Great Lakes as seen by Topex/Poseidon

Image of the Month - August 1999

Lake Ontario water level change since September 1992. Seasonal variations show typical level minima in January and level maxima in June-July. The 1999 minima was 20-30 cm lower than previous years.

The Topex/Poseidon Altimetry satellite has been optimized to measure the level of the oceans. However, inland seas and lakes are also easily observable, offering an expanse of water for the instrument to view and monitor.

 The Great Lakes, situated in the North-East of the United States, are among the largest fresh water lakes on Earth. Flown over by Topex/Poseidon, we have been able to monitor surface water levels and their seasonal variations since 1992. At the end of 1998, some of the lakes (e.g. Lake Ontario) experienced lower than normal minimum levels possibly due to the El Niño/La Niña phenomenon.


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