COMPARISON OF VERTICAL LAND MOTION SOLUTIONS DERIVED FROM CAMPAIGN GPS MEASUREMENTS AND COMBINED INSAR AND CONTINUOUS GNSS DATA IN THE CHESAPEAKE BAY

Relative sea level rise can increase coastal hazards, including flooding and aquifer saltwater intrusion, while also deteriorating the coastal environment’s biodiversity and stability. Vertical land motion (VLM) impacts relative sea level rise and varies spatially across the U.S. East Coast. The Chesapeake Bay region is a hotspot of negative vertical land motion (subsidence) with previous average measurements ranging from -1.5 mm/yr to more than -5 mm/yr. In collaboration with a consortium led by the USGS, a new VLM solution was derived for the Chesapeake Bay region from over 55 campaign Global Positioning System (GPS) observations collected annually from 2019 to 2023. We utilize this campaign GPS-derived solution as a baseline for comparison with a recently published solution for the U.S. East Coast based on a combination of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite Systems (GNSS). In the Chesapeake Bay region, the combined InSAR and GNSS-based VLM solution leverages a combination of data from 11 continuous GNSS stations made available by the Nevada Geodetic Laboratory and SAR datasets from Sentinel-1 A/B and ALOS. Discrepancies between the combined InSAR and GNSS solution and the campaign GPS-derived VLM solution are evaluated by first selecting the common VLM solutions within a 1 km region with additional tests for smaller regions. Second, we apply several analytical techniques to compare the campaign GPS-derived VLM solution with the pixel-based measurements from the combined InSAR-GNSS solution. Regions of the highest difference between the two VLM solutions are identified, and new GPS measurements are planned to be obtained in these regions to improve quantification of VLM. Satellite remote sensing InSAR VLM analysis offers a low-cost solution to monitor large spatial regions of coastline over long timescales. Comparing the remote sensing results with a separate set of in-situ GPS data will help refine our VLM solution for the Chesapeake Bay. Broader implications for this work include improving our understanding of how to combine multiple observation techniques for VLM velocity solutions and contributing to methods that can refine relative sea-level rise measurements.