The Surface Water and Ocean Topography Mission (SWOT) Prior Lake Database (PLD): Lake Mask and Operational Auxiliaries

Lakes are among the most prevalent and predominant water repositories on the Earth's land surface. A primary objective of the Surface Water and Ocean Topography (SWOT) satellite mission is to monitor surface water elevation, area, and storage change in lakes globally. To meet this objective, prior information on lakes, such as locations and benchmark extents, is required to organize SWOT's KaRIn observations for computing lake storage variation over time. Here, we present the SWOT mission Prior Lake Database (PLD) to fulfill this requirement. This paper emphasizes the development of the “operational PLD,” which consists of (a) a high-resolution mask encompassing approximately 6 million lakes and reservoirs that meet the minimum size criterion of 1 ha, as defined in SWOT’s lake observation science goals, and (b) multiple operational auxiliaries that support the lake mask in generating SWOT's standard lake vector data products. We built the prior lake mask by harmonizing the UCLA Circa-2015 Global Lake Dataset and several state-of-the-art reservoir databases. Operational auxiliaries were produced from multi-theme geospatial data to provide essential information for PLD functionality, including lake catchments and influence areas, ice phenology, relationship with SWOT prior rivers, and spatiotemporal coverage by SWOT overpasses. Globally, over three quarters of the prior lakes are smaller than 10 ha. About 97% of the lakes, constituting half of the global lake area, are fully observed at least once per orbit cycle. The PLD will be recursively improved throughout the mission lifetime and serves as a critical framework for organizing, processing, and interpreting SWOT observations over lacustrine environments with fundamental significance to lake system science.