Jonathan Amos wrote this article in BBC:

The American space agency Nasa has launched a satellite that's expected to transform our view of water on Earth.

The Swot mission will map the precise height of rivers, reservoirs and lakes, and track ocean surface features at unprecedented scales.

It should improve flood and drought forecasts, and help researchers better understand how the climate is changing.

British scientists have been asked to help set up the spacecraft using the Bristol Channel as a benchmark.

The UK researchers are putting a suite of sensors in the estuary to "ground truth" the observations made by the satellite as it flies overhead at an altitude of 890km (550 miles).

Lift-off for the Surface Water and Ocean Topography mission occurred from California. A Falcon rocket took it skyward at 03:46 local time (11:46 GMT).

Swot is led principally by Nasa and Cnes, the French space agency, with contributions from the UK and Canadian space agencies.

It will be a few months before Swot comes fully into operation; its French-built Ka-band Radar Interferometer (KaRIn) has long booms that must be unpacked first.

Once in position, however, the instrument's antennas will begin pulsing the Earth's surface, counting the time that reflections take to come back to the spacecraft.

It's these echoes that allow Swot to make very precise determinations of height.

Essentially, the satellite will be imaging water bodies, assessing their rise and fall in detail and across a very wide swath.

Swot should be able to resolve all rivers at least 100m wide, and see all lakes larger than 6 hectares (15 acres).

"The amount of data from Swot on rivers and lakes will be orders of magnitude more than currently exists," said Nasa project scientist Dr Lee-Lueng Fu.

"For instance, only 10s of 1,000s of lakes have been well surveyed. We'll be surveying millions of lakes."

For the ocean, Swot will see the bulges and depressions in the water surface associated with currents and eddies as small as 20km (12 miles) across. It's the swirling of water in eddies that pulls heat and carbon dioxide out of the atmosphere, tempering the impact of global warming.

"The unprecedented information can also be used to improve our understanding of ocean circulation, and this then has the potential to yield important information for a wide range of industries like shipping, fishing, and even recreation," explained Ben Hamlington, a Nasa sea-level scientist.

"We also know that small-scale features are responsible for transporting pollutants around the ocean and then to our coasts. Examples of this would be oil spills, or ocean debris following tsunamis."

Britain has put £12m ($15m) into the mission, most of which was spent in UK industry.

Dr Beth Greenaway, the head of Earth observation at the UK Space Agency, attended the launch in California. She told BBC News: "I am very proud to be representing the UK elements of the build - the part that provides the radar pulses through the instrument at never before seen frequencies. The UKSA's partnership with the French space agency, Cnes, enabled the engineers in Honeywell UK to build this complex duplexer."