Mapping directional sea surface slopes associated with seamounts from SWOT and validation with ICESat-2

Observations from satellite altimeters are essential to mapping the marine gravity field and bathymetry. As most of the ocean basins are yet to be mapped by sonar, obtaining reliable data of sea surface height and sea surface slopes is key to improving our understanding of the marine gravity field and bathymetry. Improvement in altimeter systems has enabled the marine gravity field to be determined to a few mGal, however with conventional satellite altimetry, improvements are challenging.

The major challenge is the sampling geometry of conventional satellite altimeters, with along-track (majorly north-south) sea surface slopes being much better determined than across-track slopes (east-west). With the KaRIn instrument on the Surface Water and Ocean Topography (SWOT) satellite, swath-altimetry with 2-dimensional observations of the sea surface height is possible. From these observations, the directional sea surface slopes in both along-track and across-track can be determined. However, determining the resolution and precision with which the sea surface slope is determined, is of fundamental importance for the improvement of the mapping of the marine gravity field.

We present directional sea surface slopes associated with a major seamount using SWOT L2 data and with a minor seamount using SWOT pixel-cloud data, demonstrating the quantum leap forward possible with SWOT. With three parallel beams, ICESat-2 is another satellite that can determine the east-west sea surface slope. From observing the difference in sea surface height between beams, we can determine the directional sea surface slopes in north-south and east-west components, with auspicious results. With data from ICESat-2, we aim to validate the SWOT directional sea surface slopes at cross-overs between SWOT and ICESat-2 and determine the relative initial performance.