Estimating bathymetry and water storage of lakes at the regional scale by integrating multiple methods and multi-source satellite observations

Globally over 100 million lakes hold 87% of Earth´s liquid surface freshwater and provide vital ecosystem services. Understanding lake water storage and its changes under environmental and climate stressors is crucial.

Bathymetric data, characterizing lake underwater topography, are essential for quantifying water storage and conducting related studies.

Conventionally, lake bathymetry data are obtained from underwater topographic surveys using shipborne sonar sensors or airborne lidar sensors.

However, such approaches are time-consuming and labor-intensive, limiting the mapping of large areas or numbers of lakes.

Consequently, most lakes globally lack bathymetry data, hindering our understanding of regional/global lake water storages and their hydrological-ecological impacts.

Urgent action is needed to address this gap.Satellite remote sensing presents a promising tool for obtaining lake bathymetry at large scales cost-effectively and efficiently.

Three main methods have been explored: (1) Type-1 method using multispectral/hyperspectral satellite imagery and empirical/physical-based models; (2) Type-2 method using digital elevation models (DEM) and interpolation methods based on geomorphological similarity between lake bathymetry and lakeside land areas; (3) Type-3 method uses the combination of water elevation derived from satellite altimetry and water surface extents from satellite imagery data to estimate the topography between the highest and lowest water level, while the remaining topography below the lowest water level needs to be interpolated similar to Type-2 method.

Each type of methods has its pros and cons.

So far, no study has systematically compared, evaluated or integrated all three types of methods for estimating lake bathymetry at regional scales.This project will address these research gaps by estimating bathymetry and water storage of lakes at the regional scale with an unprecedented spatial coverage and accuracy.

This project will improve and combine the three aforementioned methods using multi-source satellite observations, including satellite altimetry, satellite imagery and DEM.

Four work packages(WPs) are designed: WP1-3 focuses on improving and evaluating each of the three methods individually, and WP4 compares and integrates these methods with multi-source satellite data to develop a new dataset of bathymetry and water storage for lakes in Sweden. Spatiotemporal patterns of water storage changes in lakes and their climatic drivers will be analyzed.

Our methods will also be tested in lakes in Germany, Switzerland, Brazil and China together with our collaborators to demonstrate their applicability in different regions.This project aligns with international efforts, such as the Lakes-Climate Change Initiative led by European Space Agency (ESA) and Global Lake Ecological Observatory Network.

The ESA Lakes CCI lacks data on lake bathymetry and water storage. We will address significant gaps in the ESA Lakes CCI by this project. We will leverage intermediate variables provided by ESA Lakes CCI for comparison and cross-validation.

Our project contributes to the development and application of various Earth Observation missions, including Sentinel, Landsat, existing satellite altimeters, and new Surface Water and Ocean Topography (SWOT) mission.

It also contributes to calibration/validation(Cal/Val) activities using comprehensive in-situ data and advances climate change studies.

The findings will enhance our understanding of bathymetry and water storage in global lakes, supporting better water resources management and benefiting related studies such as quantitative understanding of the regional water cycle, water quality modeling, hydrological modeling, and regional climate modeling in lake regions.

We will actively disseminate our findings to the research community, the public and stakeholders for broader implication and future inter-disciplinary cooperation to tackle challenging research questions on lakes.