Satellite shoreline images expose fine-scale tide variations within bays
Researchers have developed a method using decades of Landsat satellite photos to estimate tide levels along coastlines at 100-meter intervals. The technique reveals that tidal heights can differ by nearly a meter within a single bay, offering far more local detail than traditional gauges or radar satellites. This could improve flood risk modeling and navigation planning.
The method treats beach slopes as natural measuring instruments, converting shoreline positions captured in Landsat imagery into sea-level readings through trigonometric calculations. This indirect approach bypasses the limitations of radar satellites, which typically offer only tens of kilometers of resolution near coastlines, and tide gauges, which are fixed to single points.
Applying the technique to Pacific coastlines produced tidal estimates for every 100-meter segment studied. The South Taranaki Bight showed tidal height differences approaching one meter across its roughly 90-kilometer span, while Christchurch's Pegasus Bay registered tides about 40 centimeters higher than beaches south of the city near the Rakaia River.
This technique could significantly improve coastal flood forecasting by revealing local tidal variations that current models miss, potentially helping communities better prepare for storm surges and high-water events. Mariners navigating shallow harbors and bays may benefit from more precise tide predictions, while coastal engineers designing infrastructure could use the data to account for localized conditions. As sea levels rise, understanding how tidal patterns shift regionally may become increasingly important for long-term planning and risk assessment.