Exploring Sea Level Change in the Northwest Atlantic Coastal Zone with Sentinel-3A SRAL

The coastal ocean along the North American Eastern seaboard is notorious for its complex dynamics and poor correspondence between altimetry and tide gauge (TG) measurements. Obtaining a reliable estimate for sea surface topography could elucidate relationship between open ocean and coastal sea level near TG, allowing us to better estimate future sea level rise at the coastal sites. Since 2016, we can benefit from global SAR altimeter (SRAL) coverage with Sentinel-3A, which has increased the reliability and resolution of sea surface height (SSH) estimates. However, the ability of Sentinel-3A SRAL to distinguish coherent sea level change can vary due to selected processing. To determine the optimal product for coastal SSH monitoring in the Northwest Atlantic region, we compare currently available products with 1 Hz, 20 Hz and 80 Hz posting rate and with/without retrackers. We used RADS (Radar Altimetry Database System) L2 and ALES-retracked SSH 1 Hz products, in addition to SAMOSA++ at 20 Hz and 80 Hz posting rate around selected TG to compare the output of SRAL products with TG records and determine the spatial extent and pattern of decorrelation between them. We find a diminishing correlation towards the coast, which starts to appear within 30 km for many TG, in particular south of Mid-Atlantic Bight, consistent among different products. We also find an improvement in coherence at higher posting rates with a coastal waveform retracker. Further to that, we are investigating the origin of sea level signals and properties they exhibit in the coastal altimetry versus TG record.