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Ocean tides are not simple.

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If our planet had no continents,

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tides would be hemispheric-sized bulges of water moving westward with the moon and sun.

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This animation shows the tides as a complex system of rotating and trapped waves with a mixture of frequencies.

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In many oceans we see waves rotating clockwise or anticlockwise,

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with small amplitudes in the middle of the ocean and high amplitudes around the boundaries,

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especially along the coasts of northwest Europe and Britain.

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Waves are trapped and rotating around New Zealand,

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causing a high tide on one side of the islands with a simultaneous low tide on the other side.

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The Topex/Poseidon and Jason satellite altimeter missions were designed to observe and record this complexity.

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Altimeters, on these missions,

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acted as flying tide gauges.

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After several years collecting data,

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researchers could analyze the signals at each ocean location to determine the tidal characteristics.

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With that knowledge,

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plus near-perfect knowledge of the motion of the sun and moon,

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the tide can be predicted at any location and at any time in the future.

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Even now,

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after three decades of measurements,

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we continue to add new details to the picture.

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The large, short-scale waves on continental shelves and marginal seas,

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as well as polar regions outside the orbits of Topex and Jason,

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are still inadequately known.

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Scientists expect that SWOT,

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the wide-swath altimeter launching soon,

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will help improve tidal knowledge in these regions.