SCEC Award Number 19122 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Bias due to soil moisture variability in InSAR time series along sedimentary-basement contacts in the Mojave
Investigator(s)
Name Organization
Rowena Lohman Cornell University
Other Participants Kyle Murray
SCEC Priorities 1a, 2a, 3e SCEC Groups Geodesy, SAFS, Geology
Report Due Date 04/30/2020 Date Report Submitted 04/20/2020
Project Abstract
 The SCEC Community Geodetic Model (CGM), has the goal of developing a consensus model characterizing deformation in Southern California. One of the inputs into the CGM is derived from synthetic aperture radar (SAR) data, which has become much more frequently acquired and easily available in the past few years. InSAR is sensitive to displacements of the ground surface, but also to variations in the troposphere and ionosphere. For the most part, the latter variations tend to be random in time, and their impact can be mitigated through temporal-spatial filtering and/or comparisons with weather models.

Another source of error in InSAR time series analysis comes from variations in surface reflective properties, including those due to variations in soil moisture in the uppermost few cm of the subsurface. We show cases where comparisons of GPS and InSAR clearly show that these shallow surface property variations can introduce errors in the inferred secular rate that are not due to deep sources (i.e., faults), but may be instead associated with changes in mineralogy within the upper few 10's of cm.
Intellectual Merit The activity supports the development of the community geodetic model (CGM).
Broader Impacts The activity supported efforts to constrain seismic hazard in Southern California with InSAR observations, through better understanding of a process that may mimic fault-related ground deformation and bias such results.
Exemplary Figure Figure 1: InSAR vs. GPS velocity when projected into the satellite radar line-of-sight (LOS). Average rate of the entire study area has been removed from both GPS and InSAR datasets, such that there is no sensitivity to deformation over spatial scales larger than approximately the width of the Imperial Valley. Date points are colored by the percent pixel coverage for the InSAR data, i.e., how many pixels are not masked out due to decorrelation in the vicinity of the GPS point. Vertical bars indicate measures of the spatial and temporal variability of the InSAR-inferred rates in the vicinity of each GPS site.