NASA launched Saturday a satellite to observe levels of salt on the surface of the world\'s oceans and measure how changes in salinity may be linked to future climate. The US$400 million (Aquarius/SAC-D) spacecraft, a partnership with Argentina, launched from Vandenberg Air Force Base in California. The orbiting science instrument will aim to map the entire open ocean every seven days from its position 657 km above Earth, producing monthly estimates that show how salt levels change over time and location. \"Data from this mission will advance our understanding of the ocean,\" said Michael Freilich, director of NASA\'s Earth Science Division in Washington. NASA said the mission will survey salinity at the ocean\'s surface in \"the most detailed summary of conditions ever undertaken\".