One of the most powerful Earth observation tools ever put in orbit is now gathering data about the planet. IceSat-2 was launched just under three months ago to measure the shape of the ice sheets to a precision of 2cm. But the Nasa spacecraft's laser instrument is also now returning a whole raft of other information. It is mapping the height of the land, of rivers, lakes, forests; and in a remarkable demonstration of capability - even the depth of the seafloor. (BBC News)