PARIS: An Earth-observation satellite developed by European and US space agencies set to lift off Saturday will measure sea level rise, tracking changes threatening to disrupt tens of millions of lives within a generation.

If all goes according to plan, the payload will be hoisted into a low-Earth 1,300-kilometre (800-mile) orbit by a Space X Falcon 9 rocket, with lift-off from Vandenberg Air Force Base in California at 17:17 GMT. Sentinel-6a will be the first of two identical satellites - the second to be launched in five years - that will provide measurements of unprecedented precision until at least 2030.

Each Sentinel-6 probe carries a radar altimeter, which measures the time it takes for radar pulses to travel to Earth's surface and back again.

The satellites will circle the planet in the same orbit as earlier missions that supplied sea-surface height data over the last three decades, mapping 95 percent of Earth's ice-free ocean every ten days. Accelerating sea level rise is arguably the climate change impact that will affect the largest number of people over the next three decades. Nearly 800 million people live within five metres of sea level, and even an increase in sea level of a few centimetres can translate into vastly more damage from high tides and storm surges.