How accurately can we measure the ocean's deepest point?

How deep is the deepest ocean—and how precisely can we actually measure it? A Japanese research team led by the National Institute of Polar Research (NIPR), SOKENDAI, the University of Tokyo and other Japanese institutions has mapped the Challenger Deep in the Mariana Trench using the EM124 multibeam echosounder aboard the research vessel Hakuho-maru. Their study is published in the journal Scientific Data.