The government Saturday started its first full-fledged investigation to assess the size of methane hydrate reserves in the Sea of Japan.
Japan succeeded in extracting natural gas from methane hydrate contained in geologic layers hundreds of meters below the Pacific seabed in March, but exploration under the Sea of Japan has lagged because the next-generation energy source is believed to exist in a form more difficult to exploit.
A survey ship equipped with a device to scan the geological formation of the Sea of Japan's seafloor with sound waves left port from the city of Joetsu, Niigata Prefecture, on Saturday morning.