Marine DC resistivity and self-potential survey in the hydrothermal deposit areas using multiple AUVs and ASV

摘要

Detecting resistivity and self-potential (SP) anomalies is useful for the exploration of hydrothermal deposits. Using autonomous underwater vehicles (AUVs) can increase survey effectiveness because it allows stable posture control without a towing wire cable from a ship. We propose a new style for geophysical surveys using multiple AUVs without a towing electrode cable for marine direct current resistivity (MDCR) and SP survey. We used two AUVs for electrical signal transmission and their receiver. We successfully conducted MDCR and SP surveys ill hydrothermal deposit areas using two AUVs with 20 m tow-rods. One AUV was assisted by an autonomous surface vehicle (ASV) for monitoring and controlling via satellite and the public broadband mobile communications radiowave. The survey covered an area of about 1 square kilometer, spending only 4 hr observation time near the seafloor with the vehicle's speed maintained at 2 - 2.5 blots at distance between the AUVs of 200 - 300 m during most of the survey. The SP and apparent resistivity were calculated along the main survey line crossing known hydrothermal mounds of sulfide ore. The distribution of the negative SP anomalies obtained in the dive is similar to that obtained from our earlier survey using a deep-tow. The apparent resistivity is generally low (0.2 ohm-m or less) above the mounds. The averaged distance between the vehicles and the averaged altitude are respectively about 250 and 70 m. Therefore, the estimated apparent resistivities are the averaged value to several tens of meters below the seafloor. These positions show good agreement with the locations of blown hydrothermal deposits.