progress reported here was, and continues to be, informed and guided by those regular meetings, as new barriers are identified and solutions proposed and tested.
Intellectual Merit The CGM is one of the Community Models, which are fundamental to SCEC research objectives. Our contributions have advanced understanding of subtle and previously underappreciated components of specifically InSAR time series and velocity products, particularly when compared to GNSS products. These components are likely critical to the eventual and successful combination of GNSS and InSAR to form coherent and compatible geodetic displacement and velocity fields. These form a fundamental basis for not only the CGM but research within the community that may be constrained by geodetic products, for example strain localization, and spatial and temporal variations of slip accumulation and release on faults.
Broader Impacts The CGM involves many SCEC researchers who contribute to the geodetic expertise within the community. We are part of that but also the leading coordinators of the activity. Our work supports the gamut of researchers from students and postdocs to established career scientists, and we continue to encourage the involvement of all interested contributors in virtual meetings every two weeks.
Exemplary Figure Figure 2 Comparison of InSAR line-of-sight velocities, relative to each track’s reference pixel, corresponding to the continuous GNSS station marked with a red circle (top row), and CGM GNSS velocities projected into the same line of sight over the four tracks covering Southern California. The top row shows the (original) line-of-sight velocities and the second row shows the associated uncertainties. The third row shows the calculated line-of-sight velocity change due to motion of the North America plate relative to the ITRF2014 implicit in the SAR orbit products. This correction, relative to the reference pixel, subtracted from the raw InSAR velocities is the transformation to a North America reference frame. The fourth and bottom rows compare the InSAR line-of-sight velocities with the CGM GNSS velocities projected into the line of sight before and after plate motion correction, respectively. [Credit: M. Floyd and E. Tymofyeyeva]
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