Think of the ocean on a calm day. Ignoring the rise and fall of the waves, you might imagine the surface was dead flat the whole way across. You’d be wrong. Hills and valleys are as much a feature of the sea as the land, albeit on a much smaller scale.
These undulations have a variety of causes. Tides, currents, eddies, winds, river flow and changes in salinity and temperature push the sea level up in some places and down in others by as much as 2 metres. Ever tried swimming uphill?
How do we map these oceanic hills and…
