SWOT Seasonal HR Mask

The Surface Water and Ocean Topography (SWOT) mission aims to provide valuable data and information about the world's oceans and its terrestrial surface water such as lakes, rivers, and wetlands. SWOT is being developed jointly by National Aeronautics and Space Administration (NASA) and Centre National D'Etudes Spatiales (CNES), with contributions from the Canadian Space Agency (CSA) and United Kingdom Space Agency (UKSA). SWOT successfully launched on December 16, 2022. Since then, over land, SWOT provides measurements of water storage changes (surface water area and water depth) of major lakes, reservoirs, rivers, and wetlands, and support derived estimates of river discharge, which aid in assessing water resources. SWOT observes rivers wider than 100 m and lakes with a surface area of 6,25 hectares or more (i.e., an outline of 250 m x 250 m).

On this platform, you can find, visualize, plot and download the full set of Level-2 High Rate (L2 HR) collections focusing on continental surfaces. The High Rate (HR) mask gathers all earth regions where the SWOT High-Rate processings are applied. This mask is seasonnaly updated following SWOT Science Team recommendations to monitor new regions or scene of particular scientific interest. For example:

• Given the latest SWOT Science Team in October 2025, new estuary/coastal regions were added to the HR mask,
• During winter mask, frozen areas are added for specific monitoring (e.g. sea ice),
• and are withdrawn in summer mask.

When downloading a given seasonnal HR mask, you will simultaneously get a pass-based KML file, a swath-based shapefile and a nadir-focused shapefile. You can also visualize on the platform map the swath-based shapefile. In each file, the following attributes are available:

• "ID_SEG" gives the absolute segment number over the entire mask,
• "ID_PASS" identifies the associated pass,
• "START_TIME" set the cycle relative start time when the satellite travels through this segment.

Complete timeline of SWOT HR masks evolution: