Tracking Coastal Change in American Samoa by Mapping Local Vertical Land Motion with PS-InSAR.

Characterizing diverse contributions to coastal land change is a key step to mitigating the effects of rising sea levels that threaten coastal communities. This task is particularly critical for small island communities in tectonically active regions, which are highly vulnerable to the effects of sea level rise. We highlight here a case study to extract regional estimates of vertical land motion (VLM) over American Samoa, which in recent years has observed increased nuisance flooding. We used persistent scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) to derive high-resolution estimates of crustal deformation in populated regions over Tutuila Island from 2016 to 2021. While the area is small and highly vegetated and poses challenges for InSAR, we were able to construct a regional map of the estimated deformation rate in these areas and validate the time-series with a local GPS station. Our preliminary results suggest that PS-InSAR has the ability to capture local and regional deformation patterns. Further work to refine our VLM estimate will include models to account for more complex atmospheric effects and estimates of error margins, as well as integration of our results into models of sea-level change that can be used by local stakeholders.