How do we know oceans are not flat ?

Looking beyond the effect of waves and tides and the fact that our planet is curved, you could think the ocean's surface is perfectly flat on average.

In fact the ocean has bumps and dips. The shape of the ocean surface topography tells us about ocean currents in the same way that a pressure chart of the atmosphere tells us about winds and weather systems.

The bumps cover such large expanses that they can't be detected by the naked eye but they can be measured by satellite.

Check it out in tutorial
Currents in the oceans measured from space !

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Artist's view of the TOPEX/POSEIDON altimeter. Source: NASA.

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