Reconstructing the ocean floor using sea surface measurements

Knowledge of the topography of the ocean floor, such as seamounts, plateaus and other features, is necessary for understanding ocean circulation and mixing, which are crucial factors in determining Earth’s climate. One way to map the ocean floor, known as bathymetry, is by using sonars from ships. However, this method is laborious and expensive, and even after decades of measurements, 90 percent of the seafloor remains unmapped at high resolution.

In this paper, the authors propose a new technique to reconstruct ocean topography from free surface elevation and velocity field measurements. The method uses the fact that large-scale oceanic flows can be linked to observable features on the ocean surface. For example, the underwater flow over a bump in the ocean floor will produce a dip in the water’s surface that can be detected by satellite imaging.

The authors demonstrated that ocean bathymetry can be calculated using surface data, and tested their method on a toy ocean model. They then simulated flow in the Mediterranean Sea using a global circulation model known as “MITgcm” initialized with real data. Additional tests were carried out for both the Red Sea and the Mediterranean using existing data. Both Red and Mediterranean sea bathymetries were reconstructed with approximately 90 percent accuracy.

The authors noted that this method is not yet practical due to the low horizontal resolution of current satellite altimetry data. However, the upcoming Surface Water Ocean Topography (SWOT) satellite mission is expected to provide information at the scale of 15-25 kilometers, which will allow this technique to be useful.

Source: “Letter: Ocean bathymetry reconstruction from surface data using hydraulics theory,” by Subhajit Kar and Anirban Guha, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5055944 .