Quantifying the effects of a coastal submersion requires a high temporal resolution over large scenes monitoring. Most satellite imageries, provided with long time-series, suffer from either a coarse spatial resolution or a coarse temporal resolution. The advent of the PlanetScope (PS) constellation successfully collects multispectral imagery at both high spatial (3 m) and temporal (daily) resolutions. The submersion process of Beaussais’ marsh, following a breach in March 2020, has been surveyed using a monthly time-series of 59 PS imageries, from February 2017 to April 2022. The calculation of the Normalized Difference Vegetation Index (NDVI) across enabled to (1) map the variance, and (2) analyze the time-series of eight virtual stations (as a profile from the breach to marsh’s back). For the pre-breach period (from February 2017 to March 2020), the NDVI showed a constant decrease for the stations out of the channel (just behind the dyke), which might reflect the marine intrusions in the groundwater. The breach’s aperture (in March 2020) provoked an abrupt augmentation, like a tipping point, of all NDVI’s stations. The post-breach period (from March 2020 to April 2022) reflected the successive (1) first colonization of lower marsh vegetation, (2) large marine sediment deposit due the breach’s widening, and (3) gradual growth of lower marsh vegetation due to the breach’s stabilization.