Abstract: In a gas collecting method for collecting gas yielding from source material on a sea bottom, [1] releasing a collecting membrane into water, a fixture being connected with a lower end of the collecting membrane and the collecting membrane being flared downward from its top; [2] keeping a three-dimensional position of the fixture at a target position with its autonomous navigation by a position maintainer provided in the fixture; [3] based on vertical water temperature distribution, setting the lower end at a position that is higher than the sea bottom and shallower than a water depth where the source material separates from its solid state into water and gas and setting the top at a deeper position than a water depth where bubbles of the gas disappear due to mixture of the gas with seawater; and [4] collecting the gas released from the sea bottom by the collecting membrane.

Abstract: In a gas collecting method for collecting gas yielding from source material on a sea bottom, [1] releasing a collecting membrane into water, a fixture being connected with a lower end of the collecting membrane and the collecting membrane being flared downward from its top; [2] keeping a three-dimensional position of the fixture at a target position with its autonomous navigation by a position maintainer provided in the fixture; [3] based on vertical water temperature distribution, setting the lower end at a position that is higher than the sea bottom and shallower than a water depth where the source material separates from its solid state into water and gas and setting the top at a deeper position than a water depth where bubbles of the gas disappear due to mixture of the gas with seawater; and [4] collecting the gas released from the sea bottom by the collecting membrane.

Abstract: A seabed resource exploration system includes: a vibrator 1 for transmitting a sound wave into the sea and receiving a scattered wave in which the sound wave is reflected on a boundary surface between seawater and a mixture of methane gas and methane hydrate, which exists in the seawater; and an analyzer 17 for determining that the methane hydrate exists in a seabed immediately under the mixture when backscattering strength, calculated by the transmitted sound wave and the received scattered wave, is in a predetermined relationship. The predetermined relationship satisfies a relationship that a maximum value of the backscattering strength is ?60 to ?30 dB and an average value of the backscattering strength is ?70 to ?50 dB. The backscattering strength is on a grid obtained by cutting the mixture into round slices in the depth direction by a predetermined width, in a range from the seabed to a predetermined height.

Abstract: A seabed resource exploration system includes: a vibrator 1 for transmitting a sound wave into the sea and receiving a scattered wave in which the sound wave is reflected on a boundary surface between seawater and a mixture of methane gas and methane hydrate, which exists in the seawater; and an analyzer 17 for determining that the methane hydrate exists in a seabed immediately under the mixture when backscattering strength, calculated by the transmitted sound wave and the received scattered wave, is in a predetermined relationship. The predetermined relationship satisfies a relationship that a maximum value of the backscattering strength is ?60 to ?30 dB and an average value of the backscattering strength is ?70 to ?50 dB. The backscattering strength is on a grid obtained by cutting the mixture into round slices in the depth direction by a predetermined width, in a range from the seabed to a predetermined height.